At 06:52 PM 6/14/01, Michael L. Williams wrote:
>Isn't arp a layer 2 protocol? I realize the goal of ARP is to find a MAC
>for a given layer 3 address, but the broadcast is done on layer 2, and the
>remote station responds with layer 2....
That's a good way of thinking about it that I don't think the rest of us
thought of, Michael.
An ARP frame has no Layer 3, contrary to what so many books claim. Here is
an ARP frame for reference. Note that there is no IP layer. The ARP header
references IP addressing information, but there's no IP header.
Flags: 0x00
Status: 0x00
Packet Length:64
Timestamp: 16:10:31.101000 06/14/2001
Ethernet Header
Destination: FF:FF:FF:FF:FF:FF Ethernet Broadcast
Source: 00:00:0E:D5:C7:E7
Protocol Type:0x0806 IP ARP
ARP - Address Resolution Protocol
Hardware: 1 Ethernet (10Mb)
Protocol: 0x0800 IP
Hardware Address Length: 6
Protocol Address Length: 4
Operation: 1 ARP Request
Sender Hardware Address: 00:00:0E:D5:C7:E7
Sender Internet Address: 10.0.0.1
Target Hardware Address: 00:00:00:00:00:00 (ignored)
Target Internet Address: 10.0.0.2
Some people might argue that the frame format isn't a good way to
characterize a layer, but I think it is.
And you make a good point that this frame would not go through a router,
which is another argument in favor of it being at Layer 2. The frame stays
on its local segment. It's a broadcast frame and it has no layer 3.
Priscilla
>the layer 3 information in the ARP
>request and response is just encapsulated data at that point...... which I
>don't think qualifies it as a layer 3 procotol. If that were the case, TCP
>could be considered a layer 4-7 protocol because all of the data it
>encapsulates comes from all of the above layers......
>
>Mike W.
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=8662&t=8335
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