mysql_connect(): Lost connection
 

I'm having a problem connecting one server to another server's mysql installation.

We have servers 1, 2, 3, and 4. 1 contains a database which we've migrated over to 2. Server 2 is already serving database connections for servers 3 and 4, with no issues.

However, when we try and connect via PHP from server 1 to server 2's database (using port 3306) the connection fails with the following:

mysql_connect(): Lost connection to MySQL server during query

Ports are open on both server 1 and server 2, and connecting via telnet is successful.

MySQL is listening on 0.0.0.0:3306, and `netstat -apn` shows connections established for servers 3 and 4.

The my.cnf file is set up with a high level of user connections, a good amount of RAM allocation for various caches, and timeouts are as default.

Can anyone suggest a reason as to why this might be happening, or some way to track down what the problem might be?