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Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
OL-9639-06
Chapter 19 Configuring DHCP Features and IP Source Guard
Configuring DHCP Features
Configuring the DHCP Server
The switch can act as a DHCP server. By default, the Cisco IOS DHCP server and relay agent features
are enabled on your switch but are not configured. These features are not operational.
For procedures to configure the switch as a DHCP server, see the “Configuring DHCP” section of the
“IP addressing and Services” section of the Cisco IOS IP Configuration Guide, Release 12.2.
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 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 and the switch is running
the metro IP access image, 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 Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
service dhcp Enable the DHCP 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
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.