I think that's basically it, but I'd add two modifications.
At the beginning of the process, I always find it helpful to mention
why a station would initiate an ARP request in the first place. By
comparing the IP address of the destination with it's own IP address and
subnet mask, it will know whether it needs to initiate an ARP request or
send the packet to the default gateway. I know that you know that, I
just like to make it clear when I'm explaining it to someone else.
As for that last step about the router returning its own MAC address
for destinations not on the local subnet, this is true only if proxy ARP
is turned on AND if the originating device doesn't realize that the end
station is not on the same local network. If the originating device
knows that the destination device is not on the local subnet, it wil not
send a broadcast ARP. It will send a unicast packet to the default
gateway.
Regards,
John
>>> "Dennis Laganiere" 9/11/01 4:17:50 PM
>>>
I'm trying to describe the ARPing process. It something I've always
taken
for granted, but now I'm trying to actually write it down. Let me know
your
thoughts...
When a workstation attempts to communicate with an IP address it
follows
this process:
IP devices maintain an ARP cache that store any recently acquired
IP-to-MAC
address combinations. If the appropriate address is there,
communication is
established.
If the IP address is not in the local ARP table, the source host will
send
an ARP request packet containing the Network-layer address, seeking to
be
resolve it to a MAC-layer address for the desired destination.
All hosts on the network receive this request, but only the host with
the
specified network address will respond. If present and functioning,
the
host with the specified address responds with an ARP Reply packet
containing
its MAC-layer address. The originating device receives the ARP Reply
packet, stores the MAC/IP address combination its ARP cache for future
use,
and begins exchanging packets with the host.
If the host is not on the local network, the router on the local
network
will look up the network address in its route table and if it finds a
match,
it will return the MAC address of its local interface to the ARP-ing
source
station.
Message Posted at:
http://www.groupstudy.com/form/read.php?f=7&i=19497&t=19489
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