Caching vs. Replication in DNS

[phn at icke-reklam.ipsec.nu]

Andersen <alibandali at hotmail.com> wrote:
> Hi,

> I don't really understand the relationship between caching and 
> replication in DNS. Isn't replication used very little, you only have a 
> master and slave server typically for each zone?  And the root servers 
> are 16 replicas?

13 ( + some ip's exists in several parts of the globe ) 


> What I really want to understand is where caching is being used. It is 
> said that it takes time before updates are propagated due to caching, 
> where does this apply? If I just want to change the IP address of an 
> existing hostname, shouldn't an update to the corresponding nameserver 
> immediately make the change visible around the globe. Yes.

Or how long would 
> it take?

The problems is that the nameserver You ask might have saved the results
from a prevíous query ( caching). Before asking authorative servers
a nameserver will examine it's cache for an answer, if found it's used.

Every entry in the cache will have a lifetime associated with it,
given by the authorative server, when the data has been stored 
for that time it's discarded ( and new queries will result in 
getching data from authorative servers). The "time-to-live" is called 
TTL in dns jargong.


> What if I want to insert another level, for instance I have d.c.b.a 
> running, I want to create e.d.c.b.a? That would be reflected immediately 
> right?
Unless cached data exists.

> regards,
> Andersen


-- 
Peter Håkanson         
        IPSec  Sverige      ( At Gothenburg Riverside )
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