[pptp-server] MPPE issue--packets stop flowing with 2nd client or re-establishing PPP

[Josh Howlett]

Are you trying to have multiple clients over a masq'd connection?  If
so, it won't work.

josh.

On Tue, 25 Sep 2001, Jim Roland wrote:

> 
> Perhaps you have seen this without me having to spam up email with sending 2
> samples of debug and messages logs.  No errors come up except discussion
> about pptpd buffering and reordering packets.  This was normal at working
> and non-working moments.
> 
> I am running the following:
> RedHat 7.1
> kernel 2.4.2-2
> ppp-2.4.0 (via source code)
> pptpd-1.0.1 (upgraded to 1.1.2 to eliminate "GRE: Discarded out of order
> packet" errors)
> linux-2.4.0-openssl-0.9.6-mppe.patch.gz (patches to kernel)
> ppp-2.4.0-openssl-0.9.6-mppe.patch.gz (patches to pppd)
> [Linux PPTP server]
> [Windows 2000 client]
> 
> 
> I am having 2 strange problems:
> 1) Single client only:  All works fine if ppp_mppe module is NOT already
> loaded into memory when I establish a VPN connection.
>     * I leave a window pinging an IP on the inside of the VPN and watch the
> /var/log/messages log on the VPN box for errors.
>     * If I disconnect the VPN connection, re-establish a few seconds or
> minutes later (before a cronjob for rmmod runs removing ppp_mppe), packets
> stop pinging the instant the "MPPE 128 bit, stateless compression enabled"
> message comes up on.
>     * Packets do flow ping during the time between IP address assignment and
> the "MPPE 128-bit..." entry in the log.  As soon as the MPPE message comes
> up, packets stop flowing (no ping, no communication at all).
>     Workaround:  If I put in a line such as "/sbin/rmmod -ar ppp_mppe" in
> the /etc/ppp/ip-down script, all works fine for a SINGLE CLIENT only...
>         This workaround unregisters the MPPE module when PPPd exits.  When I
> reestablish a connection again, the module is reloaded into memory and all
> works like it should.
> 
> 2) Multiple clients:  I am presently unable to make a 2nd client work with
> the above programs and patches (packet flow confirmed by infinite pinging
> window to an IP on the inside of the VPN).
>     * I connect client #1.  MPPE registers, a few notes in the messages log
> about PPTPd buffering out of order packets, and all flows fine.
>     * I connect client #2.  Packets flow as soon as the IP address is
> assigned, but immediately stop after "MPPE  128-bit" message comes up.
>     * Even though client #2 stops communicating, client #1 keeps running
> fine.
> 
> 
> ** Other issue:  For whatever reason, the MPPE-40 option ("mppe-40") in
> /etc/ppp/options, if the 40-bit is enabled, no packets flow at all anywhere.
> As soon as I only allow mppe-128 and mppe-stateless to work (only those two
> enabled), packets work as noted above.
> 
> ** I have already tried running pptpd with a single local IP and multiple
> local IPs in /etc/pptpd.conf (remote IPs are always multiple) and there is
> no change.
> 
> ** I downloaded the generic ppp_mppe_compressed_data_fix.diff and tried to
> apply to the ppp_mppe.c file (in ppp-2.4.0 and it's patches noted above, the
> .c file is located in /usr/src/linux-2.4.2/drivers/net/ppp_mppe.c)...The
> patch will not apply at all (hunks not found).
> 
> 
> Please help!!  I have got to make this work for multiple simultaneous
> clients.
> 
> Regards,
> Jim Roland, RHCE
> 
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> 

---------------------------------------
Josh Howlett, Network Supervisor,
Networking & Digital Communications,
Information Systems & Computing,
University of Bristol, U.K.
0117 928 7850 | josh.howlett at bris.ac.uk
---------------------------------------