2015-02-18 - News - Tony Finch
DNS updates now occur every hour at 53 minutes past the hour. (There is a mnemonic for the new timing of DNS updates: 53 is the UDP and TCP port number used by the DNS.) Previously, the interval between DNS update runs was four hours.
The update job takes a minute or two to run, after which changes are immediately visible on our public authoritative DNS servers, and on our central recursive servers 131.111.8.42 and 131.111.12.20.
We have also reduced the TTL of our DNS records from 24 hours to 1 hour. (The time-to-live is the maximum time old data will remain in DNS caches.) This shorter TTL means that users of other recursive DNS servers around the University and elsewhere will observe DNS changes within 2 hours of changes to the IP Register database.
There are two other DNS timing parameters which were reduced at the time of the new DNS server rollout.
The TTL for negative answers (in response to queries for data that is not present in the DNS) has been reduced from 4 hours to 1 hour. This can make new entries in the DNS available faster.
Finally, we have reduced the zone refresh timer from 4 hours to 30 minutes. This means that unofficial "stealth secondary" nameservers will fetch DNS updates within 90 minutes of a change being made to the IP Register database. Previously the delay could be up to 8 hours.