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In the JNCIA study guide, it is stated that there are currently 120k routes on the internet and that Juniper supported up to 450k. How did they arrive at the 120k? If I wanted to know how many exact routes, how could I find that by myself?

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3 Answers 3

up vote 7 down vote accepted

The backbone routers of ISPs (to be precise, Tier-1 ISPs) constitute what is known as the "default-free zone." In this zone, there are no default routes -- every route that is announced on the Internet is carried in the router's route table.

It's simply a matter of counting the table entries.

If you want to count yourself, you have to arrange a BGP peering session with your ISP and have them send you all routes.

Happy counting!

P.S. the exact number is constantly changing as new networks come on-line or get disconnected.

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"The backbone routers of ISPs" is misinformation - not all ISPs will be default-free, and if they are default-free it also doesn't mean they're not paying another provider for transit (or settlement-based peering). Would suggest editing to note "tier one ISPs" - while even still not 100% accurate, it's closer than "ISPs" in general. –  John Jensen Apr 24 at 16:34
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Ron, this still doesn't change the fact that you've given the OP a rather difficult way of calculating the number of routes on the internet, assuming they do not already have a peering session with their upstream. –  Mike Pennington Apr 25 at 13:04

I think your study guide is a little outdated. Currently we are at about 500k routes on the Internet. Geoff Huston is collecting stats weekly. You can find his reports here.

If you want to see for yourself goto http://www.routeviews.org/ and get access to some real systems on the internet.

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Thank you. I have selected Ron's answer as I am a complete router-newbie and I found his approach was more enlightening in a practical sense, but I appreciate these links and added info. Very good to know! :) –  CaseyJones Apr 22 at 12:00
    
Casey, Ron offers one way of counting internet routes; however the reality is that building a bgp peering session with your upstream is more trouble than necessary because the information is available without all that work. Potaroo and RouteViews.org are good options, which don't require your own bgp ASN or coordinating a change with your upstream. –  Mike Pennington Apr 22 at 13:03

In addition to the good answers already given by Jens Link and Ron:

There's no absolute, objective answer how many routes are active on the internet. The number constantly changes due to networks connecting and disconnecting, routers having outages, etc. Some prefixes are announced only to specific other networks (e.g. using a no-export community) and are meant to be seen only in specific parts of the internet.

In addition to that, there's filtering: not every network filters routes it receives the same way. Some don't at all, some filter so that small prefix (/24 upto /32 in IPv4, /48 upto /128 in IPv6) won't be accepted.

Every network has its own view of the internet. And more prefixes in a routing table isn't always better, it can also mean bad filtering, accepting a lot of deaggregated routes, etc.

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