This topic has come up a few times in the past and I don't think we ever
came to a common agreement. Several people made good arguments on both
sides. I don't recall the specific argument, but I believe someone even
made a convincing argument that it was an application layer function.
Perhaps someone here remembers that thread and could refresh our
memories.
When most people think of host-to-host communications they think of one
layer on one device speaking to the corresponding layer of another
device. In this case of ARP I personally feel that we have the network
layer of one device speaking to the datalink layer of another. Even
that point is a little shaky because at the destination the packet must
reach the network layer to be recognized, but the information desired
from the end station is layer two, not layer three.
I would also suggest that we determine the layer at which a function
resides by looking at the layer that originated the request for
information. In this case, it's the desire of the network layer in one
device to speak to the network layer of another device that initiates
this entire process. An ARP is generated at the request of the network
layer. This ARP seeks out the destination device, gathers the necessary
information, and delivers that information to the network layer of the
originating device.
Because of those two arguments I'd say that the ARP function overlaps
both the network and datalink layer. It is a datalink frame generated
at the request of the network layer, and it just doesn't fit perfectly
into either layer.
Then again, I may be wrong. :-)
Regards,
John
>>> "Dr Rita Puzmanova" 6/13/01 7:58:53 AM >>>
Hi all,
Trivial yet fundamental question. I have seen ARP described as part of
the network (internet) layer so many times that I have started to
believe it belongs there (although I know well that it operates "as
if"
the Layer 2 protocol - as per OSI RM). Now I have eventually come
across
Doug Comer's statement: "It's part of the network interface layer."
I should not ask where the truth is but still I will. That would mean
quite a lot of books are incorrect in this (including Cisco
materials).
Rita
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