DNS records change time

Kevin Darcy kcd at daimlerchrysler.com
Mon Feb 6 22:36:12 UTC 2006

Tester wrote:

>Hi there,
>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
Barring any connectivity issues, it could take as long as SOA.REFRESH 
for a zone to propagate from a master to a slave. Once the change is on 
all of the slaves, it is visible to caching resolvers once their 
existing cache entries for the relevant record(s) time out, which could 
take as long as an additional TTL seconds, where TTL is the TTL value 
set on the record(s) in quuestion. So, if you know you're going to 
change that/those record(s), and you want the change(s) to be visible 
quickly, then you could lower the TTL value(s) prior to the change. Just 
remember to change them back, since it's anti-social to have low TTLs 
(e.g. on the order of minutes or seconds) without a compelling reason.

                                                            - Kevin

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