HP 3500YL - Manual (Page 302)

IP Routing Features
Configuring DHCP Relay
Broadcast Forwarding
The packets are forwarded using broadcast forwarding if the IP address of the
DHCP server is a subnet address or IP broadcast address (255.255.255.255).
The DHCP relay agent sets the DHCP server IP address to broadcast IP address
and will be forwarded to all VLANs with configured IP interfaces (except the
source VLAN).
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 a ProCurve routing switch.
However, if DHCP has been disabled, you can re-enable it by entering the
following command at the global configuration level:
ProCurve(config)# dhcp-relay
To disable the DHCP Relay function, enter the no form of the command:
ProCurve(config)# no dhcp-relay
Configuring a BOOTP/DHCP Relay Gateway
The DHCP relay agent selects the lowest-numbered IP address on the interface
to use for DHCP messages. The DHCP server then uses this IP address when
it assigns client addresses. However, this IP address may not be the same
subnet as the one on which the client needs the DHCP service.
This feature provides a way to configure a gateway address for the DHCP relay
agent to use for DHCP requests, rather than the DHCP relay agent automati­
cally assigning the lowest-numbered IP address.
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