RE: AS numbers and multiple site best practices

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I've had trouble finding any technical reason not to use it.

What is important to you about having QA and Corporate use separate AS numbers? Does using the same AS number result in a reduction of separation?

For my part it's mostly a desire to make sure that changes to QA or Corp BGP configs could never impact BGP for our Production datacenter. So far it looks like it may just be a fear of the unknown on my part as I can't think of a good example of how one might actually affect one BGP installation by making changes to another BGP installation purely based on sharing an AS number (clearly you could have impact if you are advertising the same space from both locations).