A quick summary of what you have learned so far

From our troubleshooting so far, we have identified that the blog server is able to establish a connection to the database server over port 22. This connection is actually able to perform a full three-way handshake unlike our previous chapter. However, the blog server is not able to perform a three-way handshake with the database server over port 3306, the database port.

When the blog server attempts to establish a connection to the database server over port 3306, the database server is sending an ICMP destination unreachable packet back to the blog server. This packet is essentially telling the blog server that the connection attempt to the database is being rejected. Yet, the database service is up and listening on port 3306 (verified with netstat). In addition to the port being listened to, if we telnet to port 3306 locally, from the database server itself the connection is established.

Given all of these data points, it is possible that the...