[Gllug] Pinging a machine that is down

[Alain Williams]

On Sat, Jan 09, 2010 at 09:40:19PM +0000, Robert McKay wrote:
> On 1/9/10, Alain Williams <addw at phcomp.co.uk> wrote:
> > I have just rebooted a customer's machine (to run a new kernel).
> >
> > I left a ping running so that I could login once it had rebooted.
> >
> > I noticed that the ''Destination Host Unreachable'' appear in 3s with the
> > one before
> > the first of the 3 missing. Eg in the sequence below 100,101,102 all appear
> > at once,
> > there is then a pause before 104,105,106 appear.
> >
> > Anyone any idea why it behaves like that ?
> 
> Not really, but maybe some combination of overlapping caching/probing
> of the route phasing in and out of sync at different levels/hops.
> 
> You've got the gateway to your host.. it's going to be arp'ing for the
> host.. but it will probably wait for a while before deciding that it
> isn't going to get a reply (possibly allowing multiple ping packets to
> queue up) it may then also cache the fact that it didn't get a reply
> for a little while.

I should have said that both machines are on the same network, a couple of feet apart.

-- 
Alain Williams
Linux/GNU Consultant - Mail systems, Web sites, Networking, Programmer, IT Lecturer.
+44 (0) 787 668 0256  http://www.phcomp.co.uk/
Parliament Hill Computers Ltd. Registration Information: http://www.phcomp.co.uk/contact.php
Past chairman of UKUUG: http://www.ukuug.org/
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