nslookup - returned IP address priority

Question

_{Tuesday, July 1, 2014 12:20 PM}

Hello,

We have a server that has two IPs. there this issue I can't get my head around.

When running nslookup against one dns server, the IPs are correctly returned. Basically server IP is first and a second IP is used for a web app on the very same machine.

Running nslookup against another DNS, returns the IPs in a switched order, meaning the web app IP is first and the server IP is second.

I have run out of ideas :-(, the server owner encounters issues when querying is resources.

Is there a way to set a priority? What dictates the way IPs are returned when running nslookup?

Regards,

Dominique.

All replies (1)

_{Wednesday, July 2, 2014 6:48 AM ✅Answered}

Hi,

As far as I know, we can’t set the priority of A records manually.

By default, the DNS Server service uses local subnet prioritizing as the method for giving preference to IP addresses on the same network when a client query resolves to a host name that is mapped to more than one IP address. This feature requires that the client application attempt to connect to the host using its closest (and typically fastest) IP address available for connection.

The DNS Server service uses local subnet priority as follows:

1. The DNS Server service determines if local subnet prioritization is needed to order the query response.
        If more than one A resource record (RR) matches the queried host name, the DNS Server service can reorder the records by their subnet location. If the queried host name only matches a single A resource record, or if the IP network address of the client does not match an IP network address for any of the mapped addresses in an answer list of multiple RRs, no prioritizing is necessary.
2. For each RR in the matched answer list, the DNS Server service determines which records (if any) match the subnet location of the requesting client.
3. The DNS Server service reorders the answer list so that A RRs which match the local subnet of the requesting client are placed first in the answer list.
4. Prioritized by subnet order, the answer list is returned to the requesting client.

For detailed information, please view the link below,

Prioritizing local subnets

http://technet.microsoft.com/en-us/library/cc787373(v=WS.10).aspx

Hope this helps.

Steven Lee

TechNet Community Support