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Cisco IE 3000 Switch Software Configuration Guide
OL-13018-03
Chapter 23 Configuring DHCP Features and IP Source Guard
Configuring DHCP Snooping
See the “
Configuring DHCP
” section of the “IP Addressing and Services” section of the
Cisco IOS IP
Configuration Guide, Release 12.2
from the Cisco.com page under
Documentation
>
Cisco IOS
Software
>
12.2 Mainline
>
Configuration Guides
for these procedures:
•
Checking (validating) the relay agent information
•
Configuring the relay agent forwarding policy
Enabling DHCP Snooping and Option 82
Beginning in privileged EXEC mode, follow these steps to enable DHCP snooping on the switch:
Command
Purpose
Step 1
configure terminal
Enter global configuration mode.
Step 2
ip dhcp snooping
Enable DHCP snooping globally.
Step 3
ip dhcp snooping vlan
vlan-range
Enable DHCP snooping on a VLAN or range of VLANs. The range is 1
to 4094.
You can enter a single VLAN ID identified by VLAN ID number, a series
of VLAN IDs separated by commas, a range of VLAN IDs separated by
hyphens, or a range of VLAN IDs separated by entering the starting and
ending VLAN IDs separated by a space.
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. This is the default setting.
Step 5
ip dhcp snooping information option
allow-untrusted
(Optional) If the switch is an aggregation switch connected to an edge
switch, enable the switch to accept incoming DHCP snooping packets
with option-82 information from the edge switch.
The default setting is disabled.
Note
Enter this command only on aggregation switches that are
connected to trusted devices.
Step 6
interface
interface-id
Specify the interface to be configured, and enter interface configuration
mode.
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 setting is untrusted.
Step 8
ip dhcp snooping limit rate
rate
(Optional) Configure the number of DHCP packets per second that an
interface can receive. The range is 1 to 2048. By default, no rate limit is
configured.
Note
We recommend an untrusted rate limit of not more than 100
packets per second. If you configure rate limiting for trusted
interfaces, you might need to increase the rate limit if the port is
a trunk port assigned to more than one VLAN on which DHCP
snooping is enabled.
Step 9
exit
Return to global configuration mode.