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Re: TCP/BGP vulnerability - easier than you think

  • From: Iljitsch van Beijnum
  • Date: Wed Apr 21 10:08:45 2004

On 21-apr-04, at 15:21, Daniel Roesen wrote:

As you didn't specify where to apply these filters, I guessed on the
edges. I would have never thought that someone would really suggest
to deliberately break RST for valid BGP sessions.
Try me.  :-)  But don't forget the borders, those are more important.

So I believe filtering out all BGP RSTs on all edges is
probably a good idea.

RST and SYN.
I can live with legitimate RSTs as collateral damage, but legitimate SYNs are probably best left alone... Unfortunately, at the receiving end there is no way to determine whether a packet is spoofed, so we must allow all pertinent SYNs through.

But that's still patchwork. Do anti-spoofing filtering
in general, not only mitigating _this_ thread. Don't allow packets
from source IPs of your originated IP spaces enter your network,
Of course. The problem is that this offers no protection against remote spoofers.

ADDITIONALLY to securing the transport via TCP MD5 authentication or
even better with IPSEC.
I'm not recommending this for "small" peers as the crypto DoS risk is worse than what happens when the attack is executed successfully.

Having always two lines of defense is good
security practise, especially if the doors to properly close are
many (edge interfaces).
No disagreement there.