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Re: Nessus experience
From: Barry Fitzgerald <bkfsec () sdf lonestar org>
Date: Wed, 13 Oct 2004 13:47:13 -0400

If you're looking for optimized testing, you might want to try the following:

Allow Nessus to do your port scan and turn on optimized scanning. This will tell nessus to not send attacks to services that it can't verify as being up. If port 80 isn't open on the system, do you really want to test attacks against port 80? This depends on your environment. Sometimes people set ports to not respond to sweeps and in those cases, setting nessus to optimized scanning will generate false negatives, but if you've got a standard network, this can cut down on the time it takes to scan, often dramatically.

Also, try playing with the host/connection thresholds. If you're set to only make 5 concurrent contections to 5 hosts, you may be underutilizing your processor/memory. On the other hand, overutilization of processor/memory can also slow the scan. My suggestion: find a test subset that will take about 30 minutes with the default settings. Then, monitor your system resources and run the scan. If your CPU is running at 100% constantly, you're overutilized. If you never get higher than 50%, you might want to increase the number of concurrent connections that nessus can make. Another issue is that if you're overutilizing your hardware, scans may get hung. If they do, results may be lost. It's happened to me in the past, and it's fairly transparent (meaning you may not even know).

Playing with these settings will give you the options you need to cut the time it takes to do the scan.


Mr. Rufus Faloofus wrote:

Greetings, full-disclosure!

From time to time I find myself needing to estimate the time it takes
to run Nessus against various network ranges. For some reason, it always seems to take longer than I expect, and I'm wondering if:

 1: I am doing something wrong (this is always a possibility)
2: Nessus has been getting slower over time
Specifically, with two laptops (each with 2GHz processor, and upwards
of 600MB RAM), I recently tried to scan a range of two class C-size
networks, to which I was directly connected via Ethernet. I had already done full nmaps of the hosts (this took about an hour), so I was not running nmap from within Nessus. I found that after over three hours, I had only been able to complete tests on 90-something hosts.

This strikes me as unreasonably slow, for bulk automated testing, so
first, I'd like to ask if these performance metrics are in line with
others' experiences.  I'd also solicit any hints people might have
to offer on how they optimize performance, any rules of thumb anyone
might care to share about estimating times for Nessus runs.

Thanks, in advance, to all helpful replies.


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