Cisco Systems 3750E Configuring the Dhcp Relay Agent, Specifying the Packet Forwarding Address

Chapter 22 Configuring DHCP Features and IP Source Guard

Configuring DHCP Features

Configuring the DHCP Relay Agent

Beginning in privileged EXEC mode, follow these steps to enable the DHCP relay agent on the 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.

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:

•Checking (validating) the relay agent information

•Configuring the relay agent forwarding policy

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-addressaddress 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-addresscommand 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		Purpose
Step 1
	configure terminal		Enter global configuration mode.
Step 2
	interface vlan vlan-id		Create a switch virtual interface by entering a VLAN
			ID, and enter interface configuration mode.
Step 3
	ip address ip-address subnet-mask		Configure the interface with an IP address and an IP
			subnet.
Step 4
	ip helper-address address		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.
Step 5
	exit		Return to global configuration mode.
		Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02				22-11