North American Network Operators Group|
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with a flap flap here and a flap flap there...
We were doing some testing. It involved testing advertising routes via a new box. Simple enough; discontinue an advertisement of some unimportant block from where it is normally advertised, start advertising it from the other box; in the same AS, etc. So I withdraw the first advertisement. 15 minutes later, I am still waiting for it to completely disappear from the net. My reference points are route-views.oregon-ix.net (multihop route-only peering to over a dozen ASes), route-server.cerf.net and nitrous.digex.net. At this point it has flapped up to 7 times on some paths. We are AS6171. Right now, we only advertise routes to AS852. They advertise to 1691, 577 and 1239. An example advertisement that we were seeing (which flapped enough that it was dampened!) came through the path (from route-views): 3333 1103 3300 7018 6478 1 701 814 7189 1691 852 6171, (suppressed due to dampening) 18.104.22.168 (inaccessible) from 22.214.171.124 Origin IGP, metric 20, localpref 100, valid, external Dampinfo: penalty 2729, flapped 5 times in 00:03:32, reuse in 00:27:50 The paths for some of the routes got even longer than this as time went on before they finally stopped being advertised. When it was all done, and the route was finally withdrawn everywhere I could see, an example history entry was: 3333 6905 5623 1136 3300 7018 6478 1 701 814 7189 1691 852 6171 (history entry) 126.96.36.199 from 188.8.131.52 Origin IGP, metric 20, localpref 100, external Dampinfo: penalty 2952, flapped 7 times in 00:12:09 Am I the only one that has a problem with this? You withdraw a route once, and it has flapped enough to be dampened in numerous places. I could have been half convinced that we had gone back to distance vector routing seeing this going on... Right after it was finally withdrawn everywhere, I started advertising the route again from the other box and did not have reasonable complete connectivity until 45 minutes after the start of this whole thing due to dampening. In fact, the act of dampening it causes a significant amount more flapping in some cases, although it certainly saves a lot in others. While I'm not a complete moron and understand the basic concept behind why this happens, I'm not really involved with Internet backbone engineering or operations right now and I wasn't aware that the Internet had grown enough to have this effect become so significant... Are there some networks around with very high advertisement intervals that are making this effect more pronounced, or is the Internet just that big now, or is something else going on? Comments?