Re: [nmap-svn] r6963 - nmap-exp/david/nmap-fixed-rate

[Fyodor <fyodor () insecure org>]

On Sat, Mar 22, 2008 at 12:28:31AM +0000, Brandon Enright wrote:
> I look forward to the end-result, sometime sending at N pps is exactly
> what I want Nmap to do.

Instead of offering just a fixed packet send rate (which I think is
what Scanrand and Unicornscan do), I'm starting to think we should
allow you to set a minimum and/or maximum packet send rate.  If you
are trying to speed Nmap up, you would set a minimum rate which would
override Nmap's normal congestion control algorithms if they would
otherwise slow Nmap below that rate.  But this would still allow Nmap
to ramp up to faster rates if you are scanning an unfirewalled
localhost or the like.

On the other hand, you might want to slow Nmap down to avoid IDS
systems or prevent Nmap from going so fast that it might affect other
users of the network.  In this case, you could set the maximum packet
send rate.  If you want a Unicornscan-style fixed packet rate, you
could set the min and max to the same value.  This is similar to how
Nmap handles many other performance variables.

I'm not certain that we need max packet rate option.  Perhaps
--scan-delay is enough, or maybe the max rate option would be a pain
to implement.  But I am definitely warming to the idea of offering a
minimum rate rather than fixed rate.  Or maybe the max scan rate
option would turn out to be more useful than --scan-delay.
--scan-delay is per host, while I imagine that a max packet rate would
cover all hosts being scanned at once by Nmap.  Maybe one could be
used to implement the other.

One advantage to using a minimum rather than fixed packet rate option
is that we could potentially add a minimum rate for timing templates
such as -T4 and -T5.  Though that could lead to trouble when we scan
rate-limited hosts (as is commonly encountered with UDP scan).  So I'm
not sure it is a good idea for -T4.

Cheers,
Fyodor

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