19-5
Catalyst 3550 Multilayer Switch Software Configuration Guide
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Chapter 19 Configuring DHCP Features
Configuring DHCP Features
To disable DHCP snooping, use the no ip dhcp snooping global configuration command. To disable
DHCP snooping on a VLAN or range of VLANs, use the no ip dhcp snooping vlan vlan-id global
configuration command. To disable the insertion and removal of the option-82 field, use the no ip dhcp
snooping information option global configuration command.
This example shows how to enable DHCP snooping globally and on VLAN 10 and to configure a rate
limit of 100 packets per second on Fast Ethernet port 0/1:
Switch(config)# ip dhcp snooping
Switch(config)# ip dhcp snooping vlan 10
Switch(config)# ip dhcp snooping information option
Switch(config)# interface fastethernet0/1
Switch(config-if)# ip dhcp snooping limit rate 100
Step 3
ip dhcp snooping vlan vlan-id [vlan-id] Enable DHCP snooping on a VLAN or range of VLANs. You can specify
a single VLAN identified by VLAN ID number or a start and end
VLAN ID to specify a range of VLANs. The range is 1 to 4094.
Step 4
ip dhcp snooping information option Enable the switch to insert and remove DHCP relay information
(option-82 field) in forwarded DHCP request messages to the DHCP
server.
The default is enabled.
Step 5
ip dhcp snooping information option
format snmp-ifindex
(Optional) Specify ip dhcp snooping information option format
snmp-ifindex to select an alternate format for the circuit ID and remote
ID suboption of the option-82 feature. See the “Upgrading from a
Previous Software Release” section on page 19-4 for more information.
The default setting is no ip dhcp snooping information option format
snmp-ifindex.
Step 6
interface interface-id Enter interface configuration mode, and specify the interface to be
configured.
Step 7
ip dhcp snooping trust (Optional) Configure the interface as trusted or untrusted. You can use the
no keyword to configure an interface to receive messages from an
untrusted client. The default is untrusted.
Step 8
ip dhcp snooping limit rate rate (Optional) Configure the number of DHCP packets per second than an
interface can receive. The range is 1 to 4294967294. The default is no rate
limit configured.
Note We recommend an untrusted rate limit of not more than 100
packets per second. Normally, the rate limit applies to untrusted
interfaces. If you configure rate limiting for trusted interfaces,
you will need to adjust the rate limit to a higher value because
trusted interfaces might aggregate DHCP traffic in the switch.
Step 9
end Return to privileged EXEC mode.
Step 10
show running-config Verify your entries.
Step 11
copy running-config startup-config (Optional) Save your entries in the configuration file.
Command Purpose
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