TTL

[Roy Arends]

On Fri, 9 Feb 2001, Nathan Champion wrote:

> After getting the message about having to put the $TTL value at the top
> of the zone file, I went ahead and put in $TTL 432000 (on the ISC site
> it told us to make it $TTL XXXXXX) on each of my zone files. I thought
> that the number had to be 6 digits, which I later found out to be
> incorrect.
>
> Now that I have made a change to the zone file, does this mean I must
> wait 5 days before other nameservers on the internet come back to reload
> this information?

Putting the $TTL directive in your zonefile means, if you did not specify
a TTL with a RR record, it will use the directive as default.

432000 is indeed 5 days. Cached RR records of your domain at other
nameservers will take 5 days to flush.

> Could someone tell me what the TTL actually specifies
> (I know it means Time To Live, but how  and what does it affect in terms
> of master, slave and caching servers? and how is it different to the SOA
> minimum?)

The TTL is the time to live of the RR.  This field is a 32 bit integer in
units of seconds, an is primarily used by resolvers when they cache RRs.
The TTL describes how long a RR can be cached before it should be
discarded.

Master/slaves are the same to identical to outside resolvers. TTL has
nothing to do with Master/Slaves.

The TTL value in SOA records is primarily used for negative caching. An
authorative Nameserver for your zone will specify this TTL value when it answers
that a RR does not exist.

Regards,

Roy Arends