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Re: Scalability issues in the Internet routing system
Alexei Roudnev wrote:
i respectfully disagree.Forwarding is in line cards not because of CPU issues, but because of BUS issues.
"centralized forwarding" only gets you so far on the performance scale. "distributed forwarding" is a (relatively) simple way to scale that performance.
just take a look at any 'modern' router (as in, something this century) with a requirement of (say) >10M PPS.
sure - there are reasons why one DOES have to go to a distributed model - 'bus limitations' as you say .. but i'd more classify those as phsycal chip-packaging limitations - how many pins you can put on a chip, how 'wide' the memory-bus needs to be as the PPS goes up.
once again - disagree. it _may_ be that it means that forwarding can be in software - but for the most part the determining factor here is what is the PPS required for the function.It means, that card can be software based easily.
i've previously posted a categorization of requirements in a router based on their function -- see <http://www.merit.edu/mailinglist/mailarchives/old_archive/2005-09/msg00635.html>
i think _software-based_ works for /some/ types of router functions - but nowhere near all - and certainly not a 'core' router this century.
if you're looking at routers based on their classification, clearly there isn't a requirement for all types of routers to have a full routing table.Anyway, as I said - it is only small, minor engineering question - how to forward having 2,000,000 routes. If internet will require such router - it will be crearted easily. Today we eed 160,000 routes - and it works (line cards,m software, etc - it DO WORK).
but for a 'core router' and 'transit/peering routers', the ability to work with a full routing-table view is probably a requirement - both now, and into the future.
there have been public demonstrations of released routers supporting upwards of 1.5M IPv4+IPv6 prefixes and demonstrations on routing churn convergence time. <http://www.lightreading.com/document.asp?doc_id=63606> contains one such public test.