Configuring DHCP Relay Configuring DHCP Security Features
OmniSwitch 6800/6850/9000 Network Configuration Guide March 2008 page 22-17
Enabling the Relay Agent Information Option-82
Use the ip helper agent-information command to enable the DHCP Option-82 feature for the switch. For
example:
-> ip helper agent-information enable
This same command is also used to disable this feature. For example:
-> ip helper agent-information disable
Note that because this feature is not available on a per-VLAN basis, DHCP Option-82 functionality is not
restricted to ports associated with a specific VLAN. Instead, DHCP traffic received on all ports is eligible
for Option-82 data insertion when it is relayed by the agent.
Configuring a Relay Agent Information Option-82 Policy
As previously mentioned, when the relay agent receives a DHCP packet from a client that already contains
Option-82 data, the packet is dropped by default. However, it is possible to configure a DHCP Option-82
policy that directs the relay agent to drop, keep, or replace the existing Option-82 data and then forward
the packet to the server.
To configure a DHCP Option-82 policy, use the ip helper agent-information policy command. The
following parameters are available with this command to specify the policy action:
• drop—The DHCP packet is dropped (the default).
• keep—The existing Option-82 data in the DHCP packet is retained and the packet is forwarded to the
server.
• replace—The existing Option-82 data in the DHCP packet is replaced with local relay agent data and
then forwarded to the server.
For example, the following commands configure DHCP Option-82 policies:
-> ip helper agent-information policy drop
-> ip helper agent-information policy keep
-> ip helper agent-information policy replace
Note that this type of policy applies to all DHCP packets received on all switch ports. In addition, if a
packet that contains existing Option-82 data also contains a gateway IP address that matches a local subnet
address, the relay agent will drop the packet and not apply any existing Option-82 policy.
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