how are backups implemented?
[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
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
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
participants (2)
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Ratul Mahajan -
Shiva