Re: DOS?

[Iljitsch van Beijnum <iljitsch () muada com>]

On Sat, 25 Jan 2003, Rob Thomas wrote:

> ] access-list 150 deny udp any any eq 1434 log-input

> Be _very_ careful about enabling such logging.  Some of the worm flows
> have filled GigE pipes.  I doubt you really want to log that; Netflow
> is a better option in this case.  Too much logging will raise the CPU
> utilization to the point of creating a DoS on the router.

As a general rule, yes. But:

" Access list logging does not show every packet that matches an entry.
Logging is rate-limited to avoid CPU overload. What logging shows you is
a reasonably representative sample, but not a complete packet trace.
Remember that there are packets you're not seeing.

Access lists and logging have a performance impact, but not a large one.
Be careful on routers running at more than about 80 percent CPU load, or
when applying access lists to very high-speed interfaces. "

( http://www.cisco.com/warp/public/707/22.html )

There doesn't seem to be a noticable impact on CPU usage for a C12000
GigE linecard. Can you do Netflow rather than CEF on such a beast
without a performance penalty?