Ahhh! The dial-up client is sending the Cisco a "malformed" NAK; one portion of the received LCP packet indicates CHAP (proto), and another portion of the same LCP packet implies that PAP(length). Did you obtain this info from rfc1334 (for my own future reference)? The interesting this is that I have this same prob even w/ different remote OS's and dial-up clients. They do, however, use the same make/model BRI TA (Motorola BitSrufr Pro).
Here is the entire debug:
PPP:
PPP authentication debugging is on
PPP protocol negotiation debugging is on
PPP packet display debugging is on
Multilink events debugging is on
Radius protocol debugging is on
Oct 14 19:29:12: %LINK-3-UPDOWN: Interface Serial1/0:0, changed state to up
Se1/0:0 PPP: Autodetect trying to detect PPP mode
Se1/0:0 PPP: Sampled pkt: 29 bytes (0xFF03C021010300190104)
Se1/0:0 PPP: Treating connection as a callin
Se1/0:0 PPP: Phase is ESTABLISHING, Passive Open [0 sess, 1 load]
Se1/0:0 LCP: State is Listen
Se1/0:0 PPP: I pkt type 0xC021, datagramsize 29
Se1/0:0 LCP: I CONFREQ [Listen] id 3 len 25
Se1/0:0 LCP: MRU 1600 (0x01040640)
Se1/0:0 LCP: MRRU 1600 (0x11040640)
Se1/0:0 LCP: EndpointDisc 5 5045660054 (0x130D0535303435363630303534)
Se1/0:0 LCP: O CONFREQ [Listen] id 43 len 25
Se1/0:0 LCP: AuthProto PAP (0x0304C023)
Se1/0:0 LCP: MagicNumber 0x00FC3FB6 (0x050600FC3FB6)
Se1/0:0 LCP: MRRU 1524 (0x110405F4)
Se1/0:0 LCP: EndpointDisc 1 3640 (0x13070133363430)
Se1/0:0 LCP: O CONFACK [Listen] id 3 len 25
Se1/0:0 LCP: MRU 1600 (0x01040640)
Se1/0:0 LCP: MRRU 1600 (0x11040640)
Se1/0:0 LCP: EndpointDisc 5 5045660054 (0x130D0535303435363630303534)
Se1/0:0 PPP: I pkt type 0xC021, datagramsize 14
Se1/0:0 LCP: I CONFREJ [ACKsent] id 43 len 10
Se1/0:0 LCP: MagicNumber 0x00FC3FB6 (0x050600FC3FB6)
Se1/0:0 LCP: O CONFREQ [ACKsent] id 44 len 19
Se1/0:0 LCP: AuthProto PAP (0x0304C023)
Se1/0:0 LCP: MRRU 1524 (0x110405F4)
Se1/0:0 LCP: EndpointDisc 1 3640 (0x13070133363430)
Se1/0:0 PPP: I pkt type 0xC021, datagramsize 13
Se1/0:0 LCP: I CONFNAK [ACKsent] id 44 len 9
Se1/0:0 LCP: AuthProto 0xC223 (0x0304C223)
Se1/0:0 LCP: Received bad NAK!
Se1/0:0 LCP: O CONFREQ [ACKsent] id 45 len 19
Se1/0:0 LCP: AuthProto PAP (0x0304C023)
Se1/0:0 LCP: MRRU 1524 (0x110405F4)
Se1/0:0 LCP: EndpointDisc 1 3640 (0x13070133363430)
Se1/0:0 PPP: I pkt type 0xC021, datagramsize 13
Se1/0:0 LCP: I CONFNAK [ACKsent] id 45 len 9
Se1/0:0 LCP: AuthProto 0xC223 (0x0304C223)
Se1/0:0 LCP: Received bad NAK!
Se1/0:0 LCP: O CONFREQ [ACKsent] id 46 len 19
Se1/0:0 LCP: AuthProto PAP (0x0304C023)
Se1/0:0 LCP: MRRU 1524 (0x110405F4)
Se1/0:0 LCP: EndpointDisc 1 3640 (0x13070133363430)
Se1/0:0 PPP: I pkt type 0xC021, datagramsize 13
Se1/0:0 LCP: I CONFNAK [ACKsent] id 46 len 9
Se1/0:0 LCP: AuthProto 0xC223 (0x0304C223)
Se1/0:0 LCP: Received bad NAK!
Se1/0:0 LCP: O CONFREQ [ACKsent] id 47 len 19
Se1/0:0 LCP: AuthProto PAP (0x0304C023)
Se1/0:0 LCP: MRRU 1524 (0x110405F4)
Se1/0:0 LCP: EndpointDisc 1 3640 (0x13070133363430)
Se1/0:0 PPP: I pkt type 0xC021, datagramsize 13
Se1/0:0 LCP: I CONFNAK [ACKsent] id 47 len 9
Se1/0:0 LCP: AuthProto 0xC223 (0x0304C223)
Se1/0:0 LCP: Received bad NAK!
Se1/0:0 LCP: O CONFREQ [ACKsent] id 48 len 19
Se1/0:0 LCP: AuthProto PAP (0x0304C023)
Se1/0:0 LCP: MRRU 1524 (0x110405F4)
Se1/0:0 LCP: EndpointDisc 1 3640 (0x13070133363430)
Se1/0:0 PPP: I pkt type 0xC021, datagramsize 13
Se1/0:0 LCP: I CONFNAK [ACKsent] id 48 len 9
Se1/0:0 LCP: AuthProto 0xC223 (0x0304C223)
Se1/0:0 LCP: Received bad NAK!
Se1/0:0 LCP: O CONFREQ [ACKsent] id 49 len 19
Se1/0:0 LCP: AuthProto PAP (0x0304C023)
Se1/0:0 LCP: MRRU 1524 (0x110405F4)
Se1/0:0 LCP: EndpointDisc 1 3640 (0x13070133363430)
Oct 14 19:29:18: %ISDN-6-CONNECT: Interface Serial1/0:0 is now connected to
XXXXXXXXXX unknown
Se1/0:0 PPP: I pkt type 0xC021, datagramsize 13
Se1/0:0 LCP: I CONFNAK [ACKsent] id 49 len 9
Se1/0:0 LCP: AuthProto 0xC223 (0x0304C223)
Se1/0:0 LCP: Received bad NAK!
Se1/0:0 LCP: O CONFREQ [ACKsent] id 50 len 19
Se1/0:0 LCP: AuthProto PAP (0x0304C023)
Se1/0:0 LCP: MRRU 1524 (0x110405F4)
Se1/0:0 LCP: EndpointDisc 1 3640 (0x13070133363430)
Se1/0:0 PPP: I pkt type 0xC021, datagramsize 13
Se1/0:0 LCP: I CONFNAK [ACKsent] id 50 len 9
Se1/0:0 LCP: AuthProto 0xC223 (0x0304C223)
Se1/0:0 LCP: Received bad NAK!
Se1/0:0 LCP: O CONFREQ [ACKsent] id 51 len 19
Se1/0:0 LCP: AuthProto PAP (0x0304C023)
Se1/0:0 LCP: MRRU 1524 (0x110405F4)
Se1/0:0 LCP: EndpointDisc 1 3640 (0x13070133363430)
Se1/0:0 LCP: I CONFNAK [ACKsent] id 51 len 9
Se1/0:0 LCP: AuthProto 0xC223 (0x0304C223)
Se1/0:0 LCP: Received bad NAK!
Se1/0:0 LCP: O CONFREQ [ACKsent] id 52 len 19
Se1/0:0 LCP: AuthProto PAP (0x0304C023)
Se1/0:0 LCP: MRRU 1524 (0x110405F4)
Se1/0:0 LCP: EndpointDisc 1 3640 (0x13070133363430)
Se1/0:0 PPP: I pkt type 0xC021, datagramsize 13
Se1/0:0 LCP: I CONFNAK [ACKsent] id 52 len 9
Se1/0:0 LCP: AuthProto 0xC223 (0x0304C223)
Se1/0:0 LCP: Received bad NAK!
Se1/0:0 LCP: Failed to negotiate with peer
Se1/0:0 LCP: O TERMREQ [ACKsent] id 53 len 4
Se1/0:0 PPP: I pkt type 0xC021, datagramsize 8
Se1/0:0 LCP: I TERMACK [TERMsent] id 53 len 4
Se1/0:0 LCP: State is Closed
Se1/0:0 PPP: Phase is DOWN [0 sess, 1 load]
Se1/0:0 PPP: Phase is ESTABLISHING, Passive Open [0 sess, 1 load]
Se1/0:0 LCP: State is Listen
Oct 14 19:29:18: %ISDN-6-DISCONNECT: Interface Serial1/0:0 disconnected from
XXXXXXXX unknown, call lasted 6 seconds
Oct 14 19:29:18: %LINK-3-UPDOWN: Interface Serial1/0:0, changed state to down
Se1/0:0 LCP: State is Closed
Se1/0:0 PPP: Phase is DOWN [0 sess, 1 load]
