All right, let's go ahead and jump into this topology challenge.
The goal here is to make sure we understand how
routes propagate throughout an SD-WAN environment,
as well as how we go about comparing something like
OMP to something like EIGRP.
So let's dive in here. First up,
to which device or devices does Edge 100 advertise Subnet A?
In other words, Subnet A here is directly connected to Edge 100,
at least from a Layer 3 perspective.
Who does it advertise it to?
Well, we're not advertising it out to other Edge devices.
That's not how this works.
Instead, remember, our Edges only
form peering relationships with our controllers.
That would be in our case,
Controller 1 and Controller 2.
So this would be the answer to number 1.
Now, if we take this further,
then the question is asking,
we'd know that Controllers 1 and 2 are then going to
push those routes down to the other Edge devices.
So these other Edge devices are going to
see the route from two different controllers.
We'll talk about how it navigates multiple routes like
that in coming videos and coming skills.
But that's the answer to number 1.
Number 2, which subnets are advertised automatically by OMP?
Well, remember, connected routes are automatically placed into OMP.
As a result, Subnet A is directly connected to Edge 100,
and Subnet B is directly connected to Edge 101.
If we look at Subnet C over here,
we're only attaching ourselves from
a Layer 3 perspective to a downstream switch relative to the Edges.
Therefore, the Edges are only going to know of Subnet C,
thanks to this routing protocol, in our case, EIGRP.
So as a result,
the answer here would be Subnet A and Subnet B.
Only those two subnets get automatically advertised.
Now, number 3, how many control plane tunnels are created in this topology?
Well, this is an interesting question.
We're specifically talking about the control plane,
which means that we're talking about controllers or V-smarts.
Those are the only devices in the control plane.
So it's the controllers themselves, again,
the V-smarts, and the devices they connect to.
So how many tunnels are there?
Well, Controller 1 is going to communicate to all of
the Edges and Controller 2 is going to talk to all the Edges.
Now, keep in mind, there's four tunnels on each one here.
As the question says, we're going to assume that we're only
connecting through one of the transports, T2.
So really, we're talking about
eight total control plane tunnels here between Controllers and Edges.
But let's not forget,
Controllers 1 and 2 are going to form a tunnel
and an OMP peering with one another as well.
So that's a total of nine here.
So question 3, the answer should be,
Our Controllers and our Edges using
control plane tunnels as well as Controller to Controller.
Last up, Edge 102 receives an OMP route for subnet C. So that's here.
We're receiving an OMP route for subnet C,
which notice it's also over here.
I'm also learning it via EIGRP.
So I'm basically getting a route advertised to me from two different ways.
EIGRP is also saying it sees subnet C. So does it install this route?
Well, the answer is no.
We're not going to install the OMP route
because we're going to prefer the EIGRP route.
This has to do with administrative distance,
and very importantly, we need to recall
what the administrative distances are for the common routing protocols.
EIGRP would be 90,
and then we can compare to OMP,
which is 251 on iOS devices.
Remember, Viptela devices like VEdges,
it'll show up as 250.
But when Cisco acquired Viptela,
they looked at their own router software and said,
we already used 250 for something.
That's an HRP, and so we're going to have to deploy this as 251.
Either way, it's higher than IGMP and higher numbers mean less trustworthy,
and therefore we're going to go with EIGRP route.
We're not going to accept the OMP route and install it into our routing table.
Hopefully, this is a good review as far as, again,
route propagation, thinking about control plane tunnels,
where those OMP peerings exist,
and how we use administrative distance to compare the same routes when
they're received for multiple routing protocols, including OMP.
I hope this has been informative for you,
and I'd like to thank you for viewing.