IP address distribution in a Forwarding Table

Hi,

Does any one know a resource which provides some statistics about IPv4 and IPv6 addresses stored in a forwarding table of a router. For Example, for IPv4, each entry in a forwarding table contains at least the destination address and the corresponding next hop. Destination addresses might be stored entirely or they can match a set of IP addresses. What I am looking for is some statistics that can tell me how on the average how many entries are of the form

127.123.65.42 136.121.45.12x (where 'x' means a don't care i.e. use the longest prefix matching here) 136.121.45.1xx (where 'x' means a don't care i.e. use the longest prefix matching here) 136.141.54.xxx (where 'x' means a don't care i.e. use the longest prefix matching here) 136.141.5x.xxx (where 'x' means a don't care i.e. use the longest prefix matching here) and so on.

I will really appreciate any help.

Thanks.

Reply to
gullu
Loading thread data ...

Your examples hint that you might be misunderstanding the routing table. "longest prefix matching" does not use the decimal address values: it uses the binary addresses, the "longest" is based upon the number of bits matched, not the number of decimal digits matched.

Cisco routers do not keep statistics about the routing table size (and on Cisco routers, the routing process can end up being -much- more complex than a simple forwarding table.) However, you can generate these kinds of statistics yourself by using snmp to periodically read out the forwarding table and doing some simple totalling. You want the IP-FORWARD-MIB, base OID 1.3.6.1.2.1.4.24 In particular, you might want ipCidrRouteTable 1.3.6.1.2.1.4.24.4 or the inetCidrRouteTable 1.3.6.1.2.1.4.24.7

formatting link

Reply to
Walter Roberson

You may wish to investigate the IFM IPv6 / IPv4 web page.

You've heard a lot of talk about IPv6, and you'd like to have a play with it, but your ISP doesn't offer it. This article discusses one option, 6to4, that you can use.

formatting link
as well as Microsoft SBS 2003 IPv6 Readiness:

formatting link
and the Cisco IPv6 Config Wizard:

formatting link
Sincerely,

Brad Reese Cisco Resumes

formatting link

Reply to
www.BradReese.Com

You may also wish to view:

formatting link
Sincerely,

Brad Reese

formatting link

Reply to
www.BradReese.Com

Hi Walter,

Thanks for your reply.

I know that the prefix matching is done on binary addresses. I just gave an example so that everyone can understand it.

I was wondering if CISCO collected some data about the distribution of the IP addresses in the forwarding table on order to introduce some optimizations in their future products.

Can you answer one more question? Do CISCO routers use TCAMs for IP lookup in the forward table. If so (and if you feel that you are allowed to answer this question), Can you provide me with some details about how these TCAMs are used in the routers. There are so many research papers out on IP lookup and TCAMs and I am just wondering what industry has to say about it.

Thanks.

1.3.6.1.2.1.4.24.7
formatting link
Reply to
gullu

it wouldnt make sense - there is no way my routers are sending forwarding table info to Cisco....

more importantly - why would that help?

Cisco routers get used in all sorts of environments, many of which arent even directly connected to the Internet

depends. low end boxes use software (but may use TCAM table structures).

Cisco have put TCAM logic into chips for higher performance boxes such as the 7609 with a high end processor card.

the search for "tcam forwarding table" on the cisco web site gets 1680 hits - without a CCO login....

1.3.6.1.2.1.4.24.7
formatting link
>
Reply to
stephen

Any relevant NDA I had expired long ago, so I can answer with absolute confidence: "I haven't the foggiest idea." ;-)

Reply to
Walter Roberson

Cabling-Design.com Forums website is not affiliated with any of the manufacturers or service providers discussed here. All logos and trade names are the property of their respective owners.