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Re: [RRG] Idea for shooting down
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On 2007-11-20 18:08, Robin Whittle wrote:
Hi Brian,
With your proposal:
http://www.cs.auckland.ac.nz/~brian/DFZng.pdf
I get the impression that the result would be the Internet being
much less meshed than it is at present.
Not exactly. The individual regions can be as meshed as one
wants, and they are *not* geographical regions - in fact they
are more likely to evolve as conglomerates of ISPs.
This would have negative
impacts including:
1 - Less robustness in the event of link and router failure.
As noted in the draft, there can be multiple links between
layers - as many as desired, in fact.
2 - Often longer path lengths (AKA "stretch") as a packet has to
get out of one of the many Level 1 domains (or the one Level 0
domain) up to some Level 2 domain in order to get to another
Level 1 (or the Level 0) before it could be delivered. This is
true even if the ISP border routers connecting to the sites with
the sending and receiving hosts are physically close, but happen
to be of ISPs which are in separate domains. (I assume an ISP
can only be in one domain, but perhaps I am wrong.)
Definitely more stretch. But that may be inevitable as we grow towards
ten billion hosts.
3 - Therefore, further dimensions of "Balkanisation" of the
Net, where actual packet delivery times and reliability
levels depend not just on physical (partly geographic)
topology, link capacities and traffic levels but also on
which domain each host is in and how far the packet has to
travel to go up and then down a level to the destination
domain.
I don't see why that is Balkanisation, which implies walled gardens
to me. I would counter this and the previous two arguments with the
assertion that an organised hierarchy of finite meshes is intrinsically
easier to understand and debug than a single unbounded mesh.
4 - Therefore, a lot of fuss as ISPs try to decide which domain
to be in.
I don't see this as being that much different from today's fuss
as ISPs decide who to peer with.
5 - Also, perhaps, more pressure on "sites" (as I think you
nicely describe them) to multihome to various ISPs in
different domains. However, that only helps with the
path length if the "site" is smart enough to send outgoing
packets to the optimal ISP's router. This wouldn't help
with optimising which ISP and region an incoming packet
arrives through when it is sent by a non-multihomed site
or a multihomed site without the smarts to choose the
best outgoing router.
I don't see this as any different from a site's point of view than
today. The sites will perceive ISPs, not regions. They have all those
issues today.
Also, I don't understand how your proposal would help with the
central problem we are trying to solve - of a multihomed site's
router requiring a separate route for every prefix advertised by any
site anywhere at all.
The fact that the destination site is in a different domain doesn't
alter the fact that the multihomed site's router needs a separate
route for that slice of address space, because the router still
needs to decide which of the two or more upstream ISP routers to
forward the packet to.
As I said, this idea is *orthogonal* to LISP, Ivip, etc. We
definitely need a robust solution for exit router selection
that doesn't require full routes. I haven't had time to analyse
draft-baker-6man-multiprefix-default-route-00 yet, but we need
something with that degree of simplicity and robustness.
Brian
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