Refreshing cache in other DNS servers

Matus UHLAR - fantomas uhlar at
Tue Oct 15 16:10:25 UTC 2013

On 15.10.13 22:53, babu dheen wrote:
>To: Matus UHLAR - fantomas <uhlar at>, "bind-users at"
> <bind-users at>
>Hi Matus,

you don't need to send me private copies - we are using a mailing list for
a purpose... thank you.

> If I change the TTL value on the particular zone after modifying a  record

it's already late. you must change the TTL _before_ modifying the record.

>My Redhat bind Caching DNS server cache would be refreshed after 300

The cached response will expire "TTL" seconds after it was fetched.

All caching servers should behave like this as this is how the DNS protocol
was defined. Also, they should always provide the current TTL as they
remember it - it should decrease by one each second.

> So my backend windows DNS server can get the newly modified record from
>DNS only when its contacting Redhat DNS server for the newly added date
>once Windows DNS cache is refreshed?

If your windows DNS fetches data from your caching BIND on redhat server,
the windows DNS and BIND cache should in fact have the same TTL.


I think you are mistaken in what "caching" means. If your BIND on redhat
server contains a zone definition (you said you modify records there), then
the BIND is _not_ caching but authoritative. In such case, it always
provides the TTL as defined in the zone file. 

That is why you must lower the TTL long enough prior making changes.  Thus,
If you have TTL od 43200 (12 hours), you must lower TTL at least 12 hours
before you are going to change the record itself.

Matus UHLAR - fantomas, uhlar at ;
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