We have a backup database server that has lately been periodically hanging when attempting to setup database mirroring between our principal and mirror (backup). After digging a little further I've found that I get the message "Connection Timeout Expired. The timeout period elapsed while attempting to consume the pre-login handshake acknowledgement" when trying to log on to the backup server FROM the backup server.
After reading other posts, I've verified that IPv6 is enabled and active in SQL configuration, but that does not help. I've also disabled and enabled the Windows firewall.
The only thing that solves it temporarily is restarting the SQL Server service. After that it will run fine for a bit but then hang again.