All right, now we're looking at a scenario
where Edge 2 has been configured to advertise Subnet A
with an OMP preference of 100,
and both MPLS links are given a TLOC preference
of 100 as well.
So now we're talking about two different preferences.
And remember, with preference,
we always prefer, prefer preference to be higher.
This is what we want it to be.
So 100 compared to zero in either scenario
is going to be a better path.
So let's go down that same list again,
administrative distance, it's all OMP,
it's all the same AD, which is 250 on the controllers.
Then we look at the order here of OMP preference
coming first, and then we have TLOC preference
coming second.
This is going to be the driving factor in this scenario.
I could keep going, I could look at the origin.
And we know the origin is connected,
the same in both, or the same for both edges here.
And then we also have an origin metric.
Well, for connected routes, the metric is going to be one.
So the task now is to determine
whether or not the OMP preference wins out
or the TLOC preference wins out.
And as we see here, it starts with OMP preference
and then moves to TLOC preference.
Finally, edge two has the edge over edge one.
Maybe I shouldn't say it like that.
Edge two has a better value than edge one.
And so we're going to list out the edge two paths first,
because it's going to automatically
snag those first three slots.
And then edge one's going to get the fourth slot.
The question is, what order do the paths get selected in?
Before we started with internet one and moved down
because of the private IP addresses,
but we're not going to just jump to tie breakers
because we have these other data points here.
We have a TLOC preference as well,
which means that edge two's MPLS connection
is going to be the most preferred path.
It has the highest OMP
and then the highest TLOC preference.
From there, we will use the tie breaker process
because it's internet one and internet two paths
are the same otherwise.
And so we're going to go in order of lowest private address,
which as we talked about, these are public addresses,
but they fit into the private address slot
when NAT isn't being used.
And so lastly here, we need a path through edge one
as our fourth.
And because again, TLOC preference of 100
is sitting here on MPLS,
we are going to select the MPLS path.
Now, this part is very interesting.
If I'm looking at this from the controller's perspective,
I might expect that I'm going to just send things
in this order.
Here's the problem.
We have said that we're ignoring TLOC preference
when we look at it from a controller's perspective.
And the reason for that
is because I might have an edge down here
that doesn't have a TLOC to one of the transports
and the controllers aren't keeping track of that.
And that could also dynamically change
as circuits go up and down.
So we don't really want them tracking that.
At this point with the controllers,
we have to pick four paths
and we're not going to pay attention to TLOC preference,
which is where things get a little more interesting.
So we have established the order here
from our perspective with the TLOC preference,
but now the controllers are not going to
pay attention to it.
So that means we actually have a different result.
We're going to send the same three paths for edge two
but the order is going to be different.
It's going to go back to the tiebreaker
and then we're going to also send the internet one path.
This is very important.
We might've thought that, hey, well, this,
well, not that one.
Edge ones MPLS would be sent instead of the internet path,
but that's not what happens here
because we're not paying attention to TLOC preference
from the controllers.
So these four get sent down to edge three.
What does edge three do?
Edge three does evaluate the TLOC preference now.
And so it's going to install them in a different order.
It's going to install the MPLS first,
like we have over here,
and then it will install internet one
and then it will install internet two.
And lastly, it's going to install the only other route
that it got, which is internet one.
So different from this and different from this.
And we might be looking at an OMP database
and looking at it and saying,
why is it going in this particular fashion?
And this is why.
We always have to keep in mind
how this path selection criteria works.
We need to know the order of the evaluation,
but we also need to understand that the controller
does not evaluate TLOC preference
in order to try to prevent black hole scenarios.
Although as we know, black hole scenarios can still exist.
And that's why we covered backup paths
in a great amount of detail.
So at this point, mark this skill
as a potential second look worthy,
or it's worthy of a second look
as you're preparing for the exam.
If you're going to take the exam,
go over this review again in the future.
For right now, if you've got 80 or 90% of this down,
then you're in really good shape and you can move forward.
If a lot of this tripped you up,
I'd recommend going back and reviewing some of those skills
before moving on and we go even deeper
into the world of SD-WAN.
In the meantime, I hope this has been informative for you
and I'd like to thank you for viewing.