North American Network Operators Group

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That pesky AS path corruption bug...

  • From: Blaine Christian
  • Date: Tue May 23 12:38:15 2000

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.