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I started moving accounts from one cPanel server to another at a different hosting facility. The accounts were being moved from my Colocated servers to a VPS.

During the transfer I also wanted to change the nameservers for all the domains we are hosting because the current nameservers use a name from a previous business entity.

I was doing fine with the transfer until the VPS started going crazy on me. Apparently the VPS has a 1mil inode limit. This was an issue.

Now we have decided to go with a dedicated server. Currently the domains I have already transferred are pointing to the new nameservers which are both directed at the VPS.

Now I need to start moving accounts to the dedicated server which means the DNS zone records will not be on the VPS, but only on the dedicated box.

My question then is this:

If I change these domain's nameservers to the new hostnames is it possible to point one of the nameservers at the dedicated box and leave the other pointed to the VPS?

This way every zone record, whether it is on the VPS or dedicated box would be available, correct?

OR does the DNS server look at the first NS machine and if it receives any answer at all, such as "Domain doesn't exist", simply stop the lookup without checking the other NS?

I'm sorry this is so convoluted. If anyone knows a better way to go about this, please let me know. I'm on a limited timetable because the colocated servers will be turned off in a few days.

UPDATE: By the way, I have been testing and when I use nslookup on a domain that I've removed from the first NS it says "No answer" ... Will that cause a failover to another NS or cause the resolver to give up?

Thanks, Tom

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3 Answers 3

up vote 1 down vote accepted

There is a difference between a NXDOMAIN reply and a REFUSED or SERVFAIL reply.

NXDOMAIN says: The host record you are trying to look up does not exist (the resolver should stop looking)

REFUSED says: You are not allowed to ask me this question (the resolver should check another NS)

SERVFAIL says: I am supposed to be able to answer this question, but an unable to at this time (the resolver should check another NS)

Sounds like your setup would have your two machines responding either correctly or with a REFUSED/SERVFAIL. Ensure this is so and you'll be fine.

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How do I ensure that my NS will reply with REFUSED or SERVFAIL instead of NXDOMAIN for all domains that are not contained in a zone file? ... Please also look at the update in my question. Thanks. –  TomWilsonFL Jul 27 '10 at 17:43
    
That depends on what you nameserver is. By the way, your question is very hard to read - it's very flow-of-consciousness. But yes, 'No Answer' will cause the resolver to try another NS. –  MikeyB Jul 27 '10 at 18:02
    
If you think my question is hard to read, you should try talking to me in person right now. I've been reading DNS books for hours and hours. :) Thanks for your help. –  TomWilsonFL Jul 27 '10 at 18:07
    
:) Just ensure that each domain is either correctly configured on at least one nameserver, or not at all. –  MikeyB Jul 28 '10 at 14:05

When using "dig" (also available on windows) you get the right answers like MikeB gives. When using nslookup you should get:

Query refused = REFUSED
Non-existent domain = NXDOMAIN
No response from server = SERVFAIL

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You can configure the parent to point to both servers. Consider leaving the old servers active during switchover. (You should always have at least 2 domain servers.) For domains not available on a server there will be periodic delays during failover to the available server.

Consider the following approach.

  • Create new configuration on new server using old configuration. Add new server as a nameserver, replacing old nameserver. Change timeouts to small value (1 day or less) to enable quicker reconfiguration. Enalbe zone transerfers to old nameserver.
  • Load new configuration on new server.
  • Change parent configuration to point to new nameserver(s). Use final nameserver list.
  • Slave old server(s) from new server.
  • Wait a day or more. Preferably at least half the old servers timeout.
  • Shutdown old nameserver, and disable zone transfers to it.
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