[60909] in North American Network Operators' Group
Re: Why do you use Netflow
daemon@ATHENA.MIT.EDU (Jack Bates)
Tue Aug 19 17:26:38 2003
Date: Tue, 19 Aug 2003 16:23:14 -0500
From: Jack Bates <jbates@brightok.net>
To: Jason Frisvold <friz@corp.ptd.net>
Cc: lance_tatman@agilent.com, nanog@merit.edu
In-Reply-To: <1061325167.3109.107.camel@dhcp9-52.noc.corp.ptd.net>
Errors-To: owner-nanog-outgoing@merit.edu
Jason Frisvold wrote:
>
> We used ip accounting the other night to detect and disable a large
> number of worm infected users that took out the router completely.. I
> think net flow would have been too much overhead at the time... Once we
> were down to a more manageable number of infected users, we used netflow
> to pinpoint them immediately... (Note, we don't leave netflow on all
> the time)
One method for limiting netflow accounting to manageable ammounts is to
access-list the port involved. This is why I did institute 135 blocking.
This flags the flow as inactive which only holds it for like 15 seconds
on default. Of course, this still may not be enough for some routers. I
just happen to have prepared for this actual event due to constant DDOS
attacks about nine months ago (reverse view, change rule matches).
-Jack
