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Re: Alternative to BGP-4 for multihoming?

  • From: Marc Slemko
  • Date: Mon Mar 13 01:59:33 2000

On 12 Mar 2000, Paul Vixie wrote:

> > 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.

That doesn't solve one of the growing uses of such systems, which is
so-called "geographical redundancy".  More and more, it simply isn't
acceptable to have a single location with a bunch of network links, with
an attempt being made to optimize how those links are used.  A single
location is a single location no matter what you do with it.  You need
multiple locations, with a reasonably robust and somewhat (although not
necessarily completely) transparent failover between them.  In these
cases, any best path benefits are secondary.

The ways to do this sort of thing are very limited.

Whatever you do, you end up needing either "smart" (ie. sometimes lame)
DNS servers or to originate BGP routes from multiple locations with the
same IP address actually going to different machines depending on which
route is used (which is lame even more often, although it is not as bad if
one facility is normally an unused backup one, but that introduces lots of
other issues).

If you have a better solution for this, I'm sure the world would love to
hear it.  Yes, many or most or all of the current implementations do or
can be configured to do some questionable things.  However, your solution
doesn't address the whole "distributed" aspect of it.






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