Summary
There appears to be a bug in the current releases in both the 15M and 15T code trains. I've tested with 15.4.3M2, 15.5.1T1, and 15.5.2T with the same results. From what I can tell, the bug is specifically in the PAP implementation in these releases.
Diagnosis
I've had a PPPoE/PAP implementation up for years. Upon installing any of the above IOS releases, that implementation stopped working. The symptom is the connection flapping (up/down) continuously. I got a hint this was an IOS bug by googling the symptom. These PPP bugs have evidently manifested themselves in previous releases.
Turning up debug is really the only way to narrow down what is happening:
router#debug ppp authentication router#debug ppp error router#debug pppoe errorsHere's a sampling of the error messages you'll see:
PPPoE: Failed to add PPPoE switching subblock PPPoE: Unexpected Event!. PPPoE switching Subblockdestroy called Vi2 LCP: Sent too many CONFNAKs. Switch to CONFREJI've had CHAP shut off on this implementation (again, for years) with this configured on the Dialer interface:
ppp chap refuse
Implementation
Turning on CHAP (and removing the 'refuse' command) seems to fix things for me. That IOS CHAP code apparently is not bug-ridden and my ISP evidently will allow a CHAP authentication. If yours doesn't, this won't help you. Your only option is drop back to a stable release and wait till Cisco corrects the PPP/PAP bug in a future release.
interface Dialer1 ip address negotiated ip mtu 1492 encapsulation ppp ip tcp adjust-mss 1452 dialer pool 1 dialer-group 1 ppp authentication pap chap callin ppp chap hostname yourName ppp chap password yourPassword ppp pap sent-username yourName password yourPassword no cdp enableCopyright ©1993-2024 Joey E Whelan, All rights reserved.
