North American Network Operators Group

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Re: Alternative to BGP-4 for multihoming?

  • From: Peter A. van Oene
  • Date: Mon Mar 13 17:00:32 2000

>> 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
>> 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