Re: Understanding DNS, Create an "Failover"
On Tue, 28 Oct 2014 09:51:11 +0100
basti <black.fledermaus@arcor.de> wrote:
> Hello,
> last weekend my primary DNS-Server goes down, and some of my server
> can't find each other.
>
> I have a Primary and a Secondary DNS-Server using bind9.
> The resolv.conf file looks like:
>
> nameserver <MyPrimaryDNS>
> nameserver <OneOfMyISP>
> nameserver <2'ndOfISP>
>
> For understanding:
> Is the secondary DNS just a backup of the Master for "loadBalancing"?
> What does the secondary DNS do if master is down?
>
> How can I fix this?
>
>
If the DNS information does not change frequently, then you can make
the changes to both databases manually. You may be able to just copy
the zone files, I'm not sure, but you will need to update the serial
numbers. BIND will not use a zone file that has an unexpected serial
number. If you are using dynamic DNS updates, or have other
frequently-changing information, you probably need to set up
replication between the DNS servers, and I can't be of any help there.
The two servers will run independently, but exchange DNS data
periodically.
You will need to include both your DNS servers in all computers'
nameserver lists. If you have a number of workstations on DHCP,
this information can be distributed automatically. There's no point in
including the ISP's servers, they won't contain your local information,
they will only provide public DNS information.
As Laurent said, the listed DNS servers are not used randomly, the
highest on the list will always be used first. I don't know how the
Linux resolver works, but a Windows resolver will not re-check any
failed servers for a particular timeout period, so once it finds a
responsive DNS server, it will stay with it for a while before
re-trying the top priority server.
--
Joe
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