DNS records change time

John Hascall john at iastate.edu
Mon Feb 6 22:49:17 UTC 2006

> If I will change some DNS records on my external DNS name server Bind 9, how
> long it will take to propagate around the world, in other words when all
> clients will be able to connect to these hosts whose IPs I changed from
> outside? Thanks a lot, Calin

Worst case?  Forever.
Normal case: (refresh-time or ~0) + TTL

In a fairly typical setup you would update your master nameserver.
If you are using "notify" it would tell any secondary nameservers "real soon"
to pull a new copy of the data from the master.  If notify was not in use,
then the secondary nameservers poll the master at an interval specified
in the SOA record for the zone.  However, external users are not using
either your master or secondary nameservers directly.  If they contact
a nameservers which has just cached a previous query for your data then
they will have to wait for TTL seconds (specified in the zone file either
globally or for each record) for fresh data.  HOWEVER, there are a whole
lot of applications out there that do nameserver lookups exactly once
and then never try again -- remembering old data far past its staleness.


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