The Domain Name System (DNS) provides an important user service that should be used on every system connected to the Internet. The vast majority of Unix implementations of DNS are based on the Berkeley Internet Name Domain (BIND) software. BIND provides both a DNS client and a DNS server.
The BIND client issues name queries and is implemented as library routines. It is called the resolver. The resolver is configured in the resolv.conf file. All systems run the resolver.
The BIND server answers name queries and runs as a daemon. It is called named. named is configured by the named.conf file, which defines where the server gets the DNS database information and the type of server being configured. The server types are master, slave, and caching servers. Because all servers are caching servers, a single configuration often encompasses more than one server type.
The original DNS database source files are found on the master server. The DNS database file is called a zone file. The zone file is constructed from standard resource records (RRs) that are defined in RFCs. The RRs share a common structure and are used to define all DNS database information.
The DNS server can be tested using nslookup. This test tool is included with the BIND release.
In this chapter we have seen how to configure and test DNS. In the next chapter, we configure several other services.
Sunday, September 21, 2008
Local Network
The Network File System (NFS)
The Line Printer Daemon (LPD) and the Line Printer (LP) service
Windows file and print services (Samba)
The Network Information Service (NIS)
Dynamic Host Configuration Protocol (DHCP)
The Post Office Protocol (POP)
Internet Message Access Protocol (IMAP)
All of these software packages are designed to provide service to systems within your organization and are not intended to service outsiders. Essential services that are as important to external users as they are to in-house users, such as email, web service, and name service, are covered in separate chapters.
We begin our discussion of local network services with NFS, which is the server that provides file sharing on Unix networks.
The Line Printer Daemon (LPD) and the Line Printer (LP) service
Windows file and print services (Samba)
The Network Information Service (NIS)
Dynamic Host Configuration Protocol (DHCP)
The Post Office Protocol (POP)
Internet Message Access Protocol (IMAP)
All of these software packages are designed to provide service to systems within your organization and are not intended to service outsiders. Essential services that are as important to external users as they are to in-house users, such as email, web service, and name service, are covered in separate chapters.
We begin our discussion of local network services with NFS, which is the server that provides file sharing on Unix networks.
Sunday, September 14, 2008
Common Routing Configurations
Routing Table: IPv4
Destination Gateway Flags Ref Use Interface
-------------------- -------------------- ----- ----- ------ ---------
172.16.12.0 172.16.12.15 U 1 8 dnet0
224.0.0.0 172.16.12.15 U 1 0 dnet0
127.0.0.1 127.0.0.1 UH 20 3577 lo0
The first entry is the route to network 172.16.12.0 through interface dnet0. Address 172.16.12.15 is not a remote gateway address; it is the address assigned to the dnet0 interface on this host. The other two entries do not define routes to real physical networks; both are special software conventions. 224.0.0.0 is the multicast address. This entry tells Solaris to send multicast addresses to interface 172.16.12.15 for delivery. The last entry is the loopback route to localhost created when lo0 was configured.
Look at the Flags field for these entries. All entries have the U (up) flag set, indicating that they are ready to be used, but no entry has the G (gateway) flag set. The G flag indicates that an external gateway is used. The G flag is not set because all of these routes are direct routes through local interfaces, not through external gateways.
The loopback route also has the H (host) flag set. This indicates that only one host can be reached through this route. The meaning of this flag becomes clear when you look at the Destination field for the loopback entry. It shows that the destination is a host address, not a network address. The loopback network address is 127.0.0.0. The destination address shown (127.0.0.1) is the address of localhost, an individual host. Some systems use a route to the loopback network and others use a route to the localhost, but all systems have some route for the loopback interface in the routing table.
Although this routing table has a host-specific route, most routes lead to networks. One reason network routes are used is to reduce the size of the routing table. An organization may have only one network but hundreds of hosts. The Internet has thousands of networks but millions of hosts. A routing table with a route for every host would be unmanageable.
Our sample table contains only one route to a physical network, 172.16.12.0. Therefore, this system can communicate only with hosts located on that network. The limited capability of this routing table is easily verified with the ping command. ping uses the ICMP Echo Message to force a remote host to echo a packet back to the local host. If packets can travel to and from a remote host, it indicates that the two hosts can successfully communicate.
To check the routing table on this system, first ping another host on the local network: % ping -s crab
PING crab.wrotethebook.com: 56 data bytes
64 bytes from crab.wrotethebook.com (172.16.12.1): icmp_seq=0. time=11. ms
64 bytes from crab.wrotethebook.com (172.16.12.1): icmp_seq=1. time=10. ms
^C
----crab.wrotethebook.com PING Statistics----
2 packets transmitted, 2 packets received, 0% packet loss
round-trip (ms) min/avg/max = 10/10/11
ping displays a line of output for each ICMP ECHO_RESPONSE received.When ping is interrupted, it displays some summary statistics. All of this indicates successful communication with crab. But if we check a host that is not on network 172.16.12.0, say a host at O'Reilly, the results are different.
Sun's ping would display only the message "crab is alive" if the -s option was not used. Most ping implementations do not require the -s option. % ping 207.25.98.2
sendto: Network is unreachable
Here the message "sendto: Network is unreachable" indicates that this host does not know how to send data to the network that host 207.25.98.2 is on. There are only three routes in this system's routing table, and none is a route to 207.25.98.0.
Even other subnets on books-net cannot be reached using this routing table. To demonstrate this, ping a host on another subnet. For example: % ping 172.16.1.2
sendto: Network is unreachable
These ping tests show that the minimal routing table created when the network interfaces were configured allows communication only with other hosts on the local network. If your network does not require access to any other TCP/IP networks, this may be all you need. However, if it does require access to other networks, you must add more routes to the routing table.
Wednesday, September 3, 2008
Servers Configuration
The powerful features that add to the utility and flexibility of TCP/IP also add to its complexity. TCP/IP is not as easy to configure as some other networking systems. TCP/IP requires that the configuration provide hardware, addressing, and routing information. It is designed to be independent of any specific underlying network hardware, so configuration information that can be built into the hardware in some network systems cannot be built in for TCP/IP. The information must be provided by the person responsible for the configuration. This assumes that every system is run by people who are knowledgeable enough to provide the proper information to configure the system. Unfortunately, this assumption does not always prove correct.
Configuration servers make it possible for the network administrator to control TCP/IP configuration from a central point. This relieves the end user of some of the burden of configuration and improves the quality of the information used to configure systems.
TCP/IP has used three protocols to simplify the task of configuration: RARP, BOOTP, and DHCP. We begin with RARP, the oldest and most basic of these configuration tools.
3.6.1 Reverse Address Resolution Protocol
RARP, defined in RFC 903, is a protocol that converts a physical network address into an IP address, which is the reverse of what Address Resolution Protocol (ARP) does. A Reverse Address Resolution Protocol server maps a physical address to an IP address for a client that doesn't know its own IP address. The client sends out a broadcast using the broadcast services of the physical network.The broadcast packet contains the client's physical network address and asks if any system on the network knows what IP address is associated with the address. The RARP server responds with a packet that contains the client's IP address.
Like ARP, RARP is a Network Access Layer protocol that uses physical network services residing below the Internet Layer. See the discussion of TCP/IP protocol layers.
The client knows its physical network address because it is encoded in the Ethernet interface hardware. On most systems, you can easily check the value with a command. For example, on a Solaris 8 system, the superuser can type: # ifconfig dnet0
dnet0: flags=1000843 mtu 1500 index 2
inet 172.16.12.1 netmask ffffff00 broadcast 172.16.12.255
ether 0:0:c0:dd:d4:da
The ifconfig command can set or display the configuration values for a network interface,dnet0 is the device name of the Ethernet interface. The Ethernet address is displayed . In the example, the address is 0:0:c0:dd:d4:da.
for information about the ifconfig command.
The RARP server looks up the IP address that it uses in its response to the client in the /etc/ethers file. The /etc/ethers file contains the client's Ethernet address followed by the client's hostname. For example: 2:60:8c:48:84:49 clock
0:0:c0:a1:5e:10 ring
0:80:c7:aa:a8:04 24seven
8:0:5a:1d:c0:7e limulus
8:0:69:4:6:31 arthropod
To respond to a RARP request, the server must also resolve the hostname found in the /etc/ethers file into an IP address. DNS or the hosts file is used for this task. The following hosts file entries could be used with the ethers file shown above: clock 172.16.3.10
ring 172.16.3.16
24seven 172.16.3.4
limulus 172.16.3.7
arthropod 172.16.3.21
Given these sample files, if the server receives a RARP request that contains the Ethernet address 0:80:c7:aa:a8:04, it matches it to 24seven in the /etc/ethers file. The server uses the name 24seven to look up the IP address. It then sends the IP address 172.16.3.4 out as its ARP response.
RARP is a useful tool, but it provides only the IP address. There are still several other values that need to be manually configured. Bootstrap Protocol (BOOTP) is a more flexible configuration tool that provides more values than just the IP address and can deliver those values via the network.
BOOTP is defined in RFCs 951 and 1532. The RFCs describe BOOTP as an alternative to RARP; when BOOTP is used, RARP is not needed. BOOTP, however, is a more comprehensive configuration protocol than RARP. It provides much more configuration information and has the potential to offer still more. The original specification allowed vendor extensions as a vehicle for the protocol's evolution. RFC 1048 first formalized the definition of these extensions, which have been updated over time and are currently defined in RFC 2132. BOOTP and its extensions became the basis for the Dynamic Host Configuration Protocol (DHCP). DHCP has superseded BOOTP, so DHCP is the configuration protocol that you will use on your network
Configuration servers make it possible for the network administrator to control TCP/IP configuration from a central point. This relieves the end user of some of the burden of configuration and improves the quality of the information used to configure systems.
TCP/IP has used three protocols to simplify the task of configuration: RARP, BOOTP, and DHCP. We begin with RARP, the oldest and most basic of these configuration tools.
3.6.1 Reverse Address Resolution Protocol
RARP, defined in RFC 903, is a protocol that converts a physical network address into an IP address, which is the reverse of what Address Resolution Protocol (ARP) does. A Reverse Address Resolution Protocol server maps a physical address to an IP address for a client that doesn't know its own IP address. The client sends out a broadcast using the broadcast services of the physical network.The broadcast packet contains the client's physical network address and asks if any system on the network knows what IP address is associated with the address. The RARP server responds with a packet that contains the client's IP address.
Like ARP, RARP is a Network Access Layer protocol that uses physical network services residing below the Internet Layer. See the discussion of TCP/IP protocol layers.
The client knows its physical network address because it is encoded in the Ethernet interface hardware. On most systems, you can easily check the value with a command. For example, on a Solaris 8 system, the superuser can type: # ifconfig dnet0
dnet0: flags=1000843
inet 172.16.12.1 netmask ffffff00 broadcast 172.16.12.255
ether 0:0:c0:dd:d4:da
The ifconfig command can set or display the configuration values for a network interface,dnet0 is the device name of the Ethernet interface. The Ethernet address is displayed . In the example, the address is 0:0:c0:dd:d4:da.
for information about the ifconfig command.
The RARP server looks up the IP address that it uses in its response to the client in the /etc/ethers file. The /etc/ethers file contains the client's Ethernet address followed by the client's hostname. For example: 2:60:8c:48:84:49 clock
0:0:c0:a1:5e:10 ring
0:80:c7:aa:a8:04 24seven
8:0:5a:1d:c0:7e limulus
8:0:69:4:6:31 arthropod
To respond to a RARP request, the server must also resolve the hostname found in the /etc/ethers file into an IP address. DNS or the hosts file is used for this task. The following hosts file entries could be used with the ethers file shown above: clock 172.16.3.10
ring 172.16.3.16
24seven 172.16.3.4
limulus 172.16.3.7
arthropod 172.16.3.21
Given these sample files, if the server receives a RARP request that contains the Ethernet address 0:80:c7:aa:a8:04, it matches it to 24seven in the /etc/ethers file. The server uses the name 24seven to look up the IP address. It then sends the IP address 172.16.3.4 out as its ARP response.
RARP is a useful tool, but it provides only the IP address. There are still several other values that need to be manually configured. Bootstrap Protocol (BOOTP) is a more flexible configuration tool that provides more values than just the IP address and can deliver those values via the network.
BOOTP is defined in RFCs 951 and 1532. The RFCs describe BOOTP as an alternative to RARP; when BOOTP is used, RARP is not needed. BOOTP, however, is a more comprehensive configuration protocol than RARP. It provides much more configuration information and has the potential to offer still more. The original specification allowed vendor extensions as a vehicle for the protocol's evolution. RFC 1048 first formalized the definition of these extensions, which have been updated over time and are currently defined in RFC 2132. BOOTP and its extensions became the basis for the Dynamic Host Configuration Protocol (DHCP). DHCP has superseded BOOTP, so DHCP is the configuration protocol that you will use on your network
Tuesday, September 2, 2008
DNS
DNS overcomes both major weaknesses of the host table:
DNS scales well. It doesn't rely on a single large table; it is a distributed database system that doesn't bog down as the database grows. DNS currently provides information on approximately 100,000,000 hosts, while fewer than 10,000 were listed in the host table.
DNS guarantees that new host information will be disseminated to the rest of the network as it is needed.
Information is automatically disseminated, and only to those who are interested. Here's how it works. If a DNS server receives a request for information about a host for which it has no information, it passes on the request to an authoritative server. An authoritative server is any server responsible for maintaining accurate information about the domain being queried. When the authoritative server answers, the local server saves, or caches, the answer for future use. The next time the local server receives a request for this information, it answers the request itself. The ability to control host information from an authoritative source and to automatically disseminate accurate information makes DNS superior to the host table, even for networks not connected to the Internet.
In addition to superseding the host table, DNS also replaces an earlier form of name service. Unfortunately, both the old and new services were called name service. Both are listed in the /etc/services file. In that file, the old software is assigned UDP port 42 and is called nameserver or name; DNS name service is assigned port 53 and is called domain. Naturally, there is some confusion between the two name servers. There shouldn't be—the old name service is outdated. This text discusses DNS only; when we refer to "name service," we always mean DNS.
DNS scales well. It doesn't rely on a single large table; it is a distributed database system that doesn't bog down as the database grows. DNS currently provides information on approximately 100,000,000 hosts, while fewer than 10,000 were listed in the host table.
DNS guarantees that new host information will be disseminated to the rest of the network as it is needed.
Information is automatically disseminated, and only to those who are interested. Here's how it works. If a DNS server receives a request for information about a host for which it has no information, it passes on the request to an authoritative server. An authoritative server is any server responsible for maintaining accurate information about the domain being queried. When the authoritative server answers, the local server saves, or caches, the answer for future use. The next time the local server receives a request for this information, it answers the request itself. The ability to control host information from an authoritative source and to automatically disseminate accurate information makes DNS superior to the host table, even for networks not connected to the Internet.
In addition to superseding the host table, DNS also replaces an earlier form of name service. Unfortunately, both the old and new services were called name service. Both are listed in the /etc/services file. In that file, the old software is assigned UDP port 42 and is called nameserver or name; DNS name service is assigned port 53 and is called domain. Naturally, there is some confusion between the two name servers. There shouldn't be—the old name service is outdated. This text discusses DNS only; when we refer to "name service," we always mean DNS.
Saturday, August 30, 2008
Names and Addresses
The Internet Protocol document defines names, addresses, and routes as follows:
RFC 791, Internet Protocol, Jon Postel, ISI, 1981.
A name indicates what we seek. An address indicates where it is. A route indicates how to get there.
Names, addresses, and routes all require the network administrator's attention. Routes and addresses were covered in the previous chapter. This section discusses names and how they are disseminated throughout the network. Every network interface attached to a TCP/IP network is identified by a unique 32-bit IP address. A name (called a hostname) can be assigned to any device that has an IP address. Names are assigned to devices because, compared to numeric Internet addresses, names are easier to remember and type correctly. Names aren't required by the network software, but they do make it easier for humans to use the network.
In most cases, hostnames and numeric addresses can be used interchangeably. A user wishing to telnet to the workstation at IP address 172.16.12.2 can enter: % telnet 172.16.12.2
or use the hostname associated with that address and enter the equivalent command: % telnet rodent.wrotethebook.com
Whether a command is entered with an address or a hostname, the network connection always takes place based on the IP address. The system converts the hostname to an address before the network connection is made. The network administrator is responsible for assigning names and addresses and storing them in the database used for the conversion.
Translating names into addresses isn't simply a "local" issue. The command telnet rodent.wrotethebook.com is expected to work correctly on every host that's connected to the network. If rodent.wrotethebook.com is connected to the Internet, hosts all over the world should be able to translate the name rodent.wrotethebook.com into the proper address. Therefore, some facility must exist for disseminating the hostname information to all hosts on the network.
There are two common methods for translating names into addresses. The older method simply looks up the hostname in a table called the host table. The newer technique uses a distributed database system called the Domain Name System (DNS) to translate names to addresses. We'll examine the host table first.
RFC 791, Internet Protocol, Jon Postel, ISI, 1981.
A name indicates what we seek. An address indicates where it is. A route indicates how to get there.
Names, addresses, and routes all require the network administrator's attention. Routes and addresses were covered in the previous chapter. This section discusses names and how they are disseminated throughout the network. Every network interface attached to a TCP/IP network is identified by a unique 32-bit IP address. A name (called a hostname) can be assigned to any device that has an IP address. Names are assigned to devices because, compared to numeric Internet addresses, names are easier to remember and type correctly. Names aren't required by the network software, but they do make it easier for humans to use the network.
In most cases, hostnames and numeric addresses can be used interchangeably. A user wishing to telnet to the workstation at IP address 172.16.12.2 can enter: % telnet 172.16.12.2
or use the hostname associated with that address and enter the equivalent command: % telnet rodent.wrotethebook.com
Whether a command is entered with an address or a hostname, the network connection always takes place based on the IP address. The system converts the hostname to an address before the network connection is made. The network administrator is responsible for assigning names and addresses and storing them in the database used for the conversion.
Translating names into addresses isn't simply a "local" issue. The command telnet rodent.wrotethebook.com is expected to work correctly on every host that's connected to the network. If rodent.wrotethebook.com is connected to the Internet, hosts all over the world should be able to translate the name rodent.wrotethebook.com into the proper address. Therefore, some facility must exist for disseminating the hostname information to all hosts on the network.
There are two common methods for translating names into addresses. The older method simply looks up the hostname in a table called the host table. The newer technique uses a distributed database system called the Domain Name System (DNS) to translate names to addresses. We'll examine the host table first.
Wednesday, August 27, 2008
Network Services
The functions performed by the servers
Name service for converting IP addresses to hostnames
Configuration servers that simplify the installation of networked hosts by handling part or all of the TCP/IP configuration
Electronic mail services for moving mail through the network from the sender to the recipient
File servers that allow client computers to transparently share files
Print servers that allow printers to be centrally maintained and shared by all users.
Servers on a TCP/IP network should not be confused with traditional PC LAN servers. Every Unix host on your network can be both a server and a client. The hosts on a TCP/IP network are "peers." All systems are equal, and the network is not dependent on any one server. All of the services discussed in this chapter can be installed on one or several systems on your network.
We begin with a discussion of name service. It is an essential service that you will certainly use on your network.
Name service for converting IP addresses to hostnames
Configuration servers that simplify the installation of networked hosts by handling part or all of the TCP/IP configuration
Electronic mail services for moving mail through the network from the sender to the recipient
File servers that allow client computers to transparently share files
Print servers that allow printers to be centrally maintained and shared by all users.
Servers on a TCP/IP network should not be confused with traditional PC LAN servers. Every Unix host on your network can be both a server and a client. The hosts on a TCP/IP network are "peers." All systems are equal, and the network is not dependent on any one server. All of the services discussed in this chapter can be installed on one or several systems on your network.
We begin with a discussion of name service. It is an essential service that you will certainly use on your network.
Monday, August 25, 2008
DATA POSTING
we touched on the basic architecture and design of the TCP/IP protocols. From that discussion, we know that TCP/IP is a hierarchy of four layers. In this chapter, we explore in finer detail how data moves between the protocol layers and the systems on the network. We examine the structure of Internet addresses, including how addresses route data to its final destination and how address structure is locally redefined to create subnets. We also look at the protocol and port numbers used to deliver data to the correct applications. These additional details move us from an overview of TCP/IP to the specific implementation issues that affect your system's configuration. To deliver data between two Internet hosts, it is necessary to move the data across the network to the correct host, and within that host to the correct user or process. TCP/IP uses three schemes to accomplish these tasks:
Addressing
IP addresses, which uniquely identify every host on the network, deliver data to the correct host.
Routing
Gateways deliver data to the correct network.
Multiplexing
Protocol and port numbers deliver data to the correct software module within the host.
Each of these functions—addressing between hosts, routing between networks, and multiplexing between layers—is necessary to send data between two cooperating applications across the Internet. Let's examine each of these functions in detail.
To illustrate these concepts and provide consistent examples, we'll use an imaginary corporate network. Our imaginary company brings together authors to write computer books and conduct training. Our company network is made up of several networks at our training facilities and publishing office, as well as a connection to the Internet. We are responsible for managing the Ethernet in the computing center. This network's structure, or topology.
The icons in the figure represent computer systems. There are, of course, several other imaginary systems on our imaginary network, but we'll use the hosts rodent (a workstation) and crab (a system that serves as a gateway) for most of our examples. The thick line is our computer center Ethernet, and the oval is the local network that connects our various corporate networks. The cloud is the Internet, and the numbers are IP addresses
Addressing
IP addresses, which uniquely identify every host on the network, deliver data to the correct host.
Routing
Gateways deliver data to the correct network.
Multiplexing
Protocol and port numbers deliver data to the correct software module within the host.
Each of these functions—addressing between hosts, routing between networks, and multiplexing between layers—is necessary to send data between two cooperating applications across the Internet. Let's examine each of these functions in detail.
To illustrate these concepts and provide consistent examples, we'll use an imaginary corporate network. Our imaginary company brings together authors to write computer books and conduct training. Our company network is made up of several networks at our training facilities and publishing office, as well as a connection to the Internet. We are responsible for managing the Ethernet in the computing center. This network's structure, or topology.
The icons in the figure represent computer systems. There are, of course, several other imaginary systems on our imaginary network, but we'll use the hosts rodent (a workstation) and crab (a system that serves as a gateway) for most of our examples. The thick line is our computer center Ethernet, and the oval is the local network that connects our various corporate networks. The cloud is the Internet, and the numbers are IP addresses
Friday, August 22, 2008
TCP/IP OVERVIEW
The TCP/IP protocols were adopted as Military Standards in 1983, and all hosts connected to the network were required to convert to the new protocols. To ease this conversion, funded Bolt, Beranek, and Newman (BBN) to implement TCP/IP in Berkeley (BSD) Unix. Thus began the marriage of Unix and TCP/IP. In 1985 the National Science Foundation (NSF) created NSFNet and connected it to the then-existing Internet. The original NSFNet linked together the five NSF supercomputer centers. It was smaller than the ARPAnet and no faster: 56Kbps. Still, the creation of the NSFNet was a significant event in the history of the Internet because NSF brought with it a new vision of the use of the Internet. NSF wanted to extend the network to every scientist and engineer in the United States. To accomplish this, in 1987 NSF created a new, faster backbone and a three-tiered network topology that included the backbone, regional networks, and local networks. In 1990 the ARPAnet formally passed out of existence, and in 1995 the NSFNet ceased its role as a primary Internet backbone network. Today the Internet is larger than ever and encompasses hundreds of thousands of networks worldwide. It is no longer dependent on a core (or backbone) network or on governmental support. Today's Internet is built by commercial providers. National network providers, called tier-one providers, and regional network providers create the infrastructure. Internet Service Providers (ISPs) provide local access and user services. This network of networks is linked together in the United States at several major interconnection points called Network Access Points (NAPs). The Internet has grown far beyond its original scope. The original networks and agencies that built the Internet no longer play an essential role for the current network. The Internet has evolved from a simple backbone network, through a three-tiered hierarchical structure, to a huge network of interconnected, distributed network hubs. It has grown exponentially since 1983—doubling in size every year. Through all of this incredible change one thing has remained constant: the Internet is built on the TCP/IP protocol suite. A sign of the network's success is the confusion that surrounds the term internet. Originally it was used only as the name of the network built upon IP. Now internet is a generic term used to refer to an entire class of networks. An internet (lowercase "i") is any collection of separate physical networks, interconnected by a common protocol, to form a single logical network. The Internet (uppercase "I") is the worldwide collection of interconnected networks, which grew out of the original ARPAnet, that uses IP to link the various physical networks into a single logical network. In this book, both "internet" and "Internet" refer to networks that are interconnected by TCP/IP.
Wednesday, August 20, 2008
Making a RJ45 cable tester
Crossover Cable Pin-out-
One End
----
Other End
Pin 1
Pin 3
Pin 2
Pin 6
Pin 3
Pin 1
Pin 4
Pin 4
Pin 5
Pin 5
Pin 6
Pin 2
Pin 7
Pin 7
Pin 8
Pin 8
Straight Through Connection
Pin 1 - TxD+ Pin 2 - TxD-Pin 3 - RxD+Pin 4 - Pin 5 - Pin 6 - RxD-Pin 7 -Pin 8 -
Cable: Here is what the internals of the cable look like:
Figure 1 - Internal Cable Structure and Color Coding
RJ45 Ends: Here is a diagram and pinout:
Figure 2 - RJ45 Jack and Plug Pinout
Ethernet Cables:
Standard, Straight-Through Wiring (both ends are the same):
RJ45 Pin #
Wire Color
Wire Diagram
Signal*
1
White/Orange
Transmit+
2
Orange
Transmit-
3
White/Green
Receive+
4
Blue
Unused
5
White/Blue
Unused
6
Green
Receive-
7
White/Brown
Unused
8
Brown
Unused
Table 1 - Straight-Through Cable Pinout
Cross-Over Cable:
RJ45 Pin # (END 1)
Wire Color
Diagram End #1
1
White/Orange
2
Orange
3
White/Green
4
Blue
5
White/Blue
6
Green
7
White/Brown
8
Brown
RJ45 Pin # (END 2)
Wire Color
Diagram End #2
1
White/Green
2
Green
3
White/Orange
4
Blue
5
White/Blue
6
Orange
7
White/Brown
8
Brown
Tables 2 & 3 - Cross-Over Cable Pinouts
Cross Cabling:
Wiring Diagrams for Straight Through, Cross Over and Y cables
Note: The hook is underneath in all cases and Pin one is always on the Left
Straight Through Cable
Color Code
Color
Pin 1 Pin 2 Pin 3 Pin 4 Pin 5 Pin 6 Pin 7 Pin 8
white orange orange white green blue white blue green white brown brown
Cross Over Cable
Color Code
Color
Pin 1 Pin 2 Pin 3 Pin 4 Pin 5 Pin 6 Pin 7 Pin 8
white green green white orange blue white blue orange white brown brown
Y Cable
Color Code
Color
Pin 1 Pin 2 Pin 3 Pin 6
Pin 1 Pin 2 Pin 3 Pin 6
white orange orange white green green
blue white blue white brown brown
LAN CABLING
Standard, Straight-Through Wiring (both ends are the same)(PC to HUB or HUB to HUB)
RJ45 Pin #
Wire Color
Wire Diagram
Signal*
Pin 1
White/Orange
Transmit+
Pin 2
Orange
Transmit-
Pin 3
White/Green
Receive+
Pin 4
Blue
Unused
Pin 5
White/Blue
Unused
Pin 6
Green
Receive-
Pin 7
White/Brown
Unused
Pin 8
Brown
Unused
Table 1: Straight-Through Cable Printout
Cross-Over Cable: (End 1 Side Straight & others side follows)(PC to PC)
RJ45 Pin # (END 1)
Wire Color
Diagram End #1
RJ45 Pin # (END 2)
Wire Color
Diagram End #2
Pin 1
White/Orange
Pin 1
White/Green
Pin 2
Orange
Pin 2
Green
Pin 3
White/Green
Pin 3
White/Orange
Pin 4
Blue
Pin 4
Blue
Pin 5
White/Blue
Pin 5
White/Blue
Pin 6
Green
Pin 6
Orange
Pin 7
White/Brown
Pin 7
White/Brown
Pin 8
Brown
Pin 8
Brown
Tables 2: Cross - Over Cable Printouts
Cross-Over Cable: (4 line cable)(PC to PC)
RJ45 Pin # (END 1)
Wire Color
Diagram End #1
RJ45 Pin # (END 2)
Wire Color
Diagram End #2
Pin 1
Yellow
Pin 1
Red
Pin 2
Green
Pin 2
Black
Pin 3
Red
Pin 3
Yellow
Pin 4
Pin 4
Pin 5
Pin 5
Pin 6
Black
Pin 6
Green
Pin 7
Pin 7
Pin 8
Pin 8
Tables 3: (4 line cable) Cross - Over Cable Printouts
Monday, August 18, 2008
IP EXAMPLES
Your company has a network ID of 212.107.8.0 .One router divides the network into four subnets. Each of the subnets will have a maximum of 50 hosts. What subnet mask should you use
255.255.255.128
255.255.255.192
255.255.255.224
255.255.255.240
To subdivide this network address into four subnets, use the mask 255.255.255.192. Note that
255.255.255.192=11111111.111111111.11111111.11000000
the fourth octet is used to subdivide this class c network.The two ones in the last octet present the 192, which gives 22=4 subnets. The six zeros give 26-2=62 host IDs per subnet
A computer with the IP address 12.14.231.78 is located on subnet 1. Its subnet mask is 255.255.255.0. Which computers are not local to this computer ?
121.14.231.29
120.14.231.8
121.14.102.100
121.14.231.150
121.10.231.42
Computer2 is local to computer 1 if they have the same network ID. If the computer2 has a network id different than computer1’s ID then computer2 is remote. In other words, local hosts are on the same subnet, a remote host is on the different subnet
Applying the subnet mask 255.255.255.0 to the IP address 121.14.231.78 to obtain the network ID 12.14.231.0. Note that this subnet mask identifies the first three octects of the IP address as the network ID. Therefore, any IP address that starts with 12.14.231 is on the same subnet as the computer in the question. IP addresses that start with anything else are not local to the computer in question
Which are the legitimate subnet mask ?
255.250.0.0
255.126.0.0
255.255.248.0
255.255.248.0
255.254.128.0
255.240.192.0
255.128.0.0
255.255.255.224
subnet mask must be composed of contiguous 1s followed by contiguous 0s
Consider the IP address 128.10.150.1/19 and 128.10.158.8/19 . Are the computers local or remote in location to each other ?
To determine whether two computers are local or remote to each other, calculate the network ID for each computer.If the network ID are the same, the computers are local. In others words they are the same subnet. If the network id are different, the computers are remote. A router is required to send messages between the two computers.
Computer 1
IP Address 128.10.150.1/19 10000000 00001010 10010110 00000001
Subnet mask 11111111 11111111 11100000 00000000
Network ID 10000000 00001010 10000000 00000000
Network ID in CIDR notation 128.10.128.0/19
Computer2
IP Address 128.10.158.8/19 10000000 00001010 10011110 00001000
Subnet Mask 11111111 11111111 11100000 00000000
Network ID 10000000 00001010 10000000 00000000
Network ID in CIDR notation 128.10.128.0/19
Your company uses the Class C address 201.20.5.0. You need to create five subnets with up to 25 host IDs per subnet. Which subnet mask should you use for this type of network
255.255.255.224
255.255.255.240
255.255.255.248
255.255.255.252
To subdivide this network address into five subnets, using the mask 255.255.255.224. Note that
255.255.255.224= 11111111.11111111.11111111.11100000
The fourth octect is used to subdivide the network. The subnet mask has three ones in the fourth octect. This gives 23 = 8 possible network (covering your 5). The five zeors in the fourth octect give 25 – 2 =30 possible hosts per subnet .( you need 25)
In CIDR notation this is 210.20.5.0/27
255.255.255.128
255.255.255.192
255.255.255.224
255.255.255.240
To subdivide this network address into four subnets, use the mask 255.255.255.192. Note that
255.255.255.192=11111111.111111111.11111111.11000000
the fourth octet is used to subdivide this class c network.The two ones in the last octet present the 192, which gives 22=4 subnets. The six zeros give 26-2=62 host IDs per subnet
A computer with the IP address 12.14.231.78 is located on subnet 1. Its subnet mask is 255.255.255.0. Which computers are not local to this computer ?
121.14.231.29
120.14.231.8
121.14.102.100
121.14.231.150
121.10.231.42
Computer2 is local to computer 1 if they have the same network ID. If the computer2 has a network id different than computer1’s ID then computer2 is remote. In other words, local hosts are on the same subnet, a remote host is on the different subnet
Applying the subnet mask 255.255.255.0 to the IP address 121.14.231.78 to obtain the network ID 12.14.231.0. Note that this subnet mask identifies the first three octects of the IP address as the network ID. Therefore, any IP address that starts with 12.14.231 is on the same subnet as the computer in the question. IP addresses that start with anything else are not local to the computer in question
Which are the legitimate subnet mask ?
255.250.0.0
255.126.0.0
255.255.248.0
255.255.248.0
255.254.128.0
255.240.192.0
255.128.0.0
255.255.255.224
subnet mask must be composed of contiguous 1s followed by contiguous 0s
Consider the IP address 128.10.150.1/19 and 128.10.158.8/19 . Are the computers local or remote in location to each other ?
To determine whether two computers are local or remote to each other, calculate the network ID for each computer.If the network ID are the same, the computers are local. In others words they are the same subnet. If the network id are different, the computers are remote. A router is required to send messages between the two computers.
Computer 1
IP Address 128.10.150.1/19 10000000 00001010 10010110 00000001
Subnet mask 11111111 11111111 11100000 00000000
Network ID 10000000 00001010 10000000 00000000
Network ID in CIDR notation 128.10.128.0/19
Computer2
IP Address 128.10.158.8/19 10000000 00001010 10011110 00001000
Subnet Mask 11111111 11111111 11100000 00000000
Network ID 10000000 00001010 10000000 00000000
Network ID in CIDR notation 128.10.128.0/19
Your company uses the Class C address 201.20.5.0. You need to create five subnets with up to 25 host IDs per subnet. Which subnet mask should you use for this type of network
255.255.255.224
255.255.255.240
255.255.255.248
255.255.255.252
To subdivide this network address into five subnets, using the mask 255.255.255.224. Note that
255.255.255.224= 11111111.11111111.11111111.11100000
The fourth octect is used to subdivide the network. The subnet mask has three ones in the fourth octect. This gives 23 = 8 possible network (covering your 5). The five zeors in the fourth octect give 25 – 2 =30 possible hosts per subnet .( you need 25)
In CIDR notation this is 210.20.5.0/27
JOB VIVA 6
1.What is Mail Gateway?
It is a system that performs a protocol translation between different electronic mail delivery protocols.
2.What is IGP (Interior Gateway Protocol)?
It is any routing protocol used within an autonomous system.
3.What is EGP (Exterior Gateway Protocol)?
It is the protocol the routers in neighboring autonomous systems use to identify the set of networks that can be reached within or via each autonomous system.
4.What is autonomous system?
It is a collection of routers under the control of a single administrative authority and that uses a common Interior Gateway Protocol.
5.What is BGP (Border Gateway Protocol)?
It is a protocol used to advertise the set of networks that can be reached with in an autonomous system. BGP enables this information to be shared with the autonomous system. This is newer than EGP (Exterior Gateway Protocol).
6.What is Gateway-to-Gateway protocol?
It is a protocol formerly used to exchange routing information between Internet core routers.
7.What is NVT (Network Virtual Terminal)?
It is a set of rules defining a very simple virtual terminal interaction. The NVT is used in the start of a Telnet session.
8.What is a Multi-homed Host?
It is a host that has a multiple network interfaces and that requires multiple IP addresses is called as a Multi-homed Host.
9.What is Kerberos?
It is an authentication service developed at the Massachusetts Institute of Technology. Kerberos uses encryption to prevent intruders from discovering passwords and gaining unauthorized access to files.
10.What is OSPF?
It is an Internet routing protocol that scales well, can route traffic along multiple paths, and uses knowledge of an Internet's topology to make accurate routing decisions.
11.What is Proxy ARP?
It is using a router to answer ARP requests. This will be done when the originating host believes that a destination is local, when in fact is lies beyond router.
12.What is SLIP (Serial Line Interface Protocol)?
It is a very simple protocol used for transmission of IP datagrams across a serial line.
13.What is RIP (Routing Information Protocol)?
It is a simple protocol used to exchange information between the routers.
14.What is source route?
It is a sequence of IP addresses identifying the route a datagram must follow. A source route may optionally be included in an IP datagram header.
It is a system that performs a protocol translation between different electronic mail delivery protocols.
2.What is IGP (Interior Gateway Protocol)?
It is any routing protocol used within an autonomous system.
3.What is EGP (Exterior Gateway Protocol)?
It is the protocol the routers in neighboring autonomous systems use to identify the set of networks that can be reached within or via each autonomous system.
4.What is autonomous system?
It is a collection of routers under the control of a single administrative authority and that uses a common Interior Gateway Protocol.
5.What is BGP (Border Gateway Protocol)?
It is a protocol used to advertise the set of networks that can be reached with in an autonomous system. BGP enables this information to be shared with the autonomous system. This is newer than EGP (Exterior Gateway Protocol).
6.What is Gateway-to-Gateway protocol?
It is a protocol formerly used to exchange routing information between Internet core routers.
7.What is NVT (Network Virtual Terminal)?
It is a set of rules defining a very simple virtual terminal interaction. The NVT is used in the start of a Telnet session.
8.What is a Multi-homed Host?
It is a host that has a multiple network interfaces and that requires multiple IP addresses is called as a Multi-homed Host.
9.What is Kerberos?
It is an authentication service developed at the Massachusetts Institute of Technology. Kerberos uses encryption to prevent intruders from discovering passwords and gaining unauthorized access to files.
10.What is OSPF?
It is an Internet routing protocol that scales well, can route traffic along multiple paths, and uses knowledge of an Internet's topology to make accurate routing decisions.
11.What is Proxy ARP?
It is using a router to answer ARP requests. This will be done when the originating host believes that a destination is local, when in fact is lies beyond router.
12.What is SLIP (Serial Line Interface Protocol)?
It is a very simple protocol used for transmission of IP datagrams across a serial line.
13.What is RIP (Routing Information Protocol)?
It is a simple protocol used to exchange information between the routers.
14.What is source route?
It is a sequence of IP addresses identifying the route a datagram must follow. A source route may optionally be included in an IP datagram header.
Thursday, August 14, 2008
JOB VIVA 5
1. What is virtual channel?
Virtual channel is normally a connection from one source to one destination, although multicast connections are also permitted. The other name for virtual channel is virtual circuit.
2. What is virtual path?
Along any transmission path from a given source to a given destination, a group of virtual circuits can be grouped together into what is called path.
3. What is packet filter?
Packet filter is a standard router equipped with some extra functionality. The extra functionality allows every incoming or outgoing packet to be inspected. Packets meeting some criterion are forwarded normally. Those that fail the test are dropped.
4. What is traffic shaping?
One of the main causes of congestion is that traffic is often busy. If hosts could be made to transmit at a uniform rate, congestion would be less common. Another open loop method to help manage congestion is forcing the packet to be transmitted at a more predictable rate. This is called traffic shaping.
5. What is multicast routing?
Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.
6. What is region?
When hierarchical routing is used, the routers are divided into what we will call regions, with each router knowing all the details about how to route packets to destinations within its own region, but knowing nothing about the internal structure of other regions.
7. What is silly window syndrome?
It is a problem that can ruin TCP performance. This problem occurs when data are passed to the sending TCP entity in large blocks, but an interactive application on the receiving side reads 1 byte at a time.
48. What are Digrams and Trigrams?
The most common two letter combinations are called as digrams. e.g. th, in, er, re and an. The most common three letter combinations are called as trigrams. e.g. the, ing, and, and ion.
49. Expand IDEA.
IDEA stands for International Data Encryption Algorithm.
50. What is wide-mouth frog?
Wide-mouth frog is the simplest known key distribution center (KDC) authentication protocol.
Virtual channel is normally a connection from one source to one destination, although multicast connections are also permitted. The other name for virtual channel is virtual circuit.
2. What is virtual path?
Along any transmission path from a given source to a given destination, a group of virtual circuits can be grouped together into what is called path.
3. What is packet filter?
Packet filter is a standard router equipped with some extra functionality. The extra functionality allows every incoming or outgoing packet to be inspected. Packets meeting some criterion are forwarded normally. Those that fail the test are dropped.
4. What is traffic shaping?
One of the main causes of congestion is that traffic is often busy. If hosts could be made to transmit at a uniform rate, congestion would be less common. Another open loop method to help manage congestion is forcing the packet to be transmitted at a more predictable rate. This is called traffic shaping.
5. What is multicast routing?
Sending a message to a group is called multicasting, and its routing algorithm is called multicast routing.
6. What is region?
When hierarchical routing is used, the routers are divided into what we will call regions, with each router knowing all the details about how to route packets to destinations within its own region, but knowing nothing about the internal structure of other regions.
7. What is silly window syndrome?
It is a problem that can ruin TCP performance. This problem occurs when data are passed to the sending TCP entity in large blocks, but an interactive application on the receiving side reads 1 byte at a time.
48. What are Digrams and Trigrams?
The most common two letter combinations are called as digrams. e.g. th, in, er, re and an. The most common three letter combinations are called as trigrams. e.g. the, ing, and, and ion.
49. Expand IDEA.
IDEA stands for International Data Encryption Algorithm.
50. What is wide-mouth frog?
Wide-mouth frog is the simplest known key distribution center (KDC) authentication protocol.
Wednesday, August 13, 2008
JOB VIVA 4
1. What is the difference between TFTP and FTP application layer protocols?
The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide reliability or security. It uses the fundamental packet delivery services offered by UDP.
The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to another. It uses the services offer by TCP and so is reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another for control information.
2. What are major types of networks and explain?
Ø Server-based network
Ø Peer-to-peer network
Peer-to-peer network, computers can act as both servers sharing resources and as clients using the resources.
Server-based networks provide centralized control of network resources and rely on server computers to provide security and network administration
3. What are the important topologies for networks?
Ø BUS topology:
In this each computer is directly connected to primary network cable in a single line.
Advantages:
Inexpensive, easy to install, simple to understand, easy to extend.
Ø STAR topology:
In this all computers are connected using a central hub.
Advantages:
Can be inexpensive, easy to install and reconfigure and easy to trouble shoot physical problems.
Ø RING topology:
In this all computers are connected in loop.
Advantages:
All computers have equal access to network media, installation can be simple, and signal does not degrade as much as in other topologies because each computer regenerates it.
4. What is mesh network?
A network in which there are multiple network links between computers to provide multiple paths for data to travel.
5. What is difference between baseband and broadband transmission?
In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.
6. Explain 5-4-3 rule?
In a Ethernet network, between any two points on the network ,there can be no more than five network segments or four repeaters, and of those five segments only three of segments can be populated.
7. What MAU?
In token Ring , hub is called Multistation Access Unit(MAU).
8. What is the difference between routable and non- routable protocols?
Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are designed to work on small, local networks and cannot be used with a router
9. Why should you care about the OSI Reference Model?
It provides a framework for discussing network operations and design.
10. What is logical link control?One of two sublayers of the data link layer of OSI reference model, as defined by the IEEE 802 standard. This sublayer is responsible for maintaining the link between computers when they are sending data across the physical network connection
The Trivial File Transfer Protocol (TFTP) allows a local host to obtain files from a remote host but does not provide reliability or security. It uses the fundamental packet delivery services offered by UDP.
The File Transfer Protocol (FTP) is the standard mechanism provided by TCP / IP for copying a file from one host to another. It uses the services offer by TCP and so is reliable and secure. It establishes two connections (virtual circuits) between the hosts, one for data transfer and another for control information.
2. What are major types of networks and explain?
Ø Server-based network
Ø Peer-to-peer network
Peer-to-peer network, computers can act as both servers sharing resources and as clients using the resources.
Server-based networks provide centralized control of network resources and rely on server computers to provide security and network administration
3. What are the important topologies for networks?
Ø BUS topology:
In this each computer is directly connected to primary network cable in a single line.
Advantages:
Inexpensive, easy to install, simple to understand, easy to extend.
Ø STAR topology:
In this all computers are connected using a central hub.
Advantages:
Can be inexpensive, easy to install and reconfigure and easy to trouble shoot physical problems.
Ø RING topology:
In this all computers are connected in loop.
Advantages:
All computers have equal access to network media, installation can be simple, and signal does not degrade as much as in other topologies because each computer regenerates it.
4. What is mesh network?
A network in which there are multiple network links between computers to provide multiple paths for data to travel.
5. What is difference between baseband and broadband transmission?
In a baseband transmission, the entire bandwidth of the cable is consumed by a single signal. In broadband transmission, signals are sent on multiple frequencies, allowing multiple signals to be sent simultaneously.
6. Explain 5-4-3 rule?
In a Ethernet network, between any two points on the network ,there can be no more than five network segments or four repeaters, and of those five segments only three of segments can be populated.
7. What MAU?
In token Ring , hub is called Multistation Access Unit(MAU).
8. What is the difference between routable and non- routable protocols?
Routable protocols can work with a router and can be used to build large networks. Non-Routable protocols are designed to work on small, local networks and cannot be used with a router
9. Why should you care about the OSI Reference Model?
It provides a framework for discussing network operations and design.
10. What is logical link control?One of two sublayers of the data link layer of OSI reference model, as defined by the IEEE 802 standard. This sublayer is responsible for maintaining the link between computers when they are sending data across the physical network connection
JOB VIVA 3
1. What is Bandwidth?
Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited range is called the bandwidth.
2. What are the types of Transmission media?
Signals are usually transmitted over some transmission media that are broadly classified in to two categories.
a) Guided Media:
These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.
b) Unguided Media:
This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony.
3. What is Project 802?
It is a project started by IEEE to set standards to enable intercommunication between equipment from a variety of manufacturers. It is a way for specifying functions of the physical layer, the data link layer and to some extent the network layer to allow for interconnectivity of major LAN
protocols.
It consists of the following:
Ø 802.1 is an internetworking standard for compatibility of different LANs and MANs across protocols.
Ø 802.2 Logical link control (LLC) is the upper sublayer of the data link layer which is non-architecture-specific, that is remains the same for all IEEE-defined LANs.
Ø Media access control (MAC) is the lower sublayer of the data link layer that contains some distinct modules each carrying proprietary information specific to the LAN product being used. The modules are Ethernet LAN (802.3), Token ring LAN (802.4), Token bus LAN (802.5).
Ø 802.6 is distributed queue dual bus (DQDB) designed to be used in MANs.
4. What is Protocol Data Unit?
The data unit in the LLC level is called the protocol data unit (PDU). The PDU contains of four fields a destination service access point (DSAP), a source service access point (SSAP), a control field and an information field. DSAP, SSAP are addresses used by the LLC to identify the protocol stacks on the receiving and sending machines that are generating and using the data. The control field specifies whether the PDU frame is a information frame (I - frame) or a supervisory frame (S - frame) or a unnumbered frame (U - frame).
5. What are the different type of networking / internetworking devices?
Repeater:
Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the network before it becomes weak, regenerates the original bit pattern and puts the refreshed copy back in to the link.
Bridges:
These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller segments. They contain logic that allow them to keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment containing the intended recipent and control congestion.
Routers:
They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical, data link and network layers. They contain software that enable them to determine which of the several possible paths is the best for a particular transmission.
Gateways:
They relay packets among networks that have different protocols (e.g. between a LAN and a WAN). They accept a packet formatted for one protocol and convert it to a packet formatted for another protocol before forwarding it. They operate in all seven layers of the OSI model.
6. What is ICMP?
ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to send notification of datagram problems back to the sender. It uses the echo test / reply to test whether a destination is reachable and responding. It also handles both control and error messages.
7. What are the data units at different layers of the TCP / IP protocol suite?
The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and finally transmitted as signals along the transmission media.
8. What is difference between ARP and RARP?
The address resolution protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used by a host or a router to find the physical address of another host on its network by sending a ARP query packet that includes the IP address of the receiver.
The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its physical address.
9. What is the minimum and maximum length of the header in the TCP segment and IP datagram?
The header should have a minimum length of 20 bytes and can have a maximum length of 60 bytes.
10. What is the range of addresses in the classes of internet addresses?
Class A 0.0.0.0 - 127.255.255.255
Class B 128.0.0.0 - 191.255.255.255
Class C 192.0.0.0 - 223.255.255.255
Class D 224.0.0.0 - 239.255.255.255
Class E 240.0.0.0 - 247.255.255.255
Every line has an upper limit and a lower limit on the frequency of signals it can carry. This limited range is called the bandwidth.
2. What are the types of Transmission media?
Signals are usually transmitted over some transmission media that are broadly classified in to two categories.
a) Guided Media:
These are those that provide a conduit from one device to another that include twisted-pair, coaxial cable and fiber-optic cable. A signal traveling along any of these media is directed and is contained by the physical limits of the medium. Twisted-pair and coaxial cable use metallic that accept and transport signals in the form of electrical current. Optical fiber is a glass or plastic cable that accepts and transports signals in the form of light.
b) Unguided Media:
This is the wireless media that transport electromagnetic waves without using a physical conductor. Signals are broadcast either through air. This is done through radio communication, satellite communication and cellular telephony.
3. What is Project 802?
It is a project started by IEEE to set standards to enable intercommunication between equipment from a variety of manufacturers. It is a way for specifying functions of the physical layer, the data link layer and to some extent the network layer to allow for interconnectivity of major LAN
protocols.
It consists of the following:
Ø 802.1 is an internetworking standard for compatibility of different LANs and MANs across protocols.
Ø 802.2 Logical link control (LLC) is the upper sublayer of the data link layer which is non-architecture-specific, that is remains the same for all IEEE-defined LANs.
Ø Media access control (MAC) is the lower sublayer of the data link layer that contains some distinct modules each carrying proprietary information specific to the LAN product being used. The modules are Ethernet LAN (802.3), Token ring LAN (802.4), Token bus LAN (802.5).
Ø 802.6 is distributed queue dual bus (DQDB) designed to be used in MANs.
4. What is Protocol Data Unit?
The data unit in the LLC level is called the protocol data unit (PDU). The PDU contains of four fields a destination service access point (DSAP), a source service access point (SSAP), a control field and an information field. DSAP, SSAP are addresses used by the LLC to identify the protocol stacks on the receiving and sending machines that are generating and using the data. The control field specifies whether the PDU frame is a information frame (I - frame) or a supervisory frame (S - frame) or a unnumbered frame (U - frame).
5. What are the different type of networking / internetworking devices?
Repeater:
Also called a regenerator, it is an electronic device that operates only at physical layer. It receives the signal in the network before it becomes weak, regenerates the original bit pattern and puts the refreshed copy back in to the link.
Bridges:
These operate both in the physical and data link layers of LANs of same type. They divide a larger network in to smaller segments. They contain logic that allow them to keep the traffic for each segment separate and thus are repeaters that relay a frame only the side of the segment containing the intended recipent and control congestion.
Routers:
They relay packets among multiple interconnected networks (i.e. LANs of different type). They operate in the physical, data link and network layers. They contain software that enable them to determine which of the several possible paths is the best for a particular transmission.
Gateways:
They relay packets among networks that have different protocols (e.g. between a LAN and a WAN). They accept a packet formatted for one protocol and convert it to a packet formatted for another protocol before forwarding it. They operate in all seven layers of the OSI model.
6. What is ICMP?
ICMP is Internet Control Message Protocol, a network layer protocol of the TCP/IP suite used by hosts and gateways to send notification of datagram problems back to the sender. It uses the echo test / reply to test whether a destination is reachable and responding. It also handles both control and error messages.
7. What are the data units at different layers of the TCP / IP protocol suite?
The data unit created at the application layer is called a message, at the transport layer the data unit created is called either a segment or an user datagram, at the network layer the data unit created is called the datagram, at the data link layer the datagram is encapsulated in to a frame and finally transmitted as signals along the transmission media.
8. What is difference between ARP and RARP?
The address resolution protocol (ARP) is used to associate the 32 bit IP address with the 48 bit physical address, used by a host or a router to find the physical address of another host on its network by sending a ARP query packet that includes the IP address of the receiver.
The reverse address resolution protocol (RARP) allows a host to discover its Internet address when it knows only its physical address.
9. What is the minimum and maximum length of the header in the TCP segment and IP datagram?
The header should have a minimum length of 20 bytes and can have a maximum length of 60 bytes.
10. What is the range of addresses in the classes of internet addresses?
Class A 0.0.0.0 - 127.255.255.255
Class B 128.0.0.0 - 191.255.255.255
Class C 192.0.0.0 - 223.255.255.255
Class D 224.0.0.0 - 239.255.255.255
Class E 240.0.0.0 - 247.255.255.255
JOB VIVA 2
1. What is NETBIOS and NETBEUI?
NETBIOS is a programming interface that allows I/O requests to be sent to and received from a remote computer and it hides the networking hardware from applications.
NETBEUI is NetBIOS extended user interface. A transport protocol designed by microsoft and IBM for the use on small subnets.
2. What is RAID?
A method for providing fault tolerance by using multiple hard disk drives.
3. What is passive topology?
When the computers on the network simply listen and receive the signal, they are referred to as passive because they don’t amplify the signal in any way. Example for passive topology - linear bus.
4. What is Brouter?
Hybrid devices that combine the features of both bridges and routers.
5. What is cladding?
A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.
6. What is point-to-point protocol
A communications protocol used to connect computers to remote networking services including Internet service providers.
7. How Gateway is different from Routers?
A gateway operates at the upper levels of the OSI model and translates information between two completely different network architectures or data formats
8. What is attenuation?
The degeneration of a signal over distance on a network cable is called attenuation.
9. What is MAC address?
The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture. MAC address is usually stored in ROM on the network adapter card and is unique.
10. Difference between bit rate and baud rate.
Bit rate is the number of bits transmitted during one second whereas baud rate refers to the number of signal units per second that are required to represent those bits.
baud rate = bit rate / N where N is no-of-bits represented by each signal shift
NETBIOS is a programming interface that allows I/O requests to be sent to and received from a remote computer and it hides the networking hardware from applications.
NETBEUI is NetBIOS extended user interface. A transport protocol designed by microsoft and IBM for the use on small subnets.
2. What is RAID?
A method for providing fault tolerance by using multiple hard disk drives.
3. What is passive topology?
When the computers on the network simply listen and receive the signal, they are referred to as passive because they don’t amplify the signal in any way. Example for passive topology - linear bus.
4. What is Brouter?
Hybrid devices that combine the features of both bridges and routers.
5. What is cladding?
A layer of a glass surrounding the center fiber of glass inside a fiber-optic cable.
6. What is point-to-point protocol
A communications protocol used to connect computers to remote networking services including Internet service providers.
7. How Gateway is different from Routers?
A gateway operates at the upper levels of the OSI model and translates information between two completely different network architectures or data formats
8. What is attenuation?
The degeneration of a signal over distance on a network cable is called attenuation.
9. What is MAC address?
The address for a device as it is identified at the Media Access Control (MAC) layer in the network architecture. MAC address is usually stored in ROM on the network adapter card and is unique.
10. Difference between bit rate and baud rate.
Bit rate is the number of bits transmitted during one second whereas baud rate refers to the number of signal units per second that are required to represent those bits.
baud rate = bit rate / N where N is no-of-bits represented by each signal shift
Tuesday, August 12, 2008
JOB VIVA 1
Computer Networks
1. What are the two types of transmission technology available?
(i) Broadcast and (ii) point-to-point
2. What is subnet?
A generic term for section of a large networks usually separated by a bridge or router.
3. Difference between the communication and transmission.
Transmission is a physical movement of information and concern issues like bit polarity, synchronisation, clock etc.
Communication means the meaning full exchange of information between two communication media.
4. What are the possible ways of data exchange?
(i) Simplex (ii) Half-duplex (iii) Full-duplex.
5. What is SAP?
Series of interface points that allow other computers to communicate with the other layers of network protocol stack.
6. What do you meant by "triple X" in Networks?
The function of PAD (Packet Assembler Disassembler) is described in a document known as X.3. The standard protocol has been defined between the terminal and the PAD, called X.28; another standard protocol exists between hte PAD and the network, called X.29. Together, these three recommendations are often called "triple X"
7. What is frame relay, in which layer it comes?
Frame relay is a packet switching technology. It will operate in the data link layer.
8. What is terminal emulation, in which layer it comes?
Telnet is also called as terminal emulation. It belongs to application layer.
9. What is Beaconing?
The process that allows a network to self-repair networks problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.
10. What is redirector?
Redirector is software that intercepts file or prints I/O requests and translates them into network requests. This comes under presentation layer.
1. What are the two types of transmission technology available?
(i) Broadcast and (ii) point-to-point
2. What is subnet?
A generic term for section of a large networks usually separated by a bridge or router.
3. Difference between the communication and transmission.
Transmission is a physical movement of information and concern issues like bit polarity, synchronisation, clock etc.
Communication means the meaning full exchange of information between two communication media.
4. What are the possible ways of data exchange?
(i) Simplex (ii) Half-duplex (iii) Full-duplex.
5. What is SAP?
Series of interface points that allow other computers to communicate with the other layers of network protocol stack.
6. What do you meant by "triple X" in Networks?
The function of PAD (Packet Assembler Disassembler) is described in a document known as X.3. The standard protocol has been defined between the terminal and the PAD, called X.28; another standard protocol exists between hte PAD and the network, called X.29. Together, these three recommendations are often called "triple X"
7. What is frame relay, in which layer it comes?
Frame relay is a packet switching technology. It will operate in the data link layer.
8. What is terminal emulation, in which layer it comes?
Telnet is also called as terminal emulation. It belongs to application layer.
9. What is Beaconing?
The process that allows a network to self-repair networks problems. The stations on the network notify the other stations on the ring when they are not receiving the transmissions. Beaconing is used in Token ring and FDDI networks.
10. What is redirector?
Redirector is software that intercepts file or prints I/O requests and translates them into network requests. This comes under presentation layer.
Supernetting
Supernetting and Classless Interdomain Routing
With the recent growth of the Internet, it became clear to the Internet authorities that the class B network IDs would soon be depleted. For most organizations, a class C network ID does not contain enough host IDs and a class B network ID has enough bits to provide a flexible subnetting scheme within the organization.
The Internet authorities devised a new method of assigning network IDs to prevent the depletion of class B network IDs. Rather than assigning a class B network ID, InterNIC assigns a range of class C network IDs that contain enough network and host IDs for the organization's needs. This is known as supernetting. For example, rather than allocating a class B network ID to an organization that has up to 2,000 hosts, the InterNIC allocates a range of eight class C network IDs. Each class C network ID accommodates 254 hosts, for a total of 2,032 host IDs.
Although this technique helps conserve class B network IDs, it creates a new problem. Using conventional routing techniques, the routers on the Internet now must have eight class C network ID entries in their routing tables to route IP packets to the organization. To prevent Internet routers from becoming overwhelmed with routes, a technique called Classless Interdomain Routing (CIDR) is used to collapse multiple network ID entries into a single entry corresponding to all of the class C network IDs allocated to that organization.
Conceptually, CIDR creates the routing table entry: [Starting Network ID, count], where Starting Network ID is the first class C network ID and the count is the number of class C network IDs allocated. In practice, a supernetted subnet mask is used to convey the same information. To express the situation where eight class C network IDs are allocated starting with network ID 220.78.168.0:
Starting Network ID
220.78.168.0
11011100 01001110 10101000 00000000
Ending Network ID
220.78.175.0
11011100 01001110 10101111 00000000
Note that the first 21 bits (underlined) of all the above Class C network IDs are the same. The last three bits of the third octet vary from 000 to 111. The CIDR entry in the routing tables of the Internet routers becomes:
Network ID
Subnet Mask
Subnet Mask (binary)
220.78.168.0
255.255.248.0
11111111 11111111 11111000 0000000
In network prefix or CIDR notation, the CIDR entry is 220.78.168.0/21.
A block of addresses using CIDR is known as a CIDR block.
With the recent growth of the Internet, it became clear to the Internet authorities that the class B network IDs would soon be depleted. For most organizations, a class C network ID does not contain enough host IDs and a class B network ID has enough bits to provide a flexible subnetting scheme within the organization.
The Internet authorities devised a new method of assigning network IDs to prevent the depletion of class B network IDs. Rather than assigning a class B network ID, InterNIC assigns a range of class C network IDs that contain enough network and host IDs for the organization's needs. This is known as supernetting. For example, rather than allocating a class B network ID to an organization that has up to 2,000 hosts, the InterNIC allocates a range of eight class C network IDs. Each class C network ID accommodates 254 hosts, for a total of 2,032 host IDs.
Although this technique helps conserve class B network IDs, it creates a new problem. Using conventional routing techniques, the routers on the Internet now must have eight class C network ID entries in their routing tables to route IP packets to the organization. To prevent Internet routers from becoming overwhelmed with routes, a technique called Classless Interdomain Routing (CIDR) is used to collapse multiple network ID entries into a single entry corresponding to all of the class C network IDs allocated to that organization.
Conceptually, CIDR creates the routing table entry: [Starting Network ID, count], where Starting Network ID is the first class C network ID and the count is the number of class C network IDs allocated. In practice, a supernetted subnet mask is used to convey the same information. To express the situation where eight class C network IDs are allocated starting with network ID 220.78.168.0:
Starting Network ID
220.78.168.0
11011100 01001110 10101000 00000000
Ending Network ID
220.78.175.0
11011100 01001110 10101111 00000000
Note that the first 21 bits (underlined) of all the above Class C network IDs are the same. The last three bits of the third octet vary from 000 to 111. The CIDR entry in the routing tables of the Internet routers becomes:
Network ID
Subnet Mask
Subnet Mask (binary)
220.78.168.0
255.255.248.0
11111111 11111111 11111000 0000000
In network prefix or CIDR notation, the CIDR entry is 220.78.168.0/21.
A block of addresses using CIDR is known as a CIDR block.
V L Subnetting
Variable Length Subnetting
One of the original uses for subnetting was to subdivide a class-based network ID into a series of equal-sized subnets. For example, a 4-bit subnetting of a class B network ID produced 16 equal-sized subnets (using the all-ones and all-zeros subnets). However, subnetting is a general method of utilizing host bits to express subnets and does not require equal-sized subnets.
Subnets of different size can exist within a class-based network ID. This is well-suited to real-world environments, where networks of an organization contain different numbers of hosts, and different-sized subnets are needed to minimize the wasting of IP addresses. The creation and deployment of various-sized subnets of a network ID is known as variable length subnetting and uses variable length subnet masks (VLSM).
Variable length subnetting is a technique of allocating subnetted network IDs that use subnet masks of different sizes. However, all subnetted network IDs are unique and can be distinguished from each other by their corresponding subnet mask.
The mechanics of variable length subnetting are essentially that of performing subnetting on a previously subnetted network ID. When subnetting, the network ID bits are fixed and a certain number of host bits are chosen to express subnets. With variable length subnetting, the network ID being subnetted has already been subnetted.
For example, given the class-based network ID of 135.41.0.0/16, a required configuration is one subnet with up to 32,000 hosts, 15 subnets with up to 2,000 hosts, and eight subnets with up to 250 hosts.
One Subnet with up to 32,000 Hosts
To achieve a requirement of one subnet with approximately 32,000 hosts, a 1-bit subnetting of the class-based network ID of 135.41.0.0 is done, producing 2 subnets, 135.41.0.0/17 and 135.41.128.0/17. This subnetting allows up to 32,766 hosts per subnet. 135.41.0.0/17 is chosen as the network ID, which fulfills the requirement.
Table 1.12 shows one subnet with up to 32,766 hosts per subnet.
Table 1.12 One Subnet with up to 32,766 Hosts
Subnet Number
Network ID (Dotted Decimal)
Network ID (Network Prefix)
1
135.41.0.0, 255.255.128.0
135.41.0.0/17
Fifteen Subnets with up to 2,000 Hosts
To achieve a requirement of 15 subnets with approximately 2,000 hosts, a 4-bit subnetting of the subnetted network ID of 135.41.128.0/17 is done. This produces 16 subnets (135.41.128.0/21, 135.41.136.0/21 . . . 135.41.240.0/21, 135.41.248.0/21), allowing up to 2,046 hosts per subnet. The first 15 subnetted network IDs (135.41.128.0/21 to 135.41.240.0/21) are chosen as the network IDs, which fulfills the requirement.
Table 1.13 illustrates 15 subnets with up to 2,046 hosts per subnet.
Table 1.13 Fifteen Subnets with up to 2,046 Hosts
Subnet Number
Network ID (Dotted Decimal)
Network ID (Network Prefix)
1
135.41.128.0, 255.255.248.0
135.41.128.0/21
2
135.41.136.0, 255.255.248.0
135.41.136.0/21
3
135.41.144.0, 255.255.248.0
135.41.144.0/21
4
135.41.152.0, 255.255.248.0
135.41.152.0/21
5
135.41.160.0, 255.255.248.0
135.41.160.0/21
6
135.41.168.0, 255.255.248.0
135.41.168.0/21
7
135.41.176.0, 255.255.248.0
135.41.176.0/21
8
135.41.184.0, 255.255.248.0
135.41.184.0/21
9
135.41.192.0, 255.255.248.0
135.41.192.0/21
10
135.41.200.0, 255.255.248.0
135.41.200.0/21
11
135.41.208.0, 255.255.248.0
135.41.208.0/21
12
135.41.216.0, 255.255.248.0
135.41.216.0/21
13
135.41.224.0, 255.255.248.0
135.41.224.0/21
14
135.41.232.0, 255.255.248.0
135.41.232.0/21
15
135.41.240.0, 255.255.248.0
135.41.240.0/21
Eight Subnets with up to 250 Hosts
To achieve a requirement of eight subnets with up to 250 hosts, a 3-bit subnetting of subnetted network ID of 135.41.248.0/21 is done, producing eight subnets (135.41.248.0/24, 135.41.249.0/24 . . . 135.41.254.0/24, 135.41.255.0/24) and allowing up to 254 hosts per subnet. All 8 subnetted network IDs (135.41.248.0/24 to 135.41.255.0/24) are chosen as the network IDs, which fulfills the requirement.
Table 1.14 illustrates eight subnets with 254 hosts per subnet.
Table 1.14 Eight subnets with up to 254 Hosts
Subnet Number
Network ID (Dotted Decimal)
Network ID (Network Prefix)
1
135.41.248.0, 255.255.255.0
135.41.248.0/24
2
135.41.249.0, 255.255.255.0
135.41.249.0/24
3
135.41.250.0, 255.255.255.0
135.41.250.0/24
4
135.41.251.0, 255.255.255.0
135.41.251.0/24
5
135.41.252.0, 255.255.255.0
135.41.252.0/24
6
135.41.253.0, 255.255.255.0
135.41.253.0/24
7
135.41.254.0, 255.255.255.0
135.41.254.0/24
8
135.41.255.0, 255.255.255.0
135.41.255.0/24
One of the original uses for subnetting was to subdivide a class-based network ID into a series of equal-sized subnets. For example, a 4-bit subnetting of a class B network ID produced 16 equal-sized subnets (using the all-ones and all-zeros subnets). However, subnetting is a general method of utilizing host bits to express subnets and does not require equal-sized subnets.
Subnets of different size can exist within a class-based network ID. This is well-suited to real-world environments, where networks of an organization contain different numbers of hosts, and different-sized subnets are needed to minimize the wasting of IP addresses. The creation and deployment of various-sized subnets of a network ID is known as variable length subnetting and uses variable length subnet masks (VLSM).
Variable length subnetting is a technique of allocating subnetted network IDs that use subnet masks of different sizes. However, all subnetted network IDs are unique and can be distinguished from each other by their corresponding subnet mask.
The mechanics of variable length subnetting are essentially that of performing subnetting on a previously subnetted network ID. When subnetting, the network ID bits are fixed and a certain number of host bits are chosen to express subnets. With variable length subnetting, the network ID being subnetted has already been subnetted.
For example, given the class-based network ID of 135.41.0.0/16, a required configuration is one subnet with up to 32,000 hosts, 15 subnets with up to 2,000 hosts, and eight subnets with up to 250 hosts.
One Subnet with up to 32,000 Hosts
To achieve a requirement of one subnet with approximately 32,000 hosts, a 1-bit subnetting of the class-based network ID of 135.41.0.0 is done, producing 2 subnets, 135.41.0.0/17 and 135.41.128.0/17. This subnetting allows up to 32,766 hosts per subnet. 135.41.0.0/17 is chosen as the network ID, which fulfills the requirement.
Table 1.12 shows one subnet with up to 32,766 hosts per subnet.
Table 1.12 One Subnet with up to 32,766 Hosts
Subnet Number
Network ID (Dotted Decimal)
Network ID (Network Prefix)
1
135.41.0.0, 255.255.128.0
135.41.0.0/17
Fifteen Subnets with up to 2,000 Hosts
To achieve a requirement of 15 subnets with approximately 2,000 hosts, a 4-bit subnetting of the subnetted network ID of 135.41.128.0/17 is done. This produces 16 subnets (135.41.128.0/21, 135.41.136.0/21 . . . 135.41.240.0/21, 135.41.248.0/21), allowing up to 2,046 hosts per subnet. The first 15 subnetted network IDs (135.41.128.0/21 to 135.41.240.0/21) are chosen as the network IDs, which fulfills the requirement.
Table 1.13 illustrates 15 subnets with up to 2,046 hosts per subnet.
Table 1.13 Fifteen Subnets with up to 2,046 Hosts
Subnet Number
Network ID (Dotted Decimal)
Network ID (Network Prefix)
1
135.41.128.0, 255.255.248.0
135.41.128.0/21
2
135.41.136.0, 255.255.248.0
135.41.136.0/21
3
135.41.144.0, 255.255.248.0
135.41.144.0/21
4
135.41.152.0, 255.255.248.0
135.41.152.0/21
5
135.41.160.0, 255.255.248.0
135.41.160.0/21
6
135.41.168.0, 255.255.248.0
135.41.168.0/21
7
135.41.176.0, 255.255.248.0
135.41.176.0/21
8
135.41.184.0, 255.255.248.0
135.41.184.0/21
9
135.41.192.0, 255.255.248.0
135.41.192.0/21
10
135.41.200.0, 255.255.248.0
135.41.200.0/21
11
135.41.208.0, 255.255.248.0
135.41.208.0/21
12
135.41.216.0, 255.255.248.0
135.41.216.0/21
13
135.41.224.0, 255.255.248.0
135.41.224.0/21
14
135.41.232.0, 255.255.248.0
135.41.232.0/21
15
135.41.240.0, 255.255.248.0
135.41.240.0/21
Eight Subnets with up to 250 Hosts
To achieve a requirement of eight subnets with up to 250 hosts, a 3-bit subnetting of subnetted network ID of 135.41.248.0/21 is done, producing eight subnets (135.41.248.0/24, 135.41.249.0/24 . . . 135.41.254.0/24, 135.41.255.0/24) and allowing up to 254 hosts per subnet. All 8 subnetted network IDs (135.41.248.0/24 to 135.41.255.0/24) are chosen as the network IDs, which fulfills the requirement.
Table 1.14 illustrates eight subnets with 254 hosts per subnet.
Table 1.14 Eight subnets with up to 254 Hosts
Subnet Number
Network ID (Dotted Decimal)
Network ID (Network Prefix)
1
135.41.248.0, 255.255.255.0
135.41.248.0/24
2
135.41.249.0, 255.255.255.0
135.41.249.0/24
3
135.41.250.0, 255.255.255.0
135.41.250.0/24
4
135.41.251.0, 255.255.255.0
135.41.251.0/24
5
135.41.252.0, 255.255.255.0
135.41.252.0/24
6
135.41.253.0, 255.255.255.0
135.41.253.0/24
7
135.41.254.0, 255.255.255.0
135.41.254.0/24
8
135.41.255.0, 255.255.255.0
135.41.255.0/24
Subnetting
Subnetting
Although the conceptual notion of subnetting by utilizing host bits is straightforward, the actual mechanics of subnetting are a bit more complicated. Subnetting requires a three step procedure:
Determine the number of host bits to be used for the subnetting.
Enumerate the new subnetted network IDs.
Enumerate the IP addresses for each new subnetted network ID.
Step 1: Determining the Number of Host Bits
The number of host bits being used for subnetting determines the possible number of subnets and hosts per subnet. Before you choose the number of host bits, you should have a good idea of the number of subnets and hosts you will have in the future. Using more bits for the subnet mask than required saves you the time of reassigning IP addresses in the future.
The more host bits that are used, the more subnets (subnetted network IDs) you can have — but with fewer hosts. Using too many host bits allows for growth in the number of subnets but limits the growth in the number of hosts. Using too few hosts allows for growth in the number of hosts but limits the growth in the number of subnets.
In practice, network administrators define a maximum number of nodes they want on a single network. Recall that all nodes on a single network share all the same broadcast traffic; they reside in the same broadcast domain. Therefore, growth in the number of subnets is favored over growth in the number of hosts per subnet.
Follow these guidelines to determine the number of host bits to use for subnetting.
Determine how many subnets you need now and will need in the future. Each physical network is a subnet. WAN connections can also count as subnets depending on whether your routers support unnumbered connections.
Use additional bits for the subnet mask if:
You will never require as many hosts per subnet as allowed by the remaining bits.
The number of subnets will increase in the future, requiring additional host bits.
To determine the desired subnetting scheme, start with an existing network ID to be subnetted. The network ID to be subnetted can be a class-based network ID, a subnetted network ID, or a supernet. The existing network ID contains a series of network ID bits that are fixed and a series of host ID bits that are variable. Based on your requirements for the number of subnets and the number of hosts per subnet, choose a specific number of host bits to be used for the subnetting.
Table 1.6 shows the subnetting of a class A network ID. Based on a required number of subnets, and a maximum number of hosts per subnet, a subnetting scheme can be chosen.
Table 1.6 Subnetting a Class A Network ID
Required Number of Subnets
Number of Subnet Bits
Subnet Mask
Number of Hosts per Subnet
1-2
1
255.128.0.0 or /9
8,388,606
3-4
2
255.192.0.0 or /10
4,194,302
5-8
3
255.224.0.0 or /11
2,097,150
9-16
4
255.240.0.0 or /12
1,048,574
17-32
5
255.248.0.0 or /13
524,286
33-64
6
255.252.0.0 or /14
262,142
65-128
7
255.254.0.0 or /15
131,070
129-256
8
255.255.0.0 or /16
65,534
257-512
9
255.255.128.0 or /17
32,766
513-1,024
10
255.255.192.0 or /18
16,382
1,025-2,048
11
255.255.224.0 or /19
8,190
2,049-4,096
12
255.255.240.0 or /20
4,094
4,097-8,192
13
255.255.248.0 or /21
2,046
8,193-16,384
14
255.255.252.0 or /22
1,022
16,385-32,768
15
255.255.254.0 or /23
510
32,769-65,536
16
255.255.255.0 or /24
254
65,537-131,072
17
255.255.255.128 or /25
126
131,073-262,144
18
255.255.255.192 or /26
62
262,145-524,288
19
255.255.255.224 or /27
30
524,289-1,048,576
20
255.255.255.240 or /28
14
1,048,577-2,097,152
21
255.255.255.248 or /29
6
2,097,153-4,194,304
22
255.255.255.252 or /30
2
Table 1.7 shows the subnetting of a class B network ID.
Table 1.7 Subnetting a Class B Network ID
Required Number of Subnets
Number of Subnet Bits
Subnet Mask
Number of Hosts per Subnet
1-2
1
255.255.128.0 or /17
32,766
3-4
2
255.255.192.0 or /18
16,382
5-8
3
255.255.224.0 or /19
8,190
9-16
4
255.255.240.0 or /20
4,094
17-32
5
255.255.248.0 or /21
2,046
33-64
6
255.255.252.0 or /22
1,022
65-128
7
255.255.254.0 or /23
510
129-256
8
255.255.255.0 or /24
254
257-512
9
255.255.255.128 or /25
126
513-1,024
10
255.255.255.192 or /26
62
1,025-2,048
11
255.255.255.224 or /27
30
2,049-4,096
12
255.255.255.240 or /28
14
4,097-8,192
13
255.255.255.248 or /29
6
8,193-16,384
14
255.255.255.252 or /30
2
Table 1.8 shows the subnetting of a class C network ID.
Table 1.8 Subnetting a Class C Network ID
Required Number of Subnets
Number of Subnet Bits
Subnet Mask
Number of Hosts per Subnet
1-2
1
255.255.255.128 or /25
126
3-4
2
255.255.255.192 or /26
62
5-8
3
255.255.255.224 or /27
30
9-16
4
255.255.255.240 or /28
14
17-32
5
255.255.255.248 or /29
6
33-64
6
255.255.255.252 or /30
2
Step 2: Enumerating Subnetted Network IDs
Based on the number of host bits you use for your subnetting, you must list the new subnetted network IDs. There are two main approaches:
Binary—List all possible combinations of the host bits chosen for subnetting and convert each combination to dotted decimal notation.
Decimal—Add a calculated increment value to each successive subnetted network ID and convert to dotted decimal notation.
Either method produces the same result: the enumerated list of subnetted network IDs.
To create the enumerated list of subnetted network IDs using the binary method
Based on n, the number of host bits chosen for subnetting, create a three-column table with 2n entries. The first column is the subnet number (starting with 1), the second column is the binary representation of the subnetted network ID, and the third column is the dotted decimal representation of the subnetted network ID.
For each binary representation, the bits of the network ID being subnetted are fixed to their appropriate values and the remaining host bits are set to all 0's. The host bits chosen for subnetting vary.
In the first table entry, set the subnet bits to all 0's and convert to dotted decimal notation. The original network ID is subnetted with its new subnet mask.
In the next table entry, increase the value within the subnet bits.
Convert the binary result to dotted decimal notation.
Repeat steps 3 and 4 until the table is complete.
For example, create a 3-bit subnet of the private network ID 192.168.0.0. The subnet mask for the new subnetted network IDs is 255.255.224.0 or /19. Based on n = 3, construct a table with 8 (= 23) entries. The entry for subnet 1 is the all 0's subnet. Additional entries in the table are successive increments of the subnet bits, as shown in Table 1.9. The host bits used for subnetting are underlined.
Table 1.9 Binary Subnetting Technique for Network ID 192.168.0.0
Subnet
Binary Representation
Subnetted Network ID
1
11000000.10101000.00000000.00000000
192.168.0.0/19
2
11000000.10101000.00100000.00000000
192.168.32.0/19
3
11000000.10101000.01000000.00000000
192.168.64.0/19
4
11000000.10101000.01100000.00000000
192.168.96.0/19
5
11000000.10101000.10000000.00000000
192.168.128.0/19
6
11000000.10101000.10100000.00000000
192.168.160.0/19
7
11000000.10101000.11000000.00000000
192.168.192.0/19
8
11000000.10101000.11100000.00000000
192.168.224.0/19
Step 3: Enumerating IP Addresses for Each Subnetted Network ID
Based on the enumeration of the subnetted network IDs, you must now list the valid IP addresses for new subnetted network IDs. To list each IP address individually would be too tedious. Instead, enumerate the IP addresses for each subnetted network ID by defining the range of IP addresses (the first and the last) for each subnetted network ID. There are two main approaches:
Binary—Write down the first and last IP address for each subnetted network ID and convert to dotted decimal notation.
Decimal—Add values incrementally, corresponding to the first and last IP addresses for each subnetted network ID and convert to dotted decimal notation.
Either method produces the same result: the range of IP addresses for each subnetted network ID.
To create the range of IP addresses using the binary method
Based on n, the number of host bits chosen for subnetting, create a three-column table with 2n entries. The first column is the subnet number (starting with 1), the second column is the binary representation of the first and last IP address for the subnetted network ID, and the third column is the dotted decimal representation of the first and last IP address of the subnetted network ID. Alternately, add two columns to the previous table used for enumerating the subnetted network IDs.
For each binary representation, the first IP address is the address in which all the host bits are set to 0 except for the last host bit. The last IP address is the address in which all the host bits are set to 1 except for the last host bit.
Convert the binary representation to dotted decimal notation.
Repeat steps 2 and 3 until the table is complete.
For example, the range of IP addresses for the 3 bit subnetting of 192.168.0.0 is shown in Table 1.11. The bits used for subnetting are underlined.
Table 1.11 Binary Enumeration of IP Addresses
Subnet
Binary Representation
Range of IP Addresses
1
11000000.10101000.00000000.00000001 -11000000.10101000.00011111.11111110
192.168.0.1 - 192.168.31.254
2
11000000.10101000.00100000.00000001 -11000000.10101000.00111111.11111110
192.168.32.1 - 192.168.63.254
3
11000000.10101000.01000000.00000001 - 11000000.10101000.01011111.11111110
192.168.64.1 - 192.168.95.254
4
11000000.10101000.01100000.00000001 -11000000.10101000.01111111.11111110
192.168.96.1 - 192.168.127.254
5
11000000.10101000.10000000.00000001 - 11000000.10101000.10011111.11111110
192.168.128.1 - 192.168.159.254
6
11000000.10101000.10100000.00000001 - 11000000.10101000.10111111.11111110
192.168.160.1 - 192.168.191.254
7
11000000.10101000.11000000.00000001 -11000000.10101000.11011111.11111110
192.168.192.1 - 192.168.223.254
8
11000000.10101000.11100000.00000001 - 11000000.10101000.11111111.11111110
192.168.224.1 - 192.168.255.254
Although the conceptual notion of subnetting by utilizing host bits is straightforward, the actual mechanics of subnetting are a bit more complicated. Subnetting requires a three step procedure:
Determine the number of host bits to be used for the subnetting.
Enumerate the new subnetted network IDs.
Enumerate the IP addresses for each new subnetted network ID.
Step 1: Determining the Number of Host Bits
The number of host bits being used for subnetting determines the possible number of subnets and hosts per subnet. Before you choose the number of host bits, you should have a good idea of the number of subnets and hosts you will have in the future. Using more bits for the subnet mask than required saves you the time of reassigning IP addresses in the future.
The more host bits that are used, the more subnets (subnetted network IDs) you can have — but with fewer hosts. Using too many host bits allows for growth in the number of subnets but limits the growth in the number of hosts. Using too few hosts allows for growth in the number of hosts but limits the growth in the number of subnets.
In practice, network administrators define a maximum number of nodes they want on a single network. Recall that all nodes on a single network share all the same broadcast traffic; they reside in the same broadcast domain. Therefore, growth in the number of subnets is favored over growth in the number of hosts per subnet.
Follow these guidelines to determine the number of host bits to use for subnetting.
Determine how many subnets you need now and will need in the future. Each physical network is a subnet. WAN connections can also count as subnets depending on whether your routers support unnumbered connections.
Use additional bits for the subnet mask if:
You will never require as many hosts per subnet as allowed by the remaining bits.
The number of subnets will increase in the future, requiring additional host bits.
To determine the desired subnetting scheme, start with an existing network ID to be subnetted. The network ID to be subnetted can be a class-based network ID, a subnetted network ID, or a supernet. The existing network ID contains a series of network ID bits that are fixed and a series of host ID bits that are variable. Based on your requirements for the number of subnets and the number of hosts per subnet, choose a specific number of host bits to be used for the subnetting.
Table 1.6 shows the subnetting of a class A network ID. Based on a required number of subnets, and a maximum number of hosts per subnet, a subnetting scheme can be chosen.
Table 1.6 Subnetting a Class A Network ID
Required Number of Subnets
Number of Subnet Bits
Subnet Mask
Number of Hosts per Subnet
1-2
1
255.128.0.0 or /9
8,388,606
3-4
2
255.192.0.0 or /10
4,194,302
5-8
3
255.224.0.0 or /11
2,097,150
9-16
4
255.240.0.0 or /12
1,048,574
17-32
5
255.248.0.0 or /13
524,286
33-64
6
255.252.0.0 or /14
262,142
65-128
7
255.254.0.0 or /15
131,070
129-256
8
255.255.0.0 or /16
65,534
257-512
9
255.255.128.0 or /17
32,766
513-1,024
10
255.255.192.0 or /18
16,382
1,025-2,048
11
255.255.224.0 or /19
8,190
2,049-4,096
12
255.255.240.0 or /20
4,094
4,097-8,192
13
255.255.248.0 or /21
2,046
8,193-16,384
14
255.255.252.0 or /22
1,022
16,385-32,768
15
255.255.254.0 or /23
510
32,769-65,536
16
255.255.255.0 or /24
254
65,537-131,072
17
255.255.255.128 or /25
126
131,073-262,144
18
255.255.255.192 or /26
62
262,145-524,288
19
255.255.255.224 or /27
30
524,289-1,048,576
20
255.255.255.240 or /28
14
1,048,577-2,097,152
21
255.255.255.248 or /29
6
2,097,153-4,194,304
22
255.255.255.252 or /30
2
Table 1.7 shows the subnetting of a class B network ID.
Table 1.7 Subnetting a Class B Network ID
Required Number of Subnets
Number of Subnet Bits
Subnet Mask
Number of Hosts per Subnet
1-2
1
255.255.128.0 or /17
32,766
3-4
2
255.255.192.0 or /18
16,382
5-8
3
255.255.224.0 or /19
8,190
9-16
4
255.255.240.0 or /20
4,094
17-32
5
255.255.248.0 or /21
2,046
33-64
6
255.255.252.0 or /22
1,022
65-128
7
255.255.254.0 or /23
510
129-256
8
255.255.255.0 or /24
254
257-512
9
255.255.255.128 or /25
126
513-1,024
10
255.255.255.192 or /26
62
1,025-2,048
11
255.255.255.224 or /27
30
2,049-4,096
12
255.255.255.240 or /28
14
4,097-8,192
13
255.255.255.248 or /29
6
8,193-16,384
14
255.255.255.252 or /30
2
Table 1.8 shows the subnetting of a class C network ID.
Table 1.8 Subnetting a Class C Network ID
Required Number of Subnets
Number of Subnet Bits
Subnet Mask
Number of Hosts per Subnet
1-2
1
255.255.255.128 or /25
126
3-4
2
255.255.255.192 or /26
62
5-8
3
255.255.255.224 or /27
30
9-16
4
255.255.255.240 or /28
14
17-32
5
255.255.255.248 or /29
6
33-64
6
255.255.255.252 or /30
2
Step 2: Enumerating Subnetted Network IDs
Based on the number of host bits you use for your subnetting, you must list the new subnetted network IDs. There are two main approaches:
Binary—List all possible combinations of the host bits chosen for subnetting and convert each combination to dotted decimal notation.
Decimal—Add a calculated increment value to each successive subnetted network ID and convert to dotted decimal notation.
Either method produces the same result: the enumerated list of subnetted network IDs.
To create the enumerated list of subnetted network IDs using the binary method
Based on n, the number of host bits chosen for subnetting, create a three-column table with 2n entries. The first column is the subnet number (starting with 1), the second column is the binary representation of the subnetted network ID, and the third column is the dotted decimal representation of the subnetted network ID.
For each binary representation, the bits of the network ID being subnetted are fixed to their appropriate values and the remaining host bits are set to all 0's. The host bits chosen for subnetting vary.
In the first table entry, set the subnet bits to all 0's and convert to dotted decimal notation. The original network ID is subnetted with its new subnet mask.
In the next table entry, increase the value within the subnet bits.
Convert the binary result to dotted decimal notation.
Repeat steps 3 and 4 until the table is complete.
For example, create a 3-bit subnet of the private network ID 192.168.0.0. The subnet mask for the new subnetted network IDs is 255.255.224.0 or /19. Based on n = 3, construct a table with 8 (= 23) entries. The entry for subnet 1 is the all 0's subnet. Additional entries in the table are successive increments of the subnet bits, as shown in Table 1.9. The host bits used for subnetting are underlined.
Table 1.9 Binary Subnetting Technique for Network ID 192.168.0.0
Subnet
Binary Representation
Subnetted Network ID
1
11000000.10101000.00000000.00000000
192.168.0.0/19
2
11000000.10101000.00100000.00000000
192.168.32.0/19
3
11000000.10101000.01000000.00000000
192.168.64.0/19
4
11000000.10101000.01100000.00000000
192.168.96.0/19
5
11000000.10101000.10000000.00000000
192.168.128.0/19
6
11000000.10101000.10100000.00000000
192.168.160.0/19
7
11000000.10101000.11000000.00000000
192.168.192.0/19
8
11000000.10101000.11100000.00000000
192.168.224.0/19
Step 3: Enumerating IP Addresses for Each Subnetted Network ID
Based on the enumeration of the subnetted network IDs, you must now list the valid IP addresses for new subnetted network IDs. To list each IP address individually would be too tedious. Instead, enumerate the IP addresses for each subnetted network ID by defining the range of IP addresses (the first and the last) for each subnetted network ID. There are two main approaches:
Binary—Write down the first and last IP address for each subnetted network ID and convert to dotted decimal notation.
Decimal—Add values incrementally, corresponding to the first and last IP addresses for each subnetted network ID and convert to dotted decimal notation.
Either method produces the same result: the range of IP addresses for each subnetted network ID.
To create the range of IP addresses using the binary method
Based on n, the number of host bits chosen for subnetting, create a three-column table with 2n entries. The first column is the subnet number (starting with 1), the second column is the binary representation of the first and last IP address for the subnetted network ID, and the third column is the dotted decimal representation of the first and last IP address of the subnetted network ID. Alternately, add two columns to the previous table used for enumerating the subnetted network IDs.
For each binary representation, the first IP address is the address in which all the host bits are set to 0 except for the last host bit. The last IP address is the address in which all the host bits are set to 1 except for the last host bit.
Convert the binary representation to dotted decimal notation.
Repeat steps 2 and 3 until the table is complete.
For example, the range of IP addresses for the 3 bit subnetting of 192.168.0.0 is shown in Table 1.11. The bits used for subnetting are underlined.
Table 1.11 Binary Enumeration of IP Addresses
Subnet
Binary Representation
Range of IP Addresses
1
11000000.10101000.00000000.00000001 -11000000.10101000.00011111.11111110
192.168.0.1 - 192.168.31.254
2
11000000.10101000.00100000.00000001 -11000000.10101000.00111111.11111110
192.168.32.1 - 192.168.63.254
3
11000000.10101000.01000000.00000001 - 11000000.10101000.01011111.11111110
192.168.64.1 - 192.168.95.254
4
11000000.10101000.01100000.00000001 -11000000.10101000.01111111.11111110
192.168.96.1 - 192.168.127.254
5
11000000.10101000.10000000.00000001 - 11000000.10101000.10011111.11111110
192.168.128.1 - 192.168.159.254
6
11000000.10101000.10100000.00000001 - 11000000.10101000.10111111.11111110
192.168.160.1 - 192.168.191.254
7
11000000.10101000.11000000.00000001 -11000000.10101000.11011111.11111110
192.168.192.1 - 192.168.223.254
8
11000000.10101000.11100000.00000001 - 11000000.10101000.11111111.11111110
192.168.224.1 - 192.168.255.254
IP Addressing 3(subnet)
Subnets and Subnet Masks……3
The Internet Address Classes accommodate three scales of IP internetworks, where the 32-bits of the IP address are apportioned between network IDs and host IDs depending on how many networks and hosts per network are needed. However, consider the class A network ID, which has the possibility of over 16 million hosts on the same network. All the hosts on the same physical network bounded by IP routers share the same broadcast traffic; they are in the same broadcast domain. It is not practical to have 16 million nodes in the same broadcast domain. The result is that most of the 16 million host addresses are unassignable and are wasted. Even a class B network with 65 thousand hosts is impractical.
In an effort to create smaller broadcast domains and to better utilize the bits in the host ID, an IP network can be subdivided into smaller networks, each bounded by an IP router and assigned a new subnetted network ID, which is a subset of the original class-based network ID.
This creates subnets, subdivisions of an IP network each with their own unique subnetted network ID. Subnetted network IDs are created by using bits from the host ID portion of the original class-based network ID.
Consider for an example -the class B network of 139.12.0.0 can have up to 65,534 nodes. This is far too many nodes, and in fact the current network is becoming saturated with broadcast traffic. The subnetting of network 139.12.0.0 should be done in such a way so that it does not impact nor require the reconfiguration of the rest of the IP internetwork.
Network 139.12.0.0 is subnetted by utilizing the first 8 host bits (the third octet) for the new subnetted network ID. When 139.12.0.0 is subnetted, as shown in Figure 1.8, separate networks with their own subnetted network IDs (139.12.1.0, 139.12.2.0, 139.12.3.0) are created. The router is aware of the separate subnetted networks IDs and routes IP packets to the appropriate subnet.
Note that the rest of the IP internetwork still regards all the nodes on the three subnets as being on network 139.12.0.0. The other routers in the IP internetwork are unaware of the subnetting being done on network 139.12.0.0 and therefore require no reconfiguration.
A key element of subnetting is still missing. How does the router who is subdividing network 139.12.0.0 know how the network is being subdivided and which subnets are available on which router interfaces? To give the IP nodes this new level of awareness, they must be told exactly how to discern the new subnetted network ID regardless of Internet Address Classes. A subnet mask is used to tell an IP node how to extract a class-based or subnetted network ID.
Subnet Masks
With the advent of subnetting, one can no longer rely on the definition of the IP address classes to determine the network ID in the IP address. A new value is needed to define which part of the IP address is the network ID and which part is the host ID regardless of whether class-based or subnetted network IDs are being used.
RFC 950 defines the use of a subnet mask (also referred to as an address mask) as a 32-bit value that is used to distinguish the network ID from the host ID in an arbitrary IP address. The bits of the subnet mask are defined as follows:
All bits that correspond to the network ID are set to 1.
All bits that correspond to the host ID are set to 0.
Each host on a TCP/IP network requires a subnet mask even on a single segment network. Either a default subnet mask, which is used when using class-based network IDs, or a custom subnet mask, which is used when subnetting or supernetting, is configured on each TCP/IP node.
Dotted Decimal Representation of Subnet Masks
Subnet masks are frequently expressed in dotted decimal notation. After the bits are set for the network ID and host ID portion, the resulting 32-bit number is converted to dotted decimal notation. Note that even though expressed in dotted decimal notation, a subnet mask is not an IP address.
A default subnet mask is based on the IP address classes and is used on TCP/IP networks that are not divided into subnets. Table 1.14 lists the default subnet masks using the dotted decimal notation for the subnet mask.
Default Subnet Masks (Dotted Decimal Notation)
Address Class
Bits for Subnet Mask
Subnet Mask
Class A
11111111 00000000 00000000 00000000
255.0.0.0
Class B
11111111 11111111 00000000 00000000
255.255.0.0
Class C
11111111 11111111 11111111 00000000
255.255.255.0
Custom subnet masks are those that differ from these default subnet masks when you are doing subnetting or supernetting. For example, 138.96.58.0 is an 8-bit subnetted class B network ID. Eight bits of the class-based host ID are being used to express subnetted network IDs. The subnet mask uses a total of 24 bits (255.255.255.0) to define the subnetted network ID. The subnetted network ID and its corresponding subnet mask is then expressed in dotted decimal notation as:138.96.58.0, 255.255.255.0
Network Prefix Length Representation of Subnet Masks
Because the network ID bits must always be chosen in a contiguous fashion from the high order bits, a shorthand way of expressing a subnet mask is to denote the number of bits that define the network ID as a network prefix using the network prefix notation: /<# of bits>. Table 1.5 lists the default subnet masks using the network prefix notation for the subnet mask.
Table 1.5 Default Subnet Masks (Network Prefix Notation)
Address Class
Bits for Subnet Mask
Network Prefix
Class A
11111111 00000000 00000000 00000000
/8
Class B
11111111 11111111 00000000 00000000
/16
Class C
11111111 11111111 11111111 00000000
/24
For example, the class B network ID 138.96.0.0 with the subnet mask of 255.255.0.0 would be expressed in network prefix notation as 138.96.0.0/16.
As an example of a custom subnet mask, 138.96.58.0 is an 8-bit subnetted class B network ID. The subnet mask uses a total of 24 bits to define the subnetted network ID. The subnetted network ID and its corresponding subnet mask is then expressed in network prefix notation as:138.96.58.0/24
Network prefix notation is also known as Classless Interdomain Routing (CIDR) notation.
Note
Because all hosts on the same network must use the same network ID, all hosts on the same network must use the same network ID as defined by the same subnet mask. For example, 138.23.0.0/16 is not the same network ID as 138.23.0.0/24. The network ID 138.23.0.0/16 implies a range of valid host IP addresses from 138.23.0.1 to 138.23.255.254. The network ID 138.23.0.0/24 implies a range of valid host IP addresses from 138.23.0.1 to 138.23.0.254. Clearly, these network IDs do not represent the same range of IP addresses.
Determining the Network ID
To extract the network ID from an arbitrary IP address using an arbitrary subnet mask, IP uses a mathematical operation called a logical AND comparison. In an AND comparison, the result of two items being compared is true only when both items being compared are true; otherwise, the result is false. Applying this principle to bits, the result is 1 when both bits being compared are 1, otherwise the result is 0.
IP performs a logical AND comparison with the 32-bit IP address and the 32-bit subnet mask. This operation is known as a bit-wise logical AND. The result of the bit-wise logical AND of the IP address and the subnet mask is the network ID.
For example, what is the network ID of the IP node 129.56.189.41 with a subnet mask of 255.255.240.0?
To obtain the result, turn both numbers into their binary equivalents and line them up. Then perform the AND operation on each bit and write down the result.10000001 00111000 10111101 00101001 IP Address11111111 11111111 11110000 00000000 Subnet Mask10000001 00111000 10110000 00000000 Network ID
The result of the bit-wise logical AND of the 32 bits of the IP address and the subnet mask is the network ID 129.56.176.0.
The Internet Address Classes accommodate three scales of IP internetworks, where the 32-bits of the IP address are apportioned between network IDs and host IDs depending on how many networks and hosts per network are needed. However, consider the class A network ID, which has the possibility of over 16 million hosts on the same network. All the hosts on the same physical network bounded by IP routers share the same broadcast traffic; they are in the same broadcast domain. It is not practical to have 16 million nodes in the same broadcast domain. The result is that most of the 16 million host addresses are unassignable and are wasted. Even a class B network with 65 thousand hosts is impractical.
In an effort to create smaller broadcast domains and to better utilize the bits in the host ID, an IP network can be subdivided into smaller networks, each bounded by an IP router and assigned a new subnetted network ID, which is a subset of the original class-based network ID.
This creates subnets, subdivisions of an IP network each with their own unique subnetted network ID. Subnetted network IDs are created by using bits from the host ID portion of the original class-based network ID.
Consider for an example -the class B network of 139.12.0.0 can have up to 65,534 nodes. This is far too many nodes, and in fact the current network is becoming saturated with broadcast traffic. The subnetting of network 139.12.0.0 should be done in such a way so that it does not impact nor require the reconfiguration of the rest of the IP internetwork.
Network 139.12.0.0 is subnetted by utilizing the first 8 host bits (the third octet) for the new subnetted network ID. When 139.12.0.0 is subnetted, as shown in Figure 1.8, separate networks with their own subnetted network IDs (139.12.1.0, 139.12.2.0, 139.12.3.0) are created. The router is aware of the separate subnetted networks IDs and routes IP packets to the appropriate subnet.
Note that the rest of the IP internetwork still regards all the nodes on the three subnets as being on network 139.12.0.0. The other routers in the IP internetwork are unaware of the subnetting being done on network 139.12.0.0 and therefore require no reconfiguration.
A key element of subnetting is still missing. How does the router who is subdividing network 139.12.0.0 know how the network is being subdivided and which subnets are available on which router interfaces? To give the IP nodes this new level of awareness, they must be told exactly how to discern the new subnetted network ID regardless of Internet Address Classes. A subnet mask is used to tell an IP node how to extract a class-based or subnetted network ID.
Subnet Masks
With the advent of subnetting, one can no longer rely on the definition of the IP address classes to determine the network ID in the IP address. A new value is needed to define which part of the IP address is the network ID and which part is the host ID regardless of whether class-based or subnetted network IDs are being used.
RFC 950 defines the use of a subnet mask (also referred to as an address mask) as a 32-bit value that is used to distinguish the network ID from the host ID in an arbitrary IP address. The bits of the subnet mask are defined as follows:
All bits that correspond to the network ID are set to 1.
All bits that correspond to the host ID are set to 0.
Each host on a TCP/IP network requires a subnet mask even on a single segment network. Either a default subnet mask, which is used when using class-based network IDs, or a custom subnet mask, which is used when subnetting or supernetting, is configured on each TCP/IP node.
Dotted Decimal Representation of Subnet Masks
Subnet masks are frequently expressed in dotted decimal notation. After the bits are set for the network ID and host ID portion, the resulting 32-bit number is converted to dotted decimal notation. Note that even though expressed in dotted decimal notation, a subnet mask is not an IP address.
A default subnet mask is based on the IP address classes and is used on TCP/IP networks that are not divided into subnets. Table 1.14 lists the default subnet masks using the dotted decimal notation for the subnet mask.
Default Subnet Masks (Dotted Decimal Notation)
Address Class
Bits for Subnet Mask
Subnet Mask
Class A
11111111 00000000 00000000 00000000
255.0.0.0
Class B
11111111 11111111 00000000 00000000
255.255.0.0
Class C
11111111 11111111 11111111 00000000
255.255.255.0
Custom subnet masks are those that differ from these default subnet masks when you are doing subnetting or supernetting. For example, 138.96.58.0 is an 8-bit subnetted class B network ID. Eight bits of the class-based host ID are being used to express subnetted network IDs. The subnet mask uses a total of 24 bits (255.255.255.0) to define the subnetted network ID. The subnetted network ID and its corresponding subnet mask is then expressed in dotted decimal notation as:138.96.58.0, 255.255.255.0
Network Prefix Length Representation of Subnet Masks
Because the network ID bits must always be chosen in a contiguous fashion from the high order bits, a shorthand way of expressing a subnet mask is to denote the number of bits that define the network ID as a network prefix using the network prefix notation: /<# of bits>. Table 1.5 lists the default subnet masks using the network prefix notation for the subnet mask.
Table 1.5 Default Subnet Masks (Network Prefix Notation)
Address Class
Bits for Subnet Mask
Network Prefix
Class A
11111111 00000000 00000000 00000000
/8
Class B
11111111 11111111 00000000 00000000
/16
Class C
11111111 11111111 11111111 00000000
/24
For example, the class B network ID 138.96.0.0 with the subnet mask of 255.255.0.0 would be expressed in network prefix notation as 138.96.0.0/16.
As an example of a custom subnet mask, 138.96.58.0 is an 8-bit subnetted class B network ID. The subnet mask uses a total of 24 bits to define the subnetted network ID. The subnetted network ID and its corresponding subnet mask is then expressed in network prefix notation as:138.96.58.0/24
Network prefix notation is also known as Classless Interdomain Routing (CIDR) notation.
Note
Because all hosts on the same network must use the same network ID, all hosts on the same network must use the same network ID as defined by the same subnet mask. For example, 138.23.0.0/16 is not the same network ID as 138.23.0.0/24. The network ID 138.23.0.0/16 implies a range of valid host IP addresses from 138.23.0.1 to 138.23.255.254. The network ID 138.23.0.0/24 implies a range of valid host IP addresses from 138.23.0.1 to 138.23.0.254. Clearly, these network IDs do not represent the same range of IP addresses.
Determining the Network ID
To extract the network ID from an arbitrary IP address using an arbitrary subnet mask, IP uses a mathematical operation called a logical AND comparison. In an AND comparison, the result of two items being compared is true only when both items being compared are true; otherwise, the result is false. Applying this principle to bits, the result is 1 when both bits being compared are 1, otherwise the result is 0.
IP performs a logical AND comparison with the 32-bit IP address and the 32-bit subnet mask. This operation is known as a bit-wise logical AND. The result of the bit-wise logical AND of the IP address and the subnet mask is the network ID.
For example, what is the network ID of the IP node 129.56.189.41 with a subnet mask of 255.255.240.0?
To obtain the result, turn both numbers into their binary equivalents and line them up. Then perform the AND operation on each bit and write down the result.10000001 00111000 10111101 00101001 IP Address11111111 11111111 11110000 00000000 Subnet Mask10000001 00111000 10110000 00000000 Network ID
The result of the bit-wise logical AND of the 32 bits of the IP address and the subnet mask is the network ID 129.56.176.0.
IP Addressing 2
Network ID Guidelines
The network ID identifies the TCP/IP hosts that are located on the same physical network. All hosts on the same physical network must be assigned the same network ID to communicate with each other.
Follow these guidelines when assigning a network ID:
The network ID must be unique to the IP internetwork. If you plan on having a direct routed connection to the public Internet, the network ID must be unique to the Internet. If you do not plan on connecting to the public Internet, the local network ID must be unique to your private internetwork.
The network ID cannot begin with the number 127. The number 127 in a class A address is reserved for internal loopback functions.
All bits within the network ID cannot be set to 1. All 1's in the network ID are reserved for use as an IP broadcast address.
All bits within the network ID cannot be set to 0. All 0's in the network ID are used to denote a specific host on the local network and are not routed.
lists the valid ranges of network IDs based on the IP address classes. To denote IP network IDs, the host bits are all set to 0. Note that even though expressed in dotted decimal notation, the network ID is not an IP address.
Class Ranges of Network IDs
Address Class
First Network ID
Last Network ID
Class A
1.0.0.0
126.0.0.0
Class B
128.0.0.0
191.255.0.0
Class C
192.0.0.0
223.255.255.0
Host ID Guidelines
The host ID identifies a TCP/IP host within a network. The combination of IP network ID and IP host ID is an IP address.
Follow these guidelines when assigning a host ID:
The host ID must be unique to the network ID.
All bits within the host ID cannot be set to 1 because this host ID is reserved as a broadcast address to send a packet to all hosts on a network.
All bits in the host ID cannot be set to 0 because this host ID is reserved to denote the IP network ID.
lists the valid ranges of host IDs based on the IP address classes.
Class Ranges of Host IDs
Address Class
First Host ID
Last Host ID
Class A
w.0.0.1
w.255.255.254
Class B
w.x.0.1
w.x.255.254
Class C
w.x.y.1
w.x.y.254
The network ID identifies the TCP/IP hosts that are located on the same physical network. All hosts on the same physical network must be assigned the same network ID to communicate with each other.
Follow these guidelines when assigning a network ID:
The network ID must be unique to the IP internetwork. If you plan on having a direct routed connection to the public Internet, the network ID must be unique to the Internet. If you do not plan on connecting to the public Internet, the local network ID must be unique to your private internetwork.
The network ID cannot begin with the number 127. The number 127 in a class A address is reserved for internal loopback functions.
All bits within the network ID cannot be set to 1. All 1's in the network ID are reserved for use as an IP broadcast address.
All bits within the network ID cannot be set to 0. All 0's in the network ID are used to denote a specific host on the local network and are not routed.
lists the valid ranges of network IDs based on the IP address classes. To denote IP network IDs, the host bits are all set to 0. Note that even though expressed in dotted decimal notation, the network ID is not an IP address.
Class Ranges of Network IDs
Address Class
First Network ID
Last Network ID
Class A
1.0.0.0
126.0.0.0
Class B
128.0.0.0
191.255.0.0
Class C
192.0.0.0
223.255.255.0
Host ID Guidelines
The host ID identifies a TCP/IP host within a network. The combination of IP network ID and IP host ID is an IP address.
Follow these guidelines when assigning a host ID:
The host ID must be unique to the network ID.
All bits within the host ID cannot be set to 1 because this host ID is reserved as a broadcast address to send a packet to all hosts on a network.
All bits in the host ID cannot be set to 0 because this host ID is reserved to denote the IP network ID.
lists the valid ranges of host IDs based on the IP address classes.
Class Ranges of Host IDs
Address Class
First Host ID
Last Host ID
Class A
w.0.0.1
w.255.255.254
Class B
w.x.0.1
w.x.255.254
Class C
w.x.y.1
w.x.y.254
Monday, August 11, 2008
IP Addressing 1
Address Classes
The Internet community originally defined five address classes to accommodate networks of varying sizes. Microsoft TCP/IP supports class A, B, and C addresses assigned to hosts. The class of address defines which bits are used for the network ID and which bits are used for the host ID. It also defines the possible number of networks and the number of hosts per network.
Class A
Class A addresses are assigned to networks with a very large number of hosts. The high-order bit in a class A address is always set to zero. The next seven bits (completing the first octet) complete the network ID. The remaining 24 bits (the last three octets) represent the host ID. This allows for 126 networks and 16,777,214 hosts per network
Class B
Class B addresses are assigned to medium-sized to large-sized networks. The two high-order bits in a class B address are always set to binary 1 0. The next 14 bits (completing the first two octets) complete the network ID. The remaining 16 bits (last two octets) represent the host ID. This allows for 16,384 networks and 65,534 hosts per network
Class C
Class C addresses are used for small networks. The three high-order bits in a class C address are always set to binary 1 1 0. The next 21 bits (completing the first three octets) complete the network ID. The remaining 8 bits (last octet) represent the host ID. This allows for 2,097,152 networks and 254 hosts per network.
Class D
Class D addresses are reserved for IP multicast addresses. The four high-order bits in a class D address are always set to binary 1 1 1 0. The remaining bits are for the address that interested hosts recognize. Microsoft supports class D addresses for applications to multicast data to multicast-capable hosts on an internetwork.
Class E
Class E is an experimental address that is reserved for future use. The high-order bits in a class E address are set to 1111.
The Internet community originally defined five address classes to accommodate networks of varying sizes. Microsoft TCP/IP supports class A, B, and C addresses assigned to hosts. The class of address defines which bits are used for the network ID and which bits are used for the host ID. It also defines the possible number of networks and the number of hosts per network.
Class A
Class A addresses are assigned to networks with a very large number of hosts. The high-order bit in a class A address is always set to zero. The next seven bits (completing the first octet) complete the network ID. The remaining 24 bits (the last three octets) represent the host ID. This allows for 126 networks and 16,777,214 hosts per network
Class B
Class B addresses are assigned to medium-sized to large-sized networks. The two high-order bits in a class B address are always set to binary 1 0. The next 14 bits (completing the first two octets) complete the network ID. The remaining 16 bits (last two octets) represent the host ID. This allows for 16,384 networks and 65,534 hosts per network
Class C
Class C addresses are used for small networks. The three high-order bits in a class C address are always set to binary 1 1 0. The next 21 bits (completing the first three octets) complete the network ID. The remaining 8 bits (last octet) represent the host ID. This allows for 2,097,152 networks and 254 hosts per network.
Class D
Class D addresses are reserved for IP multicast addresses. The four high-order bits in a class D address are always set to binary 1 1 1 0. The remaining bits are for the address that interested hosts recognize. Microsoft supports class D addresses for applications to multicast data to multicast-capable hosts on an internetwork.
Class E
Class E is an experimental address that is reserved for future use. The high-order bits in a class E address are set to 1111.
Sunday, August 10, 2008
Network Administration Overview
In MOF(Microsoft operation framework), a network consists of the infrastructure components through which computer systems and shared peripherals communicate with each other. It is the most basic level of an IT infrastructure—without network facilities, there is no infrastructure, just a collection of individual computers. The Network Administration SMF(service management function) is focused on the operation of this basic service.
The Network Administration SMF is situated in the MOF Operating Quadrant, illustrated below in Figure 1. It is closely related to the Storage Management, Directory Services Administration, and Job Scheduling SMFs since it provides a similar foundation on which higher-order IT layers are built.
Figure 1. The MOF Process Model, with SMFs. The Network Administration SMF resides in the Operating Quadrant.
The Network Administration SMF is situated in the MOF Operating Quadrant, illustrated below in Figure 1. It is closely related to the Storage Management, Directory Services Administration, and Job Scheduling SMFs since it provides a similar foundation on which higher-order IT layers are built.
Figure 1. The MOF Process Model, with SMFs. The Network Administration SMF resides in the Operating Quadrant.
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