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Query regarding DNS suffix

Posted on 2009-04-05
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Last Modified: 2012-05-06
Hi All

My domain is uk.kam.com. I am running Windows XP machines with Windows 2003 servers.

Most servers are configured in DNS as server1.uk.kam.com  = i.e. with their full FQDN.

I notice that on some servers, if I enter http://server1 (or ping server1), then I get a reply back from server1.uk.kam.com (i.e with the full domain name)

What is it that I have on my local PC settings that states my machine is already in the uk.kam.com DNS domain, and therefore I don't always have to enter the suffix?
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Question by:kam_uk
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Expert Comment

by:FOTC
ID: 24072506
set up a DNS CNAME in your DNS server(s).

give it the name u want ie:  kam    then point it to the A Record of the server you want.

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Expert Comment

by:FOTC
ID: 24072512
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by:kam_uk
ID: 24072698
Sorry - I think I didn't explain this properly..

Basically, the question is why I don't have to ping a server by its FQDN to get a response.
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Expert Comment

by:FOTC
ID: 24072753
im not quite sure i understand what you are asking.

if you want to be able to ping server1 and get a reply, you need to set up a cname record in dns.

when a server is joined to the domain, it creates a host record (A). which corresponds to it's ip address. you can then ping the server by its name and it will reply back with its fqdn appended to the end of the name.
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Chris Dent earned 500 total points
ID: 24075581

> What is it that I have on my local PC settings that states my machine is already in the uk.kam.com
> DNS domain, and therefore I don't always have to enter the suffix?

Either the Primary DNS Suffix, or the DNS Suffix Search List. Both are visible if you run "ipconfig /all".

The client, when it requests a name, will append each of its listed suffixes to the query before it requests just a name.

That is, if your client has these suffixes:

Primary DNS Suffix: uk.kam.com
DNS Suffix Search List: usa.kam.com
                                     nz.kam.com

And it makes a request for "server1". It will make these requests when attempting to resolve the name:

server1.uk.kam.com
server1.usa.kam.com
server1.nz.kam.com

It will stop the moment it gets a response that isn't "NXDOMAIN" (does not exist). You will find the same behaviour when looking up public domains such as www.google.com. e.g.:

www.google.com.uk.kam.com
www.google.com.usa.kam.com
www.google.com.nz.kam.com
www.google.com

Note that it only tried www.google.com at the end.

If you'd like to see this behaviour you can by running:

nslookup
set debug
www.google.com

Take a look through each of the "QUESTIONS" in the output, you will see that it appends each suffix as described above. If you were to watch the network traffic for this you would see your DNS server providing a response as well (should be NXDOMAIN until the last one).

Chris
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by:kam_uk
ID: 24075794
Hello Chris,

Thanks for the excellent answer.

Just one query..

Let's say my PC is set up as below;

Primary DNS Suffix: uk.kam.com
DNS Suffix Search List: usa.kam.com
                                     nz.kam.com

I have servers at;

server1.uk.kam.com, server1.usa.kam.com, server1.nz.kam.com

Would I be correct in saying that if I ping "server1", the inital response will be from the UK server? If the UK server didn't exist, the response would be from the USA server since that is higher in the DNS Suffix search list than the NZ one?

Also, what if Server1.uk.kam.com *was* registered in DNS but was offline? I assume the ping response would still be from the UK one, not the US. I would only get a response from the US server is the UK one did not actually exist in DNS?

Thanks again.

 
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Expert Comment

by:Chris Dent
ID: 24075819

> If the UK server didn't exist, the response would be from the USA server since that is higher in
> the DNS Suffix search list than the NZ one?

Yes. That is correct.

> Also, what if Server1.uk.kam.com *was* registered in DNS but was offline?

The Ping would time-out but the DNS lookup would succeed.

DNS doesn't care whether a resource is up or down, only if it has a valid record. If it does have a valid record it will return that to the client. So...

> I would only get a response from the US server is the UK one did not actually exist in DNS?

That's correct as well :)

Chris
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