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feasability of stopping smurfs with cisco's CAR
From: Marko Bukvic <marko () pfmc net>
Date: Wed, 29 Apr 1998 17:29:17 -0400 (EDT)


cisco's new Committed Access Rate feature lets you do real QoS rate limiting (as opposed to traffic shaping) with 
access lists.
CAR could be implemented on either ingress/egress interfaces to limit bandwidth usage by ICMP to something safe like 
This would prevent an incoming ICMP flood from consuming your aggregation links, while it still might inconvenience a 
T1 customer.
If placed on the outgoing access-list it can prevent your network from originating unfriendly amounts of ICMP.
CAR can either discard or decrease the priority of the offending traffic.

A couple of questions:

I am unfamiliar with what tier 1 providers use as aggregation routers(routers their T3+ customers connect to). Due to 
potentially CPU intensive nature (when dealing with access-list based traffic limiting compared to address based 
limiting), would
an "ICMP permit with exceed-action drop" filter constitute an unacceptable load on the CPU and memory of these routers?

If I only had 1 multi-megabit transit pipe, is it reasonable(in the future) of me to ask/require my upstream provider 
to protect
my pipe from being wasted by large amounts of ICMP? If I only put it on my side, the pipe still gets wasted. 

Are there any other vendors who offer a similar feature without the use of ATM? 

Thank you.


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  • feasability of stopping smurfs with cisco's CAR Marko Bukvic (Apr 29)
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