Configuring The Dhcp Relay Agent; Specifying The Packet Forwarding Address - Cisco Catalyst 3750-X Software Configuration Manual

Chapter 24 Configuring DHCP Features and IP Source Guard

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 for these procedures:
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Specifying the Packet Forwarding Address

If the DHCP server and the DHCP clients are on different networks or subnets, you must configure the
switch with the ip helper-address address interface configuration command. The general rule is to
configure the command on the Layer 3 interface closest to the client. The address used in the ip
helper-address command can be a specific DHCP server IP address, or it can be the network address if
other DHCP servers are on the destination network segment. Using the network address enables any
DHCP server to respond to requests.
Beginning in privileged EXEC mode, follow these steps to specify the packet forwarding address:
Command
Step 1
configure terminal
Step 2
interface vlan vlan-id
Step 3
ip address ip-address subnet-mask
Step 4
ip helper-address address
Step 5 exit
OL-21521-01
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.
Create a switch virtual interface by entering a VLAN
ID, and enter interface configuration mode.
Configure the interface with an IP address and an IP
subnet.
Specify the DHCP packet forwarding address.
The helper address can be a specific DHCP server
address, or it can be the network address if other
DHCP servers are on the destination network
segment. Using the network address enables other
servers to respond to DHCP requests.
If you have multiple servers, you can configure one
helper address for each server.
Return to global configuration mode.
Catalyst 3750-X and 3560-X Switch Software Configuration Guide
Configuring DHCP Features
24-11