[Irtf-rr] IP Table Size

[Curtis Villamizar]

In message <016f01c2cba6$c9329420$b629f59b at essex.ac.uk>, "Poh Tze Ven" writes:
> Hi,
> 
> I need some information from ISPs (more ISPs the better) regarding active
> network elements (in particular, routers) that capable of routing IP packets 
> in
> their networks. The information is needed only for statistical purpose. The
> following are what I seek for:
> 
> (i)  The average size of IP forwarding table (in term of number of IP prefixe
> s)
> excluding AS border routers.
> 
> (ii) The average number of external prefixes in the forwarding table (exclude
>  AS
> border routers).
> 
> (iii) The average number of external prefixes in forwarding table of an AS
> border router.
> 
> (iv) Rough estimation of number of routers in the domain.
> 
> Please reply directly to my e-mail address.
> 
> Thank you in advance.


It would help if your categorization made more sense.  With a few
hundred thousand routes, why exclude the few hundred (at most) ASBR?
Unless you mean exclude the ASE routes and count the intra-area and
inter-area routes.  The routing information base (RIB) is what really
matters, not the FIB, unless you are trying to build hardware and
looking for what the ASIC FIB sizes should be.  If you are interested
in the IGP size you need to know number of nodes (routers in an OSPF
area, IS in an ISIS level) and adjacencies, which is relevant if your
interest is computational scaling.  It might help to first learn the
terminology and get a clue as to what questions make sense to ask
before asking.

You might also have more success looking at the various sites that
provide full routing information and counting the routes yourself.
You won't find the number of unaggregated routes inside any given ISP,
just the global routing information.  You also won't find the number
of nodes and adjacencies if that is what you are after.

Last I heard it was around 250,000 routes for the largest ISPs with
some routers having 1,000,000 route instances (more than one way to
get there from here).  Its a moving target.  You can find number of
routers and a rough idea of out degree (leading to number of links)
from some past presentations at NANOG or elsewhere.

Curtis

ps - If you ask really nicely Saddam might tell you where all his
weapons are.  Some ISPs can at times seem just about as open with
information about size of their network.  Good luck.