How to cure error 1456 when adding witness to database mirroring?

Question

Database administration

I'm trying to set up mirroring between databases with a witness to automatically switch roles. I have 3 machines in a test environment (2 servers 2012r2 and a Win7 laptop). I set up mirroring between servers, authorization by certificates (on SQL2012Standart servers). When I try to add a win7 witness (SQL express) I get an error

Error 1456 level 16 state 3 The ALTER DATABASE command could not be sent to the remote server instance. Verify that the server is connected and try again

I also tried another computer with win10 installed instead of Win7, the result is the same. Endpoints are configured and running, logins are created and granted grants (CONNECT on endpoint), firewall is disabled on all machines. I also checked the ports on the witness with telnet, they are open.

Answer 1

Hello everyone,
I want to share a solution: considering the network settings and FQDN, I noticed that the suffix on the DNS witness is not the same as on machines with databases. After changing the DNS suffix on the witness and editing the hosts file on all machines, the connection between the mirror and the witness went up.