Why do packets to cause dial-up?

Richard Smith rdls at rdls.net
Thu Mar 30 13:12:45 BST 2000

Nik Clayton wrote:
> Hi guys,
> This is a bit of a noddy question, but I'm damned if I'm exposing my
> ignorance to the entirety of the world via -questions.  The whole of
> the UK (and certain small European countries, hi Brad) should be more
> than sufficient.
> I've got a bog standard PPP set up at home, dialling in to Demon.  No
> PPP filters yet, though there will be soon.  I'm running Samba on the
> FreeBSD box.
> Periodically, as shown by "tcpdump -i tun0" Samba is sending packets like
> this:
>     09:51:21.680366 localhost.nothing-going-on.org.netbios-dgm \
>         > udp 220
>     09:52:31.678547 nothing-going-on.demon.co.uk.netbios-ns \
>         > udp 50
>     09:52:33.698393 nothing-going-on.demon.co.uk.netbios-ns \
>         > udp 50
> This will bring the modem line up.

Looks like samba is broadcasting on all interfaces, using (badly) the
localhost as the source address. Why broadcast packets should appear on
tun0, when the BROADCAST flag for that interface is not set, I do not
know. I have never seen this problem myself, I think, because my
firewall (ipfw) is pretty selective on which UDPs I allow through.


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