Re: [Idr] draft on virtual aggregation

Paul Francis <francis@cs.cornell.edu> Thu, 31 July 2008 22:42 UTC

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References: Your message of "Fri, 11 Jul 2008 06:39:57EDT."<37BC8961A005144C8F5B8E4AD226DE1109D860@EXCHANGE2.cs.cornell.edu><200807151457.m6FEv4Cs032524@harbor.brookfield.occnc.com><15B86BC7352F864BB53A47B540C089B605E92736@xmb-rtp-20b.amer.cisco.com> <37BC8961A005144C8F5B8E4AD226DE1110DAA0@EXCHANGE2.cs.cornell.edu>
From: Paul Francis <francis@cs.cornell.edu>
To: "Paul Francis" <francis@cs.cornell.edu>, "Rajiv Asati (rajiva)" <rajiva@cisco.com>, <curtis@occnc.com>
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Subject: Re: [Idr] draft on virtual aggregation
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> -----Original Message-----
> From: idr-bounces@ietf.org [mailto:idr-bounces@ietf.org] On Behalf Of
> Paul Francis
> Sent: Thursday, July 31, 2008 6:11 PM
> To: Rajiv Asati (rajiva); curtis@occnc.com
> Cc: idr@ietf.org
> Subject: Re: [Idr] draft on virtual aggregation
> 
> Bottom line is that if the router doesn't have the full RIB, then it
> can't
> participate fully in eBGP.  People already know how to shrink RIB and
> FIB in
> edge routers that don't need to be full eBGP speakers.  Virtual
> Aggregation
> makes it possible to shrink the FIB in any router.

Well, alright, as somebody (Robert or Curtis?) pointed out already, you could
have a core router do multihop eBGP with the external peer and configure it
to dump only part of the RIB to the edge router...

But I must say that I find FIB suppression, as a general tool, to be quite
interesting.  The FIB is often the bottleneck in scaling, and if you have a
tool to control that, then I think long-term things will work out better.
(Which again is why I'm wondering what your concerns are.)

PF


> 
> You are certainly right that trouble shooting becomes more complex.
> The
> admin has to ask if the route is installed or not, and if not figure
> out what
> aggregation point the packet is supposed to go to and so on.  This is
> one of
> the trade-offs that the ISP has decide if it is worth making.
> 
> Could you be more clear about what you mean by "increases the
> complexity of
> the RIB and FIB interaction"?
> 
> PF
> 
> 
> > -----Original Message-----
> > From: Rajiv Asati (rajiva) [mailto:rajiva@cisco.com]
> > Sent: Thursday, July 31, 2008 9:07 AM
> > To: curtis@occnc.com; Paul Francis
> > Cc: idr@ietf.org
> > Subject: RE: [Idr] draft on virtual aggregation
> >
> >
> > The idea to keep FIB out-of-sync with RIB is a bit discomforting when
> > the troubleshooting has to be done for the traffic outage. Also, this
> > unnecessarily increases the complexity of the RIB and FIB
> interaction.
> >
> > For a lot of network operators, it may be cleaner to not even install
> > the qualified BGP paths into the RIB. FIB suppression would happen
> > automatically.
> >
> > Note that the decision to advertise the BGP paths to the downstream
> BGP
> > speaker can be independent of whether the paths are suppressed or not
> > in
> > the RIB/FIB. This may be proposed by this specification.
> >
> > Perhaps, you could clarify the rationale/advantages for keeping the
> > routes in the RIB. Thanks.
> >
> > Cheers,
> > Rajiv
> >
> >
> > > -----Original Message-----
> > > From: idr-bounces@ietf.org [mailto:idr-bounces@ietf.org] On
> > > Behalf Of Curtis Villamizar
> > > Sent: Tuesday, July 15, 2008 10:57 AM
> > > To: Paul Francis
> > > Cc: idr@ietf.org
> > > Subject: Re: [Idr] draft on virtual aggregation
> > >
> > >
> > > In message
> > > <37BC8961A005144C8F5B8E4AD226DE1109D860@EXCHANGE2.cs.cornell.edu>
> > > Paul Francis writes:
> > > >
> > > > To be clear, we are talking about one new attribute, zero changes
> > to
> > > > the data plane, zero changes to the existing BGP decision
> > > > process....just some rules for automatically setting up tunnels
> and
> > > > new address aggregates (virtual prefixes).  Better to do
> > > this now well
> > > > before the next generation of routers runs out of FIB.
> > > >
> > > > PF
> > >
> > >
> > > Paul,
> > >
> > > Most providers amortize their routers in three years but keep them
> in
> > > service for five or more.  Typical growth rates in healthy
> providers
> > > are a doubling in about 1.5-2 years with some providers reporting 1
> > > year (unconfirmed).  They keep routers in service by moving them
> > > closer to the edge where the lower capacity of the router is less
> of
> > > an issue, sometime redeploying from major cities to lesser cities.
> > >
> > > A smart provider looks at their current default free routing size
> and
> > > looks for at least 2 and better 4 or more times that in FIB and RIB
> > > capacity, with RP memory size also dictated by the number of BGP
> > peers
> > > and peer groups that are expected to be supported.
> > >
> > > Most of the providers with very large FIB and RIB are those top
> tiers
> > > that do not do a good job of aggregating the routes for their own
> > > infrastructure.  To aggregate well, they have to first allocate
> > blocks
> > > of addresses by POP and also subdivide their network into areas and
> > > aggregate at area boundaries (possibly the only functionality where
> > > confederations may be more straightforward and less error prone
> than
> > > RR, but that is another topic).
> > >
> > > If my memory serves me correctly, the target for major router
> vendors
> > > (dictated by certain tier-1 providers) was over 1 million circe
> late
> > > 1990s, about 2 million early 2000 and some asked for as much as 4
> > > million just to have headroom (and got it from some vendors).
> > >
> > > RAM is cheap.  Once you go off chip (RAM off the forwarding ASIC)
> > > memory bandwidth is much more an issue than memory size.
> > >
> > > The problem is mainly "enterprise switch/routers" with on chip CAM
> > and
> > > TCAM and no provision for off chip RAM that have been a problem.
> To
> > a
> > > lesser extent a few routers inteded as large enterprise routers or
> > > default free provider routers will now require that you replace the
> > > forwarding cards.
> > >
> > > IMHO again: I think this is not a hack that IDR should pursue.  But
> I
> > > have mostly worked with tier-1 providers and I am open to other
> > > opinions.  Lets hear from some providers on this.
> > >
> > > Curtis
> > > _______________________________________________
> > > Idr mailing list
> > > Idr@ietf.org
> > > https://www.ietf.org/mailman/listinfo/idr
> > >
> _______________________________________________
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