DHCP Relay Agent Information Options

When forwarding local UDP broadcasts from a local client, the DHCP relay agent needs to include information about itself in order for the DHCP server to determine which pool of client addresses to pull the lease from. Including Option 82 and its sub-options in the DHCP relay information provides the required DHCP relay information.

Several commands are available to configure which DHCP relay agent information options are used by the switch to affect the selection of a lease when it is operating as a DHCP relay agent.

Use the ip dhcp relay source-interface command, in global or interface configuration mode, to specify the source interface (VLAN or loopback) to be used used in the Relay Agent packets sent to the DHCP server or other relay agent. This command should be used in conjunction with the ip dhcp relay information option server-override or ip dhcp relay information option vpn commands, which cause the server identifier override (11) sub-option to be added to the Relay Agent DHCP packets sent to the DHCP server.

Note

Note

The source interface specified with the ip dhcp relay source-interface command must belong to the same VRF specified with the ip helper-address command.

Command Order of Precedence

The following precedence rules apply to the DHCP relay agent information commands that can be configured in both router global and interface configuration modes.

If the ip dhcp relay information option commands or ip dhcp relay source-interface command are configured in global configuration mode but not configured in interface configuration mode, the global configuration is applied to all interfaces.

If the ip dhcp relay information option commands or ip dhcp relay source-interface command are configured in both global configuration mode and interface configuration mode, the interface configuration command takes precedence over the global configuration command. However, the global configuration is applied to interfaces that have not been configured at the interface level.

If the ip dhcp relay information option commands or ip dhcp relay source-interface command are not configured in global configuration mode but are configured in interface configuration mode, only the interfaces that have been configured are affected. All other interfaces are not impacted by the configuration.