Cisco Catalyst 3550

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Catalyst 3550 Multilayer Switch Command Reference
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Chapter 2 Catalyst 3550 Switch Cisco IOS Commands
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.
ip dhcp snooping information option
no ip dhcp snooping information option
Syntax Description This command has no arguments or keywords.
Defaults DHCP option-82 data insertion is enabled.
Command Modes Global configuration
Command History
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 or snmp-ifindex, 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.
In Cisco IOS Release 12.1(19)EA1, the implementation for the option-82 subscriber identification
changed from the previous release. The new option-82 format uses a different circuit ID and remote ID
suboption, vlan-mod-port. The previous version uses the snmp-ifindex circuit ID and remote ID
suboption.
You can select the previous option-82 format by using the ip dhcp snooping information option
format snmp-ifindex global configuration command. When DHCP snooping is enabled globally,
option-82 information (in the selected format) is only inserted on snooped VLANs.
Release Modification
12.1(19)EA1 This command was introduced.