Configuring PPP on a Serial Line (Optional Commands): Authentication

Router(config)#username routerb password cisco

Sets a username of routerb and a password of cisco for authentication from the other side of the PPP serial link. This is used by the local router to authenticate the PPP peer

Router(config)#int s 0/0


Router(config-if)#ppp authentication pap

Turns on PAP authentication only

Router(config-if)#ppp authentication chap

Turns on CHAP authentication only

Router(config-if)#ppp authentication pap chap

Defines that the link will use PAP authentication, but will try CHAP if PAP fails or is rejected by other side

Router(config-if)#ppp authentication chap pap

Defines that the link will use CHAP authentication, but will try PAP if CHAP fails or is rejected by other side

Router(config-if)#ppp pap sent-username routerb password cisco

This command must be set if using PAP in Cisco IOS Software Release 11.1 or later


When setting authentication, make sure that your usernames match the name of the router on the other side of the link, and that the passwords on each router match the other. Usernames and passwords are case sensitive. Consider the following example:

Edmonton(config)#username Calgary password cisco

Calgary(config)#username Edmonton password cisco

Edmonton(config)#int s 0/0

Calgary(config)#int s 0/0

Edmonton(config-if)#encapsulation ppp

Calgary(config-if)#encapsulation ppp

Edmonton(config-if)#ppp authentication chap

Calgary(config-if)#ppp authentication chap


Because Password Authentication Protocol (PAP) does not encrypt its password as it is sent across the link, recommended practice is that you use Challenge Handshake Authentication Protocol (CHAP) as your authentication method.

CCNA Self-Study(c) CCNA Portable Command Guide
CCNA Portable Command Guide
ISBN: 1587201585
EAN: 2147483647
Year: 2006
Pages: 261
Authors: Scott Empson

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