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Okay, so moving on we're going to look at IPv6 stateless
DHCP. Again, same topology.
We're not going to change anything around in the topology right now,
okay? So, again, this is going to be between 3 and 6.
We already had this set up from the last lesson.
I haven't changed anything.
Router 3 going to router 6 where 3 is acting like the router.
6 is at the moment acting like an IPv6 slack or stateless address
auto configuration client.
So he's getting his address and everything,
but this is where things get a little bit different is stateless
DHCP is basically running DHCP to get the options but not having
the address assignment coming from DHCP itself.
So just to review here real quickly before we jump in,
where we are on Router 6, he's not getting anything from DHCP that
we looked at before.
All he has is an address and a default route - that's all fine.
Router 3 at the moment is doing nothing but sitting over here,
sending out router advertisement messages,
debugs are still on.
What I'm going to do to start here though,
we've seen the router advertisement messages,
so now I'm going to say-- turn off the debuggings and say,
do debug IPv6 DHCP, and we're just going to watch the DHCP debugging
on both of these guys.
So we can watch what happens.
Now, what's cool about this is there's really nothing to do on the
client side. What I need to do is I need to go back to the server
side. We switch back over here and go over some of the stuff with
you here before we start. So we're going to go over configuring IPv6.
Now the router side is going to get the scope and again we're going
to be using the router for the DHCP server.
You could of course use Windows, whatever DHCP server it is you want
to use for IPv6, it doesn't really matter as long as - and this is
probably the only little requirement here for stateless DHCP.
By the way, just to throw this out there,
this topic, I've heard this referred to as DHCP Lite as well for
IPv6, although stateless DHCP is definitely more popular of a term.
But again, what's going to happen here is we configure IPv6 DHCP
scope, so we'll start with that.
So switching over to our server we're going to do this on router
3 and there's a couple things that are a little bit different with
configuring an IPv6 DHCP server although it's not a whole lot.
So it's really just IPv6 DHCP pool - and let's give it a name,
I'll call it something like 6 pool or something like that.
It doesn't really matter - this drops us into DHCP pool config mode
for DHCP version 6.
Now, normally - and we'll do this in our next lesson where we're
going to do full blown DHCP - the thing a lot of people want to do
right off the bat is give it an address to hand out.
On IPv4, of course we know we would put in a network statement.
But that's not how we do stateless.
The whole idea behind stateless is that,
the DHCP server actually isn't handing out the addressing at all.
The idea here is, all it's going to hand out are the options.
For example, I could say something like-- let's see what I'll put
in. DNS servers.
It's actually DNS server.
I always type name server and that's not it.
So, DNS server-- what?
2001 DB8:100:100::-- yeah, I know it's incomplete.
::1. That's not accurate.
It's not a DNS server, but I can certainly put that in.
How about a domain name?
INE.com - whatever it is you want to put in.
Remember what we said in the last lesson that the problem with slack
is that it gives you no way to get other DHCP options to be sent
to the client.
And basically what we're doing here is we're creating a DHCP server
who is doing nothing but handing out scope information.
And the other thing I want to point out is that none of these are
about a default route or anything else.
Like I said, the default router is coming from neighbor discovery
router advertisement messages, not from here.
So, what we do need to do though-- and this is a little bit different
from IPv4 if you've ever run IPv4 DHCP on a router.
It's certainly not my recommended practice but it's just easiest
to do it here this way today.
What I'm going to do is use this.
But one thing that's a little bit different is,
you have to go into the interface.
So in our case, it's Fa0/0.36 and you have to say,
IPv6 DHCP server, and call to the pool name that we created.
As soon as we do this - since we have the debugging on - we
should see the DHCP server start up.
There it goes.
So, IPv6 DHCP server is now started.
But notice that, we also have gotten no requests whatsoever.
And just to show you that it's not going to happen - like,
do a reset or something like that - I'd watch you shut this interface
on Router 6. We'll bring this thing down.
And just so you know, I do have IP version 4 running underneath all
of this, because we will need it for some stuff later.
So when you see that go down, that's just OSPF for IPv4 running underneath.
It's also a pretty good indicator that our sub-interface is down
there too. So now we'll say, no shut and we'll see that he still
doesn't make a DHCP request and that's because we're not quite done
yet. He's sitting here doing nothing.
If I were to say, you know what?
Why don't you show me the DHCP information?
Nothing. If you take a look at router 3,
he's not done anything except fire up the server.
We've seen nothing else going on.
Now, the next thing we can do - we're going to actually say we have
to do - is simply to configure the router advertisement message.
I'm going to finish off the last two points I have on here and that
is to actually configure the IPv6 host and controlling the host portion
with the link local address.
Now that part hasn't really changed from what we did in the last
section. If I were to go to router 6 and say,
Do Show Run Interface gigabit 0/0.36, we already have our link local
address configured, which is, of course,
controlling the IPv6 address, and the fact that we have IPv6 address
autoconfig with default still there from before.
Those are the two things that those last two bullet points were meant
for, and we've already done those in the previous section.
But just as a reminder, they're still there.
He's still pulling his address, but see,
nothing there says anything about DHCP.
So basically, router 6 is sitting here,
going, yeah, got my prefix, got my route,
got everything I need.
Maybe he's thinking to himself, I'm not inside the router.
I don't know what he's thinking, but maybe he's sitting there
thinking, you know it'd be really handy if I had a DNS server and a domain name
here - he doesn't, obviously.
But the point of course, is this;
we need to tell Router 6 to get that information.
This is actually done on the server side through a router advertisement
message. Also on the subinterface, we need to say IPv6 neighbor discovery,
and the command is, other config flag.
This is sort of the golden command, if you will.
This is the one you might want to go write down here at the moment.
This is what makes this DHCP light or stateless DHCP.
Two real factors. Number one, obviously,
there has to be a DHCP server, and it has to be set up with options.
And what I was saying earlier, there was a little bit of a caveat
with using other devices as your DHCP server.
The caveat is they have to support creating DHCP options without
having the DHCP scope actually set.
So as soon as we turn this on, we will then see router 6 immediately
go, oh, I'm supposed to get more information.
See that? He immediately starts the DHCP client,
sends out a request for more information,
gets the reply, and look at this.
Now, we have the DNS server and the domain name just like we wanted.
You can also, of course, look at the router 3 side and see that he
received the request, used the pool from the interface,
and sent the information out that interface.
So now, if we were to go back here and look at our DHCP for the interface,
we can see what happened. He already got his information.
Prefix state he wasn't even trying to get,
but the important thing is he got those two pieces of information
right there. The rest of the stuff on here,
of course, we'll go over in the next section where we're going to
do a full-blown DHCP.
So that's where we're going to head next,
but this is simply DHCP Lite, or like I said,
the real proper common more recent name is stateless DHCP.
And again, the big thing to remember on that is that it is simply
DHCP with a scope with options, but no actual pool of addresses to
hand out. All we're doing is supplementing slack and using slack
in combination with DHCP to get a client everything they need to
be on the network, not just the prefix,
not just the default gateway, but also DNS and any other DHCP options
they need to actually be a full-blown functional machine on the network.
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