Clear ip bgp, Outage Question

[richardwiseman]

When you use the clear ip bgp x.x.x.x command after changing BGP timers, how long would the service interuption be?

I done the clear ip bgp x.x.x.x command on a test router with three external bgp neighbors.( one neighbor at a time), and I see from the logs the reset took 30 seconds, 1.21 seconds and 0.3 seconds.

I have another router, which I need to update the times, and availability is important, would 30 seconds be the maximum you would expect the interuption to be.

Regards

[Peter Paluch]

Hello,

Using the command clear ip bgp x.x.x.x, it is generally hard to estimate how long the outage will take. That depends on the behavior of the remote router - whether it decides to bring up the BGP neighborship immediately back up, or whether it makes a fallback to the IDLE state and waits for up to 30 seconds before making an active attempt to create a BGP connection. In addition, the outage duration will be increased by the time necessary to synchronize the BGP databases between the routers.

Therefore, I would strongly suggest using the command clear ip bgp x.x.x.x soft instead that only resynchronizes the BGP databases of both routers instead of dropping the BGP peering completely and waiting for it to reestablish.

Best regards,

Peter

[richardwiseman]

Hi Peter

Many thanks for response.

I tried various soft commands, they did not show they timers had changed.

My routers do not have a large routing table or prefixes, so would you say a sub one minute outage is a conservative estimate.

Regards

[John Blakley]

Richard,

Like Peter said, when resetting BGP with "clear ip bgp x.x.x.x" you clear the association completely and all routes fall from the table, meaning that you'll lose connection to your provider momentarily until the BGP peers reestablish connection. with the "soft" command at the end, you don't lose the connection at all (and it's generally preferred unless there's a pressing need to bring them down) and the peers just sync the changes between them.

HTH,

John