SYN spoofing and Ciscos crashing

jlewis at jlewis at
Wed Jul 28 20:42:17 UTC 1999

On Wed, 28 Jul 1999, bryan s. blank wrote:

> % 	ip verify unicast reverse-path
> % 
> % and according to Paul Ferguson (co-author of RFC 2267) it's in use by
> % many ISPs. Apparently this is very-low overhead. Paul has also indicated
> % the use of extended access lists on Cisco routers is very low overhead,
> % especially on routers using distributed express forwarding.
> 	while i hate to question mr. ferguson, it's my understanding
> 	that many isps have found this feature to be unusable due to
> 	network design.

I just took out a 7206 by applying ip verify unicast reverse-path to a T3
link on a PA2T3 and attempting to spoof packets from the POP on the other
end of that T3.

The 7206 is running c7200-inu-mz.111-25.CC.  Fortunately, it rebooted
after it crashed.

System restarted by bus error at PC 0x605F88CC, address 0x10024 at
20:29:49 UTC Wed Jul 28 1999

This router had been up over 8 weeks without a crash (ever since Cisco
replaced the previous 7206 in this POP that was either posessed or a
lemon).  The memory is Cisco memory.  All the parts came directly from

Is this known to be unstable in 111-25.CC?  Is it known to be stable in
some other release that supports the PAT3, PA2T3, and PA-MCT3?

----don't waste your cpu, crack team enzo---
 Jon Lewis *jlewis at*|  Spammers will be winnuked or 
 System Administrator        |  nestea'd...whatever it takes
 Atlantic Net                |  to get the job done.
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