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BGP4 routing table size

Posted on 2004-04-20
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Last Modified: 2012-05-04
This should be easy but I don't have the time to look for it..

I have to internet routers connected to the internet. Both are running BGP to their respective ISP. They are also running IBGP between them to load share and have better route selection.

I am taking full routes on both routers...

What is the current size of the BGP routing table that I should see and where can I find it for future refference.

Thanks
Scott
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Question by:Scotty_cisco
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by:Scotty_cisco
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Ok not number of routes ... the amount of memory that they should be taking ...sorry for the confusion... and roughly not exactly.

Thanks
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td_miles earned 125 total points
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It's hard to put an exact figure on it, as it will be implementation dependant. This is why you see the BGP route table described in terms of the number of entries usually.

If you look at this Cisco page (which is about using AS filters to reduce BGP table size):
http://www.cisco.com/warp/public/459/41.shtml
down the bottom there is a table that shows the following:

            Number of Prefixes     Memory Consumed
Full Routes     98,410     70,882,248
AS Filter     31,667     28,132,528

The table is obviously to illustrate the the saving you can achieve. If from that table you calculate the about of memory per BGP entry, it comes out at 720 bytes & 888 bytes respectively. If you take the higher of those two figures (888 bytes/BGP entry) and apply that to the current size of the BGP table:
http://bgp.potaroo.net/index-bgp.html
(lets take the higest value), you get:

164378 BGP entries * 888 bytes/BGP entry  = 145967664 bytes  (ie. 146 MB)

That's just my stab at it, feel free to take it or leave it. I've seen you around, you should be able to work out if this looks correct or not. I don't have a router that has the full BGP table on it that I can check on at the moment, hence why I'm working it out mathematically. That Cisco page also shows you how to see how much memory the BGP is using.
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by:Scotty_cisco
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that is pretty close to what I was seeing in my router and it all makes sense... for the the numbers set forth actually.

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