Hi Bill,
Maybe I misunderstand how MPLS is used with respect to Internet routing. Please correct: As I understand it, an IPv4 packet arrives at [A], an MPLS encoding router. The router looks up the destination in its routing table and determines that [B], a border router to another system, should deal with the packet next. So, [A] tags the packet with "555" which means "send to router B," and then passes the packet router C which appears to currently have the shortest path to [B]. Router C knows that tag 555 means pass the packet to [B], so it sends it to router D which appears to currently have the shortest path to [B]. Rinse and repeat until it gets to [B] which knows that it owns tag 555 which means decapsulate the packet back to IPv4 and route it using the BGP table. In that use case, tag 555 is most certainly a locator within the scope of the MPLS system.
Even in the simplest cases, the label value is almost always allocated on a hop-by-hop basis. Thus, 555 is only valid for a single hop and the router that receives this will SWAP it for another value.
The only cases where 555 itself would act as a true locator would be if someone is doing global label allocation, and that's very rare, AFAIK.
There are many, many more complicated uses, especially using TE, that would also argue that a label itself is nothing but an index into a computed path. The only time you'd have an object that truly would seem to "name a point of attachment" is during signaling, when the RSVP Explicit Route Object (ERO) would contain the full path. Note that this is somewhat different than how we think of a locator, as normally we consider a locator to be an absolute name of a location, not the relative path to a location.
Tony _______________________________________________ rrg mailing list [email protected] http://www.irtf.org/mailman/listinfo/rrg
