Re: Multihoming draft available

[Pekka Savola <pekkas@netcore.fi>]

On Fri, 31 Aug 2001, Ramakrishna Gummadi wrote:
> Hi all,
> I finished a draft that describes one way of doing scalable multihoming.
>
> http://www.cs.berkeley.edu/~ramki/draft-ramki-multi6-nlmp-00.txt
>
> Comments are highly appreciated. I plan to submit this as an internet
> draft soon. The abstract is below:

The draft implies only one EBR.  More often than not, it's customer's box
that breaks, and at least some folks require enterprise to have two exit
routers in order to get real high availibility.  Well, I guess EBR's could
be easily duplicated and routes exchanged with e.g. route reflectors to
keep databases in sync.

Tunneling mechanism seems to be aiming to automate:

             IPv6 multihoming support at site exit routers
                   draft-ietf-ipngwg-ipv6-2260-02.txt

(at pseudo wg last call)

I have some doubts about Selective Announcements.  Has there been any
research on how big 'set difference between the prefixes heard from the
two providers' might be?  Somehow I have a gut feeling, this could vary a
lot even though there is nothing special going on.

Nonetheless, there's also a worry about the scalability of this -- if this
was ever applied to IPv4, or a lot of prefixes.  That is, if a prominent
transit breaks, it could be that 1,000 or 5,000 or even 10,000 prefixes
would have to be readvertised _in a very fine-grained fashion to specific
neighbours_ using this mechanism?  That is, a big load of advertisements
would have to go "upstream" hop-by-hop checking AS-PATH list, modifying it
and selectively advertising prefixes.  To me this at least _sounds_ like
an awfully heavy task; current global advertisements are plain and simple.

If this method _could_ be heavy, it would also reflect on the convergence
times, and if it takes too long, the whole might become moot if
connections might practically break anyway.

(naturally, this wouldn't be a big worry with very aggregated DFZ such as
IPv6 currently is).

-- 
Pekka Savola                 "Tell me of difficulties surmounted,
Netcore Oy                   not those you stumble over and fall"
Systems. Networks. Security.  -- Robert Jordan: A Crown of Swords