how are backups implemented?

Fri Sep 21 04:58:27 UTC 2001

This would be seen when an enterprise (with ASY) is multihomed to to 
ISPs and with smaller blocks out ISPs (Say A and B) blocks and do 
conditional advertisement...  such that when link to A goes down the 
smaller block from A is advertised out via B. Maybe 4hours is the ckt 
restore interval...  Does this fit what you are seeing?

-shiva

Ratul Mahajan wrote:

>
>let me repeat my question, this time more clearly. we, at uw, are
>analyzing bgp tables for possible errors (misconfigurations). one of the
>strange things (question 3 below) we are observing is the following.
>
>a prefix 10.10.0.0/16 (for instance) is announced by AS X. sometimes, some
>of its more-specifics (like 10.10.1.0/24, 10.10.56.0/24 ....) would appear
>for a short time (for example, 4 hours) and then disappear again.  
>furthermore, these more-specifics would have an origin AS Y (Y != X). 
>
>i am curious if this behavior can be caused by some sort of backup
>arrangements i don't understand, or some router/administrator mess-up. 
>clues?
>
>	thanks,
>	-- ratul
>
>On Thu, 20 Sep 2001, Ratul Mahajan wrote:
>
>>
>>[posting this message after having looked for answers elsewhere including
>>the archives, but found no satisfactory answers]
>>
>>i wanted to ask the operations community about how backups are typically
>>implemented. i am more interested in backup implementations, in which a
>>failure would expose a different origin AS (this would exclude prepending
>>based backups).
>>
>>1. when a network is multihomed, and one of the links fails, would you
>>expect a smooth transition (as seen in the bgp tables of a remote AS) from
>>one origin AS to another (modulo convergence effects)?
>>
>>2. can a failure (anywhere in the network) ever expose another origin AS
>>for some AS's while it stays the same for some?  i guess it can, when the
>>network is being persistently announced from both origins, and under
>>normal scenario one origin could be hidden from some AS's. would this also
>>hold for a routing table as rich as routeviews?
>>
>>3. can a failure ever cause more-specifics with a different (from the
>>origin of the less-specific) origin AS to appear (again, as seen from a
>>remote AS)? this might depend on how backups are implemented - so what i
>>am asking is, is this a common/possible case?
>>
>>
>>	thanks,
>>	-- ratul
>>
>>
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