Re: arp cache incomplete entries

[Panayiotis Karabassis <panayk@gmail.com>]

On 10/12/2012 04:08 AM, Neal Murphy wrote:
> On Thursday, October 11, 2012 08:47:37 PM Celejar wrote:
>>
>> I'm no expert, but my impression is that any machine which is asked to
>> connect to some other host by IP address will issue such an ARP
>> request, so if I do 'ping x.x.x.x', and x.x.x.x has not been recently
>> in contact with my machine, my machine will issue an ARP request.
> 
> Recall that all ethernet communication (layer 2) is done using MAC addresses. 
> Also recall that point-to-point links do not use ARP.
> 
> A little more specifically, if the IP->MAC translation entry is not in the 
> cache, the host will issue the ARP request. If the address is not on the local 
> LAN, the host will issue an ARP request for the appropriate gateway.

Thanks to all.

In a pattern that is becoming all too familiar, the problematic machine
sends an ARP request, to which the nameserver replies. But the reply is
never received by the asking machine. So says wireshark.

Could this be a fault NIC, or is the packet lost somewhere else?

Another curious thing is that the problematic machine can lose the MAC
address of the nameserver, even after it has obtained it and put it in
the cache. Possibly, the router has rebooted (or at least reestablished
the ADSL connection) in the meanwhile, which may have caused the LAN
connection to be reset too. Or not.

I'm going for an 11-day trip now. I'll look more into it when I get back.

Thanks,
Panayiotis