How does DNS replication work?

[Brad Knowles]

At 7:30 AM -0700 8/7/01, Christopher Dillon wrote:

>  My question is, do all the servers agree at one time to start using a
>  replicated record?

	Nope.

>                      Surely, a number of servers don't do bursty
>  transfers and use whatever they have ...

	The secondary nameserver(s) check the SOA serial number of the 
primary, and if they notice a difference, then they schedule a zone 
transfer and get a copy of the updated zone.  However, their timing 
of when they do this isn't something you can really control directly.

	You can indirectly influence this process by reducing the refresh 
(how often the secondaries check) and retry (how long they'll wait to 
retry a check, if the previous attempt failed) intervals, but you 
don't want to reduce them too much.


	Modern versions of BIND will have the primary send out a NOTIFY 
signal to each of the secondaries (and the other IP addresses you 
list in the "also-notify" clause), which will cause the secondaries 
to schedule a check in the very near future, but that is the limit of 
the control you and your primary nameserver can have over the process.

>  Let's say that one server somewhere DOES get replicated to, could I do
>  a dig lookup on that server and be successful?

	Yes, you should be able to do so.

-- 
Brad Knowles, <brad.knowles at skynet.be>

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