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Re: Cisco filter question

  • From: Paul A. Bradford
  • Date: Fri Aug 22 13:13:45 2003

Geo,
   Not sure if I want to answer. is this OT for NANOG?  :)

   the key is:

IP: Total Length = 92 (0x5C)

normal ICMP packets are not 92 bytes in length.... our friend Nachi does
use 92 byte packets.

BTW: good luck trying the route-map on 2948G-L3s...  ;)

Thanks,
Paul


On Fri, 2003-08-22 at 12:55, Jack Bates wrote:
> Scott McGrath wrote:
> 
> > 
> > Geo,
> > 
> > Look at your set interface Null0 command the rest is correct
> > you want to set the next hop to be Null0.  How to do this is left as an 
> > exercise for the reader.
> > 
> 
> Interface Null0 works fine. Here's a quick check.
> 
> Inbound (from peers) policy matches
> route-map nachi-worm, permit, sequence 10
>    Match clauses:
>      ip address (access-lists): 199
>      length 92 92
>    Set clauses:
>      interface Null0
>    Policy routing matches: 10921 packets, 1048416 bytes
> 
> Outbound (to internal network) accesslist matches
> Extended IP access list 181
>      deny tcp any any eq 135 (1994 matches)
>      permit icmp any any echo (757 matches)
>      permit icmp any any echo-reply (381 matches)
>      permit ip any any (381370 matches)
> 
> I cleared 181 first, then cleared route-map counters. I then checked 
> route-map counters first before checking access-list counters. This 
> means the access-list has more time to accrue maches yet it is 
> considerably smaller. The checks were a matter of seconds. I'd say the 
> policy is working. The echo/echo-reply could easily be everyday pings 
> which are up abit due to various networks having performance issues.
> 
> IOS Versioning can sometimes have issues. There's also the question of 
> if the packet came in the inbound interface that had the policy applied.
> 
> -Jack
-- 
Paul A Bradford
Senior Network Engineer
Adelphia Cable Communications
814-274-1353






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