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[MUSIC PLAYING]

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So let's begin by
jumping in and getting

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an introduction to
MPLS, the concept,

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as far as what it is, why
we want it or need it,

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and what it brings to the
table as far as networking

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and supported applications.

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Now, this is mostly a
service provider topic.

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But keep in mind that a
lot of large enterprises

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use MPLS in their core as well.

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Now, if you are already familiar
with MPLS, a lot of this

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will probably be a
little bit of a review.

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But review never hurts.

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And I want to go over
some of the basics

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anyway, just because MPLS is
a new topic to a lot of people

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coming from a route
switch background.

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So on that note, let's just
go ahead and get started

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going over some of
those MPLS basics,

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and talk about what this
is really all about.

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So at its core, the
main idea behind MPLS

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is that we want
to do our traffic

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forwarding using labels,
rather than the destination IP

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address.

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Now, the reason for
this, of course,

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we're going to build on as we
go through this and other videos

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and other skills.

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But this is the
fundamental idea,

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is we're going to
start using labels.

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Now, on many platforms,
doing label-based forwarding

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actually gives a
performance increase.

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Now, the reason we're
being careful to say

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on many platforms,
Cisco actually

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uses something called CEF,
or Cisco Express Forwarding.

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With Cisco Express Forwarding,
we do our IP forwarding

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based on the FIB, or the
Forwarding Information Base,

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and we do our label
switching based on the LFIB,

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or the Label Forwarding
Information Base.

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Now, if those two things
sound very similar,

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it's because they are.

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On a Cisco device,
doing IP forwarding

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and doing label switching
really isn't any difference

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in performance.

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That's not why we're doing
it on a Cisco platform.

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So let's get into why we are.

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So just to get it in writing,
here's what we just said.

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Because of CEF, again, there
is little to no performance,

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probably immeasurable, between
using regular IP forwarding

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and using MPLS.

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Now, because of
this, we're clearly

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using MPLS for other things.

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And just to get a small
piece of terminology

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out of the way, these
devices, or routers,

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that are doing label
switching, these

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are called LSRs, or
Label Switch Routers.

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So again, just a
terminology thing.

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But that's what we call these
routers once we enable MPLS.

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So again, clearly
the question becomes,

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why are we using MPLS then?

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And the answer to
that is to support

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many other applications.

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Now, the first one
we list here is

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the one we've already
been talking about,

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IP forwarding, both
unicast and multicast.

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And again, if this
is all we were doing,

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there would be no
reason whatsoever

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to do this on a Cisco platform.

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Again, keep in mind,
some other vendors

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may very well benefit from doing
MPLS just for IP forwarding.

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But on Cisco, we don't.

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It's using the same
table structure

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and the same forwarding
engine for both.

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So clearly, we're going to
use it for IP forwarding,

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but only to go on and add to
that these other applications.

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What are those applications?

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Well, first is
traffic engineering--

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and we're going to talk about
this in more detail in a few

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videos--

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and VPNs, or Virtual
Private Networks.

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MPLS supports both Layer
2 and Layer 3 VPNs.

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As a service provider, we
can offer either one of these

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to our customers,
or of course, both.

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And the traffic
engineering is really more

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for our internal use to optimize
the service provider core,

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but it's also things we can
offer to customers as well.

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Now, just a quick note here.

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As we're jumping
in and just getting

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started with MPLS,
when we're focusing

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on things like the
structure, and the labels,

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and all this kind of stuff
just to sink our teeth in,

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we're going to be focusing
for right now, just

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on the IP forwarding.

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Again, it's the
fundamental building block

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to be able to do
the rest of this.

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So we're going to start
with IP forwarding.

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We're just not
going to stop there.

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We're going to go on
to other applications.

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Now MPLS itself, is
not a routing protocol.

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It is a method of
forwarding traffic.

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So for that IP
forwarding, we're still

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going to use the IGP for
finding our networks, just

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like regular
traditional routing.

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And it will use any IGP.

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Because what we're
going to do is we're

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going to be building MPLS
off of the routing table.

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And we don't even
necessarily have

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to learn all of the routes.

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Really, only the core
routes need to be learned.

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Specifically,
loopback interfaces.

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And mostly, we're
talking about on the PE,

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or the Provider Edge routers.

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This is what we truly need
to be able to support.

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Particularly when we
get to things like VPN,

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like we mentioned up here.

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And remember how we said
that we create a label based

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on the routing table?

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Since it's based on the
routing table, that's

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why any IGP is
supported, it doesn't

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matter how the routing
table gets populated.

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Once it's populated, we build
labels for those routes.

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Now, once we've
created those labels,

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they do have to be exchanged
with our neighbors.

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We actually don't
use our own labels.

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Our neighbors use those labels
when delivering traffic to us.

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So since they get
used by our neighbors,

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these labels are,
of course, going

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to have to be exchanged
between the routers.

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Now, how those
labels get exchanged

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does depend on the application.

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We have something called LDP.

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We'll be talking about this
in more detail as well.

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Well, actually, we'll
be talking about all

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of these in more detail.

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But LDP is really used
for the IP forwarding.

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We have multi-protocol
BGP, which

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is used for our Layer
2 and our Layer 3 VPNs.

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We have RSVP, which is used
for traffic engineering.

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So depending what the label is
for, based on the application,

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it's going to depend on
which of these protocols

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is actually used to
exchange the labels.

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Now, as we mentioned,
the forwarding

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is done using the
FIB and the LFIB.

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And it really depends on
how a packet comes in,

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how a packet is going to be
sent, which of these tables

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we use.

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So for example, an IP
packet could come in and get

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forwarded as an IP packet.

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In that case, we would
be using the FIB.

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An IP packet can come in and
have a label imposed on it,

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and forwarded as labeled.

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Now, the interesting
thing about that is it's

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still using the FIB.

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The FIB is used to
impose the label.

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The only time we
look at the LFIB

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is when a labeled
packet arrives.

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When a labeled packet arrives,
we then look at the LFIB,

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and really make one
of two choices .

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Are we going to swap the
label with a different label,

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and forward it as still labeled?

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Or, if that labeled
packet arrives,

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maybe what we need to do is
remove that label, and then

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forward it as an IP packet.

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Now, depending on
the exact situation,

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we'll talk more
about this later.

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But this last option might
actually use both tables.

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We may have to do a
lookup in the LFIB.

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And then once it's an IP packet,
do another lookup in the FIB

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to determine how to forward it.

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Again, that depends
on the situation.

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And we'll talk in more detail
about that in upcoming videos

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and skills.

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So in this video, we just
got a quick introduction

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to MPLS, the basic
concept that we're

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forwarding traffic
based on labels,

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rather than the destination
IP address, as well

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as the different applications--

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such as Layer 2 and Layer 3
VPN, MPLS traffic engineering--

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that can build on top
of our IP forwarding

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to bring even more
functionality to MPLS.

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Now, if we're going to be
forwarding traffic using

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labels, we probably need
to talk a little bit more

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about those labels.

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And that's exactly
what we get 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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