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Date:      Sun, 8 Sep 2002 12:53:05 +0100
From:      Matthew Seaman <m.seaman@infracaninophile.co.uk>
To:        Robert Tan <tar@transfer.nl>
Cc:        "freebsd-questions@FreeBSD. ORG" <freebsd-questions@FreeBSD.ORG>
Subject:   Re: tcpdump VJC
Message-ID:  <20020908115305.GB4731@happy-idiot-talk.infracaninophi>
In-Reply-To: <DPEDIFKGFNJACMLKGOEGKEMOCDAA.tar@transfer.nl>
References:  <20020907160140.GA274@happy-idiot-talk.infracaninophi> <DPEDIFKGFNJACMLKGOEGKEMOCDAA.tar@transfer.nl>

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On Sun, Sep 08, 2002 at 09:35:05AM +0200, Robert Tan wrote:

> But what kind of traffic is it. The reason for
> asking is that I've configured my isdn connection,
> to the internet, to hang up after a given amount 
> of time, when there is no traffic over the link. 
> 
> So my connection is not closing, and I'm assuming
> because of the VJC stuff. Where does it come from?

That's possible, but all the VJC stuff is just more familiar sorts of
traffic run through the compression algorithm.  To tell what it is
that's stopping your ISDN connection timing out properly, you're
(almost definitely) going to have to switch off the VJ compression
temporarily while you run tcpdump and work out what's keeping you up
all hours.  You should be able to do that fairly readily: as I
understand it, using VJC is negociated between the PPP endpoints when
the link is bought up.

For instance, if you're using the usermode ppp(8) you can put:

    deny vjcomp
    disable vjcomp

into /etc/ppp/ppp.conf (deny ... means that this end refuses if the
other end asks for it, disable ... means this end won't ask for it.)
Other PPP implementations should have equivalent knobs to twiddle.  If
you're using the isdn4bsd stuff, I think you need a command something
like:

    ispppcontrol isp0 disable-vj

but that's just my interpretation of the ispppcontrol(8) man page.

	Cheers,

	Matthew

-- 
Dr Matthew J Seaman MA, D.Phil.                       26 The Paddocks
                                                      Savill Way
                                                      Marlow
Tel: +44 1628 476614                                  Bucks., SL7 1TH UK

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