Cisco CCNA 200-301 – IPv6 Addressing and Routing

1. Introduction

This section, you will start learning about IPV Six, starting with how the addressing works. Now, if you’re an engineer working for a company, there’s actually quite a good chance that you won’t even be using IPV Six at all, particularly if you’re working for a small to medium sized company in a Western country. But you still need to know IPV Six. If you go work for a service provider or a larger company, or a company, maybe in another area, there’s a good chance that you will be configuring IPV Six on a daily basis. And even if you don’t, for sure it’s going to come up in conversations.

So you do need to understand IPV Six. Now, when you first see IPV Six, it can seem a lot more complicated than IPV Four because the address is so long. But as you’re going to learn over the course of this section, IPV Six actually isn’t any more difficult than IPV Four at all. For configuring everything, it’s almost all done exactly the same way that we configure IPV Four, we just use addresses that are in a different format. So IPV Six nothing to be scared of. We’ll start covering it in this section.

2. Why We Need IPv6

You’ll learn about IPV six Global Unicast addresses. The different types of addresses that we’ve got in IPV Six are Global Unicast unique local, and Link local. We’ll cover unique local and link local in a later lecture. In this section, this lecture, we’re going to focus on Global Unicast. Global Unicast addresses are similar to IPV Four public addresses, meaning not private addresses. It is an IPV Four public address that’s publicly reachable but was assigned by the Internet authorities. So global Unicast addresses in IPV Six are equivalent to that. They’re assigned to an individual host and have global reachability everywhere on the Internet unless blocked by security policy like on a firewall. And they’re assigned from the range 2000 Doublecolon Three. The Internet authorities assign blocks from that overall 2000 Double Colon free range to different organizations that need to communicate on the Internet. And a common assignment for a company is a Slash 48 block.

For example, 20010 Double Coulomb 48. So the example is a company has applied through a service provider for a block of IP addresses, and they were given that. So normally it will be a Slash 48, but a larger size block can be assigned depending on the size of the company. So a larger company can get more addresses, a smaller company will get less addresses. And if you’re using IPV Six at home, just yourself, individually, you’ll be given a 64, which will be assigned by DHCP. Typically, the reason that an individual would be assigned to 64 is that the IPV Six standards state that addresses assigned to individual hosts should use a 64 mask. So that doesn’t just apply to you at home, every organization, everywhere as well, even when they’re using a large block of addresses for their individual hosts, every individual host should use a 64. It’s not like an IPV Four where we can be using a 24 or a 16 or a 30 on point to point links. For example, everywhere we’re expected to use a 64. Now, the IPV Six address is 128 bits long, so a 64 splits it in half.

Half of the address is going to be the network portion, and the other half is the host portion. And if a company is assigned a 48 address by the Internet authorities, which is common and uses 64 host addresses, which is what they’re supposed to do, that leaves 16 bits that the company can use to assign to its internal subnets to its different links. For example, if the company was assigned 20010 Double Colon 48 by the Internet authorities, then that leaves subnets 2000 and 110 100 Slash 64 to 2000 and 110 Ten FF F 64 to be available to be assigned to its internal network segments. So they’ve got 16 bits that they can play with for dividing up the larger 48 block. In smaller subnets, 16 bits means 65,534 possible subnets. So that should be plenty for most situations.

That also leaves us 64 bits left over for the host address. And you can see the number on the slide here. It’s a huge amount of hosts that you could have in the one subnet. You’re never going to get up to anywhere near that kind of number. And if you look at the last bullet point in the slide here, you can see a common way that the IP V six address is going to be divided up, that the first three hex TETS are the overall 48 block that was assigned to the company. The next, the fourth hexet is going to be divided up into different subnets. And the last four hextets are what is assigned to the individual host.

So we’ve got an example here where a company has been assigned the 48 block, 2001 colon DB eight, colon zero. So that fourth hexet is what they’re going to use for each of their different subnets. And you can see the example here on the link between R One and R two that’s subnet 2001 DB 80 one. The link between R Two and R Three is 2001 DB 80 two. If you look below R One on its Fast 20 interface, that’s 2001 DB 80 zero. And on the link going down from R Three on its Fast 20 interface, that’s 2001 DB 80 three. So you can see that here for this organization, all of their IPV six addresses everywhere begin with 2001 DB 80. That was the 48 block that they were assigned the next hex debt. Well, the first subnet is zero, the next subnet is one, the next one is two, and so on and so on. They’re still going to make sure that when they allocate those subnets, that they do it in contiguous blocks because that’s going to help with the summarization that they’re going to configure on their routers. Okay, next thing is we’re going to have to configure IP addresses on the hosts as well.

So on that link between R One and R two, on the R One side on its Fast zero interface, we give it IP address 2001 DB 80 One, which is the subnet, and then the host address. On the link between R two and R three. On the R three side on its Fast 10 interface, we’ve given it IP address 2001 DB 802001. So you can see how the IPV six address works here. We’re also going to take that on a stage as well because we’re going to do the address shortening, so we’re going to remove that contiguous blocks of zeros. So again, that same interface on R one, the fast zero interface, it gets IP address 2001 DB 80 one, doublecoolon 164. That’s just another way of writing the address that you saw earlier, where we’ve stripped out those contiguous blocks of zeros, and we just write it as a double colon one at the end. So that was the address on R one, the address on R Three on its Fast 10 interface is 2001. DB 80 two for the subnet double on one. If you have a look on the other side of that link on R two, on R two’s fast 10 interface, it would get IP address 2001 colon DB eight, colon zero two because it’s on the same subnet and then double colon two.

So the host portion of the address is different. And now we’re going to have connectivity between all of our different hosts that you see in the diagram there. Now, using a 64 for all network subnets, including pointtopoint links and look back addresses can seem wasteful. In IPV four, you don’t do that. Definitely, if you were using actual public IP addresses and IPV four, it’s pretty standard that we use a Slash 30 for point to point links because that gives us an address on one side and address on the other side. For loopback addresses, it’s standard that we use a 32, but in IPV six, you don’t do that. You always use slash 64s everywhere. Old school engineers can have a bit of a problem with this because we’ve had it drummed into us for years that we don’t waste addresses.

But for IPV six, the official line from the authorities is that there’s that many addresses, but it doesn’t matter if you waste huge chunks of them. So it’s recommended use 64 is everywhere. That simplifies the overall addressing plan, and it also enables the use of Eui 64 addresses that you’re going to learn about later in this section. So how do we actually configure this? First thing that we need to do is to enable IPV Six routing with the IPV Six unicast routing command. But actually, it’s probably about time to wrap up this lecture. So let’s do the configuration in the next lecture where I’ll also show you how to do it.