spare swamp space?

Steven nash snash at
Wed Aug 19 22:34:22 UTC 1998

I too have a similar setup for my network since we as well
run an Efnet irc server, however, CAR really won't do much if
you set it up inside your own network.  The smurf will still enter
and saturate your pipes.  The best thing to do is to have your upstreams
setup rate-limits on their side of your pipes so the feed coming into your
router is limited before it even hits your router.

Here is a question though,  what kind of CPU drain does rate-limiting cause
on the CPU of the routers running it? I flipped through CCO and couldn't find
any information regarding this...

Alex Bligh wrote:

> > servers, one for the outside world and one for our customers only.  The
> > public server will be connected via a T1 to a smurf tracing friendly
> > transit provider for external connectivity.  This T1 will be used for this
> OK, tell me where this falls down. Set up two IP addresses for your
> IRC server on the same machine. On the router upstream from the machine,
> allow only your customers to connect to one IP address, and anyone else
> to connect to the other IP. Now go to your border routers, enable CEF
> and configure something like:
> ! impose limits
> access-list 100 permit ip any host
> access-list 100 permit ip any host
> access-list 101 deny ip any host
> ! i/f config for borders
> interface myinterface
>  ip access-group 101 in
>  rate-limit input access-group 102 512000 512000 512000 conform-action transmit exceed-action drop
> Effectively this means that if your public IP gets smurfed, it's b/w
> usage internally on your network is limited. If your private IP gets
> smurfed, it all gets dropped (thinking about it if you made exceptions
> for IRC peering you could do the whole thing on one IP if your customers
> never use border router i/fs).
> If you are paying per bit, you'll still pay for smurfs, but they'll have
> to be 45Mb/s in size to cause any real damage. You'll probably find BGP
> flapping up and down as your T1 saturates is more of a problem.
> --
> Alex Bligh
> GX Networks (formerly Xara Networks)

                             -(@ @)-
Steven Nash                            uin: 9021398
Cisco Certified Design Specialist       em: snash at
Network Engineer
Lightning Internet Services LLC

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