Why ping-ing to the internal AD domain name sometimes responded by different domain controllers in totally different subnets?

Question

Folks,

I have a single forest Active Directory domain, called DOMAIN.COM.

AD Site 1 - 10.10.1.0/24 subnet
SITE1DC1-VM
SITE1DC2-VM
SITE1-DFSR-VM
SITE1PC1
SITE1PC2
SITE1PC3
...
SITE1PCN


AD Site 2 - 10.10.2.0/24 subnet
SITE2DC1-VM
SITE2DC2-VM
SITE2-DFSR-VM
SITE2PC1
SITE2PC2
SITE2PC3
...
SITE2PCN


AD Site 3 - 192.168.3.0/24 subnet
SITE3DC1-VM
SITE3DC2-VM
SITE3-DFSR-VM
SITE3PC1
SITE3PC2
SITE3PC3
...
SITE3PCN

I need some explanation in how the Active Directory works when users access DFS-Replicated File share or ping-ing the internal AD DOMAIN.com name.

The issue that I'm facing:

1. When the users in Site 1 trying to access the file servers \domain.com\DFSR\domain\Data, each user in the same office locations are getting the files from different file servers, despite their IP address are the same subnet?

2. When I ping the DOMAIN.com from the same floor or users PC internally, why the response is coming from different Domain Controllers from SIte-1, Site-2 and sometimes Site-3?

Why this strange behaviour of Active Directory exists. How to rectify this issue correctly.

Considering the AD sites are on geographically different locations and I would assume the nearest Domain Controllers will always respond to each respective PC ping request locally and assign DFS-R servers nearest or within the same subnet.

Thank you in advance.

Answer 1

When I ping the DOMAIN.com from the same floor or users PC internally, why the response is coming from different Domain Controllers from SIte-1, Site-2 and sometimes Site-3?

That is the expected behavior, unless the local DNS server is configured for the correct localnetpriority mask.

https://support.microsoft.com/en-us/help/842197/description-of-the-netmask-ordering-feature-and-the-round-robin-featur

For DFS to function as expected, the referral method would need to be Lowest Cost or Exclude Targets Outside of the Client's Site.

https://docs.microsoft.com/en-us/windows-server/storage/dfs-namespaces/set-the-ordering-method-for-targets-in-referrals