? DNS UPDATE ? NSUPDATE ? DYNAMIC DNS ?

[Kevin Darcy]

You can sorta do this with the rrset-order option available in BIND 8.2 and
beyond, but, since rrset-order data is not transferred between nameservers,
you'd need to set this on *every* server which is answering for the name,
and even then most nameservers answering from cache -- including servers
you don't control -- will round-robin the answers (you can, of course,
limit the effects of caching by setting low TTL values for the records, but
only at the expense of increasing query traffic). So expect some
"spillover" to your failover servers using this approach.

Note that the caching complication is going to bite you even if you
implement a homegrown scripted NSUPDATE approach. Any failover approach
which relies on switching IP addresses around is going to run into the same
problem.

If you want a "perfect" solution, you'll need to do it at a lower (network)
level, having a single address which is then somehow magically
assigned/reassigned behind the scenes in case of a failure, using most
likely a commercial redundancy/load-balancing product from Cisco, IBM or
whomever.


- Kevin

Mike Hunter wrote:

> I have a situation where I need a DNS record to point to 3 different
> servers.  I cannot use round-robin because it needs to resolve in a
> specific order.  For example:
>
> www1    in    a    10.10.10.1
> www2    in    a    10.10.10.2
> www3    in    a    10.10.10.3
> www     in    a    10.10.10.1
>         in    a    10.10.10.2
>         in    a    10.10.10.3
>
> I need to have DNS to resolve, in order, the first ip address
> 10.10.10.1, and if it fails, then resolve to 10.10.10.2.  If it fails on
>
> the second, then resolve to the third (10.10.10.3).  All automatically.
> We have looked into possibly using NSUPDATE and writing scripts, but was
>
> wondering if there is any way this can be done automatically.
>
> Any assistance would be most appreciated.
>
> --
> Mike Hunter                           Schlumberger Omnes
> UNIX / WAN Element Manager            5599 San Felipe Suite 400
> Office: 713-513-3233                  Houston TX 77056 USA
> Fax: 713-513-3150                     Email: mhunter at smc.omnes.slb.com