[MUSIC PLAYING]
So let's begin by jumping in and getting
an introduction to MPLS, the concept,
as far as what it is, why we want it or need it,
and what it brings to the table as far as networking
and supported applications.
Now, this is mostly a service provider topic.
But keep in mind that a lot of large enterprises
use MPLS in their core as well.
Now, if you are already familiar with MPLS, a lot of this
will probably be a little bit of a review.
But review never hurts.
And I want to go over some of the basics
anyway, just because MPLS is a new topic to a lot of people
coming from a route switch background.
So on that note, let's just go ahead and get started
going over some of those MPLS basics,
and talk about what this is really all about.
So at its core, the main idea behind MPLS
is that we want to do our traffic
forwarding using labels, rather than the destination IP
address.
Now, the reason for this, of course,
we're going to build on as we go through this and other videos
and other skills.
But this is the fundamental idea,
is we're going to start using labels.
Now, on many platforms, doing label-based forwarding
actually gives a performance increase.
Now, the reason we're being careful to say
on many platforms, Cisco actually
uses something called CEF, or Cisco Express Forwarding.
With Cisco Express Forwarding, we do our IP forwarding
based on the FIB, or the Forwarding Information Base,
and we do our label switching based on the LFIB,
or the Label Forwarding Information Base.
Now, if those two things sound very similar,
it's because they are.
On a Cisco device, doing IP forwarding
and doing label switching really isn't any difference
in performance.
That's not why we're doing it on a Cisco platform.
So let's get into why we are.
So just to get it in writing, here's what we just said.
Because of CEF, again, there is little to no performance,
probably immeasurable, between using regular IP forwarding
and using MPLS.
Now, because of this, we're clearly
using MPLS for other things.
And just to get a small piece of terminology
out of the way, these devices, or routers,
that are doing label switching, these
are called LSRs, or Label Switch Routers.
So again, just a terminology thing.
But that's what we call these routers once we enable MPLS.
So again, clearly the question becomes,
why are we using MPLS then?
And the answer to that is to support
many other applications.
Now, the first one we list here is
the one we've already been talking about,
IP forwarding, both unicast and multicast.
And again, if this is all we were doing,
there would be no reason whatsoever
to do this on a Cisco platform.
Again, keep in mind, some other vendors
may very well benefit from doing MPLS just for IP forwarding.
But on Cisco, we don't.
It's using the same table structure
and the same forwarding engine for both.
So clearly, we're going to use it for IP forwarding,
but only to go on and add to that these other applications.
What are those applications?
Well, first is traffic engineering--
and we're going to talk about this in more detail in a few
videos--
and VPNs, or Virtual Private Networks.
MPLS supports both Layer 2 and Layer 3 VPNs.
As a service provider, we can offer either one of these
to our customers, or of course, both.
And the traffic engineering is really more
for our internal use to optimize the service provider core,
but it's also things we can offer to customers as well.
Now, just a quick note here.
As we're jumping in and just getting
started with MPLS, when we're focusing
on things like the structure, and the labels,
and all this kind of stuff just to sink our teeth in,
we're going to be focusing for right now, just
on the IP forwarding.
Again, it's the fundamental building block
to be able to do the rest of this.
So we're going to start with IP forwarding.
We're just not going to stop there.
We're going to go on to other applications.
Now MPLS itself, is not a routing protocol.
It is a method of forwarding traffic.
So for that IP forwarding, we're still
going to use the IGP for finding our networks, just
like regular traditional routing.
And it will use any IGP.
Because what we're going to do is we're
going to be building MPLS off of the routing table.
And we don't even necessarily have
to learn all of the routes.
Really, only the core routes need to be learned.
Specifically, loopback interfaces.
And mostly, we're talking about on the PE,
or the Provider Edge routers.
This is what we truly need to be able to support.
Particularly when we get to things like VPN,
like we mentioned up here.
And remember how we said that we create a label based
on the routing table?
Since it's based on the routing table, that's
why any IGP is supported, it doesn't
matter how the routing table gets populated.
Once it's populated, we build labels for those routes.
Now, once we've created those labels,
they do have to be exchanged with our neighbors.
We actually don't use our own labels.
Our neighbors use those labels when delivering traffic to us.
So since they get used by our neighbors,
these labels are, of course, going
to have to be exchanged between the routers.
Now, how those labels get exchanged
does depend on the application.
We have something called LDP.
We'll be talking about this in more detail as well.
Well, actually, we'll be talking about all
of these in more detail.
But LDP is really used for the IP forwarding.
We have multi-protocol BGP, which
is used for our Layer 2 and our Layer 3 VPNs.
We have RSVP, which is used for traffic engineering.
So depending what the label is for, based on the application,
it's going to depend on which of these protocols
is actually used to exchange the labels.
Now, as we mentioned, the forwarding
is done using the FIB and the LFIB.
And it really depends on how a packet comes in,
how a packet is going to be sent, which of these tables
we use.
So for example, an IP packet could come in and get
forwarded as an IP packet.
In that case, we would be using the FIB.
An IP packet can come in and have a label imposed on it,
and forwarded as labeled.
Now, the interesting thing about that is it's
still using the FIB.
The FIB is used to impose the label.
The only time we look at the LFIB
is when a labeled packet arrives.
When a labeled packet arrives, we then look at the LFIB,
and really make one of two choices .
Are we going to swap the label with a different label,
and forward it as still labeled?
Or, if that labeled packet arrives,
maybe what we need to do is remove that label, and then
forward it as an IP packet.
Now, depending on the exact situation,
we'll talk more about this later.
But this last option might actually use both tables.
We may have to do a lookup in the LFIB.
And then once it's an IP packet, do another lookup in the FIB
to determine how to forward it.
Again, that depends on the situation.
And we'll talk in more detail about that in upcoming videos
and skills.
So in this video, we just got a quick introduction
to MPLS, the basic concept that we're
forwarding traffic based on labels,
rather than the destination IP address, as well
as the different applications--
such as Layer 2 and Layer 3 VPN, MPLS traffic engineering--
that can build on top of our IP forwarding
to bring even more functionality to MPLS.
Now, if we're going to be forwarding traffic using
labels, we probably need to talk a little bit more
about those labels.
And that's exactly what we get to do next.
Until then, I hope this has been informative for you,
and I'd like to thank you for viewing.