IBM SC30-3681-08 manual Device as a Bootp Relay Agent, Enabling/Disabling Bootp Forwarding

Using the Boot CONFIG Process

A Device as a BOOTP Relay Agent

If BOOTP request requires multiple hops before reaching the BOOTP server, the BOOTP relay agent routes the packet via IP to all BOOTP servers that it knows about. If any other router receives this packet while it is being routed via IP, it will examine the packet to determine whether it is a BOOTP packet and route that packet toward the BOOTP servers that it knows about. The following describes the BOOTP relay agent forwarding process:

1.A device acting as the local BOOTP relay agent, receives the BOOTP request packet from the BOOTP client, modi®es the checksum, places an IP header on the packet with the relay agent's IP address copied into the body of the BOOTP request, and routes the packet to all BOOTP servers.

2.The BOOTP servers receive the request and look up the client's MAC address

in their database. If a server ®nds the client's address, it formats a BOOTP reply containing the client's IP address, the location of its boot ®le, and the boot server name. The reply is then sent to the BOOTP relay agent.

3.The BOOTP relay agent receives the reply, makes an entry in its ARP table for the client, and then forwards the reply to the BOOTP client.

4.The client then continues to boot using the information that is contained in the BOOTP reply packet to initiate a TFTP request to the boot server.

Enabling/Disabling BOOTP Forwarding

To enable or disable BOOTP forwarding on the router, enter the following appropriate command at the IP con®guration prompt:

IP Config> enable bootp

IP Config> disable bootp

When enabling BOOTP, you are prompted for the following values:

vMaximum number of application hops you want the BOOTP request to go.

This is the maximum number of BOOTP relay agents that can forward the packet. This is not the maximum number of IP hops to the BOOTP server. A typical value for this parameter is 4.

vNumber of seconds you want the client to retry before you forward the BOOTP request. This parameter is not commonly used. A typical value for this parameter is 0.

After accepting a BOOTP request, the router forwards the BOOTP request to each BOOTP server. If there are multiple servers con®gured for BOOTP, the transmitting server replicates the packet.

Con®guring a BOOTP Server

The BOOTP server is either an AIX or UNIX host with a bootpd daemon, or a DOS host (running software available from FTP Software). The BOOTP server contains a ®le (maintained by the network administrator) that lists all the BOOTP clients that this server is responsible for, and their associated IP addresses, boot ®le locations, and boot server names.

When the BOOTP server receives a BOOTP request, it matches the MAC address of the client with the MAC address in its BOOTP ®le. If a match occurs, the server

Chapter 7. The Boot CONFIG Process 85