3.1 PPP Architecture
3.1.6 Configuring the interface addressing method for local devices
The local address is set by using the ip address or ip unnumbered command.
  • ip address command - To assign an IP address to a network interface, configure the following command at the interface configuration mode:

Router(config-if)#ip address address mask

  • ip unnumbered command - To conserve network addresses, configure the asynchronous interfaces as “unnumbered.” An unnumbered interface does not have an address. When the unnumbered interface generates a packet, it uses the address of the specified interface as the source address of the IP packet, and can be thought of as a referenced IP address. IP unnumbered can be used only in point-to-point connections. The command is as follows:

Router(config-if)#ip unnumbered type number

A loopback interface is a virtual interface that never goes down; therefore, it is an ideal line to use as the reference when using the ip unnumbered command.

Lab Activity    
  The Atlanta Bread Company has a customer that would like to utilize the dialin core router to receive E-mail. The host will specify its own address. You will configure the core router to permit the UNIX host to specify the IP address.