BGP convergence time

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Nov 22nd, 2007
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Hi All,

Please share yur observations and comments to improve the BGP convergence time. Although the standard time is 180sec but is there a way to make it instantaneous.

please share.

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milan.kulik Mon, 11/26/2007 - 03:25
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Hi,


you can use

neighbor ... timers x y

and

bgp scan-time z

commands.

See http://www.cisco.com/en/US/products/ps6350/products_command_reference_chapter09186a0080454cee.html#wp1073585


and

http://www.cisco.com/en/US/products/ps6017/products_command_reference_chapter09186a008087d5e7.html#wp1011129


bgp scan-time 10

neighbor ..... timers 3 12


will give you a very fast convergence time.


But use this with care, you can get your router overloaded if your timers are too low for a high number of prefixes in you BGP table.


BR,

Milan






gaurav_thapar79 Mon, 11/26/2007 - 03:44
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Hi Milan,

By any chance, did you try BGP fast-peering deactivation feature wherein i wouldnt be overloading my router during BGP scanner process.

Theoritically, we can achieve the faster convergence and reducing the issues related to router resources.


Please share your feedback incase you have used BGP fast-peering deactivation option instead of suggested by you.

milan.kulik Mon, 11/26/2007 - 04:46
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Hi,


I'm not using it, but

BGP fast-peering deactivation also looks good to speed-up the dead neighgor detection.

But would it make the convergence faster if the neighbor remains alive and just some subnet disappears from an IGP routing table which should be redistributed to BGP?


IMHO, decreasing scan timer can make the BGP router very fast, but it's dangerous if all 300K Internet prefixes are present within the router memory, e.g.


BR,

Milan



gaurav_thapar79 Mon, 11/26/2007 - 06:16
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Hi Milan,


How about BGP with this option in MPLS IP-VPN case. Hopefully , the convergence time must be faster than manually configuring the BGP scanner timings.

BTW, have you ever tested changing the scanner timings.

milan.kulik Thu, 11/29/2007 - 02:07
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Hi,


yes, I'm using the decreased scanner time to speed-up the secondary router to detect the primary router failure on one site.

But the number of BGP prefixes involved is cca 60, so no CPU problem at all.


BR,

Milan


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