Scott,
On 2008-12-09 16:01, Scott Brim wrote:
> Excerpts from Fleischman, Eric at 10:45:43 -0800 on Mon 1 Dec 2008:
>> I believe that map-and-encaps should solely be a network
>> infrastructure design alternative. To be effective, the hosts should
>> not be aware that map-and-encaps (or any other network topology
>> tool) exists.
>>
>> In my biased opinion this means that claims such as "LISP provides
>> an identifier-locator split" is fundamentally unrelated to the fact
>> that HIP provides an identifier-locator split. Quite obviously, HIP
>> does so in a manner that is real to the host (including
>> applications) while LISP does so in a manner that is known to
>> routers only. [My own bias is that LISP's claims in this regard are
>> marketing while HIP's claims are close to what the ROAD Group
>> originally intended.]
>
> After a lot of arguing with others, I've come to see the similarities
> wrt "locator/identifier split". Look at it this way: the difference
> is one of granularity. An endpoint-based LIS separates an identifier
> for a stack in that endpoint from its attachment point(s) to the
> topology. A network-based LIS splits a whole chunk of "identifiers"
> from its attachment point(s) to the topology. LISP calls those EID
> prefixes. Vince Fuller suggested having EID stand for "end site
> identifiers". Sometimes the "identifiers" within those chunks are
> also used by forwarding functions as locators within the scope of the
> final site, but they need not be (see GSE, ILNP etc.).
This is true and it shows the risk of trying to use a concept loosely.
I've said this from the beginning but I'll try once more: I get much
less confused about LISP if I use different terminology, because the
LISP "EID" is not an EID. Think of it as a local locator (which also
happens to be globally unique) and call it LOC0 for example. Then the
LISP "RLOC" is a less local locator that just happens to be globally
routable as well as globally unique; call it LOC1 for example. As HAIR
points out (and I pointed out last year) the obvious conclusion is a
recursive model with any number of layers of locator scope.
GSE/ILNP and HIP are deeply different in that they genuinely separate
a unique *non-locator* ID from one or more locators. Trying to use the
phrase "loc/id split" to cover both of these models is certain to
lead to confusion.
Brian
> Just as source endpoints need to keep track of which destination
> locators are functional, ITRs maintain liveness checks for an EID
> prefix and forward packets to whichever locators for the EID prefix
> are up. When the set of locators for an endpoint identifier changes,
> the endpoint updates its correspondents somehow. An ETR responsible
> for for an EID prefix will let sources sending to that identifier know
> which locators are up for it (in LISP this is done with loc-reach
> bits). And so on. Of course there are differences -- in
> map-and-encap there are no higher stack layers to utilize identifiers
> for higher layer functions -- but I think you see the parallels.
>
> Scott
>
>
>
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