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Re: [RRG] BGP Graceful Restart (was Re: Geoff Huston's article ...)




On Jun 20, 2007, at 11:20 AM, Geoff Huston wrote:

ksriram@nist.gov wrote:
For the purpose of damping BGP or reducing its churn, another important tool that should be quite useful is the BGP graceful restart (BGP-GR) mechanism (RFC 4724).

All depends on what you see as being the major factors that contribute to the BGP processing load in today's routing environment. Graceful restart is very effective, and it should be deployed ubiquitously, but from where I sit in the routing mesh the occasional spike I see in the update rate does not strike me as being a major contributor to the BGP update rate. Of course this is a subjective rather than a qualitative response and your mileage in your neck of the woods may vary!


As Geoff points out, the best that GR could do is to alleviate some churn due to software restarts. Real link failures or hardware failures are still going to result in churn.

There's also a reliability and confidence issue with GR. The presumption with GR is that a router advertising its restart capabilities will have a forwarding plane that will continue to reliably forward during a failure in the control plane. If it does not do this, then it will either blackhole or misroute traffic, which is obviously not good. Many carriers don't yet have the confidence is the implementations to put this into production. Hopefully, of course, this will change. However, I don't think we should wait for it.

Regards,
Tony

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