pool.ntp.org DNS system

Status

We've deployed the new DNS server on 4 out of the 5 pool.ntp.org name servers (September 17 2007). We're still looking for a fifth host.

How it used to work

Every 15-20 minutes a script would generate a new data file for the pool.ntp.org domain with rotated IPs for all the different sub-domains. Being in one of the busy sub-zones for that period would then give a HUGE influx of traffic. By the time we changed (September 2007) it was enough traffic to knock out lower bandwidth servers (typically on ADSL connections).

How it works now

Every 15 minutes the pool system generates a data file for pgeodns which is synced to all the DNS servers within a few minutes. Each pool zone ("global", "europe", "us", etc) has its servers divided up into the base domain and the 0, 1, 2, 3 zones (2.dk.pool.ntp.org for example).

Load distribution

On each request the nameserver picks up to 5 random servers from that zone, weighted by the configured netspeed of each server. This greatly evens out the traffic for each server through the day compared to the old system. It also makes sure each server get an amount of traffic proportional to the configured bandwidth.

Geographical targeting

As a special-case, on requests to the "base domain" (pool.ntp.org) the nameserver will try to figure out which country the request is from and then reply with servers from that country or continent. This helps keep traffic "close" which typically will make the NTP performance slightly better but more importantly helps server operators in countries that have expensive "international traffic" to mostly get traffic from their own country.

DNS Experiments

DNS Experiments and development...