Ip Dhcp Snooping Information Option - Cisco Catalyst 2950 Command Reference Manual

ip dhcp snooping information option

ip dhcp snooping information option
Use the ip dhcp snooping information option global configuration command to enable DHCP
option-82 data insertion. Use the no form of this command to disable DHCP option-82 data insertion.
Syntax Description
This command has no arguments or keywords.
Defaults DHCP option-82 data insertion is enabled.
Command Modes Global configuration
Command History Release
12.1(19)EA1
Usage Guidelines You must globally enable DHCP snooping by using the ip dhcp snooping global configuration
command for any DHCP snooping configuration to take effect.
When the option-82 feature is enabled and a switch receives a DHCP request from a host, it adds the
option-82 information in the packet. The option-82 information contains the switch MAC address (the
remote ID suboption) and the port identifier, vlan-mod-port, from which the packet is received (circuit
ID suboption). The switch forwards the DHCP request that includes the option-82 field to the DHCP
server.
When the DHCP server receives the packet, it can use the remote ID, the circuit ID, or both to assign IP
addresses and implement policies, such as restricting the number of IP addresses that can be assigned to
a single remote ID or a circuit ID. Then the DHCP server echoes the option-82 field in the DHCP reply.
The DHCP server unicasts the reply to the switch if the request was relayed to server by the switch. When
the client and server are on the same subnet, the server broadcasts the reply. The switch inspects the
remote ID and possibly the circuit ID fields to verify that it originally inserted the option-82 data. The
switch removes the option-82 field and forwards the packet to the switch port that connects to the DHCP
host that sent the DHCP request.
Examples
This example shows how to enable DHCP option-82 data insertion:
Switch(config)# ip dhcp snooping information option
You can verify your settings by entering the show ip dhcp snooping privileged EXEC command.
Catalyst 2950 and Catalyst 2955 Switch Command Reference
2-134
ip dhcp snooping information option
no ip dhcp snooping information option
Modification
This command was introduced.
Chapter 2 Catalyst 2950 and 2955 Cisco IOS Commands
OL-10102-01