#38 L2TP SCCCN response not by protocol

l2tp (3)


I'm using mpd5 on FreeBSD 7.3-STABLE.
While dialing to some ISP's l2tp server, I've noticed mpd5 return in SCCCN the AVPs it got from SCRP (the same fields, not values).
In my understanding this is not according to protocol: http://rfc-ref.org/RFC-TEXTS/2661/chapter6.html
the only AVP that can be present (besides messageType) is Challenge.

Some servers just ignore the extra fields and continue, but some, which return vendor == "Juniper Networks, Inc." just sending StopCCN upon
recival the extra fields.

For now i've "fixed" it with altering l2tp_ctrl.c line 2104
-ppp_l2tp_ctrl_send(ctrl, 0, SCCCN, ctrl->avps);
+ppp_l2tp_ctrl_send(ctrl, 0, SCCCN, NULL);

And now that Juniper server is accepting mpd5 and connected fine, however that "fix" might of introduced other problems I'm not aware of,
protocol problems or a memory leak.

I'm attaching a .cap file from the not "fixed" mpd5 ( please disregard the vendor == Microsoft, it was one of my tests, I first thought it disconnecting me because of my vendor string )


  • Yury Michurin

    Yury Michurin - 2011-02-20

    Capture of dialing to the l2tp server who hangs up

  • Dmitry S. Luhtionov

    • assigned_to: Dmitry S. Luhtionov
    • Group: -->
  • Eugene Grosbein

    Eugene Grosbein - 2017-11-05
    • labels: --> l2tp

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