Nortel Networks NN47200-503 Differences between Dhcp and BootP, Summary of Dhcp relay operation

IP routing 39

For each ingress interface and protocol, the UDP broadcast packets are forwarded only to a unicast host address (the unicast IP address of the server for example).

Dynamic Host Configuration Protocol (DHCP) / Bootstrap Protocol (BootP)

DHCP-BootP relay

The Dynamic Host Configuration Protocol (DHCP) is an extension of the Bootstrap protocol (BootP) and provides host configuration information to workstations on a dynamic basis. To lower administrative overhead, network managers prefer to configure a small number of DHCP servers in a central location. It is necessary for routers to support the BootP/DHCP relay function so that hosts can access configuration information from servers several router hops away.

Differences between DHCP and BootP

The following differences between DHCP and BootP are specified in RFC

2131 and include functions that BootP does not address:

•The Nortel Ethernet Routing Switch 5500 Series supports the Bootstrap protocol (BootP). BootP enables the retrieval of an ASCII configuration file name and configuration server address.

•A properly configured BootP server enables the switch to automatically learn its assigned IP address, subnet mask and the IP address of the default router (default gateway).

•DHCP defines mechanisms through which clients can be assigned a network address for a finite lease (allowing for reuse of IP addresses).

•DHCP provides the mechanism for clients to acquire all of the IP configuration parameters needed to operate.

DHCP uses the BootP message format defined in RFC 951. The remainder of the options field consists of a list of tagged parameters that are called "options" (RFC 2131).

Summary of DHCP relay operation

BootP/DHCP clients (workstations) generally use UDP/IP broadcasts to determine their IP addresses and configuration information. If such a host is on a network or a subnet segment (or VLAN) that does not include a DHCP server, the UDP broadcasts are by default not forwarded to the server located on a different network segment or VLAN. The Nortel Ethernet Routing Switch 5500 Series can be configured to resolve this issue by forwarding the broadcasts to the server. The router interfaces can be configured to forward DHCP broadcasts to other locally connected network segments or directly to the server’s IP address. DHCP must be enabled on a per-VLAN basis.

Nortel Ethernet Routing Switch 5500 Series

Configuration-IP Routing Protocols

NN47200-503 03.01 Standard

5.127 August 2007

Copyright © 2005-2007, Nortel Networks