Bind updating serial number for zones
Perhaps it was too busy handling other requests just then.The Retry Interval simply tells the secondary name server to wait for a period of time before trying again.It uses a special format where the "@" character is replaced with a "." (period) character and the email address ends with a period. Serial number of the zone file that is incremented each time a change is made.
Changes to the domain's resource records are made to the primary name server's zone file and are then propagated to the secondary name servers when they check for updates.Time in seconds that a secondary name server should wait before trying to contact the primary name server again after a failed attempt to check for a zone file update.There are all kinds of reasons why a zone file update check could fail, and not all of them mean that there is something wrong with the primary name server.Any change requires time before it will be seen everywhere on the Internet.But what many don't understand is that how fast or slow these updates are propagated is actually under their direct control through the SOA record. Although you have control over the speed that updates are propagated throughtout the Internet, they will never, ever, be instantenous! Your only control is over how short or long this delay will be.
Now if you control all of the authorative DNS servers for a domain (that is, the DNS servers that actually host the zone files and can answers queries for the domain as opposed to having to ask another DNS server), then with the exception of how long negative responses should be cached, these settings may not seem as important since you can force the secondary servers to update whenever needed.