[AUDIO LOGO]
Finally, let's wrap up with an introduction
to MPLS traffic engineering, and the basic idea here
is simply this.
Your routing protocols will generally pick the best path
to get to a destination, and that's
where all your traffic will go.
Now, of course, if you have multiple equal paths,
we will do ECMP or Equal-Cost Multi-Pathing.
But assuming they're not equal, maybe the second path
is a little lesser.
Maybe it has a little bit less bandwidth.
For whatever reason, that's not what
our routing protocol chose.
However, under the right situation,
like perhaps our primary path is running
at 70%, 80%, 90% utilization, of a sudden,
that secondary path is looking pretty good because, according
to our routing protocol, no traffic will
go across that link.
The idea behind traffic engineering
is we can actually move some traffic out
to these other circuits that are perfectly fine.
It's just our routing protocol hasn't
chosen to use them because routing protocols, by nature,
just choose the best path.
This, of course, is, again, where traffic engineering
comes in and lets us use some of those secondary circuits.
So let's go ahead and jump in and get that introduction
to MPLS traffic engineering.
So as we said during the introduction,
your IGP is going to choose the best path based,
of course, on given criteria depending entirely
on the protocol itself.
All of our IGP is, of course, function just a little
bit differently.
However, regardless of the IGP, the best path that it's chosen
does not change based on traffic flows.
Like we said before, if a link suddenly
goes to 70%, 80%, 90% utilization,
it may not be the best path anymore,
but your IGP is not going to react to that.
Traffic engineering is what changes this.
It allows the routers to choose a different or possibly
additional paths based on constraints.
What constraints?
Well, it could be based on maybe the bandwidth available, maybe
a certain media type, maybe a flow priority.
But there are rules in place that we
can create to choose how the router chooses
these additional paths.
But the point is it allows us to use them.
Now there is a fundamental problem with all of this.
We have to be able to do all of this without causing a loop.
That would be really bad.
We don't want to introduce routing loops.
There's generally a reason why routers choose the best route,
and part of that is usually loop prevention.
However, if we have a routing protocol that,
very specifically, is link-state,
which means that it has a database of the entire network,
it has a topology database, that routing protocol
knows if it can use alternate paths without creating loops.
So that means we require a link-state routing protocol,
which there's only two at the moment, OSPF and IS-IS.
Now both of these, of course, do require extensions
because they don't do traffic engineering by default.
So this is not a big deal.
We simply have to enable the extensions.
And, of course, it's fully supported in the code,
but just be aware that modifications
to these protocols were required to support traffic engineering.
It's not something they normally do.
Now a couple of other attributes to be
aware of a TE tunnel or a Traffic Engineering tunnel
will be created from the head end to the tail end.
These are some terms we want to get used to when we're talking
about traffic engineering.
And that means that traffic always flows from the head end
to the tail end.
All of these tunnels are unidirectional.
So if you want traffic to go bi-directional
over the same path, you will need a separate TE
tunnel in each direction.
Now traffic engineering borrows a protocol
called RSVP or Resource Reservation Protocol.
It uses this as its control plane.
The reason I say it borrows this is RSVP
was actually created for the in-serve model of QoS.
We don't commonly use it for that all that often anymore.
However, it's found the new home here with traffic engineering
to be used as the Control Protocol to signal the network.
So the two main functions that it
covers as the control plane is it's
going to handle that tunnel establishment
as well as exchanging the MPLS label that we're
going to use for the tunnel.
So in this video, we just jumped in
and got familiar with the concept of MPLS traffic
engineering, which allows us to use secondary circuits that
were not chosen as the best by our IGP,
but we can use them to send traffic
across because they may still be very viable for passing traffic
and can take some of our primary circuits.
So that concludes everything that we
need to discuss in this skill.
That means that all we have left is
a review in the form of a quiz, and that's
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.