[smokeping-users] FPing alternative

Niko Tyni ntyni+smokeping-users at mappi.helsinki.fi
Sat May 17 21:03:19 CEST 2008

On Sat, May 17, 2008 at 02:20:04PM -0400, Mike Lerley wrote:

> Fair enough; however, I have turned on and off all options I can find on the 
> router related to that sort of thing and nothing changes.  More importantly, 
> I can do this:
> root at george:~# ping -f tobeys.gotdns.com
> PING tobeys.gotdns.com ( 56(84) bytes of data.
> .......................................
> --- tobeys.gotdns.com ping statistics ---
> 3609 packets transmitted, 3570 received, 1% packet loss, time 47185ms
> rtt min/avg/max/mdev = 23.229/31.162/72.274/7.039 ms, pipe 6, ipg/ewma 
> 13.078/27.893 ms
> Clearly, there is no packet rate limiting in effect here...

It's most probably looking at the ICMP sequence number.  While the
'regular ping' increments the sequence number for each ping, fping
apparently uses is as an index to the hosts it's pinging. So the first
host gets sequence number 0 for all pings, the second one gets 1 etc.

The device probably considers the unchanging sequence number an attack
and stops responding. 

It should be quite easy to patch fping to store the information in the
payload instead and increase the sequence number like the rest of the
world does. No, no patch at least yet :)


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