Re: [RAM] Number of DFZ routers - radical improvement of BGP unlikely
Robin Whittle <rw@firstpr.com.au> Sat, 07 July 2007 01:42 UTC
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From: Robin Whittle <rw@firstpr.com.au>
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Subject: Re: [RAM] Number of DFZ routers - radical improvement of BGP unlikely
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Hi Iljitsch, Short version: I no longer have any hope that BGP could be improved so much that DFZ routers could cope indefinitely with current growth in the global routing table size - or with the larger growth I had in mind which would enable routers with RAM-based FIBs to handle millions of prefixes to /24 granularity, without concern about route aggregation. Long version: You quoted something I wrote on 29 May. Initially, I had thought that the problem with routing and addressing was with FIBs running hot and not coping with the number of routes. I proposed a RAM-based lookup system for IPv4 and IPv6 which would only make sense if the routers could use BGP to cope with 3, 10 or 20 times the ~200k routes they currently handle. I thought that wouldn't be impossible, because BGP is just a matter of a "CPU, router software, message with peers" etc., operating at much lower speeds than the gigabits per second of the FIB handling the packets themselves. By late May, I was despondent about LISP ever helping much, because I couldn't see how it could be incrementally deployed and because it seemed to be a patch-up overlay for a routing system where the FIBs surely could be made (in the 5 to 7 year timeframe) to handle IPv4 space in millions of arbitrarily located /24 granularity prefixes. So I was still thinking the best place to start was by souping up BGP enough to be able to slice and dice IPv4 space at the BGP level into millions of prefixes, with RAM-based FIBs, without concern about route aggregation. Then, I thought, what remaining problems could be solved by placing less demands on something like LISP. That was when I had only a cursory understanding of BGP. During May I learnt a lot more about the memory requirements, CPU load, software and policy complexities of BGP. I also learnt something about the current implementation of the MRAI timer and path hunting. There was a fascinating discussion about this on the RRG and then the IDR lists, starting 20 June: http://psg.com/lists/rrg/2007/maillist.html#00146 http://www1.ietf.org/mail-archive/web/idr/current/maillist.html#02422 Then I came to understand what most people have known for years - BGP uses intentionally highly simplified messages in order to help with scaling, but this gives routers only limited abilities to recognise which alternative paths may still work after another path is withdrawn. Even with the simplification, the load on CPUs and memory is extreme and the thought of handling five or ten times more routes - and then ten and twenty times more in the next ten years, is not realistic. Now I think there could be some worthwhile improvements to BGP, maybe to be developed and incrementally introduced over the next few years - but that this would at most "hold-back-the-clock" against routing table growth by a year or so. The simplest approach is probably Tony Li's and Geoff Huston's Path Length Damping - yet this will rely on router manufacturers largely restoring the RFC1771 (propagate withdrawals immediately) MRAI timer function, which I understand they generally ignored by 2002 and which RFC4271 banned in 2006! I wrote: > So if BGP could be radically improved, . . . > > Unfortunately, no BGP experts think that such improvements > are feasible. Maybe some unconventional ideas from > non-experts might be helpful. I withdraw this suggestion. I can't imagine any backwards-compatible upgrade or incrementally deployable replacement for BGP could achieve the radical improvements I was hoping for. Maybe someone else will have some great ideas for dramatically souping up BGP. BGP solves some very difficult problems. I can't think of any drastic improvements. - Robin _______________________________________________ RAM mailing list RAM@iab.org https://www1.ietf.org/mailman/listinfo/ram
- Re: [RAM] Number of DFZ routers Noel Chiappa
- Re: [RAM] Number of DFZ routers Chris L. Morrow
- Re: [RAM] Number of DFZ routers Roland Dobbins
- Re: [RAM] Number of DFZ routers Ricardo V. Oliveira
- Re: [RAM] Number of DFZ routers Tony Li
- Re: [RAM] Number of DFZ routers Robin Whittle
- [RAM] Number of DFZ routers Robin Whittle
- Re: [RAM] Number of DFZ routers HeinerHummel
- Re: [RAM] Number of DFZ routers Chris L. Morrow
- Re: [RAM] Number of DFZ routers Eliot Lear
- Re: [RAM] Number of DFZ routers Ted Seely
- Re: [RAM] Number of DFZ routers Chris L. Morrow
- Re: [RAM] Number of DFZ routers Robin Whittle
- [RAM] Re: Number of DFZ routers Stephane Bortzmeyer
- Re: [RAM] Re: Number of DFZ routers Robin Whittle
- Re: [RAM] Number of DFZ routers Simon Leinen
- Re: [RAM] Number of DFZ routers Chris L. Morrow
- Re: [RAM] Number of DFZ routers Simon Leinen
- Re: [RAM] Number of DFZ routers Chris L. Morrow
- Re: [RAM] Number of DFZ routers Iljitsch van Beijnum
- Re: [RAM] Number of DFZ routers - radical improveā¦ Robin Whittle
- Re: [RAM] Number of DFZ routers HeinerHummel
- Re: [RAM] Number of DFZ routers Robert Raszuk
- Re: [RAM] Number of DFZ routers HeinerHummel
- Re: [RAM] Number of DFZ routers HeinerHummel
- Re: [RAM] Number of DFZ routers Olivier Bonaventure
- Re: [RAM] Number of DFZ routers Noel Chiappa
- Re: [RAM] Number of DFZ routers HeinerHummel
- [RAM] Meeting at IETF-69? Ved Kafle
- Re: [RAM] Meeting at IETF-69? Tony Li
- Re: [RAM] Meeting at IETF-69? Loa Andersson
- Re: [RAM] Meeting at IETF-69? Tony Li
- Re: [RAM] Meeting at IETF-69? Marshall Eubanks
- Re: [RAM] Meeting at IETF-69? Tony Li
- Re: [RAM] Meeting at IETF-69? Loa Andersson
- Re: [RAM] Meeting at IETF-69? Marshall Eubanks
- Re: [RAM] Number of DFZ routers - radical improveā¦ Iljitsch van Beijnum