Easy and hard multihoming (was: Re: Upstreams blocking /24s)

Wed Oct 10 18:01:19 UTC 2007

--- Keegan.Holley at sungard.com wrote:

> So if one of 
> the Tier I's decides not to accept my public /29
> then the millions of 
> singlehomed subscribers go with it.  

Yep.  During normal operation, someone would be
announcing the aggregate out of which your /29 is
carved, and that provider should be someone you're
paying to carry the more-specific.  Traffic will get
to you in that case.  If your circuit to that provider
goes down, then the other customers of your other
provider will be able to reach you, but the peers and
suppliers of your other provider would likely not.

The easiest way to multihome in a way which mostly
works (tm) is to get an ASN and self-originate a
prefix which is /24 or larger.  As of right now,
multihoming is a justification for a /24 and an ASN,
so multihoming in a different way should be something
which is done for a specific reason, or to solve a
particular problem.

Yes, yes, there are multiple other ways to do this,
but their failure modes might not be as easy for your
providers to help you troubleshoot as BGP is.

-David

David Barak
Need Geek Rock?  Try The Franchise: 
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