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Re: interconnection richness effects Re: Was [Re: Sprint peeringpolicy]

  • From: Stephen J. Wilcox
  • Date: Sat Jun 29 16:42:24 2002


On Sat, 29 Jun 2002, Joseph T. Klein wrote:

> That makes sense ... many full routing tables is fare worse than
> many partial routing tables. If my last resort was buying from a
> Tier 1 after peering out most of my traffic I would prefer "paid
> peering" or "partial transit". ... and one can always not listen to
> routes that have multiple non optimized paths via transit
> connections.

How will that work? Your last resort would then have to buy paid peering from
all non-transit networks (tier 1's), which means they have to be a kind of tier
1 themselves then?

But - BGP only propogates the single best route, BGP automatically removes the
"multiple non optimized paths" and if they're non-optimized they will never be
best and hence never cause flaps within or downstream of your network.

> If you have 10 ways to an ASN and 3 or four stable and clean diverse
> routes exist ... why chew up memory and CPU listening to the poor
> routes?

I cant imagine a production router would have 10 ways tho, as above, any non
optimum routes will not be propogated past the eBGP.

... and assuming you arent taking transit then you rely upon your peerings as
the ONLY means of connectivity to their networks and their customer networks
which means multiple interconnect points and your still going to be receiving
multiple BGP routes to the same destination...

Note, I dont think I'm conflicting with the comments below which are referring
to route flaps at the source which therefore cross all networks and all bgp
routers, thats a separate issue.

Steve


> 
> --On Saturday, 29 June 2002 16:01 -0400 Richard A Steenbergen <ras@e-gerbil.net> wrote:
> 
> > On Sat, Jun 29, 2002 at 07:42:03PM -0000, Joseph T. Klein wrote:
> >>
> >> Flat designs tend to ring like a bell when instability is introduced.
> >> I think we held the world record for flapping at NAP.NET in 95-96.
> >> That was a flat design executed during a time when the Cisco architecture
> >> and software could not keep up with the growth and churn rate. The
> >> inclusion of algorithms that enhanced oscillation ringing (and since has
> >> been fixed in IOS) did not help.
> >
> > Have you ever seen an InterNAP route flap? Its good for around two minutes
> > or 120 traceroutes of pure humor, with a different loop across a different
> > backbone in a different city with every invokation.
> >
> > Extensive peering relationships don't generally cause a breakdown of BGP,
> > which is probably the reason that we have settled into using that system.
> > Extensive transit relationships on the other hand, like those used by the
> > "optimized routing" crowd to try and take advantage of all the "richness
> > of paths" out there which aren't being used efficiently, break BGP very
> > very quickly (in my experience at any rate).
> >
> > --
> > Richard A Steenbergen <ras@e-gerbil.net>       http://www.e-gerbil.net/ras
> > PGP Key ID: 0x138EA177  (67 29 D7 BC E8 18 3E DA  B2 46 B3 D8 14 36 FE B6)
> >
> 
> 
> 
> --
> Joseph T. Klein                                         jtk@titania.net
> 
>     "Why do you continue to use that old Usenet style signature?"
>                                                                 -- anon





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