BGP Convergence Time

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Jul 24th, 2009
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We have different 2 ISP's that are advertising each other's subnets using BGP. What would be an expected recovery time if one ISP fails for the other ISP to advertise the route through them?

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Rick Morris Fri, 07/24/2009 - 05:35
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There are a couple of variables. If your connection is flapping it may never come up, or may come up for a second and go right back down.


I have seen this take 15 seconds and I have seen it take up to 5 minutes. Your advertisements will be sent upstream but routing between you and the PE may take a little time. Since your routes are being announced both peers the one will take over once the other routes are withdrawn from the routing table because the connection is down.


From my experience, despite any book answer, it has averaged to around 15 seconds or less.


Here is a link I found:


http://www.ssfnet.org/Papers/icnp-2001.pdf

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