PPP Configuration Point to Point Protocol

Practice this topic in the router emulator Much like HDLC, PPP is also very easy to configure. Setting the encapsulation to PPP and the clock rate on the DCE is all that is required. Optionally, you may also configure PPP to use two authentication methods - PAP or CHAP (or both).

PPP Configuration

As HDLC is the default encapsulation  you must explicitly set PPP on your serial interface.

Router(config-if)#encapsulation ppp

Configure PPP clock rate

The DCE end of the link should have the clock rate command applied under interface configuration mode.

Router(config-if)#clock rate ?   <- will display all clock rates supported

Router(config-if)#clock rate <rate>

Configure PPP Authentication

PPP can use two types of authentication - PAP and CHAP. The former is an insecure authentication method as it sends the password in clear, while the later sends a hash making it much better when working across third party circuits. Cisco allows you to use both if you wish, with one being preferred over the other. In the example below, CHAP authentication is configured as the preferred method to authenticate a peer, followed by PAP as a fall back. Swapping around the CHAP/PAP words would reverse this and make PAP the preferred method. Omitting either would make the other the sole authentication method.

Router(config-if)#ppp authentication chap pap

Once enabled, you must now define the username and password for the device at the OTHER END of the link. The username will be the same as the remote hostname, and the password the password it sends, which must match at both ends. For example, if my remote router (with the hostname remote) is configured to send the password password1, I must set the username to remote and the password to password1 on the local router using the command below, and the same vice versa.

local(config)#username remote password password1
remote(config)#username local password password1

The final element of the configuration is only necessary if you are using PAP - you must set which username and password to send. This is done from interface configuration mode, and needs to match the username/password combo that was defined above on the remote router.

Router(config-if)#ppp pap sent-username R2 password password1

Further reading