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
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