Mininet cli

Mininet CLI (Command Line Interface)

We've already set up our scenario and verified that it's working properly. We will now detail the most important commands we can issue from of Mininet's CLI.

Command: EOF + quit + exit

These three commands are used for the same thing, to exit the Mininet CLI and finish the emulation. The source code of these three commands does not differ much, EOF and quit end up using the do_exit function at the end, so we could say that they are a bit repetitive. They offer several ways to kill the emulation so that people with different backgrounds feel "at ~". The source code taking care of exiting is:

def do_exit( self, _line ):
    "Exit"
    assert self # satisfy pylint and allow override
    return 'exited by user command'

def do_quit( self, line ):
    "Exit"
    return self.do_exit( line )

def do_EOF( self, line ):
    "Exit"
    output( '\n' )
    return self.do_exit( line )

Command: dpctl

The dpctl command is a management utility that allows some control over the OpenFlow switch (ovs-ofctl on the OpenvSwitch). This tool lets us add flows to the flow table, check the features and status of the switches or clean the table among many other things. For example, recall how we previously made a ping between h1 and h3. If we consult the flow tables we will be able to check how the rules for handling ICMP flows have been instantiated:

Note how in the first and third switches we have 3 flow instead of the default one that let's us communicate with the controller. On top of that, take a closer look at the third switch and notice how the input and output ports for the first flow are 3 and 1 respectively. The second rule has the exact opposite distribution: the input port is 1 and the output is port 3. This setup let's us establish a communication link through this switch between any machines hooked to port's 1 and 3. These are the rules the controller has automagically set for us!

This command is quite complex and powerful, and it may not be completely necessary for what we are going to do in this practice. It is nevertheless undoubtedly one of the most important commands to understand the internal workings of SDN switches. For more information, we encourage you to take a look at the documentation over at OpenvSwitch.

Command: dump + net

These commands will give us information about the emulated topology. The net command will indicate the names of the entities in the emulated topology as well as their interfaces. The dump command will also indicate the type of entity, its IP address, port when applicable, interface and the entitie's process identifier (PID).

Command: xterm + gterm

These two commands will allow us to open terminal emulators in the node identified by the accompanying argument. The command xterm will allow us to open a simple XTERM (the default terminal emulator for the X windows system) terminal emulator, and gterm launches a prettier but more resource hungry Gnome terminal. We can open several terminals at once by indicating all the nodes we want to open a terminal in. Later, when we discuss the inner workings of Mininet, we'll talk a bit more about where the bash process attached to the terminal emulator is running. You might think that this process is totally isolated from the machine on which you are running Mininet, but this is not entirely the case...

# xterm/gterm [node1] [node2]
xterm h1 h6

Command: nodes + ports + intfs

These commands will list information related to the nodes in the topology. The intfs command will list all information related to the nodes' interfaces. The nodes command will show every node in the topology. Finally, the ports command is used to list the ports and interfaces of the switches in the topology.

Command: The rest of the commands 😏

Someone once told me manpages were my friends. This doesn't apply here directly but you get the idea. If you don't know what a command does try running it without arguments and you will be presented with a help section hopefully. If your machine blows up... It wasn't our fault! (It really should't though 🙆‍♀️). You can also issue help <command_name> from the mininet CLI to gather more intel. You can also contact us directly. We didn't want this section to grow too large and we believe the above commands are more than enough for our purposes.