Customer AS

Henry Kilmer hank at
Sat Aug 17 18:30:28 UTC 1996

Randy Bush writes:
>> Not sure what you mean here concerning 'unroutable' prefixes, but the
>> issue with obtaining an allocation for one of the upstream provider's
>> CIDR block when multihomed *does* have its drawbacks, at least from
>> the end-user perspective. If said prefix (let's say a /24) is announced
>> in the 'allocating' provider's aggregate, and the more specific is
>> announced via the 'other' provider, the more specific will always be
>> preferred.
>This is brain damaged.  Given
>            AS1 ----- Sprint
>             |
>             |
>             |
>             |
>            AS2 ----- anything else not Sprint
>You can not announce a bit of Sprint space AS1->AS2->MCI as a fallback (note
>the 'extra' AS hop) because Sprint aggregates your announcement and the
>longer prefix is announced to the world via <anything else>.
>Use Sprint space, bye bye fallback.
>To the best of my knowledge (which ain't that hot), all other providers have
>discovered suppress-map.

This is mainly due to the fact that Sprint does not listen to any
announcements from its peers for anything within its "non-portable"
blocks.  Multihoming and expecting fallback to work are two different
things I guess.  Let's not even mention the AS path length stuff.

BTW, Sprint also does not listen to any of its peers ASes through
other peers so peering with Sprint and still paying someone for
transit services do not help you get more redundancy with Sprint's


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