Troubleshooting guide

To correct both authentication mismatch problems, refer to the appropriate PPPoA implementation option
configuration and reconfigure PPP authentication.
The second authentication problem scenario you may encounter is an incorrect PAP username or password.
To determine if this is the problem, issue the command debug ppp negotiation. Assuming your router is
configured for both CHAP and PAP, as the configuration outlined earlier in this guide shows, your ISP may
not be using PAP authentication.
To determine the authentication used by your ISP, check the options in the I CONFREQ packet sent to you
from your ISP. If this packet is followed by an option called AuthProto PAP, you are using PAP. If the I
CONFREQ is followed by an option called AuthProto CHAP, you are using CHAP and should proceed to
How do I know if my CHAP username and password are correct?
How do I know if my PAP username and password are correct?
After you have confirmed that your ISP is using PAP, issue the debug ppp negotiation command to confirm
that your PAP username and password are correct.
Router#debug ppp negotiation
*Mar 2 00:50:15.741: Vi1 PPP: Treating connection as a callout
*Mar 2 00:50:15.745: Vi1 PPP: Phase is ESTABLISHING, Active Open [0 sess, 1 load]
*Mar 2 00:50:15.745: Vi1 PPP: No remote authentication for call−out
*Mar 2 00:50:15.745: Vi1 LCP: O CONFREQ [Closed] id 177 Len 10
*Mar 2 00:50:15.745: Vi1 LCP: MagicNumber 0x35EB5D4F (0x050635EB5D4F)
*Mar 2 00:50:15.789: Vi1 LCP: I CONFACK [REQsent] id 177 Len 10
*Mar 2 00:50:15.793: Vi1 LCP: MagicNumber 0x35EB5D4F (0x050635EB5D4F)
*Mar 2 00:50:17.241: Vi1 LCP: I CONFREQ [ACKrcvd] id 203 Len 14
*Mar 2 00:50:17.241: Vi1 LCP: AuthProto PAP (0x0304C023)
*Mar 2 00:50:17.241: Vi1 LCP: MagicNumber 0x3E1D1E5E (0x05063E1D1E5E)
*Mar 2 00:50:17.245: Vi1 LCP: O CONFACK [ACKrcvd] id 203 Len 14
*Mar 2 00:50:17.245: Vi1 LCP: AuthProto PAP (0x0304C023)
*Mar 2 00:50:17.245: Vi1 LCP: MagicNumber 0x3E1D1E5E (0x05063E1D1E5E)
*Mar 2 00:50:17.249: Vi1 LCP: State is Open
*Mar 2 00:50:17.249: Vi1 PPP: Phase is AUTHENTICATING, by the peer [0 sess, 1 load]
*Mar 2 00:50:17.249: Vi1 PAP: O AUTH−REQ id 9 Len 14 from "cisco"
!−−− "cisco" is the PAP username configured on this DSL Router.
*Mar 2 00:50:17.297: Vi1 PAP: I AUTH−NAK id 9 Len 27 msg is "Authentication failure"
*Mar 2 00:50:17.301: Vi1 LCP: I TERMREQ [Open] id 204 Len 4
*Mar 2 00:50:17.301: Vi1 LCP: O TERMACK [Open] id 204 Len 4
*Mar 2 00:50:17.305: Vi1 PPP: Phase is TERMINATING [0 sess, 1 load]u
*Mar 2 00:50:19.305: Vi1 LCP: TIMEout: State TERMsent
*Mar 2 00:50:19.305: Vi1 LCP: State is Closed
*Mar 2 00:50:19.305: Vi1 PPP: Phase is DOWN [0 sess, 1 load]
If you have a PAP authentication problem, you should see the LCP state go to Open. Directly following the
LCP state change you should see PPP go into an Authenticating phase. If one of the next two lines contains I
AUTH−NAK, either your PAP username or PAP password is incorrect. At this point, you need to reconfigure
your PAP username and password using the following sequence of commands. Note that your PAP username
and password are case sensitive.
Router#configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
Router(config)#interface dialer 1
Router(config−if)#ppp pap sent−username <username> password <password>
Router(config−if)#end
Router#write memory
Cisco DSL Router Configuration and Troubleshooting Guide