host-centric draft

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

Hi,

I've been catching up on drafts, reaching draft-huitema-multi6-hosts-03 
just now. A few questions:

  "A strong assumption of the IPv6 architecture is that all prefixes of
   a site will have the same length; it is thus possible to derive a
   prefix from the source address of a "misdirected" packet, by
   combining this prefix with a conventional suffix."

This is very unclear as the reason to have such an anycast address in 
the first place is only given 30 or so pages later.

About ICMP/ingress filtering: if it is actual ingress filtering we're 
talking about (ie, an ISP filters packets it receives from a customer) 
ICMP error messages aren't likely to be forthcoming when an improper 
source address was used by the customer, as the ISP in question doesn't 
know that the addresses which are filtered out should go back to the 
customer in question. So in order for this to work reliably customers 
must install filters that perform the same function, but then for 
egress, as the customer border router has a good return path for the 
ICMP message.

A general problem that I have with this draft is that it explores some 
very specific mechanisms, but at the same time doesn't explore some 
other mechanisms that could lead to similar results. (For instance, a 
situation where two distinct layer 3 networks exist in parallel isn't 
explored. For source address rewriting using a special "rewrite this" 
prefix would be a possibility.) It would be better to either be brief 
or complete.

The problem that rerouting could invalidate an earlier source address 
choice isn't mentioned.

I'm unsure why we would want to inject BGP information into hosts. 
Reachability yes/no isn't very useful as the actual reachability status 
of the other side is in almost all cases hidden by aggregation. So 
basically this only indicates whether the ISP in question is available. 
Determining preference based on BGP information is also a relatively 
futile endeavor as path lengths are very often the same and relevant 
differences in topology typically don't show up in BGP. (Many large 
networks use a single AS for an entire continent or even the world, 
while obviously small networks don't.)

The 6 level deep heading numbering is somewhat excessive.

9.1.4.19 What new information should applications be aware of?

   None

I don't really agree. Applications need to try all addresses for a 
correspondent. Some do this today, most don't. And this needs to be 
done in a smart way, a four minute timout between trying successive 
addresses isn't acceptable.