Faster 'Net growth rate raises fears about routers

Mon Apr 2 13:01:31 UTC 2001

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 at creative.net.au>  from half way around the world should be viewed
			    as an accident and not a right."
					-- Adrian Chadd and Bill Fumerola