Installing and Administering LAN/9000 Software

174 Chapter7

LAN Device and Interface Terminology

RARP Conﬁguration

RARP (Reverse Address Resolution Protocol, RFC 903) conﬁguration is

an optional addressing scheme in which a freshly booted system queries

a network server for the IP address of its own networking interface.

For example, if you have a large installation with many nodes, you can

centralize the IP address database onto a system that serves as a RARP

server. When each client system wants to conﬁgure its network interface,

it queries the RARP server to provide the information listed in its

database. In this way, each client system does not need to have its own

customized version of the netconf ﬁle to contain its IP address.

When an interface needs to be conﬁgured with an IP address speciﬁed by

a RARP server, the /usr/sbin/rarpc program is used to broadcast a

RARP request over the network connected to the interface for which the

information is being requested. If there is a RARP server on that

network, and if the hardware address for the client interface is in the

server’s database, then the server will send a response to the client

containing the IP address of that interface. The IP address is then

passed to the conﬁguration script, which uses it to conﬁgure the

interface.

Setting Up a RARP Client

An interface is conﬁgured to use RARP conﬁguration when the

IP_ADDRESS variable in the /etc/rc.config.d/netconf ﬁle is assigned

the value of RARP. The IP address variable is an array, each element of

which corresponds to a particular interface number. Usually, this

variable contains an explicit IP address, which is used to conﬁgure the

interface speciﬁed by the INTERFACE_NAME variable.

To conﬁgure an interface to use RARP, the /etc/rc.config.d/netconf

ﬁle must be modiﬁed so the IP_ADDRESS variable is set to RARP. This can

be done with a text editor such as vi, and it can be done for interface

entries other than 0. For example, for interface entry 1 to use RARP, the

IP_ADDRESS line should be modiﬁed to IP_ADDRESS[1]=RARP. If the

interface name for entry 1 is speciﬁed as INTERFACE_NAME[1]=lan1,

then interface lan1 will be conﬁgured with RARP information when the

system is next booted.

When making this modiﬁcation, the IP address should be recorded so the