CANOGA PERKINS 9175 Configuration Guide - Manual (Page 238)

CanogaOSS Configuration Guide
36-1
36 Configuring DHCP
36.1 Configuration DHCP Relay
36.1.1 Overview
DHCP relay agent is any host that forwards DHCP packets between clients and servers.
Relay agents are used to forward requests and replies between clients and servers when
they are not on the same physical subnet. Relay agent forwarding is distinct from the
normal forwarding of an IP router, where IP datagrams are switched between networks
somewhat transparently. By contrast, relay agents receive DHCP messages and then
generate a new DHCP message to send out on another interface. The relay agent sets
the gateway address (giaddr field of the DHCP packet) and, if configured, adds the relay
agent information option (option82) in the packet and forwards it to the DHCP server.
The reply from the server is forwarded back to the client after removing option 82.
36.1.2 References
The DHCP Relay module is based on the following RFC:
RFC 1542 and RFC 3046
36.1.3 Terminology
Following is a brief description of terms and concepts used to describe the DHCP Relay:
Dynamic Host Configuration Protocol (DHCP)
Dynamic Host Configuration Protocol (DHCP) is a client/server protocol that
automatically provides an Internet Protocol (IP) host with its IP address and other related
configuration information such as the subnet mask and default gateway.
CHADDR
Client Hardware Address field in the DHCP payload.
GIADDR
Gateway IP Address field in the DHCP payload.
36.1.4 Topology
Figure 36-1: DHCP Relay
This figure is the networking topology for testing DHCP relay functions. We need two