On Mon, Apr 02, 2001, Hank Nussbacher wrote:
I think the current large routers can handle flapping (50,000 routes every 30 seconds): http://www.lightreading.com/document.asp?site=testing&doc_id=4009&page_number=12 and they can handle large BGP tables (Cisco: 400K, Juniper: 2.4M): http://www.lightreading.com/document.asp?site=testing&doc_id=4009&page_number=10
How many routers did they test? Did they test 2 routers? Or did they test 1000 routers? Did they plot just the BGP table withdrawl speed and the subsequent BGP table repopulation speed? What about doing some quick modelling on what affect this flapping "latency" could do to a large mesh of routers. There has been some work done on this. Its been covered at NANOG. The reason that most of its effects on reachability are masked by super-routes. (which for most of you will be the default route. :-) I'd love to see one day when every network running a full BGP table pulled out its default route(s) and ran defaultless.
The problem is all the legacy Cisco 7500s in the core that are defaultless and currently carry 99,000 routes. I think Geoff is wrong in his statement that the problem is not routing table size, but rather flapping. To quote Geoff: "It's not the size of the table, but the number of updates per second that kills a router stone dead." But the rate of flapping is proportional to the size of the routing table, IMO. If you have 1000 routes in your table, and on average 5% of the nets will flap every 60 seconds, that comes to 50. If you table is 100,000 and the same 5% will flap, that comes to 5000 every minute. Reduce the table size and you *will* affect the flapping as well.
Even if every router in the internet core was upgraded to the latest and greatest 4-way SMP 2ghz intel CPUs running the routing protocols with 4 gigabytes of RAM each, the sheer complexity of the routing system would produce some rather interesting dynamics. Hell, even if you threwq this at 100,000 routes in today's network topology, I'm pretty sure the nature of BGP would be a little different :) (Read: Just because its faster, doesn't mean its better. Sometimes something being slow acts as a regulator. People might want to try grabbing some basic CS programs to do network modelling and start playing. :-) I'll stop ranting now, since I've already ranted on this topic before. Adrian (NOTE: People are probably thinking that I'm just speaking out of my ass. Being a hardware geek, software programmer and routing person has got its advantages. One of them is that I have an insatiable desire to digest any reading I can to figure out how things work, and I currently do this for networking since my current job hat has "programmer" on it.) -- Adrian Chadd "The fact you can download a 100 megabyte file <adrian@creative.net.au> from half way around the world should be viewed as an accident and not a right." -- Adrian Chadd and Bill Fumerola