Its these cases I'm concerned with. In my mind, irrespective of the comments on the functionality of DNS for this purpose, I see little
other
choice.
DNS is not the droid you're looking for.
Using DNS response times to predict likely TCP performance is silly for at least as many reasons as using BGP aspath lengths to predict likely TCP performance is silly.
That being said, if anyone has better ideas on how to provide for high availability to millions of web sites worldwide, please let me know.
TCP performance is affected by congestion symmetry, since TCP uses the spacing of ACK packets to control the spacing of data packets. While there's no way to guarantee congestion symmetry, one of the leading indicators of whether you will have congestion symmetry is "whether you have path symmetry." Furthermore, the leading indicator of whether you have path symmetry is "whether the outbound flow's first hop is the same as the incoming flow's last hop."
Just a quick note in clarification, I am less interested in intelligently directing the traffic to the closest or most optimal server farm that I am in purely ensuring that the traffic can be balance between sites that sit within different AS's. ------- Peter Van Oene Senior Systems Engineer UNIS LUMIN Inc. www.unislumin.com