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Okay, so moving on we're going
to look at IPv6 stateless

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DHCP. Again, same topology.

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We're not going to change anything
around in the topology right now,

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okay? So, again, this is
going to be between 3 and 6.

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We already had this set
up from the last lesson.

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I haven't changed anything.

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Router 3 going to router 6 where
3 is acting like the router.

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6 is at the moment acting like an
IPv6 slack or stateless address

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auto configuration client.

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So he's getting his address and everything,

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but this is where things get a
little bit different is stateless

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DHCP is basically running DHCP to
get the options but not having

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the address assignment
coming from DHCP itself.

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So just to review here real
quickly before we jump in,

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where we are on Router 6, he's not
getting anything from DHCP that

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we looked at before.

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All he has is an address and a
default route - that's all fine.

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Router 3 at the moment is doing
nothing but sitting over here,

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sending out router advertisement messages,

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debugs are still on.

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What I'm going to do to start here though,

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we've seen the router
advertisement messages,

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so now I'm going to say-- turn
off the debuggings and say,

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do debug IPv6 DHCP, and we're just
going to watch the DHCP debugging

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on both of these guys.

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So we can watch what happens.

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Now, what's cool about this is
there's really nothing to do on the

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client side. What I need to do is
I need to go back to the server

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side. We switch back over here and
go over some of the stuff with

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you here before we start. So we're
going to go over configuring IPv6.

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Now the router side is going to get
the scope and again we're going

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to be using the router for the DHCP server.

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You could of course use Windows,
whatever DHCP server it is you want

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to use for IPv6, it doesn't really
matter as long as - and this is

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probably the only little requirement
here for stateless DHCP.

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By the way, just to throw this out there,

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this topic, I've heard this referred
to as DHCP Lite as well for

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IPv6, although stateless DHCP is
definitely more popular of a term.

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But again, what's going to happen
here is we configure IPv6 DHCP

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scope, so we'll start with that.

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So switching over to our server
we're going to do this on router

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3 and there's a couple things that
are a little bit different with

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configuring an IPv6 DHCP server
although it's not a whole lot.

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So it's really just IPv6 DHCP
pool - and let's give it a name,

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I'll call it something like 6
pool or something like that.

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It doesn't really matter - this
drops us into DHCP pool config mode

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for DHCP version 6.

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Now, normally - and we'll do this
in our next lesson where we're

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going to do full blown DHCP - the
thing a lot of people want to do

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right off the bat is give
it an address to hand out.

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On IPv4, of course we know we
would put in a network statement.

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But that's not how we do stateless.

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The whole idea behind stateless is that,

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the DHCP server actually isn't
handing out the addressing at all.

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The idea here is, all it's going
to hand out are the options.

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For example, I could say something
like-- let's see what I'll put

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in. DNS servers.

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It's actually DNS server.

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I always type name server
and that's not it.

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So, DNS server-- what?

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2001 DB8:100:100::-- yeah,
I know it's incomplete.

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::1. That's not accurate.

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It's not a DNS server, but I
can certainly put that in.

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How about a domain name?

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INE.com - whatever it
is you want to put in.

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Remember what we said in the last
lesson that the problem with slack

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is that it gives you no way to get
other DHCP options to be sent

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to the client.

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And basically what we're doing here
is we're creating a DHCP server

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who is doing nothing but
handing out scope information.

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And the other thing I want to point
out is that none of these are

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about a default route or anything else.

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Like I said, the default router
is coming from neighbor discovery

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router advertisement
messages, not from here.

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So, what we do need to do though--
and this is a little bit different

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from IPv4 if you've ever
run IPv4 DHCP on a router.

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It's certainly not my recommended
practice but it's just easiest

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to do it here this way today.

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What I'm going to do is use this.

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But one thing that's a
little bit different is,

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you have to go into the interface.

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So in our case, it's Fa0/0.36
and you have to say,

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IPv6 DHCP server, and call to
the pool name that we created.

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As soon as we do this - since
we have the debugging on - we

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should see the DHCP server start up.

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There it goes.

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So, IPv6 DHCP server is now started.

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But notice that, we also have
gotten no requests whatsoever.

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And just to show you that it's
not going to happen - like,

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do a reset or something like that
- I'd watch you shut this interface

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on Router 6. We'll bring this thing down.

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And just so you know, I do have IP
version 4 running underneath all

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of this, because we will need
it for some stuff later.

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So when you see that go down, that's
just OSPF for IPv4 running underneath.

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It's also a pretty good indicator
that our sub-interface is down

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there too. So now we'll say, no
shut and we'll see that he still

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doesn't make a DHCP request and
that's because we're not quite done

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yet. He's sitting here doing nothing.

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If I were to say, you know what?

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Why don't you show me the DHCP information?

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Nothing. If you take a look at router 3,

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he's not done anything
except fire up the server.

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We've seen nothing else going on.

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Now, the next thing we can do -
we're going to actually say we have

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to do - is simply to configure the
router advertisement message.

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I'm going to finish off the last
two points I have on here and that

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is to actually configure the IPv6
host and controlling the host portion

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with the link local address.

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Now that part hasn't really changed
from what we did in the last

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section. If I were to
go to router 6 and say,

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Do Show Run Interface gigabit 0/0.36,
we already have our link local

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address configured, which is, of course,

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controlling the IPv6 address, and
the fact that we have IPv6 address

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autoconfig with default
still there from before.

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Those are the two things that those
last two bullet points were meant

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for, and we've already done
those in the previous section.

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But just as a reminder,
they're still there.

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He's still pulling his address, but see,

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nothing there says anything about DHCP.

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So basically, router 6 is sitting here,

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going, yeah, got my prefix, got my route,

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got everything I need.

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Maybe he's thinking to himself,
I'm not inside the router.

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I don't know what he's thinking,
but maybe he's sitting there

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thinking, you know it'd be really handy
if I had a DNS server and a domain name

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here - he doesn't, obviously.

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But the point of course, is this;

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we need to tell Router 6
to get that information.

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This is actually done on the server
side through a router advertisement

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message. Also on the subinterface, we
need to say IPv6 neighbor discovery,

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and the command is, other config flag.

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This is sort of the golden
command, if you will.

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This is the one you might want to
go write down here at the moment.

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This is what makes this DHCP
light or stateless DHCP.

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Two real factors. Number one, obviously,

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there has to be a DHCP server, and
it has to be set up with options.

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And what I was saying earlier,
there was a little bit of a caveat

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with using other devices
as your DHCP server.

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The caveat is they have to support
creating DHCP options without

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having the DHCP scope actually set.

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So as soon as we turn this on, we
will then see router 6 immediately

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go, oh, I'm supposed to
get more information.

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See that? He immediately
starts the DHCP client,

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sends out a request for more information,

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gets the reply, and look at this.

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Now, we have the DNS server and the
domain name just like we wanted.

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You can also, of course, look at
the router 3 side and see that he

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received the request, used
the pool from the interface,

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and sent the information
out that interface.

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So now, if we were to go back here and
look at our DHCP for the interface,

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we can see what happened. He
already got his information.

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Prefix state he wasn't even trying to get,

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but the important thing is he got
those two pieces of information

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right there. The rest of the stuff on here,

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of course, we'll go over in the
next section where we're going to

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do a full-blown DHCP.

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So that's where we're going to head next,

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but this is simply DHCP
Lite, or like I said,

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the real proper common more
recent name is stateless DHCP.

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And again, the big thing to remember
on that is that it is simply

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DHCP with a scope with options, but
no actual pool of addresses to

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hand out. All we're doing is
supplementing slack and using slack

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in combination with DHCP to get a
client everything they need to

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be on the network, not just the prefix,

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not just the default gateway, but
also DNS and any other DHCP options

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they need to actually be a full-blown
functional machine on the network.

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