North American Network Operators Group|
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Re: That pesky AS path corruption bug...
looking for some more details about what the malformed aspath looks like. I took a router in my lab and started sending it some bogus as_paths. It seemed to accept everything I would send. Here is one aspath which doesn't include the remote-as and loops all over the place. It was happily accepted. BGP routing table entry for 10.1.2.3/32, version 414648 Paths: (1 available, best #1) Advertised to non peer-group peers: 10.254.254.1 1 2 3 4 3 2 1 2 3 4 3 2 126.96.36.199 from 188.8.131.52 (0.0.0.120) Origin EGP, localpref 100, valid, external, best Dampinfo: penalty 980, flapped 2 times in 00:00:57 pete On Tue, May 23, 2000 at 12:40:00PM -0400, Blaine Christian wrote: > > Hello all, > > After observing a recent issue regarding a router that sent corrupted AS > path (all names are witheld to protect the guilty). I took a look at the > path information that was being received and have a possible solution. > Since the corrupted AS-path does not include the AS that the route is > coming from (at least in the corruption that I saw) it seems to me that a > simple solution for all is to filter on AS i.e. only allow routes that > have the AS of your EBGP neighbor prepended to them. I realize this does > not cover all cases of wacky AS corruption problems but it may fix some of > them. I would suggest that those of you running mixed vendor EBGP (again > names witheld) should implement a version of this strategy for your own > self protection. It can certainly be implemented as part of an overall > customer access functionality. This may be obvious to some of you but I > do not believe that everyone is at this level yet. > > Of course the tirade part of this email is for all vendors involved in > this travesty. If you do not understand or dislike a route that you have > received don't just CRASH. Anyone ever thought of checking the route and > throwing it out with an error message if you don't like it? I, of course, > have heard and seen that several vendors have fixed this in the more > recent releases. This type of bug is something that everyone who writes > software has to deal with. If you raise an exception for bad input it is > bad form to crash or reset your application. > > BTW, I am sure all have heard this argument before. I just wanted to get > this topic renewed. > > Regards, > > Blaine > >