[pptp-server] a *bizarre* situation

John Leach john at ecsc.co.uk
Sun Jun 10 15:08:23 CDT 2001


Ok, now this has me doing some serious swede scratching....

This is over a local lan, with no firewalls or routers in between, just
a switch.

I have a Win2k client (actually 2, one advanced server, another pro SP2)
connecting to pptpd v1.1.2, pppd 2.4.0 (with the relevant patches to
make mppe work), on Linux kernel 2.4.3 again with the relevant patches.

I connect un-encrypted, everything works fine, things work superbly in
fact.

I connect using encryption, and everything *seems* to work fine.  auths,
connects, sets up the tunnel...  but the win2k box doesn't seem to
actually *see* the packets it receives.  But it definately does get
them.

A simple ping test from the win2k box to the other end of the ppp
connection results in an outgoing icmp request which the linux server
receives ok, which then replies with an icmp reply, which arrives at the
other end of the tunnel fine too, but the win2k box doesn't see it.

I know the packets are being received as I've used WinEthereal and have
captured them.  I've tried this with TCP connections too, win2k just
doesn't see the ack packets even tho they actually get received.

To be truthful I'm faffing around with an rpm I made last month of this
lot, which I've tested before and has been confirmed to work, I *should*
be recompiling from source manually and re-testing, but I'd really like
to know what is going on.

There are *no* packet filters of any kind active on either win2k box or
the linux box.  I wanted to test via the linux pptp client but I can't
seem to make it use mppe, it always defaults to cleartext. 

This has me stumped.  I first thought data was being corrupted
somewhere, but ethereal should pick up on that (I beleive it checks the
crcs).  I can see the incoming gre packets, and the resulting
un-encapsulated packets, but win2k never seems to actually use them.

ARGH!

John Leach. MCP, CCNA, BOFH, EGO.






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