how fast a BGP router can download all internet prefixes ?

[mohammed hashim]

hi,

assume for some mistake the BGP session was reset, and the router will start forming adjacency and downloading all internet routes (500,000+ routes).

how long could this take to get them and make best path selection process and install them in routing table?

[Reza Sharifi]

Hi,

These days there are about 600k routes on the Internet and it can take up to about 3 minutes to receive all the routes once the BGP session is established.

HTH

[Ganesh Hariharan]

Hello Mohammed,

Convergence can take from 3-4 minutes, and causes some destinations to be unreachable during that times.

Hope it Helps..

-GI

[Vinit Jain]

I dont think it can be said exactly how long it will take for the Internet table to converge. It completely depends on the memory, CPU and scale of the router that it can handle. Different platforms will show different behaviors based on their architecture and capabilities. 3-4 minutes would be an ideal value but this would again depend on the above factors along with if is there multipath, is the Internet table being learnt from one provider or two providers, other features running on the router, how big is the FIB table, etc.

Hope this helps.

Vinit

[Masoud Pourshabanian]

I am just adding more info to others. 

It is just an estimation. I want to say link bandwidth is an influential parameter.

First, negotiation takes some time. After negotiation internet routes must be downloaded.

Size of full internet routes is approximately 500-600MB equal to 3000 to 5000Mb. So if your link bandwitdh is10M(service providers have much more bandwitdh), it takes roughly 300 to 500 seconds to download all the internet routes from only one neighbor. If you have more neighbor, it would be longer.

After downloading, updaing different tables depending on you configuration(soft configuration should also be considered), choosing the best paths among all those paths, updating routing table and FIB (cef, dcef, tcam)also take time. (depending on CPU and memory and ...as VINIT mentioned).

So 3 or 4 minutes is ideal. It may take longer.

Masoud

Any feed back appreciated.