Users Guide

Layer 3 Routing Commands 1516
ip dhcp relay information option server-override
Use the ip dhcp relay information option server-override command to enable
sending sub-option 5 (link-election) and sub-option 11 (server override) in
option 82.
Syntax
ip dhcp relay information option server-override
no ip dhcp relay information option server-override
Default Configuration
Sending of sub-option 5 (link-selection) and sub-option 11 (server-override)
is not enabled globally, nor or any interface.
Command Mode
Global Configuration mode, Interface Configuration mode
User Guidelines
Configuring ip dhcp relay information option server-override enables the
insertion of sub-option 5 and sub-option 11 in relayed DHCPDISCOVER
messages. The server override and link-selection sub-options contain the
incoming interface IP address of the DCHPREQUEST. The relay agent sets
the gateway IP address (giaddr) to an IP address reachable by the DHCP
server (outgoing interface IP address or the address configured by the ip dhcp
relay source–interface command) and sets the Server Identifier Override sub-
option to an IPv4 address reachable by the DHCP host that sent the
DHCPDISCOVER.
The DHCP server uses the link selection sub-option to locate the address
pool for the DHCP client and sets the server identifier option in the
DHCPOFFER to the value of the Server Identifier Override sub-option
received from the switch relay agent. The DHCP server sends the response to
the IP address received in the giaddr option. This causes the DHCP client to
use the Server Identifier Override IP address when unicasting DHCPRENEW
messages and support behavior similar to DHCPv6 relay.