[Gllug] Pinging a machine that is down

[Christof Meerwald]

On Sat, 9 Jan 2010 21:40:19 +0000, Robert McKay wrote:
> On 1/9/10, Alain Williams <addw at phcomp.co.uk> wrote:
[...]
>> 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.

For the technical details have a look at
http://linux-ip.net/html/ether-arp.html and http://linux.die.net/man/7/arp:

  "...it will send mcast_solicit broadcast frames before altering the ARP
  cache state and returning an error to any higher layer services."

Note that by default mcast_solicit=3 and retrans_time=100 (1s).


Christof

-- 

http://cmeerw.org                              sip:cmeerw at cmeerw.org
mailto:cmeerw at cmeerw.org                   xmpp:cmeerw at cmeerw.org
-- 
Gllug mailing list  -  Gllug at gllug.org.uk
http://lists.gllug.org.uk/mailman/listinfo/gllug