Re: OT - ARP request ?

[brian moore <bem@cmc.net>]

On Wed, Mar 14, 2001 at 01:39:52AM -0700, Jimmy Richards wrote:
> On 14 Mar 2001 01:37:27 -0700, Jimmy Richards wrote:
> > Hello There,
> > 
> > I don't know too much about it, other than what it stands for Address
> > Resolution Protocol.
> > I know it's considered to be a 'low-level' protocol.
> > The following is from my 'Desktop Computer Encylopedia 2nd Edition'.
> > Anything in parentheses was
> > added by me....
> > 
> > ARP
> >           Address Resolution Protocol
> > 
> >     A TCP/IP protocol used to obtain a node's physical address(maybe
> > they mean MAC address by this?).

Yes, they're talking about the MAC id.

It looks like this:

narvi:/home/bem# tcpdump -v arp
tcpdump: listening on eth0
09:03:44.740773 arp who-has thorin.cmc.net tell www.cmc.net
09:03:44.740996 arp reply thorin.cmc.net is-at 0:60:97:24:fd:a5

Pretty simple.

> > A client station broadcats an ARP request onto the network(so you will
> > see ARP requests for other machines)
> > with the IP address of the target node it wishes to communicate with,
> > and the node with that address responds
> > by sending back it's physical address so that packets can be
> > transmitted. ARP returns the layer 2 address for
> > a layer 3 address.
> >     Since an ARP gets the message to the target machine, one might
> > wonder why bother with IP addresses in
> > the first place. The reason is that ARP requests are broadcast onto the
> > network, requiring every station in the
> > subnet to process the request. See RARP.

And IP is routable, not to mention works on media other than
ethernet....

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