updating GSE for the new millennium

[Iljitsch van Beijnum <iljitsch@muada.com>]

We've been talking about GSE earlier this month before we got 
side-tracked. I think it's time to see what a descendent of the GSE 
family would look like in the third millennium, so I want to write a 
draft. Hopefully this will give us something useful to talk about in 
Vienna.

What I'd like to do is take input from everyone and incorporate this as 
much as possible in this draft. That probably means more options and 
more complexity that we'd like to see in an actual protocol, but for 
now that's fine: we can always prune later.

If there is reasonable consensus on something, I'll use it. If there 
are several ways to do something that aren't mutually exclusive, I'll 
use all of them. If there is no feedback, I'll use my own judgement...

The first order of business is the address rewriting. It seems to me 
that the different options here (GSE-like one-way rewriting upper bits 
with globally unique lower bits, MHAP double rewriting) can be 
accommodated by doing the following:

When transmitting, for both the source and destination address: take a 
globally unique N bit label and map to one of several possible IPv6 
address suitable for routing associated with this label. When 
receiving, map the addresses back to labels.

For the source when transmitting or the destination when receiving, the 
rewriter can presumably easily find the additional information needed 
to compelete the mapping in its configuration, but for the destination 
when transmitting or the source when receiving it must first discover 
the mapping.

Is this workable?

Two additional questions:

- Is adding options or tunnel headers an option, or would this make 
this scheme too unattractive over IPv4-style multihoming?

- Can packets only be rewritten once, or can this happen several times?