Redundancy & Summarization

Hector Herrera hectorherrera at
Sat Aug 22 14:08:52 CDT 2009

On Sat, Aug 22, 2009 at 6:52 AM, Adam Greene<maillist at> wrote:
> Another option could be to announce one /17 to each upstream provider and
> use conditional BGP to announce the other /17 to the provider that's still
> active in the event that one provider goes down.

Maybe I'm wrong, but I think this method will only work when handling
local failures.  If there is a failure in a remote network which
causes ISP A to be unreachable from a third party, your routers will
not adjust the announcements since ISP A and B are still reachable to
you, but the third party will not be able to reach the network nearer
to ISP A through the ISP B connection because ISP B doesn't have an
announcement to that network.  (This is assuming that ISP A and ISP B
are not peers).


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