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Overriding the Default DHCP Relay Configuration

To override the default configuration settings for the extended DHCP relay agent, include the overrides statement:




overrides {

always-write-giaddr;

always-write-option-82;

layer2-unicast-replies;

trust-option-82;

disable-relay;
}

To override global DHCP relay agent configuration options, include the overrides statement and its subordinate statements at the [edit forwarding-options dhcp-relay] hierarchy level. To override DHCP relay agent configuration options for a named group of interfaces, include the statements at the [edit forwarding-options dhcp-relay group group-name] hierarchy level.

To remove all DHCP relay agent configuration overrides at a particular hierarchy level, include the overrides statement with no subordinate statements.

Overwriting giaddr Information

You can configure the DHCP relay agent to change the gateway IP address (giaddr) field in packets that it forwards between a DHCP client and a DHCP server.

To overwrite the giaddr of every DHCP packet with the giaddr of the DHCP relay agent before forwarding the packet to the DHCP server, include the always-write-giaddr statement.

Overriding Option 82 Information

You can configure the DHCP relay agent to add or remove the DHCP relay agent information option (option 82) in DHCP packets.

To override the default option 82 information in DHCP packets destined for a DHCP server, include the always-write-option-82 statement. The use of this statement causes the DHCP relay agent to perform one of the following actions, depending on how it is configured:

If the DHCP relay agent is configured to add option 82 information to DHCP packets, it clears the existing option 82 values from the DHCP packets and inserts the new values before forwarding the packets to the DHCP server.
If the DHCP relay agent is not configured to add option 82 information to DHCP packets, it clears the existing option 82 values from the packets, but does not add any new values before forwarding the packets to the DHCP server.

Using Layer 2 Unicast Transmission for DHCP Packets

To override the setting of the broadcast bit in DHCP request packets and instead use the layer 2 unicast transmission method to send DHCP Offer reply packets and DHCP ACK reply packets from the DHCP server to DHCP clients during the discovery process, include the layer2-unicast-replies statement.

Trusting Option 82 Information

By default, the DHCP relay agent treats client packets with a giaddr of 0 (zero) and option 82 information as if they originated at an untrusted source, and drops them without further processing. To override this behavior and instead enable the DHCP relay agent to process DHCP client packets that have a giaddr of 0 (zero) and contain option 82 information, include the trust-option-82 statement.

Disabling DHCP Relay

To disable DHCP relay on specific interfaces in a group, include the disable-relay statement.

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