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So let's start off with
an introduction to Layer 2

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VPN by talking about a
couple of different things.

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We'll start off by talking
about the different service

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types that are available,
which is basically

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a quick introduction to the VPN
types, which we'll be covering

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more in the next video.

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But then we're also going
to talk about the advantages

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to Layer 2 VPN, both from
the customer's perspective

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and from the service
provider's perspective.

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And then in the interest of some
terminology and understanding

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the moving parts,
we'll also talk a bit

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about the different
components in Layer 2 VPN.

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So, let's go ahead and
jump in and get started

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looking at those details.

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So starting with the most basic
question, what is Layer 2 VPN?

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Well, Layer 2 VPN is a
service or MPLS application

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that provides layer 2
connectivity between customer

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sites.

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And under this umbrella
of Layer 2 VPN,

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we do have a few different
services that are available.

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The first is virtual private
Wire Service or VPWS.

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This is a point to
point connection.

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So this would go directly
between two customer sites,

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and this can actually use
L2TPv3 over an IP network,

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or it can use MPLS
for the transport.

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And in that case,
we call this AToM

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or Any Transport over MPLS.

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Now, as we just indicated,
AToM is actually

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a subset of Virtual
Private Wire Service,

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and it supports a variety
of other protocols.

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So it supports
ethernet, which is

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going to be our primary focus.

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However, it also supports some
other more legacy protocols,

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such as Point to Point Protocol
or PPP, HDLC or High Level Data

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Link Control, frame relay, and
ATM or Asynchronous Transfer

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Mode.

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So this is sort of where
that "any" transport

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comes into play.

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Meaning, we can support a lot
of other layer 2 protocols

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over the MPLS environment.

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Again, we'll mostly be
focusing on ethernet here.

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Next up is your Virtual
Private Land Services or VPLS.

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Now, this one can either
be point to multipoint.

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So what we would normally call
a star topology or multipoint

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to multipoint, which would
essentially be a full mesh.

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So let's talk about L2
VPN from the standpoint

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of the advantages, and we'll
talk about the enterprise

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first.

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Now, of course, when we're
talking about the enterprise

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here, remember, we're looking
at this from the service

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provider's perspective.

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So, we could also refer
to this as the customer.

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Either way, let's talk
about the advantages.

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One of the bigger ones
is that this is actually

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identical to traditional
WAN services.

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Now, of course, one of the big
reasons this is advantageous

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is engineers are
familiar with this model.

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Network engineers have
been working with Point

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to Point Layer 2
circuits for decades.

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All the way back and even
before things like T1's, T3's,

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OC circuits, things like this--

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this has been around
for a really long time.

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So the customer is going to be
very familiar with this model.

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They're just going to see
this whole thing as a layer 2

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handoff.

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This is why through
the rest of the skill,

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we'll be using the
term pseudowire

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quite a bit because
that's effectively what

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this is for the end customer.

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They just see it as a layer 2
connection between their sites.

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And again, this is how we've
been doing WAN connections

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for a very long time.

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And of course,
part of all of that

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means that the customer is
going to have their own routing

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and service policies.

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The service provider
is not going

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to be involved in the
customer's routing.

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Some other advantages
here is this

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allows for a single
infrastructure over which,

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we can run both IP and
traditional services.

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Again, we can support
ethernet, PPP, HDLC, ATM.

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A lot of different
things can be supported

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over a single infrastructure.

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This also optimizes the
data center solution.

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Now, you may be curious
what any of this

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has to do with the data center.

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Well, things like live
migration for your servers

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require that the server
be on the same subnet

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when it reaches the other
destination, the other host.

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In order for that to be,
say, in a different data

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center like a
backup data center,

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that needs to be a
layer 2 connection.

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And that's why this
is a popular choice.

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Now, are there other
technologies to do that?

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Of course, there are.

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There are many other
ways to do this,

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but this is a good solution
because of the fact

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that it is a layer 2 handoff.

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And of course, this
maintains enterprise autonomy

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because customer A and
customer B's traffic never

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touches, never crosses.

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It's a layer 2 circuit
that's completely separate

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and carrying only that
customer's traffic.

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Now, this has advantages for
the service provider as well.

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First, it gives us a really,
really good migration path

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to go to an MPLS or IP core.

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So if we've traditionally
offered, say,

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frame relay or ATM
solutions or T1's or any

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of these sort of
legacy technologies,

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this gives us a real easy path
to move the core of our network

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over to again,
either MPLS or IP.

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Our focus right now
is going to be MPLS.

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However, it lets
us migrate to that,

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while still supporting customers
on those legacy technologies

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because of course, we have
to get our core updated

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before we can start
migrating our customers over

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to newer technologies.

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And this gives a really
good migration path.

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Although, I would
imagine that as

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of the time of this
recording, a lot of that

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is probably already done
in most service providers.

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I don't think there's too
much legacy technology still

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out there, but there's always
that little something somewhere

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that needs to be addressed.

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So sort of going along
with that first point, this

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allows us to have
service continuity

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while we're doing this
migration to an MPLS or IP core.

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It's also going
to lower our cost.

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And again, this may not
be so true these days.

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However, it allows us to keep
a single infrastructure if we

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do still have to
support things like ATM,

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frame relay, and so on.

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And just like it's an
advantage for the customer,

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it's an advantage to
the service provider

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that the customers maintain
their autonomy because again,

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they wouldn't be
happy if they weren't

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separate from other customers.

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So this is sort of
an advantage to both.

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Now for the MPLS transport,
which, as I mentioned,

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is going to be
our focus here, we

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are going to be using two
labels in the label stack.

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The first label or the
top label is the one

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that's going to be
used to transport

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the packet from the
ingress to the egress PE.

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This is commonly referred
to as the tunnel label.

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I've also heard it referred
to as the forwarding

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label, which we actually refer
to it that way a lot in Layer 3

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VPN.

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But in Layer 2 VPN, we commonly
call it the tunnel label.

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And then the second label is
only used on the egress PE,

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and it's used to identify
the egress interface.

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This way, essentially, we know
which customer to send it to.

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This one is referred to as
the VC or the Virtual Circuit

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label.

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It's identifying the
circuit that this traffic is

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going to be forwarded through.

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So finally, let's talk about
the three primary components

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of Layer 2 VPN.

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The first one is the
attachment circuit .

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And this is the circuit
that's between the customer

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edge and the provider
edge or the CE and the PE.

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This attachment circuit gets
mapped to the virtual circuit,

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which we just spoke about
a moment ago that's getting

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transported through the core.

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Then we have the pseudowire.

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The pseudowire is the part that
actually emulates the operation

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of a virtual wire.

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And again, then there's
the underlying transport.

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Like I said, we're mostly going
to be focusing here on MPLS.

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This uses targeted LDP
for the control plane.

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Remember that that
means unicast.

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Also, of course, if we wanted,
we could do this over IP

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using L2TPv3, which is Layer
2 Tunneling Protocol Version.

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That's what we would use
in an IP environment.

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Again not our focus
right now, but that

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is what we would use
on an IP transport.

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So in this video, we just
got a quick introduction

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to some of the components
and operation of Layer 2 VPN.

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We also, of course, discussed
some of the advantages,

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both to the customer and
to the service provider.

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We also discussed
the fact that this

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can run over an MPLS
transport using two labels,

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or over an IP environment
using L2TP version 3.

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We will, of course,
be focusing on MPLS.

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Now the next thing
we want to talk about

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are the different types of
VPNs that are available.

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Again, we got a quick
introduction here,m but we need

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to dive into that
in more detail.

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And that's exactly what
we're going to do next.

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Until then, I hope this has
been informative for you,

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and I'd like to thank
you for viewing.

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