[pptp-server] Unsupported protocol errors from pppd?

[Patrick J. LoPresti]

This is with pptpd-1.0.0 and ppp-2.3.10+mppe+stateless patches.

For some of our clients, PoPToP is working great.  For others, we log
a bunch of messages like the ones below.  As you can see, pppd is
complaining about "unsupported protocol" errors, after the PPP link
has been negotiated and authenticated.  There is no pattern to the
protocol numbers that I can discern.

Based on my limited knowledge of this stuff, I am guessing this is
some sort of HDLC weirdness (address/control field compression
problem?), since the protocol field comes just before the data in the
PPP/HDLC frame.

Does anyone have suggestions for sorting this out?  I am willing to
hack pptpd and/or pppd to gather more information, but suggestions
from an expert as to *what* information I should gather would be
helpful.  I also have more complete debugging logs if anyone wants to
see them.

 - Pat

(Note: IP addresses and names x'ed out below to protect the guilty)

18:23:07 pptpd: CTRL: Client xx.xx.xx.xx control connection started
18:23:07 pptpd: CTRL: Starting call (launching pppd, opening GRE)
18:23:07 kernel: CSLIP: code copyright 1989 Regents of the University of California
18:23:07 kernel: PPP: version 2.3.10 (demand dialling)
18:23:07 kernel: PPP line discipline registered.
18:23:07 kernel: registered device ppp0
18:23:07 pppd: pppd 2.3.10 started by root, uid 0
18:23:07 pppd: Using interface ppp0
18:23:07 pppd: Connect: ppp0 <--> /dev/pts/0
18:23:07 pptpd: CTRL: Ignored a SET LINK INFO packet with real ACCMs!
18:23:07 kernel: PPP BSD Compression module registered
18:23:07 kernel: PPP MPPE compression module registered
18:23:07 kernel: PPP Deflate Compression module registered
18:23:07 pppd: MSCHAP peer authentication succeeded for xxx
18:23:08 pppd: found interface eth0 for proxy arp
18:23:08 pppd: local  IP address xx.xx.xx.xx
18:23:08 pppd: remote IP address xx.xx.xx.xx
18:23:08 pppd: MPPE 40 bit, non-stateless compression enabled
18:23:13 pppd: Unsupported protocol (0x1e98) received
18:23:14 pppd: Unsupported protocol (0x5081) received
18:23:16 pppd: Unsupported protocol (0x6c02) received
18:23:22 pppd: Unsupported protocol (0x1425) received
18:23:23 pppd: Unsupported protocol (0xd53d) received
18:23:25 pppd: Unsupported protocol (0x8a99) received
18:23:31 pppd: Unsupported protocol (0x5728) received
18:23:32 pppd: Unsupported protocol (0x16d3) received
18:23:34 pppd: Unsupported protocol (0x27b) received
18:23:40 pppd: Unsupported protocol (0xecc9) received
18:23:41 pppd: Unsupported protocol (0xe32c) received
18:23:43 pppd: Unsupported protocol (0xd282) received
18:23:49 pppd: Unsupported protocol (0x3161) received
18:23:50 pppd: Unsupported protocol (0x1b8d) received
18:23:52 pppd: Unsupported protocol (0x51be) received
18:23:54 pppd: Unsupported protocol (0xb2d3) received
18:24:00 pppd: Unsupported protocol (0x27cb) received
18:24:02 pppd: Unsupported protocol (0xedb7) received
18:24:04 pppd: Unsupported protocol (0x9afd) received
18:24:04 pppd: Unsupported protocol (0xfad8) received
18:24:04 pppd: Unsupported protocol (0x2a15) received
18:24:05 pppd: Unsupported protocol (0x9d58) received
18:24:05 pppd: Unsupported protocol (0x7fc8) received
18:24:06 pppd: Unsupported protocol (0x9f23) received
18:24:07 pppd: Unsupported protocol (0xf465) received
18:24:20 pppd: Unsupported protocol (0x9532) received
18:24:20 pppd: Unsupported protocol (0xc784) received
18:24:20 pppd: Unsupported protocol (0x442c) received
18:24:21 pppd: Unsupported protocol (0x15e) received
18:24:22 pppd: Unsupported protocol (0x19a1) received
18:24:22 pppd: Unsupported protocol (0xe012) received
18:24:22 pppd: Unsupported protocol (0xa056) received
18:24:23 pppd: Unsupported protocol (0x27f7) received
18:24:23 pppd: Unsupported protocol (0x3a53) received
18:24:23 pppd: Unsupported protocol (0x86c) received
18:24:24 pppd: Unsupported protocol (0x88f3) received
18:24:24 pppd: Unsupported protocol (0x80c3) received
18:24:24 pppd: Unsupported protocol (0x75a6) received
18:24:25 pppd: Unsupported protocol (0xc361) received
18:24:25 pppd: Unsupported protocol (0x2753) received
18:24:26 pppd: Unsupported protocol (0xe80a) received
18:24:27 pppd: Unsupported protocol (0xb332) received
18:24:27 pppd: Unsupported protocol (0x287c) received
18:24:27 pppd: Unsupported protocol (0x260b) received
18:24:28 pppd: Unsupported protocol (0xac4d) received
18:24:28 pppd: Unsupported protocol (0x6626) received
18:24:29 pppd: Unsupported protocol (0xc5dd) received
18:24:30 pppd: Unsupported protocol (0x1db1) received
18:24:30 pppd: Unsupported protocol (0x8348) received
18:24:30 pppd: Unsupported protocol (0xa3bd) received
18:24:31 pppd: Unsupported protocol (0x4bd7) received
18:24:31 pppd: Unsupported protocol (0xb0f5) received
18:24:31 pppd: Unsupported protocol (0x216d) received
18:24:32 pppd: Unsupported protocol (0x73c1) received
18:24:33 pppd: Unsupported protocol (0xc00) received
18:24:33 pppd: Unsupported protocol (0x8f1d) received
18:24:34 pppd: Unsupported protocol (0xdc7a) received
18:24:35 pppd: Unsupported protocol (0x4d5e) received
18:24:48 pppd: Unsupported protocol (0xceda) received
18:24:48 pppd: Unsupported protocol (0x6ea9) received
18:24:49 pppd: Unsupported protocol (0x3d73) received
18:24:50 pppd: Unsupported protocol (0x287f) received
18:24:50 pppd: Unsupported protocol (0x6a8b) received
18:24:51 pppd: Unsupported protocol (0x536d) received
18:24:51 pppd: Unsupported protocol (0xb4b0) received
18:24:52 pppd: Unsupported protocol (0xd47f) received
18:24:52 pppd: Unsupported protocol (0x54d5) received
18:24:52 pppd: Unsupported protocol (0x161a) received
18:24:53 pppd: Unsupported protocol (0xd34f) received
18:24:53 pppd: Unsupported protocol (0x6847) received
18:24:54 pppd: Unsupported protocol (0x8e64) received
18:24:54 pppd: Unsupported protocol (0x1e38) received
18:24:55 pppd: Unsupported protocol (0xc75e) received
18:24:55 pppd: Unsupported protocol (0xba93) received
18:24:56 pppd: Unsupported protocol (0x8fce) received
18:24:56 pppd: Unsupported protocol (0x1422) received
18:24:57 pppd: Unsupported protocol (0xc7f3) received
18:24:57 pppd: Unsupported protocol (0x88f6) received
18:24:57 pppd: Unsupported protocol (0x49b2) received
18:24:58 pppd: Unsupported protocol (0xeacd) received
18:24:58 pppd: Unsupported protocol (0x96c7) received
18:24:59 pppd: Unsupported protocol (0x4bc6) received
18:24:59 pppd: Unsupported protocol (0x83e9) received
18:24:59 pppd: Unsupported protocol (0x781a) received
18:25:00 pppd: Unsupported protocol (0x48f0) received
18:25:01 pppd: Unsupported protocol (0xd278) received
18:25:01 pppd: Unsupported protocol (0x4320) received
18:25:01 pppd: Unsupported protocol (0x3523) received
18:25:01 pppd: Unsupported protocol (0x3fad) received
18:25:02 pppd: Unsupported protocol (0xbc02) received
18:25:02 pppd: Unsupported protocol (0x5bbf) received
18:25:03 pppd: Unsupported protocol (0xca33) received
18:25:03 pppd: Unsupported protocol (0x7899) received
18:25:03 pppd: Unsupported protocol (0x8ee8) received
18:25:04 pppd: Unsupported protocol (0x9a4) received
18:25:05 pppd: Unsupported protocol (0xf7c5) received
18:25:05 pppd: Unsupported protocol (0xa840) received
18:25:05 pppd: Unsupported protocol (0xafce) received
18:25:06 pppd: Unsupported protocol (0xac97) received
18:25:07 pppd: Unsupported protocol (0x573b) received
18:25:07 pppd: Unsupported protocol (0x3d50) received
18:25:07 pppd: Unsupported protocol (0x4afd) received
18:25:08 pppd: Unsupported protocol (0x304f) received
18:25:09 pppd: Unsupported protocol (0x85d5) received
18:25:09 pppd: Unsupported protocol (0x22c5) received
18:25:09 pppd: Unsupported protocol (0xbdf5) received
18:25:10 pppd: Unsupported protocol (0xa29e) received
18:25:11 pppd: Unsupported protocol (0xf3ea) received
18:25:11 pppd: Unsupported protocol (0xe805) received
18:25:11 pppd: Unsupported protocol (0x1833) received
18:25:12 pppd: Unsupported protocol (0x7876) received
18:25:13 pppd: Unsupported protocol (0xd3a4) received
18:25:13 pppd: Unsupported protocol (0xc957) received
18:25:14 pppd: Unsupported protocol (0x5746) received
18:25:16 pppd: Unsupported protocol (0x80e1) received
18:25:19 pppd: Unsupported protocol (0x8f7b) received
18:25:22 pppd: Unsupported protocol (0x109d) received
18:25:23 pppd: Unsupported protocol (0xc0dd) received
18:25:24 pppd: Unsupported protocol (0x6c9f) received
18:25:25 pppd: Unsupported protocol (0x9e6b) received
18:25:29 pppd: Unsupported protocol (0xe7d7) received
18:25:31 pppd: Unsupported protocol (0x505b) received
18:25:32 pppd: Unsupported protocol (0x231b) received
18:25:34 pppd: Unsupported protocol (0x6f80) received
18:25:34 pppd: Unsupported protocol (0xa9ab) received
18:25:39 pppd: Unsupported protocol (0xdd57) received
18:25:40 pppd: Unsupported protocol (0x5e45) received
18:25:41 pppd: Unsupported protocol (0x191c) received
18:25:43 pppd: Unsupported protocol (0xe9e8) received
18:25:46 pppd: Unsupported protocol (0xfbcf) received
18:25:49 pppd: Unsupported protocol (0x1e7b) received
18:25:50 pppd: Unsupported protocol (0xa0f5) received
18:25:52 pppd: Unsupported protocol (0x9642) received
18:25:53 pppd: Unsupported protocol (0x5a5b) received
18:26:02 pptpd: CTRL: Error with select(), quitting
18:26:02 pptpd: CTRL: Client xx.xx.xx.xx control connection finished
18:26:02 pppd: Modem hangup
18:26:02 pppd: Connection terminated.
18:26:02 pppd: Connect time 3.0 minutes.
18:26:02 pppd: Sent 16634 bytes, received 16201 bytes.
18:26:02 pppd: Exit.