Cisco CCNA 200-301 – IPv6 Addressing and Routing Part 4

7. Unique Local and Link Local Addresses

Learn about unique local and link local IPV six addresses. We’ll start off with unique local. Those are similar to IPV Four RFC 1918 private Addresses. So ten x one 7216 to one 7231 x and 192168 got x. The private addresses, they are not publicly reachable. They are assigned from the range FC zero double seven, and as always, hosts should be assigned 64 addresses. So that’s it for our unique local addresses, not so much to tell you about them, they’re pretty simple, there’s more to tell you about the link local addresses.

So link local addresses are valid for communications on their particular link only. They cannot send traffic out to another link they’re assigned from the range feat a double colon ten to Feb zero doublecolon ten. And again, as always, host should be assigned 64 addresses. So that might seem a bit confusing for now. So let’s have a look and see what we mean by link local and not being able to send traffic off their own link.

In the example here in the diagram, we’ve got routers A, B and C, and they’re all connected to the same network segment through the switch on the left. On that segment, Router A has been assigned IP address feata 64 is this link local address on that interface. Router B is FEA double colon two and router C is Fe eight a double colon three. There’s also another link here as well, which is going between B and D. B and D have also got link local addresses on that link.

B is Feat double colon four and D is Feat double colon five. Now, because these are link local addresses, FEA double colon one, feat double colon two and FEA double colon three. On that link between routers A, B and C they can communicate with each other and FEA double call on four and FEA double call on five. On the link between routers B and D they can communicate with each other as well, but feata double colon one, double colon two and double colon three, do not have any connectivity to FDA double colon four or FDA double colon five.

So link local addresses you can send and receive traffic from them, but it’s only valid on that local link, it will not get routed out another interface on the other side of a router. So you may be thinking, well, why am I ever going to use the link local addresses if it can only send traffic on their local link? They can be used for communications which should not be forwarded beyond the local link like routing protocol, hello packets and updates.

And the link local addresses are mandated on your Cisco router interfaces if IPV six is enabled on them, so they’re mandatory, and the link local addresses are automatically generated with Eui 64 addresses whenever you enable IPV six on an interface, but that automatically generated EU six. Eui 64 address can be overridden by manually configuring a link local address on there. So let’s see how this works.

The example here, we’ve got a new router which has got no IPV six configuration yet. So we do our Show IPV six interface brief and we see that we’ve got no addresses. We then configure our Global Unicast addresses on this router. So first up, IPV six unicast routing to enable IPV six routing on the router. Then on interface fast Zero, we say IPV six address 2001 DB 80 one, double call on one. So that’s a global, unicast address. And we’ve also put a Global Unicast address on interface Fast 20. If we then do a Show IPV six interface brief, I can see on fast Zero I’ve got that Global Unicast address that I just configured, 2001 DB 80 one, double colon one. And the router has also automatically generated a link local address on that interface as well. It’s given it the IPV six link local address Fe 80 double colon C eight, L one two, FFF Fe 24 and also on interface fast 20 because we configured a Global Unicast address on there, the router has also automatically configured a link local address on there.

You can easily see which are the linked local addresses because they begin with Feat notice on interface fast 10 and 30 there is no link local address on there because IPV six was not enabled on those interfaces yet. The link local addresses are valid only in the local link as we covered before. So you can use the same address on multiple interfaces because it’s unique at the interface level. It doesn’t can create a conflict if you use the same address on a different interface. So you can see that here on our one we’ve got IPV six address feat double colon one, link local on fast Zero and we’ve also configured it on Fast 20 as well. You can also see here how to configure the link local address manually. If you do this, it will override having the Eui 64 address. So this can be useful if you want to have a more logical fixed link local address on your router.

Now, let’s talk about multiple addresses on our interfaces. It’s different in IPV four than it is in IPV six. You see, in our example here, we’ve gone on to R one and an interface fast zero slash zero. I’ve said IP address ten dot ten dot ten dot one, it’s a slash 24 and then I hit enter and then I configure IP address 19216 810 124. Well, if you now do a show run, you can see that the IP address on the interface is 19216 810 one. When we entered the second IP address, it wrote over the first IP address. So if you configure multiple IPV four address commands on a router IPV four, it’s the latest one that will take effect. The older ones will be removed. If you do want to have multiple IPV four addresses on an interface on a router. The way you do that is you can see down at the bottom interface fast zero, IP address 170 216 124. And then I use the secondary keyword.

That will allow you to have two IPV four addresses on an interface. But the maximum that you can have is two. If you do configure this, then you see the example here. We’ve got IP address 19216 810 one is the primary, and 170 216 one is the secondary. Whenever you send traffic from the router itself and it’s sourced from that interface, it will use the primary IP address. It’s not normal to configure secondary IPV four addresses. This is very rarely done. Okay? So that’s how it works in IPV four. You can have a maximum of two IP addresses on an interface, and to do that, you have to use the secondary keyword. It’s different in IPV six. In IPV six you can have multiple IPV six addresses on the same interface on a router, and it’s quite happy for you to do that.

So you see the example here, we’ve got an interface fast zero. I’ve got IPV six address Fe 80 double colon one, and I save out to the Link Local address. Then IPV six address 2001 DB 80 zero doublecollon one and IPV Six address, 2001 DB 80 one, doublecollon one. And if this was an IPV four, the second one would have overwritten the first one. But an IPV six, we do a show run interface faster stratego, and I can see that all of my IP addresses are on there. So I’ve got IPV six Address Feat, double colon One, Link Local, and I’ve also got the 2001 DB eight, double colon one, and the 2001 DB 80 one, double colon one. So you can see it will take multiple IP addresses. You can also see from the example here as well that on that same interface, I’ve also got my IPV four addresses on there too. So that will work just fine. This is a dual stack router, meaning that it’s running both IPV four and IPV six.

If a packet comes into the router which has got an IPV four destination address, it will use its IPV four routing. If a packet comes in with an IPV six destination address, then it will use its IPV six routing. Whether it’s going to be IPV four or IPV six depends on the application on the end host, it’s sending traffic through the router. Okay, so to summarize our multiple IPV six addresses, link Local addresses are mandatory on IPV six enabled interfaces. Global Unicast and Unique local addresses are optional. You can have multiple addresses on the same interface and one link local address for routing protocol traffic, and one Global Unicast address for normal routing is typical on your routers. Okay, so that was our other types of addresses. In the next lecture, we’ll take a look at this with a lab demo.

8. Link Local Addresses Lab Demo

You’ll see how to configure IPV Six link local addresses with a lab demo. The scenario that we have is we have an existing network which has already been configured with IPV four, and we’re going to migrate that to a dual stack IPV four and IPV Six network. Another engineer has already been tasked with configuring R Two and R Three, and it’s our job to configure R One. So let’s go on there. Now if I do a Show IP interface brief, you can see we’ve already got the IPV four addresses on there. If I ping 100 one two, that’s the IPV photo address over on R Two. And that’s just fine as well. If I do a Show IPV Six interface brief, you can see that IPV six is not being configured on here yet. So first thing I need to do is to enable IPV Six unicast routing and then I’ll configure my IPV Six addresses on the router. So let’s check and see what I need to configure. On fast 20. It’s 2001 DB 80.

Actually, to make it easier, I will minimize my putty window so that I can see what the IP addresses are. It’s pretty hard to remember them. So I’ll go to interface fast two, slash zero and give it IPV six address. 2001 DB 80 double 64 is standard and on interface fast it’s IPV six address is 2001 DB eight doublecolon 164. And I think these interfaces were no shot already because I had IPV four already enabled on there. But let’s do a no shot anyway just to make sure. So I also do that on interface fast 20. And now I will do a Show IPV Six interface brief and you see that I do have my IPV six addresses on there now. So there is the Global Unicast address I just configured on fast Zero and the address on 20. And you can see the link local addresses have been automatically generated using Eui 64 addresses.

So as soon as I configure a Global Unicast address on the interface, it’s enabled for IPV six. So it gets that link local address. But it’s not very convenient or easy to remember an Eui 64 address. So I will override this with a manually specified link local address. So I’ll go back to Global config and on interface fast Zero, I’ll give it IPV Six address fe Eight DOUBLECOOL one. Because this is R one, I don’t need to specify the subnet mask length, I just say link local. It’s always a 64. And also for fast 20, I’m going to hit the up arrow a couple of times and I’m going to give it exactly the same link local address. That’s fine because it’s only locally significant on that particular interface. Okay, so that is my configuration done on there. Now let’s check. The R two and R three are already configured. So on R two I’ll do a Show IPV Six interface brief and I can see that that’s being configured with the Global Unicast addresses. And the engineer there has given it link local address, fe eight double call on two on both interfaces. And if I look on R three, I’ll do a show IPV six interface brief there. I can see the same thing. It’s been configured with the Global Unicast addresses and we’re using Fe eight double cool on three for the link local. So if I go on to R One, I will be able to ping R two. Let’s just check that connectivity is working okay with our Global Unicast address. So I’ll ping 2001 colon DB eight, colon zero one, double colon two four R two and that is working just fine. Now, if I ping it on its link local address, I’ll ping feat double colon two. And what’s going to happen now is the router asks me which is the output interface, because the link local address beginning with Feat is on fast zero and fast 20 as well.

So the router doesn’t know which interface to send the traffic out of. You don’t have this problem when you send to a Global Unicast address. For example, when I sent to 2001 DB 80 one, double colon two, the router knows well that is reachable out interface fast zero, so it sends it out there. But with the link local, all the interfaces are configured with the same prefix, so the router doesn’t know which interface to send traffic out of. So in this case, we’re sending this towards R two.

So the output interface is fast Ethernet. And I can see that that works just fine. But if I try to ping R Three on its link local address, well, R one is not directly connected to it. So if I say ping feata double call on three, which is a link local interface on R three and send it out into the face fast Ethernet, which points towards R three, this is going to fail. R two does not forward that packet on. It’s only valid on the local interface. Okay, so that was link local addresses. In the next lecture you’ll learn about slack stateless address auto configuration.