Hello!
I see drastic decrease in russian NTP server count 2 months ago (the same time I started to experience problems) - maybe somebody tries to DDoS russian timeservers, as described here for example. It’s interesting what was the reason. Not only bandwidth is the issue, but packet count too.
pool.ntp.org: Statistics for 46.188.16.150 - are these metrics too high?
I’ll try to decrease netspeed to minimum possible to continue providing time service (I switched from 500 Mbps to 50 Mbps with no effect), but, if enormous traffic continues, I’ll be very sorry to remove my server from the project.
BTW I have one VDS that I can use as NTP server too, but 2 servers of one person cannot serve the whole zone. =(