EX200 Red Hat Certified System Administrator RHCSA – Network configuration

1. Intro to network interfaces

Welcome all to this tutorial today I will open up a chapter on configuring network interfaces and configuring networking in general in Linux Red Hat. So in some previous tutorial I have shown you a simple command to see your IP address which was basically ifconfig and I told you that we would cover this in detail well, well, that is a partially true promise. Don’t worry, I won’t disappoint you I will teach you about networking in Linux. However, we will not be using ifconfig if you just go ahead and type in man if config there we go. It says down below where the note exists this program is obsolete for replacement, check iPadR and IP link. For statistics, use IP Hyphen S link and believe it or not, most of the users today they tend to use if config for their day to day work and system admins. They do use IP, but most of the regular users will still use if config, even though it has been labeled as obsolete. I don’t know, since before 2000, sometimes in the 1990s. But even if when I’m not doing something important or when I still have a habit of using if config, it’s just one of those commands that sticks with you. It’s fairly simple and easy to use, so people do tend to use it.

However, it is obsolete and today IP is used instead. I’ll just go ahead and clear the screen. IP command is fairly simple okay, I admit there are a considerable amount of arguments that are passed along with it and it can accept a considerable amount of arguments. It’s still not as complicated, but it definitely does not possess the simplicity of if config. So let’s go ahead and have a look at a few examples. If I type in IP, if I press tab twice, you can see that there are quite a few options here, so if I type in addr show, I will get the IP addresses for my interfaces and the interfaces in Linux can be named in three fashions. Well, I was four, but three is something that is taken as a general standard. The fourth one, the logical naming, that’s something completely different, that would be for VLANs and that is not something that we are going to cover in the Red Hat certified that is not something that you’re going to need in the Red Hat certified system administrator. Not for the time being anyway. What the naming processes? Well, the naming processes are basically BIOS naming.

So the manufacturer’s ID of the network card, you can use that one. And that is how your network cards will be named. Network cards are usually marked as Nic, like this. If you see somewhere in the network, it says Nic. It means network. Integrated card. Network cards do not need to necessarily be integrated onto your motherboard. They can also be USB adapters. So you can buy these on the net. People usually buy them for wireless. Also there is a physical type of naming which is the same as BIOS and there is a standardized way of naming interfaces which is basically just typing ETH and then ETH one, ETH two. I do believe that this is the default way of naming things on Debian, but doesn’t look like it’s the default way of naming things in Red Hat. So Red Hat has its own way of naming interfaces and this is not it. Anyway, aside from that, let’s just go ahead and clear the screen.

We will go ahead and have a list of IPS, as I have just done. Addr show. Just wanted to make the screen a little bit neater. And here we have the loopback interface, which is the first one. So lo and we have the Link loopback IP address. We’re not really that interested in it. Those things are always the same. Down below we have well, this is the loopback IP address. Actually here one hundred and twenty seven, zero one and this is always the same. It doesn’t matter really on which operating system, on all Unix Linuxlike systems it’s 127 one. I do believe that it’s exactly the same on Windows and definitely the same on Mac, if I’m not mistaken. Down below we have the interface that we are using. It’s m zero s three. And here we see the inet which is the Internet address, sorry, not the Internet address, which is the interface address. It’s the IP address which has been assigned to this interface. Let me put it so that’s the proper term to say it. So we have 192-16-8112 and this signifies 24. This signifies to which subnet does it belong?

To which network does it belong? Let me put it so perhaps it is simpler. So to which network does this belong? This is actually you can get a subnet mask from this and then you can figure out exactly to which network it belongs by calculating the range. But that is a well, I wouldn’t say complex math, it’s doable. But that is not a portion of but is not included in this course as you will definitely not need it as far as I know for the Red Hat certified system administrator exam. Anyway, let’s go ahead and have a look at some other things as well that we can do with IP. So if we type in IP Link show, this will show me my interfaces. So we see that we have Lo, it says loop back and we have NP s three. So it says Broadcast mult and we have some other things which are not that interesting to us at the moment. We will see what we can do with this later on and how we can utilize it. But you can also have a look at statistics as demand pages have said, it’s IP s Link. And now we have some interesting things here. Basically you can see the amount of errors the packets dropped, et cetera.

So that can be quite useful. Let’s see if we have anything else to cover in this introductory video. So we’re still doing an introduction to networking. We’re not going to just jump into it. Yes, we also have routes so that can be quite this is a dumb way of saying of putting it, but it’s one of those popular commands most used, I guess in accordance with statistics. Not most used, but certainly up there somewhere. Route, route show. And you can see it says Default via 19216 811 and then it says Dev for device. And then we have the network interface name. There you go. Okay, basically all the connections are our connections are routed here and this is the default gateway. This is basically my home router towards which the connections are routed so they can go on to the Internet. This can be changed, of course, you can add different routes and have a lot of fun with it. So here it says SRC, which is the source IP address 192-16-8112.

This is the IP address of this particular computer. So the one that I am using, the one that has been assigned to the interface, you can go ahead and see that this is true by typing in iPadR show M three. So you see, we can also specify the name of a particular interface here. You do not have to list everything for every single interface. So you can go ahead and clearly see that this is indeed the source IP address, that this is the interface that we are using at the moment. Keep in mind that all of these commands are like any other in uniFLOW flight systems. You can pipe them, you can redirect input, output, whatever. So if I type in grab in it and I am going to go ahead and put this into quotes because I want to grab the space as well and there you go. I have the IP address and the sudden mask prefix there. But if I go ahead and do this, you see, without the quotation marks, I will get both of them because I didn’t envelop the space part. By space part I mean I’m referring to this part here.

You see there’s a space and here it’s six and then space. If I grip the space as well, it will only print this particular line out. Anyway, I hope that I have at least introduced you to networking and Linux to a fairly good extent, but I didn’t want to burden this particular introductory tutorial with too much info. I just want to explain to you the basics of IP command, what you can do with it. Basically, IP is not only used to show stats, it can also be used to adjust stats like give an IP address, sign a route or something of a kind. This we will do in the follow up tutorials where I will explain these things in far more detail. But for the time being, one of the primary objectives is that you do not use if config anymore. Maybe some of you who are taking this tutorial are using if configure. And in all honesty, as I said, even I do use it to this day on today, use both IP and if confconfig, but it’s a good idea, and I strongly advise you to switch into IP, as that is the current standard and that is the future standard as well. For a good while now anyway. I bid you all farewell and I wish you a tumbled flock.

2. Network manager

Welcome all to this tutorial. Today I will talk a bit about Network Manager. Network Manager tools and persistent network configuration. First things first, let’s go ahead and see how a nonpersistent network configuration looks like. How would you perform it and what do I mean by nonpersistent? Well, first things first. Nonpersistent simply means that it will not survive a system wide reboot and it will not survive the interface restart. So if you bring the interface down and up, the configuration will be gone. One such example would be just to add a different IP address. If I type in iPadR Show, I will see that it has an IP address of 192-16-8112 and that is the IP address which I would like to change. So go ahead and type in iPadR. And the help menu here is a bit different from the ones that you’ve seen before. You do not require any hyphens, rather instead you just type in Help and there you have it. So here we can take a look at the help bar and what I’m interested in the most is the syntax of the command. So iPadR and then it says in the first line add, change, replace at the moment I would like to add and well then I need to type in the interface address that I would like to add. So ten 1010 I’m just giving a random interface address here without much meaning, but it doesn’t really matter.

I can now go ahead and type in dev and the dev will be ENP 30 s if I’m three s zero three s zero if I’m not mistaken, just go ahead and see. Is it ENP zero s three okay, so my bad here. Zero s, three that’s it. Operation not permitted. Why? Well, we are a regular user, we’re not root. So let’s go ahead and relog as root. No big deal. There we go. I’m just going to go ahead and copy paste this command. So let’s put it here. And now we can type in iPadR Show. Now you can see that there is an additional IP address listed here. Notice that we did not delete the previous one. We did not use a change command whether instead we have added a new IP address which is also assigned to this interface. Interfaces can have as many IP addresses as you like. I’m sure that there is a limit up there somewhere, but generally you can assign multiple IPS to a single interface. That is not a big deal. If you just take a look at the iPadR Help, you have some other options here such as to save it or to flush it. Well, sorry, no, this is not what I’m supposed to be looking at. You have a command to add it, to change it, or to replace it. For example, you have this one here to delete it. So interface address and then the dev.

Let’s go ahead and delete the one that we’ve just entered so iPadR Dell and it’s ENP. What is next. We need to type sorry, this is 1010 and then we need to type in Device. So dev, ENP, zero, s, three, press Enter. Warning executing wildcard lesion to stay compatible with old scripts. Yeah, this is a warning, not an error. So hopefully all worked out. Addr show. Excellent. The old one has indeed been deleted. It is gone. While we have the new one that remains. Well, we didn’t delete a new one, we didn’t delete the old one, we deleted a new one. But you get the idea. I mean, you would just change the IP address here that you would like to delete and type it in. No big deal really. You can type in any IP address that you want that is needed for deletion and that is all that you need to do there. No big deal anyway. That would be a typical example of well, basic configuration which is non persistent and it’s not very reliable. I mean, you would usually use this kind of configuration to test something out, not to actually implement it. Let me just show you what I mean by it.

So if I type in APDR Ad and if we type in IP, oh, this is not what I need actually, maybe well, there is a simpler way to do this. So it’s Nm CLI. This is a network manager client command line interface which I’m going to talk about in just a moment. We’re going to deal with it now, not much though, because there is a much wiser way of doing this. But let me just show it to you this way. So connection and now we would like to say down and just keep pressing tab and let’s say ENP Enter connection successfully deactivated. But notice that we have assigned an IP address prior to this. So if we type in iPadR show this interface is down, we no longer have anything there. But if we go ahead and say up, the interface is back up. But the one IP address that we have added is gone. Let me just show it to you one more time really fast. There we go. So all CDs I have added the IP address, iPadR ad and then 1010 dev and three, I will just type in ipadrshow and there you go.

We have that second IP address there. Hopefully you can see it now when I do this down and if I do up again, you see the IP address is gone. So this is not the form of permanent configuration that you can actually make on the system that is valid or anything of a kind. This is just a temporary basis, that is all. For permanent configuration you will need to go into Etsy where the config files are config network scripts. Let’s clear the screen and do this is even worse. So LS is better in this case. And here we can see the interfaces. So we have the script for the first interface. It’s ifcfgnp s three. Let’s go ahead and take a look in that script. Let’s see what’s in there.

So vim if CFG m three and here we have well, I wouldn’t say a configuration parameters to configure. We have quite a few. We can add some of our own as well. But down below you see the second to last option. It says device. And then you have there you have the name of the device. And that’s the device. And then up above sorry, a little bit up above you have the name where it says n zero, s three, just above the UUID. What else do we got that is interesting to us? We do not have the DNS service, which is odd enough. So let’s go ahead and add our DNS servers here. How do you do that? Well, it’s fairly simple. Need the insert mode first. Well, it’s fairly simple.

There’s nothing really too complicated. There’s not that much complication to it. First, let me just go ahead and check. Am I even connected to the Internet? Quit ping google. com. Okay, so I am indeed. Let’s just see iPadR show it does have an assigned IP address. Strange. So LS, am I picking up the right interface? Here I am. Okay, so it’s a virtual machine. No big deal. Let’s go ahead and type in Vim ifcfg entree. And let’s go ahead and type some of our own things here.

Network Manager has already generated a file which is here, let me just show it to you just quickly before we just show it to you quickly. It’s cats resolve. com. This is the file generated by the Network Manager. Clear? This is the file generated by the Network Manager. And you see the name servers. That’s basically the DNS servers. They are typed in here. So 208, 672222. These are the Open DNS servers which my virtual machine has picked up from my physical machine. And my physical machine has in turn picked them up from my router, where I have configured my default DNS server. So I’m not using the DNS service of my SB provider. Rather instead I’m using Open DNS, open DNS, DNS servers or name servers, whichever way you wish to refer to them.

No big deal. Anyway, if we go ahead and go back to this file, you can also type in here. Well, we can type it in anywhere, really. So on boot? Yes. Let’s go ahead and type it in second to last DNS one.

That can be for example, I don’t know the Open DNS service by heart now, sorry, but I can type in 8. 8. 8 and I can type in DNS two equals which one was it? 8. 8. 4 . 4. These are Google DNS servers, which are public and free to use for anyone. Open DNS is also free. I tend to use it. But you can also use Google. No big deal. You can use both of them as you choose and please. So these are some of the things which we can configure here. I do believe that it accepts up to three DNS, three DNS servers. So you can type in DNS three and add a third one. But this is really not necessary. If the second one fails, then something then there is a serious problem somewhere because the first one almost never, I mean almost never fails. Okay, so let’s see, what else can we change? We have the two DNS servers typed in here. Now I would like to configure a static IP address. So the first thing that I am going to do is instead of the Hcp here, I will go ahead and write static. And down below I will add a few lines as well. The first line that I shall add is an amp. So Network Manager controlled? Quite literally. So yes. And then down below I would also like to add the IP address. So iPadR equals to ten 10100.

We know that this is not the current IP address of the interface. And down below, what else would you like to type in? Well, the mask. So type in Net mask equals to 255-255-2550. Really, we just need these four lines and that should be it. Although this is definitely not going to work for multiple reasons. But I just want to show you how a permanent configuration would look like. Primarily because the router on the other side, the existing router will not accept this IP address. That’s one of the reasons why this wouldn’t work. There are a few others, but it doesn’t really matter. Not looking to connect to the Internet or anything of a kind. I just want to demonstrate, I just want to show you how can you enact permanent configuration which will survive system wide reboots and which will survive interface restarts. That’s the point. That’s the goal.

That’s the agenda of this exercise. Okay, now that we have that configured, let’s go ahead and just take a look at your Network Manager here. It says wired. You can either disconnect it, reconnected here, so it says here on and then you can say off, on, off. That should be fine. Usually it will prompt you with the second network interface here, which you can choose. And the old one will be gone. The one that you’ve modified, you can choose it there. It will have the same name. So no big deal there. In addition to that, aside from that you can actually type in Systemctl Network wait, come on. Oh yeah, of course. Systemctl restart. Network Manager Go ahead and press Enter. That will restart the network manager? Definitely. And now type in iPad Show. You will see that indeed we have ten 00:24 on our interface. If you don’t get it straight away, as I said, just go ahead and click on your Network Manager here in the upper right corner and change it.

You will be prompted with it. Another thing is to take into consideration is this 24. Let me just show you what that is. So vim CFG. Okay, so you see this net mask that I am selecting now and you’ve seen the 24 there back in that file. Let me just show you one more time so you know exactly what I’m talking about. You have slash 24 here and then in this configuration file you have 2552-255-2550. Well this is exactly the same on most devices anyway, in most places anyway. As me typing in come on, I need insert as me typing in 24. 24 represents well, maybe not the most corrective statements but sufficient for this tutorial. Slash 24 would basically represent 255-255-2550. You have different prefixes here, you can write 32 and then this mask down below would be different.

I’m not sure which one would it be? I think it would be two five two or something of a kind. But don’t hold my word to it. There is a good deal of math behind this that you do need to perform some calculations there in order to figure it out. But I’m just giving you an example so that you know what it actually means. You won’t have to bother much or at all with it during the red head certified system administrator exam. Okay? So let’s go ahead and quit this file because I am honestly not going to alter it any further. I’ll just go ahead and quit it. So you see that the interface configuration did survive the interface, us bringing the interface down and up and restarting the network manager as well. Not sure have I actually brought them down and up. Actually we can just go ahead in case I failed to do this, but interface everything has been restart by the network manager anyway. We can just go ahead and type in one of these commands. So nm CLI connection down, up, down and now we will need it to go up. So we are stating network Manager client a command line interface connection. We’re stating the status up or down and then we’re stating the interface. So up and please give me the iPadR show. You can see that the same IP address is valid again. It stands there. So whatever you do in that file is going to be permanent configuration that will survive, that will survive interface restarts. No worries there. Anyway, I am running a bit short on time here so I will bid you all farewell until next tutorial where we shall deal further with this.

3. Network manager and network configuration part 2 + some troubleshooting tools

Welcome all to this tutorial. Today I will primarily focus on the network manager. So there is a way of creating new interfaces or well, new connections should be a precise way of saying it. There is a way of creating new connections and interfaces as well via the Network Manager command line interface. Basically you type in nmcli, then you type in a rather lengthy command that you can see in the help menu that there are a lot of options here, but this is not something you want to do. I mean, it’s fairly complicated and if you are doing this during the time of the exam you are bound to make errors here. I don’t know that many people who use this command directly like this to create new connections. Rather instead what they use is NMDU and there you go. You get a terminal user interface where you can actually mess around with things. So you can set a system host name, you can activate a certain connection or you can go ahead and edit the connection. So now we have amp zero s three but we can also play around with it and say hey, we would like to add a new one. Oh, by the way, you press tab to move about to switch from one menu to the next and then you have arrows to move within a menu. So we can edit the current one, we can delete the current one or we can add a new one. Let’s go ahead and click on Edit. You can see that we have a certain settings here. So we have the profile name, we have the device Mac address here.

Mac address is the physical address, physical hardware address that is pretty much imprinted and burned into every piece of every network card out there. Every network card has one and they are unique. Down below you have addresses where we have placed our own address, basically just some random address. And then we didn’t add a gateway. The gateway would be the point of exit where we could access the net or some computer that has access to some other computer that has access to the internet or a router, which is a more common case. Down below we have entered two DNS, two separate DNS servers. So we can feel free to actually go into this file and to configure things here. So I’m just going to go ahead and press OK, we can also say add and then we can add a new connection here. So look at the type of connections that we have here. Well, what do we really need? Okay, so I use a DSL connection. So I could actually create a DSL here. Well, I don’t use it like this, but I think I used to use it a while ago in this apartment anyway, where you had to type in username and password. Rarely anybody uses this today, but some people do.

So you could basically configure your connection through this place by typing in the username and password that your Internet service provider has given to you and that would be fairly easy. So we have Ethernet, we can just say Show and then you have some of the things here that you can type in as well. I’m just going to scroll down to the bottom. This is not really that interesting primarily because it’s rather easy to set up. I mean you don’t really set up most of these things. The primary thing is the username and password without which you will not be able to log in. The rest is pretty much provided by your service Internet service provider as well. Anyway, now that you know how to edit our well just to delete it you would just click on Delete and add would just create another one. Another one next to EMP another connection so to say it would be fairly easy to create. Do try to do it yourselves. If you fail, go ahead and just address me in the discussion section. Feel free to bombard me with questions. I am quite frequently around and more than happy to answer any inquiries that you might have. Anyway, let’s go ahead and quit this.

I’m just going to go ahead and clear the screen. So clear. And now I would like to talk a bit about some of the tools that we will well we won’t use them personally but that can be of great use to you. You can download them from the net or you can get them from the official repositories. It is not that difficult. You just need to use Yam to search for them and to install them. No big deal. And in such a way you will be able to install them. But just one moment before we actually do that, there is another network manager configuration that you can go ahead and edit. There is network settings in the GUI which is not the best way to go about things. Why? Well, you won’t have GUI always let’s put it so this is your current connection. So Wired wired is 1000 megabits per second while IPV four address it’s 10100 IPV six address which is not that interesting to us primarily because it is not that well used.

Down below we have the hardware address and two DNS servers below. So even here we can mess around with settings and have some fun. So basically you can just go ahead and click here and then you can change certain information as well. Whatever you would like. You can pretty much change or add here pretty much the same configuration file as you have in your Mute tool. Now we have some other network commands which we can go ahead and test out in order to confirm connections or something of a kind. First of all we have Ping. So if I type in Pingupspinggoogle. com, it’s going to say unknown Host. Why will it say unknown host. Well, because my connection is messed up and I need to actually go ahead and change the IP settings there in order for this to actually work. So let’s go ahead and delete those settings that we have. Delete those parameters that are there. First thing that we need to do is change the boot protocol to change it to none. Strange, doesn’t really matter. Maybe I’ve misconfigured it somewhere or something of a kind, no big deal.

I’m going to go ahead and delete this and say DHCP down below. Where is it? Where is it? We can also delete this line because we don’t really need it and we don’t really need these two servers because things will be picked up from our host anyway. Also. Yeah, you see, it actually changed some other things. It said prefix equals to 24 as that is an easier notation. Now I can leave the prefix because it’s going to stay the same, but I will delete the IP address as I do not really require it. So let’s go ahead and write quit. Quit System CTL Restart network Manager thank you very much. And you see, I have a choice between my old and the new connection. So go ahead and choose the new one here. You can do the same thing in the Tui interface. It is very simple. The reason why I showed you the terminal user interface, so you do not have to type in Nmap CLI and then a long, very long command to even create an interface to even create a connection, unless something else to add some parameters or something of a kind. So that’s not something that you want to be using.

You can look into it if you wish, but there really is no justifiable reason not to use Mute as it is a fantastic tool. Okay, so let’s just go ahead and quit this anyway. Let’s go ahead and type in iPadR show. Excellent, now we have that. Let’s go ahead and clear the screen and do ping Google. com. Excellent. So now we know that we have connection and this is a foolproof way of confirming that you are actually connected to the Internet. Well, maybe not absolutely foolproof, but this is a general way of people checking whether they are connected to the Internet or not. They just ping a server somewhere and they see can they actually reach a public server or not. For example, can I reach Google. com? And Google is kind enough to allow pings usually probably around 70% to 80% cases. Servers will deny you pings. Routers will definitely deny you pings.

Most of the well configured routers anyway, and well configured servers. But some of the servers that can withstand the bandwidth, like Google, they’re kind enough to allow us to be able to ping them. And I generally use pin google. com in order to verify whether I’m connected to the net or not. So that is a very nice troubleshooting tool. But aside from that you can actually test whether you can reach a certain network or not. So do you remember the network that we SSH to? So it’s 1921-6811 and you see, I can actually get to that network. So I’m pinging it, I know that it’s alive, I know that it’s somewhere, it is replying to me and it’s functional.

So I know now that the problem can either be that I haven’t configured a firewall or that the SSH is not configured properly. Once I configured the Firewall, I know that the SSH is the problem. But how do you know that the port 80 or 22 or something of a kind? By the way, port 80 is the web server port and port four, four, three, that’s the Https for encrypted web traffic. How would you know that the port is open somewhere? Well, you can do it locally on the server itself by typing in, by using one of the tools called Netstat. So net, stat and tool pen. And here listening ports will be listed. So look, I have a 22 port that is listening and I have 31 89. That’s something else. I have literally no idea what is this and some other things as well. But I only have like 123456 ports in total where I am listening for traffic. So you can see that the foreign address, state and local address.

So, fairly simple logic, but you can also type in net statue, TCP to view your pending connection, to view your connections, I have literally none. But here I can open up a browser and that’s bound to spawn some connections, right? No, apparently not. And there we go. So it says immediately that I have established connections to here and here, and here you can see that this is the Https protocol is TCP and it says established time wait usually means if that time weight expires, the connection will be dropped and proclaimed invalid. But usually if it says time wait, it’s gone. Most likely if there is that much of a delay, by the way, if you just type in Netstat like this, you’re going to get all the sockets and these are Unix system sockets. This is not something that we’re interested in at the moment at all because these are not connections to exterior servers.

This is for intersystem communication. If you want to figure out who Googlecom was, if you had the, if you had the domain name but you didn’t have the IP address, the solution would be rather simple. You would just type in Nslookupgoogle. com and there you go. You have the addresses and you have the domains. Fairly simple, right? So it says Google. com and then giving us the addresses. So there are quite a few of them, but there’s another command for DNS servers. So you can type in like Dig google. com and there you go. So if we just scroll upwards a little bit, we got the same answers. Just so you know, it says that we do not have any errors. We’ve made one query and we got eight answers. So all of these IP addresses are attached to this domain. Google has quite a few of them. I’m just using them as an example. You can do this on your local coffee shop website and just have a look which sort of IP addresses are bound. You’re not doing anything illegal.

This information is very much public and system edmunds. Use it on daily basis, just so you know. Anyway, we do have just a few more things to actually cover. You have Trace Route, which is basically, let me show you Trace route. But this is not really working anymore anyway, because most routers today have been configured to pass traffic through and not give any responses to any queries in regards to pings or trace routes or anything of a kind. They just allow everything to pass through, but they will not provide answers. And that is what these three dots mean. So that can be quite a bit of a problem because what you are using Trace Route command is to actually see from which server to which server is your connection going and where is it traveling. See, my IP address somewhere in here. Doesn’t really matter because the dynamic IP address, it will change the moment I reset my router. And I do that quite frequently as well. So it doesn’t really matter if you saw my real IP address or not completely relevant anyway. I don’t know. Just a lot of people shy away from their IP addresses. Don’t really know why they’re dynamic anyway.

They change from day to day, so it’s really relevant. Anyway, these three dots I was saying, they just mean that the devices or the routers are not responding, but that our packet is actually passing through a device which is not communicating with us. It does not want to provide the reply to Trace route or to Ping or to anything of a kind. So we do not know the IP address, we have no information on the servers of whatsoever. And that can be a bit problematic, as I said, because if you’re trying to establish where the problem lies and you’re unable to get a reply from certain servers, it can be very inconvenient. Now, aside from netstatping, traceroute, dig and slap up, you also have Nmap. Nmap is a tool for scanning networks and probing them. Do not believe I have it installed? No, I do not. But you can just type in Yon, search Nmap. Not sure if I have to enable additional repositories for this or not. We’ll see a bit later on when we keep on adding repositories.

No, I actually do not. I can type in Yong. Install Nmap. Yes, there we go. This will install nmap. And Nmap is generally used for ill purposes or something of a kind. But there are an increasing amount of people who use the tool for the primary purpose for which the tool was designed, and that is for network admins, basically to be able to establish status of their services, to establish whether the services are vulnerable to certain occurs of attack. And most importantly of all, what people tend to use Nmap for is to verify are the ports open on a particular server. So if I type in, give me double verbosity Nmap. You should definitely educate yourselves more on that subject. You won’t be required to know it in details for the Redhead certified system administrator exam. So no worries there.

But as an administrator in general, you should really know what Nmap is, how to use it, and you should get acquainted better with it. So I’m not sure, did I actually scan the proper IP address? I typed in 101 and it says that the port 80 is filtered. That usually means that the port 80 is closed. It will either say closed, filtered or open. So for example, if I was scanning my SSH server, not sure if the IP address for the SSH server has changed, if I was scanning my SSH server and if I said, hey, why don’t I check port 22 and see what is going on there, is port 22 open? Is it responsive? So if I figure out port 22 is open, if I figure out that I can ping the server, I then know that I don’t have a problem with the firewall. And you see it says 22 TCP open SSH. I know that it’s not a problem with the firewall. Then I know that’s not a problem with connectivity. Then only one choice remains. And that one choice is that the SSH protocol or whatever protocol we are using is actually misconfigured or there’s bug there.

So we know exactly where to look for that problem. Anyway, I am going to cut the tutorial here and I will bid you all farewell until we see each other in the follow up tutorials.

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