FQDN Error:

One or more of the server network ADDRESSES lacks a FULLY qualified domain name (FQDN). Specify the FQDN for each server, and click Start Mirroring again.

The syntax for a fully-qualified TCP address is:

TCP ://< computer_name>.<domain_segment>[.<domain_segment>]:<port>

Section 1.01 

Section 1.02 II. RECTIFYING FULLY QUALIFYED NAMES

1. To View Endpoints:-SELECT * FROM sys.database_mirroring_endpoints;
2. Remove existing all Endpoints from Principal, MIRROR and Witness servers:- DROP ENDPOINT [ENDPOINT_NAME]
3. Adding "local" as the primary DNS suffix as follows:-

• Right-click My Computer, and then click PROPERTIES. The System Properties dialog box will appear.
• Click the Computer Name tab.
• Click Change. The Computer Name Changes dialog box will appear.
• Click More. The DNS Suffix and NetBIOS Computer Name dialog box will appear.
• Enter the appropriate DNS suffix for the domain.
• Select the Change primary DNS suffix when domain membership changes check box.
• Click OK to save the changes, and then click OK to exit the Computer Name Changes dialog box.
• Click OK to close the System Properties dialog box, and then restart the computer for the change to take effect.

Reconfigure the Database mirroring either GUI or T-SQL.

FQDN Error:

One or more of the server network addresses lacks a fully qualified domain name (FQDN). Specify the FQDN for each server, and click Start Mirroring again.

The syntax for a fully-qualified TCP address is:

TCP ://< computer_name>.<domain_segment>[.<domain_segment>]:<port>

Section 1.01 

Section 1.02 II. RECTIFYING FULLY QUALIFYED NAMES

Reconfigure the Database mirroring either GUI or T-SQL.