So now we're going to move on to a DHCPv6 on Cisco and look at both the
stateless and the stateful DHCPv6 configuration on a Cisco router.
I have 2 routers configured in my topology just like I
did for the DHCPv4 demonstration,
and we're going to examine the existing configuration on these routers,
and then we'll also jump into the configuration mode and see
what options are available to us when we are actually
configuring the options for DHCPv6.
Now we're looking at the existing configuration rather than configuring it from
scratch our self simply because IPv6 addresses are kind of difficult to type out
and I'm sure you don't want to sit here and watch me for 30 or 45 seconds typing
out IPv6 prefixes and IP addresses.
Another reason is that the configuration for DHCPv6 is very similar to DHCPv4,
especially in the stateful configuration,
and so a lot of that typing would simply be redundant.
So, without further talking let's jump into our lab here.
So we're going to look at the Bridge,
we will Telnet to the Console port on this guy,
and go into Enable mode,
and the first thing I'm going to do is sh run and look
at the section that includes DHCP.
So, we're going to look at the IPv6 DHCP pool clients.
It looks like this last line is a part of this configuration, but it's not.
We'll show you where that comes into play here in a bit.
You'll notice that this is stateless DHCP because all we have
defined are the DNS server and the domain name.
We don't have any prefixes, we don't have any IP addresses,
and in fact we don't even have any other options,
but we'll look at that in a moment.
Honestly, that's all there is for stateless DHCP.
Now unlike DHCPv4,
when you set up a DHCPv6 server you have to actually
assign that server to an interface,
and that's simply because DHCPv6 utilizes portions of the interface address
that it's bound to as part of the DHCP unique identifier.
You'll recall when we talked about those a little earlier in this module.
And that's where that third line comes into play, that IPv6 DHCP server client.
So if we look at the running configuration for interface g0/2 I believe it is,
you'll see that not only do we have the IPv6 DHCP server bound to this,
but since this is the subnet for our clients,
we are advertising the other config flag in the neighbor discovery packets.
Now, again we only have to do this on one device that's connected to this subnet.
Best practices are to define it on any router that's
connected to this subnet just on the off chance that one
might be offline as an example.
The thing is that unless you're at the core of the network you'll probably only
have a single router connected to any given IPv6 segment.
So let's look at some of the options available to us.
So we'll go into config mode, we'll look at the DHCP pool clients,
and we'll just hit?, and you'll see that for DHCPv6 there's
not a whole lot of options available to us.
We can set up IP address allocation using the address command at the top,
the DNS server and the domain name,
which you've seen in the configuration already,
but we're going to look at the option command.
So we'll look at option, hit?, and oh, oh look,
this isn't the same option that we get with DHCPv4.
I did that on purpose, believe it or not,
simply because I see this quite a bit with people
that are trying to set up DHCPv6, and I don't get that many questions,
and email, or social media about these kinds of configurations,
because again, not a lot of people are using DHCPv6,
but a lot of people will type in option and?
and say,
hey I can't set option 150 or set whatever option I need to set for DHCP,
and I have to point out to them that the command
you're looking for is vendor specific.
So we'll look at vendor-specific,
and with the vendor-specific option configuration you
have to know the vendor's enterprise ID,
which if you're configuring specific DHCPv6 options,
that enterprise ID is almost certainly in that vendor's configuration.
In this case, we're going to configure the equivalent of option 150,
so we're going to use Cisco's vendor ID,
which is 9, again, pulled from the configuration.
And then once we're in the vendor-specific,
we see that really the only option we have is suboption.
So we do suboption and whatever suboption number,
in this case it's suboption 1,
and again the place you get that from is the specific documentation,
and then you fill in the address, ASCII,
or hex for the specific suboption.
In this case, we'll say address, and we'll say fdaa::1.
That's a valid IPv6 address and it's easy to type.
We could specify more than one IPv6 address,
but in this case, we'll just do that, and we'll exit out.
So now if we look at the configuration for the DHCP server,
we now see the vendor-specific suboption for the DHCP server.
So we'll take a quick minute and look over at the stateful
DHCP configuration that's on the server.
So we'll Telnet to the Console port on this guy as well.
And as promised,
the only change in the configuration is the address prefix that you
see there at the top of the configuration lines.
In this case, we have the prefix that we're going to advertise,
which is almost always a /64,
although you can configure it to whatever length you want,
and we specify a lifetime.
There is the preferred time and the valid time.
You'll notice that on this guy if we do sh run int g0/1,
since this is stateful,
we are advertising the managed-config-flag in the neighbor discovery,
and we're also using Rapid Commit.
And again,
if you'll remember the Rapid Commit has to be configured on both
the client and the server for it to be valid.
The last thing we'll look at is the relay configuration,
which is again, almost identical to the IP helper address for IPv4.
We go into config mode, int gig0/1, if we do ipv6 dhcp,
we put in the relay command instead of a client or a server,
and we can specify the destination, which is quite simply the IPv6 address,
and optionally the vrf for the traffic to go out of, and that my friends concludes our discussion of DHCPv6 on Cisco.