Configuring The Dhcp Relay Agent; Enabling Dhcp Snooping And Option 82 - Cisco Catalyst 2975 Software Configuration Manual

Chapter 20 Configuring DHCP Features and IP Source Guard Features

Configuring the DHCP Relay Agent

Beginning in privileged EXEC mode, follow these steps to enable the DHCP relay agent on the switch:
Command
Step 1 configure terminal
Step 2
service dhcp
Step 3
end
Step 4 show running-config
Step 5 copy running-config startup-config
To disable the DHCP server and relay agent, use the no service dhcp global configuration command.
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:
•
•

Enabling DHCP Snooping and Option 82

Beginning in privileged EXEC mode, follow these steps to enable DHCP snooping on the switch:
Command
Step 1 configure terminal
Step 2 ip dhcp snooping
Step 3 ip dhcp snooping vlan vlan-range
Step 4 ip dhcp snooping information option
Step 5 ip dhcp snooping information option
allow-untrusted
Step 6
interface interface-id
OL-19720-02
Purpose
Enter global configuration mode.
Enable the DHCP server and relay agent on your switch. By default, this
feature is enabled.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Checking (validating) the relay agent information
Configuring the relay agent forwarding policy
Purpose
Enter global configuration mode.
Enable DHCP snooping globally.
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.
Enable the switch to insert and to remove DHCP relay information
(option-82 field) in forwarded DHCP request messages to the DHCP
server. This is the default setting.
(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
Specify the interface to be configured, and enter interface configuration
mode.
Enter this command only on aggregation switches that are
connected to trusted devices.
Catalyst 2975 Switch Software Configuration Guide
Configuring DHCP Snooping
20-11