[42775] in North American Network Operators' Group
Re: how are backups implemented?
daemon@ATHENA.MIT.EDU (Shiva)
Fri Sep 21 01:00:38 2001
Date: Thu, 20 Sep 2001 21:58:27 -0700
From: Shiva <zhiva@pacbell.net>
To: Ratul Mahajan <ratul@cs.washington.edu>
Cc: nanog@merit.edu
Message-id: <3BAAC8F3.1060309@pacbell.net>
MIME-version: 1.0
Content-type: text/plain; charset=us-ascii; format=flowed
Content-transfer-encoding: 7BIT
Errors-To: owner-nanog-outgoing@merit.edu
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
>>
>>
>
>
>
