Multiple default records

[John Wobus]

The DNS has nothing to do with whether there is
actually anything at the address.  It's just a database
that (in this case) looks up names and gives
out corresponding numbers.  However, there
are products that do what you suggest, checking
webservers, and reconfiguring DNS servers
(such as bind) accordingly.

The actual user experience is dependent upon
what clients (IP stacks and browsers) do.  Client
software does whatever the coder thought
worked best (as opposed to following any
agreed-upon protocol), and the coders are
often concerned with the avoiding huge numbers
of lookups (e.g. gif images), thus they cache.
Typical browser cache-time is a half hour.

Balancing load and handling fallback is a
whole field, with lots of lively
discussion, and products that cost
substantial amounts of money.  Probably
more than you can imagine.

John

On Aug 31, 2005, at 2:42 PM, Kvetch wrote:

> Hello, I was wondering exactly what happens with a zone that has 
> multiple
> default records and one of those records are unavailable.
> For example if I have
> foo.net.    60    IN    A    192.168.1.1
> foo.net.    60    IN    A    192.168.1.2
> foo.net.    60    IN    A    192.168.1.3
>
> If a user visits foo.net <http://foo.net>'s website and gets the
> 192.168.1.1<http://192.168.1.1>server, then 15 minutes they return to
> foo.net <http://foo.net> but 192.168.1.1 <http://192.168.1.1> had 
> crashed
> during this 15 minute interval would they automatically be sent over to
> 192.168.1.2 <http://192.168.1.2> or 192.168.1.3 <http://192.168.1.3> or
> would they continue to round robin between the 3 IP's and might get a 
> 404
> error if they hit 192.168.1.1 <http://192.168.1.1>? So basically does 
> DNS
> recognize that one of the IP's is unavailable and send the user to 
> another
> IP. Kind of like MX record's preference values.
>
> Since the TTL is 1 hour they would not have to return to our DNS server
> since they received all 3 IP's, correct?
>
> Thanks,
> Nick
>
>