Re: nmap udp scan takes too long

[Fyodor <fyodor () insecure org>]

On Thu, Jul 05, 2012 at 08:55:02AM +0200, pentester wrote:
> I agree that nmap is a cool tool. It just ain't the right tool to do
> a udp scan. The reason is that it waits for a response, if no
> response, then it retries a couple of times. There is no need
> to.

Retransmissions are important for reliable results, because packet
loss and response rate limiting are regular occurrences on networks.
But if you really want Nmap to disable retransmissions, specify
"--max-retries 0".

> Another scanner solves this issue. unicornscan typically scans al
> 64k ports in 3 minutes and 45 seconds when you use a scan rate of 300
> packets per seconds

300 packets per second won't help if the target host rate limits ICMP
port unreachable responses to one per second.  That is very common on
Linux and other systems.  So 299 of your 300 packets per second are
wasted and--even worse--lead to inaccurate results.  Unicornscan won't
catch this because, as you note, it doesn't do any sort
retransmissions or congestion control.

But if that is what you really want, Nmap lets you do it too.  Specify
"--min-rate 300" for 300 packets per second.  Nmap's performance
options are all documented at:

http://nmap.org/book/man-performance.html

I'm also happy to report that we released Nmap 6 in May, with hundreds
of improvements as described at:

http://nmap.org/6

> unicornscan beats nmap as it comes to udp scanning. It's just a
> matter of using the right tools for the job.

Suit yourself.  Their latest was in 2007 and you can download it from
http://www.unicornscan.org/

Cheers,
Fyodor

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