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Re: Addressing versus Routing (Was: Deploying IPv6 in a datacenter)

  • From: sysadmin
  • Date: Wed Dec 21 17:45:43 2005

On Wed, Dec 21, 2005 at 11:36:00PM +0100, Daniel Roesen wrote:
> On Wed, Dec 21, 2005 at 08:34:06PM +0100, Jeroen Massar wrote:
> > The issue with announcing say a /48 is though that networks which filter
> > will filter it out and will only reach you over the aggregate. Of course
> > that is their choice, just like yours is to try to announce the /48's in
> > IPv6, or the /23's for IPv4. An IPv4 /28 doesn't reach far either.
> > 
> > The problem here is though that your /48 will propagate through ISP's
> > with less strict filters and they will act as transits for your /48.
> > My experience tells that the ones not filtering also have a not so-good
> > setup thus your connectivity tends to go all around the world.
> This description of the problem ain't totally correct. The problem is
> that the more specific route propagates thru fewer paths, thus the
> average AS_PATH (and forwarding path) length is usually (much) higher
> for the more specific route than the aggregate. Routers decide on CIDR,
> so packets to the more specific will travel the long way instead of the
> short way.
> It's NOT a matter of "the ones not filtering also have a not so-good
> setup". Actually, many/most of the "big good IPv6 players" nowadays DO
> allow /48s as they recognize the need for "end site multihoming". And
> this also contributes to the fact that /48 multihoming is nowadays far
> more feasible (as long as your upstreams are "sane and well connected")
> than let's say a year ago.
> Caveat: this is a EU/US centric view. I'm not sure about the development
> in the ASPAC region on this matter as I didn't follow that closely
> (partly because it's difficult to follow anything there as it's
> network-topological "quite distant" and few hosts and accessible routers
> to test from).
> > The same as IPv4 announce a /48. Have a fallback /32 for folks who do
> > filter it out.
> As outline above, that will artificially impair connectivity
> performance.
> > Here you say it your self: "Advertisement policies" this is routing
> > again, which has not much to do with Address Space.
> It does, as long as we don't have a total decoupling between locators
> and identifiers, alongside with the required tools for traffic
> engineering with the locators.
> > One can deaggregate in IPv6 also, just don't expect it to be accepted.
> > Just like a /24 won't be accepted by most folks.
> Uhm, sorry, but that's wrong. /24s are widely(!) accepted and only very
> seldom not accepted. There are many (MANY!) folks running on /24 PI
> (== no larger covering aggregate) without problems.
> > > -- Kevin
> > > 
> > > <waits for flame war to erupt> :)
> > 
> > </me donates his asbestos suite and tin foil hat> :)
> </me shows off his designer collection of asbestos>
> >  This is the very hard part. (political and technical)
> >  But it might be years before we will hit the actual limits of BGP.
> >  We still have to be nice to our kids though as they will hit it ;)
> Really? Where are the limits of BGP? Can you show me any numbers?
> You'd be the first. I'm not aware of any protocol inherent scaling
> brickwalls like with other protocols where certain timing constraints
> place limits (or thinking of L1 systems, you remember CSMA/CD?).

Last time I checked, Ethernet is still CSMA/CD.

> That doesn't mean that there are none - I'm not a scientist or
> mathematician - I'd be happy to have any numbers to back the FUD about
> the end of world being near. :-)
> >  Most if not all of these have problems for some uses, eg Traffic
> >  Engineering is supposedly not possible anymore the way it is
> >  currently being done in BGP. Mindset changes will be required.
> For all, or only for those who are not deemed worthy of entering the
> market on the same terms and conditions like the existing players? ;)
> Best regards,
> Daniel
> -- 
> CLUE-RIPE -- Jabber: -- dr@IRCnet -- PGP: 0xA85C8AA0

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