DNS records change time

Mark Andrews Mark_Andrews at isc.org
Mon Feb 6 22:51:07 UTC 2006

> 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

	You have asked the wrong question.  DNS information doesn't
	"propagate around the world".

	The new information becomes available immediately.   The
	slaves should transfer the new content within the SOA refresh
	interval.  If NOTIFY is in effect, almost immediately.

	The question you wanted to ask is how long will the caches
	hold the old information and the answer to that is "as long
	as you have told them to hold the information".

	For positive answers, for as long as the TTL on the RRset.
	For negative answers, for as long as the SOA minimum.

	These are upper bounds.  Caches may also put their own upper
	bounds on how long they will keep responses.  They may also
	throw away a response early.

	As to which one of the above applies it depends on whether you
	are changing a existing RRset (TTL on the RRset) or adding a
	new RRset (SOA minimum).

	Assuming everything is working.

		SOA refresh + (TTL on changed RRset or SOA minimum)

Mark Andrews, ISC
1 Seymour St., Dundas Valley, NSW 2117, Australia
PHONE: +61 2 9871 4742                 INTERNET: Mark_Andrews at isc.org

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