Alcatel-Lucent 6850-48 Guida Di Rete

Configuring DHCP Relay

Configuring DHCP Security Features

OmniSwitch AOS Release 6 Network Configuration Guide

page 31-17

 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.

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 

 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.