HP 2610, Advanced Traffic Management Manual

Page: 287 / 364

IP Routing Features
Configuring DHCP Relay
However, Option 82 relay agents should be positioned at the DHCP policy
boundaries in a network to provide maximum support and security for the IP
addressing policies configured in the server.
Option 82 Server Support
To apply DHCP Option 82, the routing switch must operate in conjunction
with a server that supports Option 82. (DHCP servers that do not support
Option 82 typically ignore Option 82 fields.) Also, the routing switch applies
Option 82 functionality only to client request packets being
routed to a DHCP
server. DHCP relay with Option 82 does not apply to switched (non-routed)
client requests.
For information on configuring policies on a server running DHCP Option 82,
refer to the documentation provided for that application.
Figure 7-10. Example of a DHCP Option 82 Application
Switch “A”
10.10.10.2
VLAN
10
10.10.10.1
Client
3
DHCP
Option
82
Server
Subnets 10 and 20 in relay agent “1”
form policy boundaries that can be
defined by the IP address of the subnet
on which the client request is received.
Relay Agent “1” (Routing Switch)
with DHCP Option 82 Enabled
Client
1
Client
2
VLAN
20
10.10.20.1
Switch “B”
10.10.20.3
Client
6
Client
4
Client
5
10.10.20.2
10.10.30.1
Relay Agent “2” (Routing
Switch) without DHCP
Option 82 Enabled
Policy Boundaries
Terminology
Circuit ID: In Option 82 applications, the number of the port through which
the routing switch receives a DHCP client request. On ProCurve fixed-
port switches, the Circuit ID of a given port corresponds to the port
number appearing on the front of the switch for that port. On ProCurve
chassis switches, the port number for a given port corresponds to the
internal ifIndex number for that port. 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
Circuit ID, refer to “Circuit ID” in the bulleted list on page <zBlue>33.)
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