Effects of traffic shaping ICMP (&c.)

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1

Howdy,

When our network is being smurfed, we can call our ISPs and have them
setup an access list to block ICMP. That fixes the problem, but it
creates another (obvious) problem.

Could traffic shaping, or similar QoS configurations, be used to solve
such issues in a more general way? For example, if my source of packet
flooding is ICMP, then I'd like to be able to dedicate as much as 1/10th
(e.g.) of the bandwidth of each link to ICMP. That's plenty of ICMP, but
it's not so much that an attack using ICMP would be effective.

My question, stated briefly, is this: can you solve generic
homogenous-packet-flood problems with QoS and/or traffic shaping (if the
two can be truly distinguished), in general? If so, are current routers
capable of doing it? What would be the effect of doing so on dialup
links and backbones?

2

At the last NANOG, there was a presentation about Cisco's CAR and how
@Home was using it to limit ICMP and detect unusual ICMP activity. Well,
that was part of the talk, at least.

http://www.nanog.org/mtg-9811/ppt/witt/index.htm : presentation slides
http://www.nanog.org/mtg-9811/cartalk.ram : presentation in RealVideo

Pete.

3

==>Could traffic shaping, or similar QoS configurations, be used to solve
==>such issues in a more general way? For example, if my source of packet
==>flooding is ICMP, then I'd like to be able to dedicate as much as 1/10th
==>(e.g.) of the bandwidth of each link to ICMP. That's plenty of ICMP, but
==>it's not so much that an attack using ICMP would be effective.

Sure.

Check out my Smurf paper at http://www.quadrunner.com/~chuegen/smurf.html

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.

/cah

4

I think what is being asked is not how to rate limit what goes thru the
router, but rather to affect rate limitations on the incoming stream.
TCP can be rate limited upstream by playing with TCP window size and ACKs
as some of the bandwidth manager products do (Packeteer, Xedia, Elron to
name just a few). Unfortunately, there is nothing you can do to UDP or
ICMP flows coming your way other than rate limit them as they go thru your
box. You will still be hit by Smurfs and their ilk and they will still
eat up your bandwidth.

-Hank

5

I am not sure about traffic-shaping because this mechanism looks like an
evil's device, but it's good place to use CAR alghoritm for this.