Randy Bush randy at
Thu Nov 1 22:02:02 UTC 2001

> How is BGP potentially injecting information into the IGP? The only way
> that should be happening is if you are doing BGP -> IGP redistribution,
> in which case I'd surely hope you aren't doing IGP -> BGP as well.

you are an isp in a small country with half a dozen other isps.  the biggest
isp in the country has half a dozed prefixes.  you all meet at an exchange
point and each has an external international exit through an upstream.

you want to redistribute the bgp routes learned at the exchange point into
your dynamic igp so, when the ix is working, local traffic goes directly
there as opposed to tromboning through your default exit.  one then also
wants to receive from one's upstream transit (or inject) a bgp default route
into one's igp,

and then one wants to inject one's internal routes into the bgp exports to
both the exchange and the upstream.  if one's network is at all likely to
partition, that means one wants to redistribute one's igp into those two bgp
sessions, heavily acled of course.


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