Re: Rate limit branch for anyone interested

[João Medeiros <ignotus21 () gmail com>]

Hi David.

    I have download the branch but I did not see any data related to
the problem. Did you have sample sets (the big the better) of RTT's
for the case of rate-limit and network congestion? I can perform some
time-series analysis in this kind of data and see if this can help in
rate-limit detection.

Att, João Medeiros.

On Mon, Feb 9, 2009 at 2:30 PM, David Fifield <david () bamsoftware com> wrote:
> Hello,
>
> When I was working in the nmap-perf branch, one of the things I was not
> able to find a solution for was rate limit detection:
>
> http://seclists.org/nmap-dev/2009/q1/0049.html
>
> One of the simple changes that looked promising but wasn't merged was
> controlling the sending rate based on a maximum send rate, not a fixed
> delay between probes. Brandon at least said he would like to test out
> this idea. So I made a branch with just that change:
>
>        svn co --username guest --password "" svn://svn.insecure.org/nmap-exp/david/nmap-rate-limit
>
> Instead of waiting, say, 5 ms between probes, the code will enforce a
> maximum rate of 200 probes per second. The first time the rate is
> decreased it will become half of the current sending rate. After that it
> is halved when necessary. The only exception to this is UDP scans, in
> which the first rate drop goes directly to 20 probes per second. The
> benefit of this approach is more granularity in limiting the rate. If
> you hit a rate limit at 5000 packets per second you will drop down to
> 2500, not 250 which is what you would get with a 5 ms delay.
>
> I don't have any immediate plans for better rate limit detection so I'm
> not going to be working in the branch. Any committers may feel free to
> make changes there. This is just an experiment to see how rate limit
> detection may be improved. If you have any good ideas or testing
> results, send them in.
>
> David Fifield
>
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