NAP/ISP Saturation WAS: Re: Exchanges that matter...

Alan Hannan hannan at
Fri Dec 20 22:51:25 UTC 1996

  why even do that?  i'm not sure i want you triggering security
  mechanisms on my routers.  Especially with the overhead
  implications, though that is the thread we're currently in [may it
  die soon].

  building an acl that allows packets matching those you're
  interested in, and applying it to 'debug ip packet ACL detail'
  is fairly simple.

  just sit there doing 'clear ip cache A.B.C.D W.X.Y.Z'.  Find 
  the next hop it's coming from, trace it along, mail your 
  friendly peer or transit provider, or mail your friendly hacker's

  granted, this is limited to the domain of routers you control, 
  but it's pretty effective for finding out where the syn attack is
  coming from.

  this assumes the people who are dumb enough to keep syn-ing 
  continue to be stupid enough to use originating source addresses 


] > 3) Deal with it legally.  This is what the telco's do.  It implies that we
] > would need real mechanisms for tracking down offenders.
] 	Personally, I'd like to see a protocol that allows you to ask a 
] router to which you were directly connected to stamp an interface ID on 
] all incoming packets bound for a particular network. You could then trace 
] back router by router, interface by interface, where the packets were 
] entering a block of cooperating providers.
] 	Thus if I saw an incoming flood of SYN packets or ICMP echoes 
] with forged origin addresses, I could ask my router to ask all its direct 
] peers to begin stamping interface numbers (and/or interface IPs) on the 
] packets they send to me. My router would eat those numbers/IPs so traffic 
] would appear unaffected.
] 	Then my tracing tool would know which interface the packets were 
] coming in on and could ask that router to do the same thing (on a 
] hop-by-hop basis for security reasons). Thus I could track it back to a 
] specific enough interface path that perhaps an automated method to 
] install a filter would be sufficient.
] 	This stuff needs a lot of work, but might be a direction that 
] would both facilitate emergency filtering and effective tracing for IP 
] packets with forged origin addresses -- assuming the packets have enough 
] in common to allow them to be detected (all pings, or heavy load, or all 
] to same destination IP).
] 	David Schwartz

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