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We're going to start talking now about some of our transition mechanisms.
Specifically, we're going to talk about tunnels, and we're going to
talk about just running dual stack, which is a fairly short conversation,
but we'll wrap up with that.
Tunnels, though, we have quite a few different choices
that we're going to go through.
Choice number one is just a standard GRE,
Generic Routing Encapsulation tunnel, and we can run IPv4 over IPv4,
IPv6 over IPv4.
That's, of course, the one we're going to be looking at,
is a way to get IPv6 transported through an IPv4-only network
inside of a GRE tunnel.
Very simple, very straightforward. That will actually probably be
a very, very short lesson.
Then we have IPv6 IP tunnels.
This is a very, very short, again, transition.
I'll probably do these two in one lesson actually, GRE and IPv6 IP,
just the generic IPv6 IP tunnels.
And then from there we're going to move into some of the other IPv6.
And understand, IPv6 IP also includes 6 to 4 tunnels.
That is a type of IPv6 IP tunnel.
So now we're starting to get into some specifics under IPv6 IP tunnel types.
As we're going down here, basically what we're saying is, Okay,
you've got GRE, which means you're going to have the IPv4 header,
followed by a GRE header, followed by an IPv6 header on the inside.
And because we have a GRE header, the GRE header has a type field in it.
That allows us to run IPv4 and IPv6.
And, I guess, if you still cared, IPX/SPX, or DECnet or something over
that same tunnel, if your code even still support that stuff.
But the point is, we can run multiple protocols over the same tunnel.
When you go to IPv6 IP tunnel, you are simply eliminating the GRE header.
And just in the interest of looking at MTU and all that kind of
stuff, I think we will still separate those out.
But, the point is, all we're really doing is eliminating the GRE header
by saying, You know what?
The only thing I'm going to run over this tunnel is IPv6.
So why do I need another header to tell me what the next protocol
is if I just tell both sides, Hey, the next protocol,
the Layer 3 protocol here is IPv6.
I don't need GRE to tell me it's IPv6,
I'm going to program you to know that it's IPv6.
Now, the problem with GRE and IPv6 IP by itself,
is those are both static point-to-point tunnels.
That's great, right up until you have 200 remote sites, 400, 1000, whatever.
It gets quite a bit tedious if you have too many remote sites.
So as we move into 6 to 4, the idea was,
well, here's a way to dynamically build the tunnels.
So these are going to be dynamic multipoint tunnels.
And then you also have ISATAP, which is the same thing -
dynamic multipoint tunnels.
Little easier to configure.
I don't know, I like to refer to them as the progression from 6 to 4.
I'm not sure if that's technically accurate or not,
but they're certainly easier to configure, that's for certain.
And then we'll get into MPLS.
Now, MPLS is just another way of transporting
packets without doing IP forwarding.
So, this is again going to be an IPv4 core with IPv6 running over
top of it, and we'll look at that from two different perspectives.
We'll look at it from 6 PE, which would be more of an enterprise-type
solution, and then we'll look at it from a 6 VPE, which could also
be enterprise, it depends on how you're running your network,
but definitely what the service provider would be doing.
The service provider's not going to do 6 PE, because that does not
support multiple customer.
That would just be, like I said, one enterprise doing this in your core.
So that's another way to get 6 through another protocol, like IPv4.
In this case, instead of using GRE and tunnel encapsulation,
using MPLS for our transport.
And last but not least, we will look at GRE multipoint, which is, of course, DMVPN.
So we'll be taking a look at each one of these types of tunnels
one at a time as we go through.
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