So let's start off with an introduction to Layer 2
VPN by talking about a couple of different things.
We'll start off by talking about the different service
types that are available, which is basically
a quick introduction to the VPN types, which we'll be covering
more in the next video.
But then we're also going to talk about the advantages
to Layer 2 VPN, both from the customer's perspective
and from the service provider's perspective.
And then in the interest of some terminology and understanding
the moving parts, we'll also talk a bit
about the different components in Layer 2 VPN.
So, let's go ahead and jump in and get started
looking at those details.
So starting with the most basic question, what is Layer 2 VPN?
Well, Layer 2 VPN is a service or MPLS application
that provides layer 2 connectivity between customer
sites.
And under this umbrella of Layer 2 VPN,
we do have a few different services that are available.
The first is virtual private Wire Service or VPWS.
This is a point to point connection.
So this would go directly between two customer sites,
and this can actually use L2TPv3 over an IP network,
or it can use MPLS for the transport.
And in that case, we call this AToM
or Any Transport over MPLS.
Now, as we just indicated, AToM is actually
a subset of Virtual Private Wire Service,
and it supports a variety of other protocols.
So it supports ethernet, which is
going to be our primary focus.
However, it also supports some other more legacy protocols,
such as Point to Point Protocol or PPP, HDLC or High Level Data
Link Control, frame relay, and ATM or Asynchronous Transfer
Mode.
So this is sort of where that "any" transport
comes into play.
Meaning, we can support a lot of other layer 2 protocols
over the MPLS environment.
Again, we'll mostly be focusing on ethernet here.
Next up is your Virtual Private Land Services or VPLS.
Now, this one can either be point to multipoint.
So what we would normally call a star topology or multipoint
to multipoint, which would essentially be a full mesh.
So let's talk about L2 VPN from the standpoint
of the advantages, and we'll talk about the enterprise
first.
Now, of course, when we're talking about the enterprise
here, remember, we're looking at this from the service
provider's perspective.
So, we could also refer to this as the customer.
Either way, let's talk about the advantages.
One of the bigger ones is that this is actually
identical to traditional WAN services.
Now, of course, one of the big reasons this is advantageous
is engineers are familiar with this model.
Network engineers have been working with Point
to Point Layer 2 circuits for decades.
All the way back and even before things like T1's, T3's,
OC circuits, things like this--
this has been around for a really long time.
So the customer is going to be very familiar with this model.
They're just going to see this whole thing as a layer 2
handoff.
This is why through the rest of the skill,
we'll be using the term pseudowire
quite a bit because that's effectively what
this is for the end customer.
They just see it as a layer 2 connection between their sites.
And again, this is how we've been doing WAN connections
for a very long time.
And of course, part of all of that
means that the customer is going to have their own routing
and service policies.
The service provider is not going
to be involved in the customer's routing.
Some other advantages here is this
allows for a single infrastructure over which,
we can run both IP and traditional services.
Again, we can support ethernet, PPP, HDLC, ATM.
A lot of different things can be supported
over a single infrastructure.
This also optimizes the data center solution.
Now, you may be curious what any of this
has to do with the data center.
Well, things like live migration for your servers
require that the server be on the same subnet
when it reaches the other destination, the other host.
In order for that to be, say, in a different data
center like a backup data center,
that needs to be a layer 2 connection.
And that's why this is a popular choice.
Now, are there other technologies to do that?
Of course, there are.
There are many other ways to do this,
but this is a good solution because of the fact
that it is a layer 2 handoff.
And of course, this maintains enterprise autonomy
because customer A and customer B's traffic never
touches, never crosses.
It's a layer 2 circuit that's completely separate
and carrying only that customer's traffic.
Now, this has advantages for the service provider as well.
First, it gives us a really, really good migration path
to go to an MPLS or IP core.
So if we've traditionally offered, say,
frame relay or ATM solutions or T1's or any
of these sort of legacy technologies,
this gives us a real easy path to move the core of our network
over to again, either MPLS or IP.
Our focus right now is going to be MPLS.
However, it lets us migrate to that,
while still supporting customers on those legacy technologies
because of course, we have to get our core updated
before we can start migrating our customers over
to newer technologies.
And this gives a really good migration path.
Although, I would imagine that as
of the time of this recording, a lot of that
is probably already done in most service providers.
I don't think there's too much legacy technology still
out there, but there's always that little something somewhere
that needs to be addressed.
So sort of going along with that first point, this
allows us to have service continuity
while we're doing this migration to an MPLS or IP core.
It's also going to lower our cost.
And again, this may not be so true these days.
However, it allows us to keep a single infrastructure if we
do still have to support things like ATM,
frame relay, and so on.
And just like it's an advantage for the customer,
it's an advantage to the service provider
that the customers maintain their autonomy because again,
they wouldn't be happy if they weren't
separate from other customers.
So this is sort of an advantage to both.
Now for the MPLS transport, which, as I mentioned,
is going to be our focus here, we
are going to be using two labels in the label stack.
The first label or the top label is the one
that's going to be used to transport
the packet from the ingress to the egress PE.
This is commonly referred to as the tunnel label.
I've also heard it referred to as the forwarding
label, which we actually refer to it that way a lot in Layer 3
VPN.
But in Layer 2 VPN, we commonly call it the tunnel label.
And then the second label is only used on the egress PE,
and it's used to identify the egress interface.
This way, essentially, we know which customer to send it to.
This one is referred to as the VC or the Virtual Circuit
label.
It's identifying the circuit that this traffic is
going to be forwarded through.
So finally, let's talk about the three primary components
of Layer 2 VPN.
The first one is the attachment circuit .
And this is the circuit that's between the customer
edge and the provider edge or the CE and the PE.
This attachment circuit gets mapped to the virtual circuit,
which we just spoke about a moment ago that's getting
transported through the core.
Then we have the pseudowire.
The pseudowire is the part that actually emulates the operation
of a virtual wire.
And again, then there's the underlying transport.
Like I said, we're mostly going to be focusing here on MPLS.
This uses targeted LDP for the control plane.
Remember that that means unicast.
Also, of course, if we wanted, we could do this over IP
using L2TPv3, which is Layer 2 Tunneling Protocol Version.
That's what we would use in an IP environment.
Again not our focus right now, but that
is what we would use on an IP transport.
So in this video, we just got a quick introduction
to some of the components and operation of Layer 2 VPN.
We also, of course, discussed some of the advantages,
both to the customer and to the service provider.
We also discussed the fact that this
can run over an MPLS transport using two labels,
or over an IP environment using L2TP version 3.
We will, of course, be focusing on MPLS.
Now the next thing we want to talk about
are the different types of VPNs that are available.
Again, we got a quick introduction here,m but we need
to dive into that in more detail.
And that's exactly what we're going to do next.
Until then, I hope this has been informative for you,
and I'd like to thank you for viewing.