Re: nping: bitrate bug

[David Fifield <david () bamsoftware com>]

On Mon, Oct 08, 2012 at 04:05:41PM +0600, Мамаев Антон Владимирович wrote:
> Good day.
>
> I use nping for generate traffic with given rate. I need send
> 12mbit/s traffic ipv6:
>
> nping -6 XXXX:XXXX::2 -e eth3.3352 --tcp -p 5032 -HN --data-len 1358
> --rate 1104 -c 662739
>
> Send 662739 packet with payload 1358 byte and rate 1104 pps: 1358
> byte * 8 bit * 1104 pps ~ 12mbit/s
>
> However, i see rate much more 12 mbit/s:
>
> avm@avm:~# nping -6 XXXX:XXXX::2 -e eth3.3352 --tcp -p 5032 -HN
> --data-len 1358 --rate 1104 -c 662739
>
> Starting Nping 0.6.01 ( http://nmap.org/nping ) at 2012-10-08 15:43 YEKT
> ^C
> Max rtt: N/A | Min rtt: N/A | Avg rtt: N/A
> Raw packets sent: 107805 (148.555MB) | Rcvd: 0 (0B) | Lost: 107805 (100.00%)
> Tx time: 2.43267s | Tx bytes/s: 61066690.84 | Tx pkts/s: 44315.45
> Rx time: 2.43267s | Rx bytes/s: 0.00 | Rx pkts/s: 0.00
> Nping done: 1 IP address pinged in 2.43 seconds
>
> I see bitrate ~ 488 mbit/s!

Thank you for making this report. I think the problem is that the --rate
really only controls the inter-packet delay, and the dealy only has
millisecond precision. This code in ArgParser.cc evaluates to a delay of 0:

                /* Compute delay from rate: delay= 1000ms/rate*/
                aux32 = 1000 / aux32;
                o.setDelay(aux32);

I don't think there is an easy fix for this. Nmap has similar --min-rate
and --max-rate options that use a more sophisticated scheduler that
would obey a rate such as 1104. Nping could use something like it.

Luis: I have some old notes from the Nmap implementation at
http://www.bamsoftware.com/wiki/Nmap/FixedRate (section "Some sample
stable rate-fixing code").

David Fifield
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