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Re: Alternative to BGP-4 for multihoming?

  • From: Paul Vixie
  • Date: Mon Mar 13 01:26:42 2000

> They sit on /28's and smaller in some cases.  I'm certainly not going to
> be successful in acquiring ASN's for these people to do proper load
> balancing between multiple ISP's and most major ISP's see little benefit
> in modifying route tables to include our small netblock.

Right on man!

> 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."

Thus http://www.vix.com/pub/vixie/ifdefault/.  Try it.  If you don't know
how to apply patches to your kernel, then have a consultant do it.  I wrote
this for a pornography distributor whose pageviews-per-second went up by
a factor of 1.7 peak and 1.25 average just as a result of using "interface
defaults" rather than speaking BGP and trying to run defaultless.





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