Ip Dhcp Snooping Information Option - Cisco Catalyst 3560-X Command Reference Manual
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ip dhcp snooping information option
ip dhcp snooping information option
Syntax Description
Defaults
Command Modes
Command History
Usage Guidelines
Examples
Catalyst 3750-X and 3560-X Switch Command Reference
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Use the ip dhcp snooping information option global configuration command on the switch stack or on
a standalone switch to enable DHCP option-82 data insertion. Use the no form of this command to
disable DHCP option-82 data insertion.
ip dhcp snooping information option
no ip dhcp snooping information option
This command has no arguments or keywords.
DHCP option-82 data is inserted.
Global configuration
Release
Modification
12.2(53)SE2
This command was introduced.
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 the 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.
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 user EXEC command.
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Chapter 2
Catalyst 3750-X and 3560-X Switch Cisco IOS Commands
OL-21522-02
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