: ==>Could traffic shaping, or similar QoS configurations, be used to solve
: ==>such issues in a more general way?
:
[...]
: It has information on using Cisco's Committed Access Rate (CAR) feature
: to rate-limit traffic such as ICMP echo/echo-reply and TCP SYNs.Thanks, everyone, for your responses. It seems that lots of us agree
that CAR sounds like a wonderful mechanism for taming smurf-like
attacks. (Thanks, Cisco and others who have provided it.)So isn't this the solution(**) to smurfing that we should be lobbying for?
Consider: Using CAR to limit ICMP to a statistically normal range on
all links has these features:
* It can be implemented from the core out
* It must be implemented by clueful network operators (because they
run the core)
* It must be implemented on a relatively small handful of
rigorously-maintained routers
Implementing it on the core has some limitations. CAR works on a per
protocol basis - not on a per flow basis. This means that someone with an
OC-3 to some NAP might want to limit ICMP to 500kb/sec or some other
reasonable number. What you want is not only an upper limit but a 8kb/sec
limit on per flow or some other reasonable number. You also want a
guarantee on certain IP addresses to get through and not be limited by CAR.
When the Smurf is happening, you don't want your NOC pings and traceroutes
dropped because of some CAR limit being exceeded. So you need to create a
careful policy as to what gets bypassed by CAR limits and what gets shaped
by CAR limits.
-Hank