Unable to add DNS nameserver. The error message is "Name server already exists". But the server is never added. When you establish an SSL connection to the NetScaler and run "show dns nameserver" the DNS server it complains about already existing doesn't show. Using "add dns nameserver IP Address" also gives an error... "ERROR: Name server already exists."

1. Check if you have DNS Load Balance Virtual Server already added on NetScaler or not.

2. If yes, we need to remove DNS Load Balance Virtual Server and respective services. 

3. Try to add the nameserver again, you should be able to add it. 

4. On NetScaler we can add either dns nameserver or DNS LB VIP for same DNS server.

5. You can traverse to System > Networks > IPs  and check is there's a VIP already existing with this IP.

Best way is to run, "sh run | grep <IP Address>" from CLI to find any matching configuration.

If that doesn't work try warm restarting the NetScaler.

Problem Cause

DNS lb vip already exists.