Prerequisites For Dhcp Relay Operation; Enabling Dhcp Relay; Configuring An Ip Helper Address; Operating Notes - HP 2920 Series Multicast And Routing Manual

Prerequisites for DHCP relay operation

For the DHCP relay agent to work on the switch, you must complete the following steps:
1. Enable DHCP relay on the routing switch (the default setting.)
2. Ensure that a DHCP server is servicing the routing switch.
3. Enable IP routing on the routing switch.
4. Ensure that there is a route from the DHCP server to the routing switch and back.
5. Configure one or more IP helper addresses for specified VLANs to forward DHCP requests to
DHCP servers on other subnets.

Enabling DHCP relay

The DHCP relay function is enabled by default on an HP routing switch. However, if DHCP has
been disabled, you can re-enable it by entering the following command at the global configuration
level:
HP Switch(config)# dhcp-relay
To disable the DHCP relay function, enter the no form of the command:
HP Switch(config)# no dhcp-relay

Configuring an IP helper address

To add the IP address of a DHCP server for a specified VLAN on a routing switch, enter the ip
helper-address command at the VLAN configuration level as in the following example:
HP Switch(config)# vlan 1
HP Switch(vlan-1)# ip helper-address <ip-addr>
To remove the DHCP server helper address, enter the no form of the command:
HP Switch(vlan-1)# no ip helper-address <ip-addr>

Operating notes

You can configure up to 4000 IP helper addresses on a routing switch. The helper addresses
are shared between the DHCP relay agent and UDP forwarder feature.
A maximum of sixteen IP helper addresses is supported in each VLAN.

Verifying the DHCP relay configuration

Viewing the DHCP relay setting

Use the show config command (or show running for the running-config file) to display the
current DHCP relay setting.
NOTE: The DHCP relay and hop count increment settings appear in the show config command
output only if the non-default values are configured.
64 IP Routing Features