[Openswan Users] Trouble with xl2tpd and pppd

David Klann dxklann at gmail.com
Mon Jul 7 18:10:59 EDT 2008

I tried posting this to xl2tpd at xelerance.com, but it was rejected
(recipient unknown). It's off topic, but I'm not sure where else to
post the question.


I'm having a crazy time with xl2tpd and pppd *without* Openswan
IPSec. On bringing up the ppp0 interface, no additional traffic passes
between the LAC and the LNS.

Combinations I've tried:

  LNS: Allied Telesyn Inc. Rapier router (version unknown)

xl2tpd 1.1.12 with pppd 2.4.4 on Gentoo (without kernel pppol2tp)
xl2tpd 1.1.12 with pppd 2.4.4 on Ubuntu 8.04 (without kernel pppol2tp)
xl2tpd 1.2.0 with pppd 2.4.4 on Ubuntu 8.04 (with and without kernel pppol2tp)

  LNS: xelerance.com xl2tpd 1.1.12 (on Gentoo)

xl2tpd 1.2.0 with pppd 2.4.4 on Ubuntu 8.04 (without kernel pppol2tp)

In all cases, xl2tpd establishes a tunnel
(echo 't <dest>' > /var/run/xl2tpd/l2tp-control)

Using 'tcpdump -i eth0 udp' and xl2tpd debugging output on the LAC I
can see tunnel activity. All appears to be OK.

Then I make a call to the LNS with echo 'c <LNS>' > /var/run/xl2tpd/l2tp-control

xl2tpd execs pppd. The local pppd successfully authenticates to the
LNS (I'm using CHAP), and the LAC receives an IP address on network
interface ppp0. I can see (with tcpdump) packets coming from other
hosts on the LNS network. But when the LAC sees the first LCP Echo
Request from the LNS, the LAC begins sending packets like crazy over
ppp0. But the packets don't show up on the LNS, nor do they show up on
the LAC eth0 interface.

Using tcpdump, the packets look like recursively encapsulated L2TP
packets. I've attached a pcap file to show what I mean. I've also
included my xl2tpd.conf and ppp.options files (below).

What other information would help me troubleshoot this situation?

Thanks for any help anyone can offer!

 David Klann
 Wisconsin Independent Network

  +++ xl2tpd.conf +++
[lac mvs]
lns = <a.b.c.d>
redial = no
require chap = yes
name = dklann
length bit = yes
ppp debug = no
pppoptfile = /etc/xl2tpd/ppp-options

  +++ ppp-options +++
logfd 2
logfile /var/log/l2tpd.log
mtu 1394
mru 1400
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