3com 5500-SI Manual De Usuario

This section contains an introduction to DHCP Relay

Early DHCP implementations assumes that DHCP clients and DHCP servers are on the 
same network segment, that is, you need to deploy at least one DHCP server for each 
network segment, which is far from economical.

DHCP Relay is designed to address this problem. It enables DHCP clients of multiple 
networks to share a common DHCP server, through which DHCP clients in a LAN can 
acquire IP addresses by negotiating with DHCP servers of other networks. It decreases 
your cost and provides a centralized administration.

A DHCP relay can be a host or a switch that has DHCP relay service enabled.

Figure 35 illustrates a typical DHCP relay application.

Figure 35   Typical DHCP relay application

A DHCP relay works as follows:

■

A DHCP client broadcasts a configuration request packet in the local network 
when it starts and initiates.

■

If a DHCP server exists in the local network, it processes the configuration request 
packet directly without the help of a DHCP relay.

■

If no DHCP server exists in the local network, the network device serving as a 
DHCP relay on this network appropriately processes the configuration request 
packet and forwards it to a specified DHCP server located on another network.

■

When the DHCP server receives the packet, it generates configuration information 
accordingly and sends it to the DHCP client through the DHCP relay to complete 
the dynamic configuration of the DHCP client.

Note that such an interacting process may be repeated several times for a DHCP client 
to be successfully configured.