HP 3500YL - Manual (Page 311)

IP Routing Features
Configuring DHCP Relay
request. For a DHCP server response to an Option 82 client request, the routing
switch can optionally perform a validation check to determine whether to
forward or drop the response. Each Option 82 relay agent in the path between
a DHCP client and an Option 82 DHCP server can be configured with a unique
forwarding policy, which enhances DHCP policy control over discrete areas
of a network.
Primary Relay Agent: In the path between a DHCP client and a DHCP server,
the first routing switch (configured to support DHCP operation) that a client
DHCP request encounters in the path from the client to a DHCP server.
Relay Agent: A routing switch that is configured to support DHCP operation.
Remote ID: In Option 82 applications on ProCurve switches, either the MAC
address of a relay agent or the IP address of a VLAN or subnet configured on
a relay agent or the (optional) Management VLAN configured on a relay agent.
This value is included as a suboption in an Option 82 field that the relay agent
appends to a Client DHCP request before forwarding the request toward a
DHCP server. (For more on Remote ID, refer to “Remote ID” in the bulleted
list on page 5-138.)
Secondary Relay Agent: In the path between a DHCP client and a DHCP
server, any routing switch (configured to support DHCP operation) other than
the primary relay agent.
General DHCP Option 82 Requirements and Operation
Requirements. DHCP Option 82 operation is configured at the global config
level and requires the following:
■ IP routing enabled on the switch
■ DHCP-Relay Option 82 enabled (global command level)
■ routing switch access to an Option 82 DHCP server on a different subnet
than the clients requesting DHCP Option 82 support
■ one IP Helper address configured on each VLAN supporting DHCP clients
General DHCP-Relay Operation with Option 82. Typically, the first
(primary) Option 82 relay agent to receive a client’s DHCP request packet
appends an Option 82 field to the packet and forwards it toward the DHCP
server identified by the IP Helper address configured on the VLAN in which
the client packet was received. Other, upstream relay agents used to forward
the packet may append their own Option 82 fields, replace the Option 82
field(s) they find in the packet, forward the packet without adding another
field, or drop the packet. (Intermediate next-hop routing switches without
Option 82 capability can be used to forward—route—client request packets
5-137