A Cisco Router WAN interfaces can be configured as a DHCP client to obtain an IP Address from DHCP server. It is especially useful on Ethernet interfaces that dynamically connect to an internet service provider (ISP) or you need to configure the Router to obtain its interface IP address automatically.
Configure a DHCP Client on Cisco Router WAN Interface
To obtain an IP address on an interface using Dynamic Host Configuration Protocol (DHCP) protocol, use the ip address dhcp command in interface configuration mode. To remove any address that was acquired, use the no form of this command.
Cisco-Router(config)# interface fa0/0
Cisco-Router(config-if)#ip address dhcp
Configure DHCP Client ID and Hostname for DHCPDISCOVER Messages
Some service providers might ask you to use a client-id and/or a hostname of their own choice. The DHCPDISCOVER message has a specific hostname and client identifier that is the MAC address of the interface.
For following configuration example, the DHCP DISCOVER message sent by a Router would contain the MAC address of the FastEthernet 0/0 interface in the client-id field and the value cisco in the option 12 field.
Cisco-Router(config-if)#ip address dhcp client-id <INTname> hostname <HOST>
Cisco-Router(config-if)#ip address dhcp client-id fa0/0 hostname cisco
INTname is the interface name that will be used for the client-id
HOST is the hostname that will be used for the DHCP binding. This hostname can be different from the one that was set for the Router in the global configuration. You can use both of these parameters, one of them, or none of them.
Filed Under: DHCP
About the Author: