Linux Networking interfaces can be confusing for anyone who's just getting started. If you'd like to learn more about Linux network interfaces, you're in the right place because that's exactly what we're covering in this video. My name is David Davis, and I'm the author of The Gorilla Guide to Linux Networking 101 In this video, I'll be walking you through some of the things that I covered in my book around Linux Networking interfaces. Let's jump over into Linux and get started. All right, We've just logged into a Debian Linux system. This is a well known Linux distribution and the easiest way to find out what Linux network interfaces you have available to you already configured on this Linux host is to type IP Space link. So here with the I P Link Command, we can very quickly see that we have four interfaces. They're numbered from the left hand side 1 2 3 and 4 So the very first network interface here, which I've highlighted, is the loop back interface. The loop back interface, always abbreviated as L O represents the Linux host itself. Now you can also tell here that we have three Ethernet interfaces, starting with Ethernet zero, which is abbreviated eth zero below that is ethernet one or E. T. H. One and then finally eth two or Ethernet two. So three interfaces 01 and two with the I P Link Command that we just ran, you could very quickly see that all of these interfaces are up. We see up, up and up, which is good to see. We know all these interfaces have been configured and are available. This doesn't tell us that they have IP addresses on them specifically, or what the I P addresses are. I'll show you the command to do that in just a moment. But at least we know what interfaces we have, and we know their status, whether they're up or down Something else that's important to point out here is not just that the interface says that it's up. That up indicates that the kernel thinks that it's up, but that the interface is also lower up. That indicates that we've established a link at the physical layer. So this tells us that we have an electrical signal on this link. From here, we can also see the Ethernet address or the Ethernet Mac address, which uniquely identifies these Ethernet interfaces. So now let's try another command, and that is I P A D D R, which stands for I P address. I'll press enter on that. And again we get the same list of network interfaces, starting with the loop back interface, which scrolled off the screen here a little bit. But I want to first point out that the loop back interface always has an I P address of 1 27.0.0.1 and then the first Ethernet interface, Ethernet zero. Here we can see its I P address. 1 72 16 1 92 1 44 Of course, that's the I P Version four address. There's also an I P Version six address, which we're not going to get into in this video. Now. What's interesting about the other two Ethernet interfaces? You can see the output is shorter here because these do not have I P addresses configured on either one of those interfaces. So we really only have one network interface that's connected us to the outside world. Whatever that outside world might be. The local land or out to the Internet who really knows at this point. So that's how you show the I. P address configuration of your network interface is the I. P Address command, and then the I P Link Command shows us the status, essentially of the hardware, whether those interfaces are up or down. Now, both of these commands, besides showing the status of the network interfaces, can also reconfigure those network interfaces. For example, the I. P Link Command. If we type man space I P link, you find out that this command can be used to, for example, down an interface. So bring an interface down to reconfigure an interface, perhaps change the MTU configure a multi cast or promiscuous mode on an interface. We don't need to get into what those are exactly right now, but with the I P Link set command, you could reconfigure your network interfaces. But if you want to change the I P addresses of your network interfaces like I said, you'd want to use the I P Address Command to learn more about the I P Address command and other I P base commands. You can do man space I P which shows you all the I P based commands. For example, down here you have I p address. There are other commands, like I p route and so on. And then we can do man space i p address and that gives us all the information about configuring i p addressing with the i p outer or i p address command, for example, adding, deleting flushing and showing I p addresses now a couple of other commands that you need to be aware of when you're working with network interfaces in Linux RF down and AF up. Now these are located at least in Debian in slash sbin slash IF down with the same path for IF up. Notice how you can use the dash dash, help to list out help and get more information on these commands. You can also type man space IF up. And as you might have guessed, this gives you the power to bring up and bring down an interface in Linux. You should also note that to run these types of commands, you need to be rude or have super user privileges. I also want to point out that the I P commands used in this video are available and standard on all Linux distributions as part of the I P route to package the I f up I F down commands are as well, but some of the configuration points may be different on different Linux distributions. So those are some of the basics of Linux network configuration. Stay tuned for more videos in this series on troubleshooting Linux network interfaces and much more. And by the way, I cover not only Linux network interface configuration, but also basic Linux administration tips, how to build your entire network on a Linux foundation and much more. In my book entitled The Gorilla Guide To Linux Networking 101 available for free at Cumulus Networks dot com. Thanks for watching.
