[pptp-server] Wierd error

[Philip Van Baren]

This is probably caused by dropped and/or out-of-order packets and a bug in
ppp_mppe that causes it not to re-sync when a packet is lost.

The FAQ (http://www.vibres.com/pptpd/pptpd-FAQ.txt) has more details:


7.3.10.	The VPN link works for a while, but then stops working,
	and the /var/log/debug file shows the following:
		pppd[10544]: rcvd [Compressed data] 10 32 ae 68 c0 8e e1 92 ...

	Solution: Patch the /usr/src/linux/drivers/net/ppp_mppe.c file with
	the patch:

	http://www.vibrationresearch.com/pptpd/ppp_mppe_compressed_data_fix.diff

	and then recompile and reinstall the ppp_mppe.o module

7.3.11. The VPN link works for a while, but then stops working,
	and the /var/log/debug file shows messages like the following:
		pppd[11170]: sent [LCP ProtRej id=0xb 51 19 ...
		pppd[11170]: rcvd [proto=0xbe1b] df 60 4e 4e ...
		pppd[11170]: Unsupported protocol 0xbe1b received
	(where the hex data and the protocol numbers may vary)

	This is probably caused by dropped packets with mppe running in
	stateful mode (i.e. mppe-stateless disabled).  In stateful mode,
	decryption of a packet requires successful decryption of the previous
	packet.  In stateless mode, a packet can always be decrypted as long
	as the sequence number is known.

	Solution: add the "mppe-stateless" option to the /etc/ppp/options.pptp
	file.

> -----Original Message-----
> From: pptp-server-admin at lists.schulte.org
> [mailto:pptp-server-admin at lists.schulte.org]On Behalf Of Devin Brown
> Sent: Friday, November 24, 2000 3:19 PM
> To: pptp-server at lists.schulte.org
> Subject: [pptp-server] Wierd error
>
>
> I've just built my second PopTop Server.  The first one I build about 6
> months ago and is working fine.  This new one however, is giving me grief.
> I built it the same way as the other one with the exception that I am now
> using Redhat 6.2 as the OS instead of Debian 2.2 as I did on the
> other one.
>  I first had problems compiling the kernel with the PPP MPPE patch in it.
> I got an error complaining of an undefined PPP_MAGIC.  I
> eventually found a
> workaround but it concerned me that I didn't have to do this on the other
> server.  (I tried this compile in Debian too and it still bombed so that,
> at least, is not a RedHat issue)  I've now got the kernel compiled (2.2.16
> same as on the other server) and PopTop installed (v1.1.1.  I tried 1.0.0
> and it did the same thing.)  What it's doing is kinda strange.  The server
> is attached to our ADSL line for it's outside connection.  If I hook a
> client machine (Win98) up inside the ADSL line (so same subnet as the
> outside card in the new server) I can connect without problems.  It works
> great.  However, if I hook this same client up to our secondary internet
> connection (Shaw) and try to connect to the server through the actual
> internet I can still connect but if I start a ping to an address on the
> inside network (192.168.*.* range) it works for about 2 minutes
> then I lose
> the connection.  The PPTP connection stays up, I just can't transfer any
> data through the VPN Server.  I CAN connect reliably through this
> same Shaw
> connection to the old VPN server.
>
> The error that shows up in the syslog when a connect fails in this manner
> is "Unexpected sequence number; got 6 after 3"  The numbers are not always
> the same.  Can anybody tell me what I did wrong?
>
>
> --------------------
> Devin Brown
> Anthony MacAuley Associates
> dbrown at amavi.com
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