Re: Routing with Debian?
On Tue, 14 Apr 1998, Jonas Bofjall wrote:
> On Mon, 13 Apr 1998, Jens B. Jorgensen wrote:
>
> > The usual timeout for ARP entries is 30 seconds IIRC. That doesn't
> > mean that some hardware might do something different.
>
> I went home unsuccesful and then returned today, two days after I fought
> with this, because I had some ideas I wanted to try. So I booted the
> system and -whoa- worked perfectly without a change. I don't know what
> kind of router we have but it obviously keeps ARP values cached too long.
> I'm a bit happy though, as the problem turned out to be exactly what I had
> expected the whole time.
>
> But one question remains: I changed Ethernet cards in a workstation
> earlier the same say, and at that time I could access the net right away.
> Why did it go so fast that time? Why did I have to wait many hours when
> working on the laptop? What was the difference? I don't expect you to know
> these answers :) as I don't know anything about our router. But it's
> interesting to notice that this timeout obviously is *very* random.
>
> Unless there is some sort of "inverse" ARP which lets the workstation
> broadcast that "I am xx.xx.xx.xx with MAC xx:xx:xx:xx...".
Well I just assumed that if you actually sent packets from your NIC to
the router, it would see the MAC and start using it.
The problem comes when you don't actually send those packets. For
example, when I was testing PPP by using the internal phone system (free)
to connect machines normally on the ethernet, I found that the client
machine(isolated by pulling the BNC plug)'s proxy was fairly quickly
picked up by all the machines on campus, but not by the gateway.
The symptom was that I could ping all the machines on campus (including
those I had connected to minutes earlier) and even continue using open
telnet sessions (opened before I disconnected the ethernet). However, if
I pinged machines at other universities, nothing would come back. Until,
that is, I just put the BNC plug back on. There were the packets, still
being sent to my NIC from the router.
> > You can't force the router to forget.
>
> This is surely something that is badly needed in IP.
>
> > Be careful about assuming routers will do "the right
> > thing" or even "a sensible thing".
Cheers,
--
David Wright, Open University, Earth Science Department, Milton Keynes MK7 6AA
U.K. email: d.wright@open.ac.uk tel: +44 1908 653 739 fax: +44 1908 655 151
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