arp who-has? tell?

[John Cornelius]

I had not intended to start a religious argument here when I said the 
DHCP server ARPs to find out if the address it's going to assign is 
already in use.

John Summerfield is correct that the specification calls for an ICMP 
echo request to be sent.

Mogens is correct that the ICMP echo is the mechanism used to generate 
the ARP request and subsequently verify the existence or absence of the 
address on the segment.

ARP is the mechanism for providing an association between the physical 
link layer and the logical link layer entities. IP addresses are logical 
link layer entities and ethernet (MAC) addresses are physical link layer 
entities.

ICMP may not depend on knowing how the traffic is transported but it 
does depend on knowing that it can be transported. That's what address 
resolution is all about. If the logical address (IP) cannot be resolved 
to a MAC address it cannot be transported.

Merry Christmas, Happy Hanukah, and a prosperous New Year to you all.

--jc

Mogens Kjaer wrote:

> John Summerfield wrote:
> ..
>
>> ICMP doesn't depend on knowing how IP traffic is transported.
>
>
> If I ping (send ICMP echo request) a non-existing, local IP
> address, the first thing my machine does is sending an
> arp who-has on the wire. No ICMP package is sent before
> my machine receives the is-at answer.
>
> Mogens
>
-------------- next part --------------
An HTML attachment was scrubbed...
URL: http://lists.fedoraproject.org/pipermail/users/attachments/20071220/d0a7dba1/attachment-0001.html