[Q] NS preference ?

Kevin Darcy kcd at daimlerchrysler.com
Thu Dec 12 17:40:35 UTC 2002

Stephane wrote:

> Hello,
> I'm a named newbie and I have two (perhaps stupid) questions:
> 1) I have 1 DNS server for my domain. If it is
> down, I'd like to have a second one. Which backup
> DNS should I put ? My ISP's DNS ? My registrar's
> DNS ? Another one ?

You need to put at least one nameserver which is actually a slave for your
zone and is performing zone transfers regularly.

> Once I add this backup NS in my /var/named/master/mydomain.com
> file, which one is choosed first ?

Nameservers typically keep track of how quickly other nameservers respond
to their queries. So your nameserver will be chosen first if it responding
more quickly than the other one, otherwise the other nameserver will be
chosen first. Note that different nameservers may choose different
nameservers first, depending on whether they are "close" or "far
away" from those nameservers in network terms.

> I mean, for the MX you can
> set preferences, is there something like this for NS records ?

No, it's not really necessary. See above.

> What happens if my NS is not choosed first ?

Then the query gets answered by the other nameserver. That's why it's
important that the zone is transferring regularly; otherwise other
nameservers may get stale or inconsistent results.

> 2) My registrar has currently set the DNS for my domain to the
> company hosting my website. I can ask my registrar to change this
> to my own DNS.

You can ask. Whether they comply is another question :-) You'll have to
follow whatever procedures the registrar has published, in order to make
this change take effect.

> What happens if the company doesn't change its DNS
> settings for my domain (i.e. if they keep the zone "mydomain" / type
> "master") in their named.conf ? Is it important ?

It could be. Because of caching, other nameservers will continue to use
the nameservers, until they are restarted or reloaded and discover the new
nameservers in the delegation records. To be on the safe side, you should
have the hosting company delete the zone from their nameservers after the
delegations have been changed.

- Kevin

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