North American Network Operators Group

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Re: Alternative to BGP-4 for multihoming?

  • From: adrian
  • Date: Mon Mar 13 17:10:20 2000

On Mon, Mar 13, 2000, Peter A. van Oene wrote:
> >
> >> 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.  

How do you propose to do this? It is a non trivial solution - if you
don't believe me, go ask someone trying to do it (eg Akami). 

People forget the magic tenant things are built on here - "The less the
control you have on a network, the harder you have to work to
deliver a given quality of service", where quality of service is
something other than 'terrible' .