Error message when you try to set a witness in a database mirroring session in SQL Server 2005: "The ALTER DATABASE command could not be sent to the remote server instance 'TCP://<ServerName>:<port>'"

Consider the following scenario:

• You have a database mirroring session in Microsoft SQL Server 2005.
• The database mirroring session does not have a witness.
• You set up a witness server.
• On the principal server and on the witness server, you do not use DNS together with DHCP for name resolution. Instead, you specify that a host file should be used for name resolution.
• On the principal server instance, you try to set the witness.

In this scenario, you receive the following error message:

A database mirroring session must use a fully qualified domain name (FQDN) to resolve the name of the witness server.

To work around this problem, follow these steps:

1. On the DNS server, register all the internal IP addresses.
2. On the principal server, click Start, and then click Control Panel.
3. In Control Panel, double-click Network Connections.
4. Right-click the connection that you use to connect to the witness server, and then click Properties.
5. Under This connection uses the following items in the Connection Properties dialog box, click Internet Protocol (TCP/IP), and then click Properties.
6. In the Internet Protocol (TCP/IP) Properties dialog box, click Advanced.
7. In the Advanced TCP/IP Settings dialog box, click the DNS tab.
8. On the DNS tab, click Append these DNS suffixes (in order), and then click Add.
9. Under Domain suffix in the TCP/IP Domain Suffix dialog box, type the domain suffix, and then click Add.
10. Click OK three times.

Microsoft has confirmed that this is a problem in the Microsoft products that are listed in the "Applies to" section.

If you specify that DNS should be used together with DHCP for name resolution, the appropriate domain suffix is automatically appended to the computer name. In this case, the database mirroring session uses the FQDN to resolve the name of the witness server.