windows - Active Directory W7 Client - Primary/Secondary Failover of DNS not happening

I have 2 DC's with DNS on both as well.

• DC1 = 10.0.100.1


• DC2 = 10.0.100.2

All windows 7 client's have primary secondary ip's pointing to DC1/DC2 respectfully.

For test purposes, I shutdown DC1, and rebooted Win7 Client. Then I launched NSLOOKUP, and every time it always selecting DC1 DNS. Although it have DC2 dns as secondary but still it chooses dc1 dns always.

on W7 client, I tried

echo %logonserver% 

and its showing \DC02 correctly which means client is loggedin to secondary DC successfully.

If I manually set DC2 DNS as primary then all OK, or if manually set nslookup - dc02 then it works or if i PING DC02 or other host, fine too.

But normal nslookup, it always selecting dc1 dns and giving Timeout in every query. I have tried waiting for about an hour, rebooted client machine many times , no use.

So my question is why Win7 is not switching to Secondary DNS after primary is failed?

Answer

Nslookup is a specific DNS testing tool. It does not mimic the behavior of the DNS client resolver. Nslookup will only query the primary DNS server. It will not attempt to query the secondary DNS server. You're chasing a wild goose. You should not use nslookup as a test of the DNS client resolver as that's not what nslookup is for nor does. The DNS client resolver will correctly fail over to the secondary DNS server if the primary DNS server doesn't respond.