[time] Anecdotal evidence that NTP blocking works

[Chris Davies - NTP Manager]

Joel Reicher wrote:
> Although it's just anecdotal, it looks like I now have abusers that my
> script had almost completely gotten rid of, so just dropping packets
> mostly works.

Those users may have simply reset their devices and consequently ended up with 
different servers from the pool.

> The point at which it doesn't work is what I emailed about a couple
> of weeks ago; there seem to be some clients that fix a polling interval
> of 16s if the server is unreachable, and continue to poll until it is.
> If such clients are not blocked, their polling interval increases as soon
> as they can reach the server again.

I've noticed that sending ICMP Port Unreachable seems to shut up certain 
clients. (See the recent Dave Morgan thread,"update on my auto-firewall script" 
starting  with <3js8q0tfrmat45ns3vrpjc0je3vtd70vmu at 4ax.com>.) Different people 
may get different results.

Regards,
Chris