in the configuration below, I have configured PAP and CHAP and it worked in both cases, however I used one router as Server and one as Client.
PPP Configuration=================PPP with PAP authentication:in this configuration R1 is PAP Server and R2 is PAP clientR1(config)#int s1/0 R1(config-if)ip address 1.1.1.1 255.255.255.0 R1(config-if)#encapsulation ppp R1(config-if)#ppp authentication pap R1(config-if)#exit R1(config)#username R2 password ciscoR2(config)#int s1/0R2(config-if)ip address 1.1.1.2 255.255.255.0R2(config-if)#encapsulation ppp R2(config-if)#ppp pap sent-username R2 password cisco=================================PPP with CHAP authentication:in this configuration R1 is CHAP Client and R2 is CHAP ServerR1#configure terminalR1(config)#interface serial 1/0R1(config-if)ip address 1.1.1.1 255.255.255.0R1(config-if)#encapsulation ppp R1(config-if)#ppp chap hostname R1R1(config-if)#ppp chap password ciscoR2#configure terminalR2(config)#username R1 password ciscoR2(config)#interface serial 1/0R2(config-if)ip address 1.1.1.2 255.255.255.0R2(config-if)#encapsulation pppR2(config-if)#ppp authentication chap=================================
I believe in real world there could be scenarios where there is one server authenticating multiple clients or multiple servers authenticating each others.
I guess in the scenario where one server is authenticating multiple clients , we might just need to add the following line on the server for as many clients as we have, correct me if I am wrong:
RouterServer(config)#username client1 password cisco
RouterServer(config)#username client2 password cisco2
RouterServer(config)#username client3 password cisco3
etc....
but what about the scenario when 2 servers authenticate each other? can someone post an example ?