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Re: That pesky AS path corruption bug...

  • From: Blaine Christian
  • Date: Tue May 23 14:51:34 2000


I see that I have elicited some interesting responses <insert evil cackle
here>.  I agree with removing cruftery (thanks for point out something
that is quite valid Vijay).

Lets talk about a couple things.

1. How can everyone protect themselves RIGHT NOW.

2. A couple vendors that I know of decide to either restart routing
entirely or in the least restart more than 1 BGP session.  This behaviour
should be considered BAD.  This behaviour generally can not be corrected
quickly because new code releases take time.

3. The vendor who starts the nastiness seems to be the only one who can't
quite seem to grasp that the sort of behaviour that engenders corrupt AS
paths is BAD.

So, in light of the above statements.  Would it be safe to say that
safeguarding the Internet is our first duty and beating up on vendors is
our second?  Please note that I enjoy abusing vendors but they tend to get
worn out <grin>.  Note; I will caveat all statements by saying that some
vendors claim to have fixed this in later versions of code.
  
I concurr regarding the route-servers.  However, just about everything
else is free game.  Who besides a route-server would want to prepend an AS
besides their own.  Who wants to allow customers and perhaps even peers to
send routes prepending an AS that is not their own?

I would side with Vijay on the withdrawl issue.  Since the route update
that was received was malformed we should treat all announcements from the
EBGP peer with extreme suspicion.  Reseting the BGP session (perhaps
tearing it down and leaving it down until a human intervenes) is probably
the best idea.  A note of interest for the events I have seen is that you
do not necessarily have the BGP session you expect torn down.  Wouldn't 
you expect to tear down your EBGP session with the person who sent the
weirdness?  I can assure you that several vendors do not do things this
way.  In fact the vendors I am thinking of quite obviously propagate the
bad route AND THEN decide to reset their BGP on a larger scale<grrrr>.  

Just some additional thoughts...

Regards,

Blaine



On Tue, 23 May 2000, Vadim Antonov wrote:

> Peter T. Whiting <pwhiting@fury.ittc.ukans.edu> wrote:
> 
> > As I understand the current spec, a router, upon receiving a malformed
> > as_path is supposed to respond with a notification message (3.11) and
> > drop the BGP connection.  Your suggestion to maintain the connection
> > and drop the announcement is a practical one, but doesn't put as much
> > pressure on vendors to fix the bug.
> 
> This is not only practical, but, in fact, the only sane way to do things.
> Dropping BGP session causes withdrawal of hundreds or thousands of
> acceptable routes.  When the BGP session is reestablished, these routes
> will be acquired again, causing a wave of announcements.  When the
> invalid route shows up, the cycle is repeated.
> 
> What a perfect way to kill the Internet :)
> 
> --vadim
> 






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