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Chapter 18
Configuring DHCP Features and IP Source Guard
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
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
Step 6
interface range port-range
or
interface interface-id
Step 7
no shutdown
Step 8
switchport mode access
Step 9
switchport access vlan vlan-id
Step 10
end
Step 11
show running-config
Step 12
copy running-config startup-config
To remove the DHCP packet forwarding address, use the no ip helper-address address interface
configuration command.
78-17058-01
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.
Configure multiple physical ports that are connected
to the DHCP clients, and enter interface range
configuration mode.
or
Configure a single physical port that is connected to
the DHCP client, and enter interface configuration
mode.
Enable the interface(s), if necessary. By default, user
network interfaces (UNIs) are disabled and network
node interfaces (NNIs) are enabled.
Define the VLAN membership mode for the port.
Assign the ports to the same VLAN as configured in
Step 2.
Return to privileged EXEC mode.
Verify your entries.
(Optional) Save your entries in the configuration file.
Cisco ME 3400 Ethernet Access Switch Software Configuration Guide
Configuring DHCP Features
18-9
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