DNS Redundancy

Question

Hi,

Internal AD integrated DNS.
I need a domain name to resolve to IP #1.
If IP #1 is unavailable I want the domain name to resolve to IP #2.

As far as I understand, if I create two A records as below, round robin will occur and clients will connect to one IP then the other.
domain_nameA - IP #1
domain_nameA - IP #2

I need clients to always resolve to IP #1 unless it is unavailable.
Only when IP #1 is unavailable, do I want clients to resolve to IP #2.

Any help appreciated.

Answer 1

Hi,

Thanks for posting in Q&A.

Before we go further, I would like to know if the IP #1 and IP #2 were in same subnet?

If they are in the same subnet, to accomplish your goal, I would suggest disable round robin and netmask ordering in Properties of DNS server since if Round robin and Subnet Prioritization are both enabled, they will work together, however, Round Robin will be superseded. Meanwhile, please make sure the A record of IP #1 is always on the top of IP #2's A record.

Best Regards,
Sunny

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Answer 2

Simplest is to have your DHCP server hand out IP #1 as primary DNS and IP #2 as secondary.

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Answer 3

Thanks Sunny,

The disabling of round robin looks to be just what I needed.
What is the purpose of enabling Netmask ordering?

Thank you.

Answer 4

Hi Sunny,

Yes, they are consecutive IP addresses in the same subnet.

Thanks,

Mike

Answer 5

Hi @M_M ,

Thanks for your prompt reply. You could disable Round Robin and Network ordering in DNS server to achieve your goal.

I have done a test in my lab and here is the result for your reference.

A. I create 2 A records whose IP addresses are in the same subnet in DNS zone as below.

B. When Round Robin and Netmask ordering are enabled, the result of nslookup hostname is as below.

C. When Round Robin is disabled but Netmask ordering is enabled, the result of nslookup hostname is as below.

D. When both Round Robin and Netmask ordering are disabled, the result of nslookup hostname is as below.

Hope my answer will help you.

Best Regards,
Sunny