IBM SC30-3681-08 manual Using a Device as a Boot Server, How the Bootp Forwarding Process Works

Using the Boot CONFIG Process

You can con®gure more than one boot ®le in the boot con®guration database by specifying the path and name of each boot ®le (using theadd command described on page ªAddº on page 94). If you have more than one host server, you can use a different host server to boot the router when another host server cannot be reached over the network.

To con®gure booting:

1.Add an address record, using the add address command from the Boot config> prompt, that speci®es the interface from which you want it to boot.

2.Add the boot record, using the add boot-entrycommand from the Boot config> prompt, specifying the host address, next hop router (if necessary), and the path and ®lename of the host.

Using a Device as a Boot Server

A device can also function as a boot server. Devices that do not have an IBD can obtain their load ®les or boot ®les from a router that has an IBD. Use theadd boot-entrycommand to designate the location of the router with the boot ®le. Make

sure that you include the entire path name of the load ®le with this command. On a router with the load in IBD, this is IBD/filename.

How the BOOTP Forwarding Process Works

BOOTP (documented in RFC 951) is a bootstrap protocol used by a router or a diskless workstation to learn its IP address, the location of its boot ®le, and the boot server name. A device can act as a BOOTP client or as a BOOTP relay agent for another device. The following sections describe these two processes.

A Device as a BOOTP Client

A device acts as a BOOTP Client when it needs to ®nd the location of the boot ®le and boot server. You can speci®cally con®gure the device's boot PROM con®guration record so the router can act as a BOOTP Client, or it can become a BOOTP Client if, during booting, it does not contain a valid ®le name and path to the location of the boot ®le and server. When either of these two conditions exists, the router broadcasts a UDP packet over one of its LAN interfaces to the BOOTP server that contains the path name of the boot ®le and server.

The following describes the BOOT client forwarding process:

1.The BOOTP client copies its MAC address (either Ethernet or Token Ring) into a BOOTP packet (UDP packet) and broadcasts it onto the local LAN. BOOTP is running on top of UDP.

2.The BOOTP server receives the request and looks up the client's Ethernet address in its database. If found, 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 back over the LAN to the BOOTP client.

Note: If multiple hops are required before reaching the BOOTP server, a BOOTP relay agent receives the packet. BOOTP relay agent is explained in the next section.

3.When the router receives the BOOTP reply packet, it uses the information it contains to initiate a TFTP request to the boot server.

84MRS V3.2 Software User's Guide