Re: [RRG] Re: Should the identifier be used as local locator

[Brian E Carpenter <brian.e.carpenter@gmail.com>]

On 2008-07-05 13:38, William Herrin wrote:
> On Fri, Jul 4, 2008 at 9:10 PM, Tony Li <tony.li@tony.li> wrote:
>> And more specifically, how does the last hop router determine the MAC
>> address of the final destination?  The MAC address itself is a flat
>> identifier (and locator on the last hop) that can be embedded in the
>> endpoint identifier, or the endpoint identifier can be used for a lookup to
>> determine the MAC address.  In either case, the endpoint identifier ends up
>> being used for a local routing decision.
> 
> 
> 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.

But you're correct too. Whether a bit string is a locator or an
identifier depends entirely on context. (That's why I've objected to
EIDs in LISP being called EIDs from the start - once they hit
the site network, they become locators instantaneously; they
are only identifiers in the global context.)

    Brian

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