CompTIA Linux+ XK0-005 – Unit 09 – Networking Part 2

14. Addressing

All right, how do we communicate? Well, we talked about the protocols like TCP or UDP, and we addressed these communications to your addresses at two layers. One was layer three, the network address, which I called your network, your subnet, your broadcast domain. And once we got to that location, then your physical address or the Mac address. So let me start off by describing a Mac address. Now, first of all, all Mac addresses are specific to Ethernet. Ethernet is one of many layer two data link encapsulation protocols. It is also probably the most popular one because it is the easiest way and probably most inexpensive way for us to connect machines in our local area network.

Now, when we leave our local area network and we hit these wide area network connections, traditionally, we used a different type of encapsulation protocol. In the old days, like ten years ago, it was very prevalent to use frame relay or ATM. Then, of course, as communications have improved, we started seeing other choices. And guess what? We’re now at a point where it’s very common that service providers are providing Ethernet as their method of communications. For you to have a Win connectivity from where you are to wherever your other office is across long distances, it’s amazing, but it seems like everybody’s going after Ethernet, and these service providers are creating these VLANs through their networks that are based on Mac addresses, and they call it VPLs.

All right, I’m digressing into a whole other technology. Anyway, it comes down to the same thing. Your physical address, your Mac, is what helps these big service provider clouds figure out how to forward your traffic. It is your Ethernet address, and it stands for the Media Access Control. Technically, your Mac address does not have to be the same as what I said was your permanent address. Every Ethernet card has burned into it. An address that is called the Bia, the burned in address. Generally, unless you do something about this, your Mac address will be the same as your burned in address. And that’s appropriate. There’s very rare the reason why you need to change it, unless you’re hacking things or some other type of security related issue.

Now, that gets me to the local area. Switches that connect the land only look at Mac addresses for forwarding traffic. When you have to leave your local area network, you’ll do so by going through what we often call your gateway. But it’s a routing device that will take you from your local area network to whatever local area network you’re trying to reach, whether it’s across the Internet or across the building’s parking lot. It’s going to use an IP address to make that determination. Currently, we are using IP version four. It is a 32 bit address. We’ll talk about that a little bit more, but eventually we’re going to have IP version six coming out. And those are just ways, as I said before, of identifying your network.

We also have to deal with character names, as we talked about with the naming conventions. And a part of the communications that we use back and forth is to also include a port number. Now, I’ll talk a little bit more about ports as well as we try to talk about how all of this fits together. That’s that is your IP address, the transport protocol, the port numbers, resolving the names, and dealing with Mac addresses. But all of these things are issues that we would call addressing, and they all interact and work together.

15. Addresses

Now when we talk about addresses and we try to do some comparisons. As I said, the OSI model is probably the latest of the models that we saw TCP IP predated. It with its different levels. Now in the OSI layer, the top three that I call the upper layers application, Presentation and session generally map with the TCP protocol area of applications. Those applications are things like the email, SMTP Pop, the Time services, DHCP, all of those things. I talked about. The transport layer in the OSI model maps to the transport layer in the TCP IP protocols. That’s also generally where you’re going to start seeing ports. Technically the ports do go with the actual application because different applications have port numbers for communications.

But it is facilitated through TCP. So it’s kind of a tricky do I put port numbers up by applications or do I leave it in the transport? I kind of prefer to think of it as an issue with the transport layer, but the port numbers are also how we keep the sessions alive. So you can see where it can be a little iffy about how you want to describe it. Don’t worry, I’ll talk about them more. The network maps to the Internet layer of TCP, which is the IP address. Obviously we use IP addresses for that. Version four, version six, the data link and physical layers map to the data link layer of TCP IP, which in this case we’re talking about Ethernet as our medium. And the addresses in Ethernet are Mac addresses.

16. Internet Protocol Version 4

All right, so let’s talk about this IP address. I gave you some information about the max already. Let’s move up a layer IP. Currently we’re using version four. It is an address that is and by the way, everything in computer world is binary. We all use zeros and ones, but we don’t like to use those when we speak. We like our base ten decimal notation. So when I say to you an IP address, address is a 32 bit address and you’re saying well, no, it’s not. My address was 192 168 one 10. There was nothing binary about it. Well, technically yeah, we converted that binary into a decimal method and we did it through what’s called a dotted decimal notation.

So if you technically look at two to the 32 power there would be over 4 billion addresses that we could potentially use for everybody in the world. We really can’t use that many because of how it’s broken down into network and node on the addresses. And back in 1996 we had already used up half of the available addresses and so we kind of started panicking and said we got to do something about it. And so we began working on IP version six to take care of that problem. However, in the in between time we did some little tricks, some things called Cider, some things called Natting and Padding. And we fixed the problem temporarily. So we’re okay. But we are technically out of addresses today.

Anyway. That 32 bit is broken down into four sections of eight bits. Well, that’s still 32 bits. Each of those sections are separated by a dot, a period and those eight bits are represented by a decimal number. And that’s where you see the dotted decimal notation. Now, when we first used IP version four, it had what was called a classful address scheme. That meant the question that I said before is when I have an IP, part of it’s your network and part of it is your actual node address on that network. The classfulness helped us know how to divide it into network and node or network and host.

There was a class A, B and C that we utilized and the very first dotted decimal number basically told us that class of address. Well, today we’ve taken those classes and we’ve broken them down into further networks beyond what it was originally designed for. And that’s where the world of subnetting comes in. I’m not going to take you down that road because when I do, it’s sometimes not pretty to figure out how subnetting works. What you have have to be concerned with as the person operating your Linux server or your Linux workstation is knowing what address is going to be assigned to you from the network administrator.

17. Internet Protocol Version 6

Now, because of the problem of running out of addresses with IP version four, we are seeing the move and the migration to IP protocol version six. Now, I don’t know what happened with five. Maybe it was an experiment called bad. Anyway, the idea of IP six was to have an address base large enough that we would not run out of addresses in the foreseeable future. Without getting into too much of the history, we really screwed up things with IP version four. We gave out addresses to people who probably shouldn’t have had them. We didn’t have private addresses like we do today. We just, I mean, we just didn’t see perhaps the explosion that the Internet was going to be. IP version six is pretty much going to be set around so that everybody in the world could have their own IP address. They could have their own few hundred IP addresses. Your toaster, your refrigerator, your TV.

We have enough. It’s 128 bit address space, which is a if you did two to the 128 power, don’t know what the number is, but it’s a 39 digit number. That’s how many combinations. Now downside, they don’t use decimal notation. They do everything in hexadecimal notation, separating every two bytes with a set of colons. Now what they have done is they have already broken it down into their version of private addresses, into their versions of different types of assignments to different service providers. So they’ve actually begun a very smart deployment of IP version six. Now, back in the end of 2008, any service provider in the United States that did any type of business with the Department of Defense was required to be ready with IP version six.

Well, easily enough. Every service provider around the world, especially the ones that I’ve worked with, they’re ready for IP version six. Some are already doing it. So it is going to be here, but I can’t give you when will you see it in the North American continent. You can already see it in parts of Asia, the Asia Pacific region. So you’re already seeing IP version six out there being readily used. So it’s not one of these things that will someday happen. It’s on its way. So you should probably start getting comfortable with understanding all of those options that you have. But again, as far as a Linux administrator, it’s only a matter of what address is going to be assigned to us, how are we going to receive that address, and that’s what we need to be able to set up and configure our Linux systems to be able to work with.

18. Assigning Addresses

Now, the addresses we’ve talked about so far, some, of course, are dynamic, some are permanent, some can be static, and there’s all sorts of options. So here you go. Mac addresses are generally permanent. Now, I said that there’s a burned in address in every network interface card, every Ethernet card, and there is, unless you bought some from some unknown vendor somewhere. Your Mac address generally takes off on that burned in address, but you can change it. Generally, though, we call it a permanent address. Some people call it a physical address. IP addresses are assigned by administrators.

Now, they could be statically typed into each machine or they can be dynamically assigned through a service called the Dynamic Host Configuration Protocol. The dynamic option is considered better because we don’t worry about typing things in wrong. We don’t worry about duplicating addresses, which can cause communication errors on the network. So we consider that as a better option for us. And in fact, we can even statically assign an address through a dynamic process so that your servers just don’t suddenly change addresses in the middle of a communication. Now, there are a number of utilities that we’re going to use to be able to verify the types of configurations.

We have to verify what we have set up, and to be able to also configure the addresses on our cards and to verify the connectivity options. The utilities that you’re going to see are going to be twofold there’s if config iwconfig, which can either help you set an address or be used to see what your address is. Ping is an ICMP echo request basically sent to a target if they reply to sending echo reply. And that back and forth as a way of connecting or testing the connectivity between you and some other endpoint. And then, of course, ARP was that tool that we used to see what IP addresses have been translated to what Mac addresses that are stored on our local table. So there are tools that we can use to make the configurations and verify our configurations.

19. Demo – Examining Addresses

All right, we’re going to take a look at a couple of the commands that we would use to look at our configurations. One of the most common, I’m just going to start off with this. ifconfig that’s your interface config, and you notice it says, hey, no, that’s not found. Well, that’s when you switch to the root and then you run if config and then you see all sorts of great stuff happening. Okay, we’re not going to talk about the loopback address again, that’s a virtual address. But here we see the Ethernet zero as the only that we can see anyway, the only active Ethernet card being given address of 192-1681, up 41 broadcast address. The subnet mask that it’s running on, it has an init version six, we call IP version six address as well.

And all of that looks pretty good. Now what a lot of you might be wondering, you’re saying, well, I’m used to doing this stuff in Microsoft and I’m used to seeing the gateway. Well, you know what, the gateway is going to show up in the routing table as it should. So that’s an important aspect because just because you see a gateway on your card doesn’t mean that really is your gateway. So that’s kind of important. I think that we actually correctly see it separated here. We also see the hardware address being an Ethernet card. We know that its Mac address is listed all six bytes and it even gives me a bit of the last few minutes worth of statistics. So these are all good things that I really like seeing, that I really miss when I see or work with other operating systems.

Okay, so what we’re going to do is we’re going to add another visual component. We’re going to go to our top bar here and I’m going to add to the panel the network monitor. If I can spell enough of it in here, I’m going to add that to the panel, close the screen, and then what I’m going to do is I’m going to go to the properties of this thing, hit the support tab, and I’m going to see some of that same information that I just talked about that I had earlier. If I go to the general, of course, had I had any other Ethernet cards, I could have chosen those and also worked with them.

I like that I can click Configure and get a little window in the background where I can start working with that wired connection, general host name, domain names, DNS settings, which, by the way, we didn’t see with the if config right off the bat and anything that’s in my host file as well that are important for the DNS resolution. Okay, so anyway, those are some of the other options about how we can work with our systems. And like I said, the if config is also a very important part of what we want to be able to do. Now, one of the other things that we can do sometimes to test out if everything’s working well is utilize connectivity to commands like ping.

So I’m going to go and say, let’s see if I can ping Google. com. And one of the things you’ll see during this ping is that it actually resolved it to a DNS address there or to an IP address that was DNS. The other funny thing about ping is it just never stops on Linux unless you control C to stop that. But what I did see, of course, is that as I said, I found the actual IP address, which is important. The rest of this information, by the way, also pretty cool. It’s the time to live that I’m using to send the amount of time it takes to the return traffic gives me an indication of how good or bad my network is going. There’s a lot of options with ping.

If I put in the dash help, I can place pattern packet size, TTL interface, or source address. I mean, there’s a lot of stuff I can do to work with it and play with it, and hopefully you get the idea that you can really use it pretty well to test things that you want, even if I say ping C five. So I’m doing a count of five to Www. google. com. Even that is helpful so that I don’t have to wait forever for things to run and then hit CTRL C later on. So there’s a lot of cool stuff you can do and play around with ping commands. All right, so those are, again, some of the options that you have. Some other options you might look at is the ARP table. So I’m using the Sudo command to view my ARP table.

And the goal there is that, again, it’s one of those tables you have to be the route to be able to do. And I only have one person out there, one machine that I’ve discovered through ARP. ARP was the address resolution protocol. So that tells me the Mac address of what I do know is going to be my gateway. But we’ll examine some of those other options about gateways when we get into dealing with things like your routing tables and everything else. So there was a quick introduction to the discovering of your settings for your network cards.

• Category: Uncategorized