Cisco Systems 2960-S, 2960 Configuring the DHCP Relay Agent , Enabling DHCP Snooping and Option 82

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Catalyst 2960 and 2960-S Switch Software Configuration Guide
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Chapter 20 Configuring DHCP Features and IP Source Guard Features
Configuring DHCP Snooping
Configuring the DHCP Relay Agent
Beginning in privileged EXEC mode, follow these steps to enable the DHCP relay agent on the switch:
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:
• 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 th e switch:
Command Purpose
Step 1 configure terminal Enter global configuration mode.
Step 2 service dhcp Enable the DHCP server and relay agent on your switch. By default, this
feature is enabled.
Step 3 end Return to privileged EXEC mode.
Step 4 show running-config Verify your entries.
Step 5 copy running-config startup-config (Optional) Save your entries in the configuration file.
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 to 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.