Normally we pointed the primary dns and secodary dns to our server dns.
there are 3rd dns and 4th dns over there, normally we put it blank.
How to use the 3rd and 4th DNS? can we pointed the 3rd dns and 4th dns to another server which has similar content? and once the main server down, it will pointed to 2nd server?

Adding a 3rd and 4th that point to a different server will not provide the redundancy that you seek I think. It's going to be hit or miss as to wheter a client goes to the right server. You may get some people who go to that 2nd host, but most will continue to hit the host that's down.

Edit: Opps didn't read OP well enough.

3th and 4th dns servers are an overkill, unless you're a dns provider or an organization looking for 99.99999+% uptime. Most of the time 2, or even 3 geographically diverse dns servers will do.

Rob D: resolvers will query the next nameserver if there is a dns timeout.

Normally we pointed the primary dns and secodary dns to our server dns.
there are 3rd dns and 4th dns over there, normally we put it blank.
How to use the 3rd and 4th DNS? can we pointed the 3rd dns and 4th dns to another server which has similar content? and once the main server down, it will pointed to 2nd server?
Depending on how you do it, it can be advantageous or just a waste of time and money for you.

If your NS1 and NS2 are physically on the same servers (regardless of them using different IPs), the a NS3 and NS4 make sense. But if you have NS3 and NS4 on the same physical server with different IPs, then it will not make any difference. If your server goes down all your websites will go down.

If you have NS3 or NS4 in a completely off site thousands of miles away from NS1 and NS2, then its worth the extra time, money and effort.

One other minute detail I want to address. The zone records across all 4 DNS servers HAS to be the same, it cannot be "similar" because if all the zore records are not synced across the DNS servers then you will see errors and resolution issues all over the place. This is something most users take lightly, so be careful.

FYI, some ISPs just query the first 2 nameservers and ignores the rest.

A better plan, is to load balance your main 2 nameservers.

Your users will be switching from site to site. This may backfire and get search engines bad at delisting you. I would recommend going with a DNS service like DNSMadeEasy or something like that if you want geo-nameservers.

FYI, some ISPs just query the first 2 nameservers and ignores the rest.

A better plan, is to load balance your main 2 nameservers.

No they do not. This is not how name servers work.

ALL of your name servers that you give your registrar are put used in a round robin fashion. This is how name server have always worked (based on RFCs that are very old at this point).

Hi,

Suppose i have 4 name servers ns1 ns2 ns3 ns4 dispersed all across the world somewhat uniformly.

Now if a person access a website and the person is nearer to ns3 name server then will the query first go to ns3?

or what decides the order ?

And if on opening the webpage he again clicks a link of the same website, then will again DNS query will be made?

Regards

When deciding what name server to use it is simply randomly assigned using the round robin method. To my knowledge it won't go to the geographically closest one, especially since figuring out which server that is would take way more time than just going to a further away server.

Once a client resolves the IP address of a server, it will remain in the client computer "cached" until a specified timeout, this prevents people from having to do dns lookups every 10 seconds like you're talking about. If you're trying to test you can run ipconfig /FLUSHDNS from your windows command line to remove any DNS Cache and query the servers for a fresh ip address. You can set what this timeout is in your dns servers, so basically you can tell computers when to come back and check if that is still the IP address.

Any corrections anyone?

When deciding what name server to use it is simply randomly assigned using the round robin method. To my knowledge it won't go to the geographically closest one, especially since figuring out which server that is would take way more time than just going to a further away server.


Totally correct.
Round robin is just that.
First it goes to name server 1, then 2, then 3, then 4.
Then 1 again, then 2, then 3, then 4.




Once a client resolves the IP address of a server, it will remain in the client computer "cached" until a specified timeout, this prevents people from having to do dns lookups every 10 seconds like you're talking about. If you're trying to test you can run ipconfig /FLUSHDNS from your windows command line to remove any DNS Cache and query the servers for a fresh ip address. You can set what this timeout is in your dns servers, so basically you can tell computers when to come back and check if that is still the IP address.

Any corrections anyone?

Don't forget about your resolving name server (which has it's own cache). The OS will just ask the resolving name server. So even though you run "ipconfig /flushdns" the values can still be cached at your resolving name server.

First, you need to HAVE 3rd and 4th DNS servers. Second, they need to be pulling records from your primary DNS, otherwise, they are cache-only and won't provide any backup should 1 & 2 ever fail.