Hi Tom=E1s,

thankyou very much for your assistance here.  For some reason i did
not get the [OT] reply.

As you have pointed out I failed to realise that the arp request and
resulting arp enrty will be/should be for the gateway/router and not
for the destination IP.

Therefore the only conclusion I can draw is that the default gateway
is not configured on the install that has the extensive arp table  ie
an arp table that clearly has an arp entry for every remote device
that it connects to.

Does this sound plausable?.

For interest sake, each of these arp table entries has the ip address
of the remote device but the mac address of the gateway.  The other
install only has an entry for devices on the wire as (in my hindsight)
expected.

I will check the default gateway settings out tomorrow.  The install
that is behaving strange is out of my admin domain (5000kms away) but
from what I can gather they are having other problems that may be
related.  This is why I ended up with a capture of their arp table.

Thankyou once again.

Cheers Justin


On Thu, Aug 21, 2008 at 10:57 PM, Tom=E1s =D3 h=C9ilidhe <toe_list@lavabit.=
com> wrote:
>
> I've already responded to this under the "OT" tag so take a look at that
> reply if you're interested.
>
> For the meantime, I'll reply in sequence below:
>
>
> Justin Richards wrote:
>> Hi Folks,
>>
>> my understanding of arp tables is that when a layer 3 packet is
>> destined for a given ip an arp request is sent out the adapter.
>>
>
>
> Yes, the purpose of the ARP request is to figure out what MAC address
> the frame should be sent to.
>
>
>> The arp request is in the form of 'who has ip 192.168.0.1'.  If that
>> host 192.168.0.1 is on the network segment then it will reply with its
>> mac address.
>
>
> Correct.
>
>
>>   This is then added to the arp table and the packet is
>> encapsulated with the layer 2 frame with the destination mac it just
>> learnt.
>>
>
>
> Correct.
>
>
>> If the destination host is via a router then the router will respond
>> with its mac address and the packet is encapsulated with that mac
>> address and the router takes care of it.
>>
>
>
> If you go through a router such as 10.10.10.1, then you send out an ARP
> request for 10.10.10.1, you do *not* send out an ARP request for
> 192.168.0.1.
>
> In order to find out which router you should go through to get to a
> particular address (or even if you need to go through a router at all),
> you consult your Route Table.
>
>
>> I am experincing conflicting results on what appears to be identicle
>> setups as follows:-
>>
>> 1. Any destination ip address handled by the gateway device does NOT
>> result in an arp entry but all local ip address are added.
>>
>
>
> Correct. But it *will* results in the router's address being added to
> the ARP table.
>
>
>> 2. Any destination ip address handled by the gateway device does
>> result in an arp entry but all local ip address are added.
>>
>
> You'll never see an ARP table entry for a device that isn't on the same
> Ethernet wire. (Please don't bring up the topic of VPN's haha)
>
>  I tried to give an explanation of how it all works in my other "OT" repl=
y.
>
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