HP ProCurve 7000dl Series Basic Management And Configuration Manual page 671

Dynamic Host Configuration Protocol (DHCP)
Configuring DHCP Relay
You can set different helper addresses for different interfaces. For example,
if your LAN uses different servers for different subnets, you could configure
the router to forward DHCP requests received on one Ethernet (or VLAN)
interface to one address and requests received on another interface to a
different address.
For example:
ProCurve(config)# interface eth 0/1
ProCurve(config-eth 0/1)# ip helper-address 10.1.1.1
ProCurve(config-eth 0/1)# interface eth 0/2
ProCurve(config-eth 0/2)# ip helper-address 10.2.1.1
The router does not simply forward the DHCP packets. It also examines them,
checks their validity, and adds any appropriate changes, such as the IP address
of the interface that received the packets. The remote server uses this address
to determine from which pool it should select the IP address that it offers to
the client.
For example, an Ethernet interface with the IP address 192.168.1.1 /24 receives
a DHCP packet and forwards it to a remote server. The server searches its
database for a DHCP pool for the 192.168.1.0 /24 network and returns an offer
for IP address 192.168.1.36 to the local router at 192.168.1.1. The local router
then forwards this offer to the client.
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