Why do packets to 127.255.255.255 cause dial-up?

Richard Smith rdls at rdls.net
Thu Mar 30 13:21:01 BST 2000


Richard Smith wrote:
> 
> 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 \
> >         > 127.255.255.255.netbios-dgm: udp 220
> >     09:52:31.678547 nothing-going-on.demon.co.uk.netbios-ns \
> >         > 127.255.255.255.netbios-ns: udp 50
> >     09:52:33.698393 nothing-going-on.demon.co.uk.netbios-ns \
> >         > 127.255.255.255.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.

Second thoughts... The `to' address is 127/8 as well, doh!, I have a
firewall rule for that one too :-)

What does "netstat -rn" show?




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