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Re: MD5 for TCP/BGP Sessions

  • From: vijay gill
  • Date: Wed Mar 30 18:53:36 2005

Stephen J. Wilcox wrote:
without wishing to repeat what can be googled for.. putting acls on your edge to protect your ebgp sessions wont work for obvious reasons -- to spoof data and disrupt a session you have to spoof the srcip which of course the acl will allow in

This is why you either have a stateful firewall in your router that pushes a dynamic acl down to the linecard (or equivalent forwarding place where the for_us vs through_us decision is made), and filter it there. That makes guessing the correct 5 tuple a bit harder. Obviously GTSM is the closest we have yet to hardening (note I did not use securing) the session.

On average, the stateful filter will cause the attacker to to try 32000 times to find correct 4-tuple. Conversely, attacker resources will need to be on average 32000 times greater to adversely affect a router. The cost of attacking infrastructure has risen, but the cost to defender is minor.

Each configured BGP session already has all the state needed above to populate the filter.


/vijay




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