Implicit Withdrawal - BGP Update Message
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Maurizio Patrignani
patrigna at dia.uniroma3.it
Sun Oct 11 14:03:21 CEST 2015
Dear Ado, the term "implicit withdrawal" applies to a BGP update U_2 that comes to a BGP speaker from the same peer P that sent a previous update U_1. When the peer P sends the second update U_2, the meaning is that the previous update U_1 is implicitly withdrawn by P and replaced with U_2. In other words, the sequence U_1, U_2 has the same effect of U_1, Withdrawal, U_2. The four BGP announcements that you list in your email do not come all from the same peer of router 192.65.185.40. However, the third announcement (FROM: 192.65.185.144, AS_PATH: 6893 3561 209 297) is an implicit withdrawal of the first (FROM: 192.65.185.144, AS_PATH: 6893 8938 1 297). There is only one implicit withdrawal in the sequence. After all four announcements are received by router 192.65.185.40, router 192.65.185.40 has to choose its best route to prefix 192.152.102.0/24. The choice is among the 2nd, 3rd and 4th route, since the 1st announcement is implicitly withdrawn by the 3rd. Best, Maurizio On 10/11/2015 12:26 PM, Ado Maja wrote: > Dear all, > I am trying to account for all implicit withdrawal messages within a > certain period of time looking at BGP update messages collected at > rrc, Ripe. > Implicit Withdrawal Definition: If the sender announces a route to a > currently reachable address and the new route is identical to the > current route, this is a duplicate announcement. Otherwise, the sender > is replacing the current route with a new route and this is an > implicit withdrawal. (Wang et al. in the "Observation and Analysis of > BGP iBehavior under Stress") > What I am trying to understand is how do I count implicit withdrawals? > If for example, I have 4 BGP messages shown below that have same IP > address and different AS-PATH attribute, how many implicit withdrawals > do I have? Is it 3? If I look at consecutive messages that have same > IP address and different AS-PATH attribute the result would be 3 (I > compare first to the second, second to the third and third to the > fourth – assuming they have same IP address and different AS-PATH I > increment implicit withdrawals). But I have come across a solution > that takes a first message and compares it to the rest of the > messages. Than second message compares to the rest of the messages. > And lastly compares the third to the fourth. In this case number of > implicit withdrawals is 6. Please advise. > Thanks for your help. > TIME: 2001-9-16 00:00:06 > TYPE: BGP4MP/BGP4MP_MESSAGE AFI_IP > FROM: 192.65.185.144 > TO: 192.65.185.40 > BGP PACKET TYPE: UPDATE > ORIGIN: IGP > AS_PATH: 6893 8938 1 297 > NEXT_HOP: 192.65.185.144 > ANNOUNCED: 192.152.102.0/24 > TIME: 2001-9-16 00:00:18 > TYPE: BGP4MP/BGP4MP_MESSAGE AFI_IP > FROM: 192.65.184.3 > TO: 192.65.185.40 > BGP PACKET TYPE: UPDATE > ORIGIN: IGP > AS_PATH: 513 10764 6509 297 > NEXT_HOP: 192.65.185.9 > ANNOUNCED: 192.152.102.0/24 > TIME: 2001-9-16 00:00:36 > TYPE: BGP4MP/BGP4MP_MESSAGE AFI_IP > FROM: 192.65.185.144 > TO: 192.65.185.40 > BGP PACKET TYPE: UPDATE > ORIGIN: IGP > AS_PATH: 6893 3561 209 297 > NEXT_HOP: 192.65.185.144 > ANNOUNCED: 192.152.102.0/24 > TIME: 2001-9-16 00:00:44 > TYPE: BGP4MP/BGP4MP_MESSAGE AFI_IP > FROM: 192.65.185.130 > TO: 192.65.185.40 > BGP PACKET TYPE: UPDATE > ORIGIN: IGP > AS_PATH: 559 8933 6509 297 > NEXT_HOP: 192.65.185.130 > ANNOUNCED: 192.152.102.0/24 -- Maurizio "Titto" Patrignani Dipartimento di Ingegneria, Universita' Roma Tre Tel +39.06.57333233, Fax +39.06.57333612 http://www.dia.uniroma3.it/~patrigna -------------- next part -------------- An HTML attachment was scrubbed... URL: <https://lists.ripe.net/ripe/mail/archives/ris-users/attachments/20151011/07921c5a/attachment.html>
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