In this chapter, we experienced what seemed like a simple networking issue with our blog application connecting to its database. In our data collection phase, we used commands such as
tcpdump to inspect the network packets and quickly discovered that the blog server was receiving an ICMP packet indicating that the database server is rejecting the blog server's TCP packets.
From that point, we suspected the issue was a firewall issue, which after investigating with the
iptables command we noticed that the firewall rules were out of order.
Afterwards, we were able to use the trial and error stage to resolve the issue. This specific issue is a very common issue, something that I personally have seen in many different environments. ...