On Mon, Jul 7, 2008 at 10:04 PM, Brian E Carpenter <[EMAIL PROTECTED]> wrote: > On 2008-07-05 13:38, William Herrin wrote: >> The MAC address is strictly a locater. Depending on which interface >> you approach the host from it usually has a different MAC addresses. >> The routing system doesn't care. On the last hop, it uses the layer 3 >> locater as a key to find a layer-2 locater. > > The way I read the Ethernet specification (or Token Ring or FDDI for > that matter), the MAC address is strictly an identifier - it's when > a station sees its own MAC address in a frame that it knows the frame > is for itself.
Brian, You're right. I had completely forgotten that Ethernet was originally a broadcast network. Every station saw every packet. The card's job was to filter the packets so that the CPU only saw the ones that bore its ID or another ID of interest such as the all-stations ID. Do they even make gig-e and ten-gig-e hubs or has that been completely abandoned in favor of switches? The coaxial bus is, of course, long gone in favor of hub-and-spoke technologies like twisted pair and fiber. At any rate, with the exception of -optional- stateless autoconfiguration in IPv6, the layer 2 address is not used as an identifier by anything in layer-3 or above. As a result, layer 2 -can- use it's address strictly as a locater and change it willy-nilly if it wishes to, without disturbing anything above it. Regards, Bill Herrin -- William D. Herrin ................ [EMAIL PROTECTED] [EMAIL PROTECTED] 3005 Crane Dr. ...................... Web: <http://bill.herrin.us/> Falls Church, VA 22042-3004 -- to unsubscribe send a message to [EMAIL PROTECTED] with the word 'unsubscribe' in a single line as the message text body. archive: <http://psg.com/lists/rrg/> & ftp://psg.com/pub/lists/rrg
