Ubuntu: Using tcpdump for analysis of network traffic and port usage

tcpdump comes standard on Ubuntu servers and is an invaluable tool in determining traffic coming in and out of a host.

As network infrastructures have become more complex and security conscious, validating network flow from client hosts through potentially multiple proxies and ultimately to a destination host and port has become more important than ever.

Let me list a few of the more common use cases.

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SaltStack: Troubleshooting Basic Network Connectivity of Minion on Ubuntu

saltstack_logo-thumbnailWhen troubleshooting basic connectivity from your SaltStack minions to your Salt master, the first thing to remember is the basic flow – the minions initiate the connection to port 4505/4506 on the Salt master.

With this in mind, if you have modified /etc/salt/minion so that the master is explicitly set and logs are set to debug levels as shown below:

master: mysaltmaster
log_level_logfile: debug

And the minion key is still not showing up on the Salt master list (salt-key -L), and the minion log file (/var/log/salt/minion) is not providing any hints, you should try a basic network connectivity test using netcat.  From the console of the Salt minion:

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