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[AUDIO LOGO]

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Finally, let's wrap up
with an introduction

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to MPLS traffic engineering,
and the basic idea here

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is simply this.

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Your routing protocols will
generally pick the best path

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to get to a
destination, and that's

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where all your traffic will go.

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Now, of course, if you
have multiple equal paths,

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we will do ECMP or
Equal-Cost Multi-Pathing.

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But assuming they're not
equal, maybe the second path

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is a little lesser.

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Maybe it has a little
bit less bandwidth.

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For whatever reason,
that's not what

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our routing protocol chose.

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However, under the
right situation,

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like perhaps our
primary path is running

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at 70%, 80%, 90%
utilization, of a sudden,

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that secondary path is looking
pretty good because, according

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to our routing protocol,
no traffic will

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go across that link.

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The idea behind
traffic engineering

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is we can actually
move some traffic out

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to these other circuits
that are perfectly fine.

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It's just our routing
protocol hasn't

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chosen to use them because
routing protocols, by nature,

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just choose the best path.

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This, of course, is, again,
where traffic engineering

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comes in and lets us use some
of those secondary circuits.

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So let's go ahead and jump
in and get that introduction

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to MPLS traffic engineering.

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So as we said during
the introduction,

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your IGP is going to
choose the best path based,

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of course, on given
criteria depending entirely

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on the protocol itself.

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All of our IGP is, of course,
function just a little

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bit differently.

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However, regardless of the IGP,
the best path that it's chosen

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does not change based
on traffic flows.

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Like we said before,
if a link suddenly

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goes to 70%, 80%,
90% utilization,

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it may not be the
best path anymore,

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but your IGP is not
going to react to that.

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Traffic engineering
is what changes this.

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It allows the routers to
choose a different or possibly

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additional paths
based on constraints.

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What constraints?

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Well, it could be based on maybe
the bandwidth available, maybe

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a certain media type,
maybe a flow priority.

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But there are rules
in place that we

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can create to choose
how the router chooses

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these additional paths.

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But the point is it
allows us to use them.

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Now there is a fundamental
problem with all of this.

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We have to be able to do all
of this without causing a loop.

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That would be really bad.

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We don't want to
introduce routing loops.

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There's generally a reason why
routers choose the best route,

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and part of that is
usually loop prevention.

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However, if we have a
routing protocol that,

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very specifically,
is link-state,

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which means that it has a
database of the entire network,

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it has a topology database,
that routing protocol

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knows if it can use alternate
paths without creating loops.

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So that means we require a
link-state routing protocol,

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which there's only two at
the moment, OSPF and IS-IS.

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Now both of these, of
course, do require extensions

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because they don't do traffic
engineering by default.

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So this is not a big deal.

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We simply have to
enable the extensions.

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And, of course, it's fully
supported in the code,

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but just be aware
that modifications

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to these protocols were required
to support traffic engineering.

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It's not something
they normally do.

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Now a couple of other
attributes to be

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aware of a TE tunnel or a
Traffic Engineering tunnel

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will be created from the
head end to the tail end.

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These are some terms we want to
get used to when we're talking

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about traffic engineering.

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And that means that traffic
always flows from the head end

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to the tail end.

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All of these tunnels
are unidirectional.

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So if you want traffic
to go bi-directional

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over the same path, you
will need a separate TE

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tunnel in each direction.

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Now traffic engineering
borrows a protocol

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called RSVP or Resource
Reservation Protocol.

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It uses this as
its control plane.

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The reason I say it
borrows this is RSVP

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was actually created for
the in-serve model of QoS.

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We don't commonly use it for
that all that often anymore.

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However, it's found the new home
here with traffic engineering

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to be used as the Control
Protocol to signal the network.

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So the two main
functions that it

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covers as the
control plane is it's

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going to handle that
tunnel establishment

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as well as exchanging
the MPLS label that we're

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going to use for the tunnel.

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So in this video,
we just jumped in

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and got familiar with the
concept of MPLS traffic

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engineering, which allows us
to use secondary circuits that

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were not chosen as
the best by our IGP,

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but we can use them
to send traffic

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across because they may still be
very viable for passing traffic

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and can take some of
our primary circuits.

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So that concludes
everything that we

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need to discuss in this skill.

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That means that
all we have left is

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a review in the form
of a quiz, and that's

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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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