North American Network Operators Group Date Prev | Date Next | Date Index | Thread Index | Author Index | Historical Black holes caused by aggregation
My appologies if you have already seen this. It appears to be an operational/configuration issue that our clients might be interested in..... :) Perhaps its time to upgrade all that mbone/mrouted software out there. > From: Bill Fenner <[email protected]> > Subject: Black holes caused by aggregation > Date: Wed, 25 Oct 1995 18:52:46 PDT > > Longest-match routing was introduced in mrouted version 3.5 . Previous > versions would only accept the least specific route that it heard, and > if it heard routes that overlapped it would log a message and drop the > new route. > > People now appear to be using Cisco's route aggregation feature in > places that it shouldn't be used, which will cause problems when > forwarding through mrouted versions previous to 3.5 (which is about 75% > of the MBONE). A nice example of the breakage is net UIUC-CAMPUS-B, > 128.174. (Not to pick on UIUC in particular, but it's the easiest > example for me.) The three routes that I have in my routing tables for > 128.174 are: > > 128.174.212.0/25 > 128.174.240/24 > 128.174/16 > > Note that the last route covers the first two, and mrouted versions previous > to 3.5 will only accept the last route. In fact, if I traceroute towards > 128.174.0.0, I have a nice short route: > > Mtrace from 128.174.0.0 to 204.162.228.2 via group 224.2.0.1 > Querying full reverse path... > 0 dartvader (204.162.228.2) > -1 parc.dart.net (204.162.228.1) DVMRP thresh^ 1 200 s > -2 ames.dart.net (140.173.144.1) DVMRP thresh^ 1 200 s > -3 mbone2.nsi.nasa.gov (192.203.230.242) DVMRP thresh^ 64 200 s > -4 mbone.nsi.nasa.gov (192.203.230.241) DVMRP thresh^ 1 200 s > -5 oday.psc.edu (192.88.114.10) DVMRP thresh^ 64 176 s > -6 mbone.merit.edu (198.108.2.20) DVMRP thresh^ 64 201 s > -7 tibia.cic.net (192.217.65.100) DVMRP thresh^ 32 254 s Next router no mtrace > -8 dcl2.gw.uiuc.edu (192.17.2.8) [proteon/mrouted 1.0] doesn't support mtrace > > However, if I trace towards one of the specific routes, I end up taking > the shortest mrouted-3.5-or-greater path: > > Mtrace from 128.174.240.0 to 204.162.228.2 via group 224.2.0.1 > Querying full reverse path... > 0 dartvader (204.162.228.2) > -1 parc.dart.net (204.162.228.1) DVMRP thresh^ 1 200 s > -2 ames.dart.net (140.173.144.1) DVMRP thresh^ 1 200 s > -3 mbone2.nsi.nasa.gov (192.203.230.242) DVMRP thresh^ 64 200 s > -4 mbone.nsi.nasa.gov (192.203.230.241) DVMRP thresh^ 1 200 s > -5 mbone.sdsc.edu (198.17.47.39) DVMRP thresh^ 64 200 s > -6 VINEGAR.SESQUI.NET (128.241.0.91) DVMRP thresh^ 64 201 s > -7 mae-bone.psi.net (192.41.177.247) DVMRP thresh^ 64 128 s > -8 MBONE1.UU.NET (137.39.43.34) DVMRP thresh^ 64 201 s > -9 MBONE2.UU.NET (137.39.246.98) DVMRP thresh^ 64 201 s > -10 dec3800-2-fddi-0.SanFrancisco.mci.net (204.70.158.61) DVMRP thresh^ 64 2828 ms > -11 dec3800-2-fddi-0.Denver.mci.net (204.70.152.61) DVMRP thresh^ 1 41 s > -12 dec3800-1-fddi-0.WillowSprings.mci.net (204.70.104.29) DVMRP thresh^ 1 -24 s > -13 tibia.cic.net (192.217.65.100) DVMRP thresh^ 32 254 s Next router no mtrace > -14 dcl2.gw.uiuc.edu (192.17.2.8) [proteon/mrouted 1.0] doesn't support mtrace > Round trip time 295 ms > > Now, you might say "Well, that just means that traffic is taking a suboptimal > path, no big deal." But, because of the way DVMRP builds its forwarding > trees, traffic that matches the specific routes (e.g. 128.174.240.1) will > *not* get forwarded from a 3.5-and-up to a 3.4-and-down mrouter. Here is > a (slightly altered, since there is no active source in 128.184.240.x right > now) mtrace showing what you would see on that boundary: > > Mtrace from 128.174.240.0 to 141.210.188.1 via group 224.2.0.1 > Querying full reverse path... > 0 ? (141.210.188.1) > -1 ? (141.210.188.3) DVMRP thresh^ 1 208 s > -2 mbone.wayne.edu (141.217.1.74) DVMRP thresh^ 32 -250 s Not forwarding > -3 mbone.merit.edu (198.108.2.20) DVMRP thresh^ 32 201 s > -4 tibia.cic.net (192.217.65.100) DVMRP thresh^ 32 254 s Next router no mtrace > -5 dcl2.gw.uiuc.edu (192.17.2.8) [proteon/mrouted 1.0] doesn't support mtrace > > Note the "Not forwarding" error code on the mbone.wayne.edu line. > 141.210.188.3 is 3.4, mbone.wayne.edu is 3.5 . (Again, not to pick > on wayne.edu; this was the easiest test case that I could come up with.) > > This means that if you are one of the people advertising this kind of > specific and general routes, that you are isolating your traffic from > the specifically routed subnets to the connected cloud of 3.5-and-above > routers. Of course, the long term solution is to get the whole MBONE > able to accept this kind of routing; the short term solution, however, > is not to advertise this kind of route. Therefore, I will be periodically > posting a list of routes that fall into this category; hopefully, the > people responsible for those networks will reconfigure their routers to > either advertise only a general route or only non-overlapping specific > routes. > > The list follows. I will be posting this list (with a shorter explanation) > periodically. > > Bill > > 36.18/16 is covered by 36/8 > 36.53/16 is covered by 36/8 > 36.56/16 is covered by 36/8 > 36.103/16 is covered by 36/8 > 36.153/16 is covered by 36/8 > 36.224/16 is covered by 36/8 > 128.32.211/24 is covered by 128.32/16 > 128.32.226/24 is covered by 128.32/16 > 128.171.3/24 is covered by 128.171/16 > 128.171.10/24 is covered by 128.171/16 > 128.171.11/24 is covered by 128.171/16 > 128.171.45/24 is covered by 128.171/16 > 128.174.212.0/25 is covered by 128.174/16 > 128.174.240/24 is covered by 128.174/16 > 132.250.88.170/32 is covered by 132.250.88.160/28 > 137.194.2/23 is covered by 137.194/16 > 137.194.34/23 is covered by 137.194/16 > 137.194.98/23 is covered by 137.194/16 > 137.194.160/23 is covered by 137.194/16 > 137.194.224/23 is covered by 137.194/16 > 137.194.230/23 is covered by 137.194/16 > 137.194.232/23 is covered by 137.194/16 > -- --bill
|