aracter after a password during configuration. It's hard to catch such an error, because everything will look normal. If you believe everything is configured correctly, but it's just not working, try removing the lines with the passwords and retyping them (using cut and paste usually doesn't solve the problem). While this can happen anytime passwords are being configured, I find it especially maddening when I'm using CHAP, because I'm constantly second-guessing my configuration. One-way authentication. We'll begin with some examples of one-way authentication using CHAP. Notice that the username configured on each router matches the hostname of Basic (Non-AAA) Authentication the other router. Notice also that the password is the same for both usernames. The password must be the same on both routers: Calling side (Chicago): Hostname Chicago username NewYork password 0 Secret2 interface BRI1/0 encapsulation ppp ppp authentication chap callin Called side (NewYork): Hostname NewYork username Chicago password 0 Secret2 interface BRI1/0 encapsulation ppp ppp authentication chap Now, let's look at the debug output for a successful call using these configurations. The call was initiated from the Chicago router. If you look carefully, you'll see that the NewYork router is receiving a challenge from NewYork. The challenge entries in the debug output refer to the username, not the hostname. This can add to the confusion, as the username must match the hostname of the other router. Here's the debug output for both sides: Calling side: 20:08:11: %LINK-3-UPDOWN: Interface BRI1/0:1, changed state to up 20:08:11: BR1/0:1 PPP: Using dialer call direction 20:08:11: BR1/0:1 PPP: Treating connection as a callout 20:08:11: BR1/0:1 CHAP: I CHALLENGE id 3 len 28 from "NewYork" 20:08:11: BR1/0:1 CHAP: 0 RESPONSE id 3 len 28 from "Chicago" 20:08:11: BR1/0:1 CHAP: I SUCCESS id 3 len 4 20:08:12: %LINEPROTO-5-UPDOWN: Line protocol on Interface BRI1/0:1, changed state to up 20:08:17: %ISDN-6-CONNECT: Interface BRI1/0:1 is now connected to 780