What is the difference between Primary and Secondary DNS ?

Is there anyone that can help?

if the first one crashes you will have a backup nameserver that's why you have multiple DNS. Iguess...



tb

In the DNS terminology "secondary" does not mean "backup". It means exactly what the name says. Both name servers can be queried independently. Which server is queried as the first by the client side resolver is upon it. Unlike e.g. backup mail server. The difference between primary and secondary nameservers is that the primary nameserver has the zone configuration that the secondary one downloads from it.

Micha,

The DNS records are the same on the primary and the secondary DNS machines. Usually, a host will set everyone to use the primary first, the n the secondary in case the primary is down, rebooting, etc.

When the host starts to grow very large, all of the domain lookups are going to the primary DNS machine, where the secondary machine is sitting around, twiddling its thumbs. So, many people like to swap their DNS to use the secondary first, hoping to get their surfers to the site slightly faster.

That's the idea, anyway. The DNS lookup is fractions of a second for the surfer, but spreading the workload more evenly for the DNS servers isn't a bad idea, either. It's personal preference, and a tweak that could save precious microseconds for your consumers.

HTH

Thanks for the input

Once more -- it is not true. Secondary nameserver is not a backup nameserver. Both nameservers (or more) are replying the queries because they are queried randomly -- depends on the algorithm of resolver library on the client side, which one is queried the first. So if you run two nameservers and the secondary nameserver is not running you are in troubles because some clients queried secondary nameserver first.

It can be simply proved. If you have access to both -- primary and secondary nameserver which are authoritative for the same zone, turn the query logs on and compare them. You will see that the secondary nameserver is getting decent percentage of the clients' queries directly -- independently on the fact if primary nameserver is running or not.