PPP Authentication

OK now we have to take into perspective  when it comes to PPP Authentication one important thing , there are 2 parts of the story ... call them server and client.

Server is the device that has the command : 

ppp authentication pap            <<<<< Authenticate using PAP only 
or
ppp authentication chap          <<<<< Authenticate using chap only
or 
ppp authentication pap chap <<<<<< Try pap if other end refuse try chap

So now since this device requests authentication it must have database for authenticating (username and password) this could be done in config mode

username Device2 password cisco

In other words my PPP session won't come up until i verify that the other end username/password is correct

Client  is the device that has the command :

ppp pap sent-username Device 2 password cisco

or

ppp chap hostname Device 2
ppp chap password cisco

or
( i make a choice if server is sending pap and chap to refuse pap and accept chap)
ppp pap refuse   <<<<<<<<<< When server requests pap authentication i refuse it hence server will offer me chap to do this the server must be having the command ppp authentication pap chap

In other words my PPP session won't come up until i provide correct username/password to the remote device

Note :  we can make both devices act as server/client and in this way we require mutual authentication :) but always keep in mind the above points when configuring authentication