Re: [rrg] moving towards recommendation: the current plan

[Michael Menth <menth at informatik.uni-wuerzburg.de>]

Hi Noel,

Noel Chiappa schrieb:
>     > From: William Herrin <bill at herrin.us>
>
>     >>> a fundamental problem of Loc/ID split solutions based on address
>     >>> rewriting when hosts have only a single local address but their edge
>     >>> network is multhomed to the outside world.
>
>     > The problem is that A received a return packet from B that might have
>     > been from 3 and might have been from 4. But A has no idea what to do
>     > with a packet from 4.
>
> Ah, got it. Hence the reference to "based on address rewriting", in the
> original message. Since I'm mostly thinking in a 'wrapping' world these days,
> I'm unfamiliar with these problems... :-)
>
> The wrapping has the benefit of allowing one to not have to discard
> information (which one has to when one doesn't have enough fields at hand to
> hold them all); one can keep the original identifier, and have the locator
> too. (Which is fundamentally the problem above - trying to put the proverbial
> 10 pounds in a single 5-pound field...)
>
>     > Per Michael, the solution is either:
>     > 1. Stateful NAT. ... so that [it] can put source 3 back on the outbound packet.
>     > 2. Host modification. ... The host echos this in the return packet
>
> Well, the second is clearly infeasible. The first isn't so hot either.
>
> Which leads me, in the context of Tony's earlier observation (that the RG
> more or less unanimously now holds that separation of location and identity
> is a crucial underlying piece of foundation for solving the routing
> scalability issue), to a proposition...
>
> I wonder if we can say that, at an architectural level, wrapping solutions -
> or, more generally, any solutions which carry both the locator and the
> identifier in the packets - are inherently and inescapably superior? This
> seems fairly logical, to me: clearly, if one can't carry both locator and
> identifier, one has to throw one away; and having done that, there are almost
> inevitably going to be problems caused by cases where one needs whichever one
> of the two one no longer has...
>   
We also discovered that issue. Probably we can say, it's hard to combine 
the following three things:
1. Multihoming
2. Active multipath routing by the host
3. Local addresses hiding information about global locators which makes 
renumbering easier.

Regards,

   Michael

> 	Noel
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>   

--
Dr. Michael Menth, Assistant Professor
University of Wuerzburg, Institute of Computer Science
Am Hubland, D-97074 Wuerzburg, Germany, room B206
phone: (+49)-931/31-86644 (new), fax: (+49)-931/888-6632
mailto:menth at informatik.uni-wuerzburg.de
http://www3.informatik.uni-wuerzburg.de/research/ngn