I've been talking a lot already about network access to Linux system. It's time to look more closely at the setup and management of networking in Linux. Now, predominantly, your Linux system is going to be connected via Ethernet. Understand that this will probably be a virtual Ethernet connection. On power systems, that means a virtual Ethernet adapter in the LPAR, connected through the VI/O servers, Ethernet bridge, which is called as Shared Ethernet Adapter, if you are interested or through a virtual network interface controller, also known as a vNIC in the VIOS. That would be leveraging a Single Root I/O Virtualization adapter, also known as an SR-IOV adapter, a port on that adapter. Did you get all that? Let's just say you didn't rewind. You didn't go back and try to figure all that out. Let's just say that Ethernet adapters will be configured for the Linux LPAR. Let's focus on the Linux systems handling of those adapters and networking. We're going to leave the virtualization to another course, to another time. Networking is usually configured for the Linux operating system during installation. This might be because the setup was done using a script where the networking was defined, the installation and the setup, or it might be done via graphical menu using VNC, where the networking configuration is entered in menus. It might be an automated installation, might be a manual installation. But likely networking is going to be set up. Understand, I'm talking about standard TCP-IP network configuration here, nothing fancier than that. A host name, an IP address, subnet masks, routes. Yeah, that stuff. You're probably already familiar with the concepts. Again, some of this can be and will most likely be setup during installation. But let's look at the tools and Linux operating system to modify the configuration, do further configuration or just view it. Now, the primary tools for managing networking, and TCP-IP and Linux, are in the iproute2 package. The ip command is your primary command. It's used to show or manipulate routing, network devices, interfaces, and tunnels. The table in the graphic shows the ip command. Now, this isn't the only command in the iproute2 package, but it's the one you'll probably use the most. The ip command syntax requires an object or an argument. The route and address objects are the most commonly used, route and address. The syntax then calls for a command. Now, the possible commands are things like add, delete, list or show. Not all objects support all commands. If the command is not supplied, there is usually a default. The default is usually to list or show command. To take an example, the simplest use is ip address or addr or as lazy folks like me like to shorten it ip a. The default command is list or show. The result of entering ip a is a list of all the interfaces and their configuration. Let's think about how powerful this is. You don't know anything about a Linux operating system. You managed to get in. You're trying to get somewhere else you're not aware. You don't know why you're not getting there. Ip a will tell you what your networking configuration looks like. Very powerful. But where did that configuration information come from? Or better said, how was the configuration actually done? Well, if it wasn't done during installation, as I mentioned earlier, much probably has been, it would be done using IP adder or IPA add, for example. Now the configuration information is kept in the etc sysconfig network-scripts directory, that's etc/etc/sysconfig/network-scripts. There will be a file for each of the interfaces defined on the system, including devices like bridges or bonds. This is much more detail than you would need for your fundamental Linux networking administration. Then those files contain the interfaces configuration information. The graphic that you see now shows an example of the ifcfg-eth0 interface entry in the etc sysconfig network-scripts directory. Now by the way, eth0 is a real Ethernet adapter, in this case, not a virtual adapter. The inset graphic that appears now shows the ip commands used to configure the IP address and display the results of the configuration. Now, although unlikely, you might use the GUI to configure networking. The graphic on the screen shows the click stream you follow to reach the dialogue where IP parameters can be entered. As with most things in Linux, networking is controlled by a service. The service is called appropriately, networking. Now, as you see on the graphic, the system control arguments are pretty straightforward: start, stop and restart. Of course, if you're going to be stopping network, be sure you're accessing the Linux system via a console and not the network. The networking service will start automatically, when the system boots. Finally, if you want to see the status of the networking service, you use the status argument. An example is shown here in the graphic, look for the active status line. In the example case, the service is active.
