In the previous video, we took a look at the concepts
for the feasible successor-- the conditions that have to exist--
the feasibility condition-- for a backup route
to be considered in EIGRP.
In this video and lab, we're going
to go ahead and take that concept to the CLI,
and verify it in action.
[MUSIC PLAYING]
So we're going to use this topology
to reinforce the concepts from the previous video.
And as a quick reminder, we've got these four routers
that we're focusing on.
Here's their feasible distance for each of them WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Here's their feasible distance for each of them
regarding this specific route.
And only one of these routers, based
on our previous discussion in the previous video--
only one of these routers is going to have a backup route.
And that's because only one of these routers
has an alternate path that is meeting the feasibility
condition, which is that if we take R3's feasible
distance for that route, it's the only router out of all four
of these that's receiving advertisements
from another router--
as opposed to the one it's using for the successor path-- WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
as opposed to the one it's using for the successor path--
it's the only one in these four routers
that's receiving an advertisement that
is less than the reported distance,
is less than its current feasible distance,
and that's why R3 is going to have that backup route.
So here they are in measurable terms.
So in R3, our feasible distance is 2,173,184.
We'll verify that in lab in just a moment.
And the primary path is going up through R1.
And then in addition to that, R4 is advertising
its reported distance-- which is its feasible distance being
advertised-- and that system, right here, ending in 416. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
advertised-- and that system, right here, ending in 416.
And check this out--
that reported distance of 2,172,416--
that is less than the current feasible distance
that R3 is using.
And as a result, R3 will be aware
and consider that a viable backup route in the event
the primary route goes down.
So let's take a road trip up to R3,
and let's take a look at the EIGRP topology table
and verify exactly that.
So here in the lab, if we go to R3--
it's always good to go to the right router,
and just show ip eigrp topology and press Enter-- WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
and just show ip eigrp topology and press Enter--
that's going to show us the topology table for EIGRP
on this router.
And the route we're looking for--
I'm going to go ahead and press the key other than Space.
The route we're looking for is this one right here--
the 10.2.68.0/24.
We have one successor.
That's the metric for the winning route.
That metric matches right here.
We've touched on that in previous videos.
And this is the reported distance from the neighbor.
In this case, it's going to be R1 for that winning route.
Now, below that we have this route right here
that has a metric of 2,174,976. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
that has a metric of 2,174,976.
Now, this route didn't win because it
doesn't have as good of a metric as the successor route.
But check this out--
this is the route that's being advertised from R4.
We can also see the interface there,
where we received that update.
And the advertised metric-- or the advertised distance,
I should say--
is 2,172,416, which is less than the current feasible distance.
And so the feasibility condition,
which says that the reported distance must be less than-- WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
which says that the reported distance must be less than--
not equal to, but less than the current feasible distance--
that is true.
And we can look at that here.
So the reported distance for that alternate route
is 2,172,416, as being advertised by R4.
And that is less than our current feasible distance
of 2,173,000 and change.
So the advertised distance is 172 for that backup route,
and the current feasible distance for the successor
route is 173, and so that is true.
And as a result, we now have a feasible successor. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And as a result, we now have a feasible successor.
And if you want to take a look at the details for that,
we could do a show ip eigrp topology again, and then
plug in that route.
So 10.2.68.0/24-- I'll just Copy/Paste that.
And then it will give us more detail on exactly that.
So there's the command right there--
show ip eigrp topology for that specific network.
And it's, once again, showing us the information, including
the metric, the feasible distance for the winner,
the reported distance, and this is the metric
for the backup route. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
for the backup route.
And this is the reported distance,
or advertised distance, that we're learning from R4.
And again, because this number here
is less than our current feasible distance,
it meets the feasibility condition,
and now we have a backup route.
Now, if we took out the primary route,
this one would just, boom, kick in immediately.
And-- and-- as we'll talk about in a separate video,
we can also do unequal cost load balancing
if we want with EIGRP as long as the alternate routes meet
the feasibility condition-- which, once again, is
that the reported distance for any other routes WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
that the reported distance for any other routes
has to be less than our current feasible distance
to be considered.
So we could say, on R3, that R3 has one successor winning
route, and it has one feasible successor-- a backup route--
because that backup route meets the feasibility condition.
Now, unfortunately, both of these routes
are not being used.
We just put the winner in the winner's table.
However, we can do unequal cost load balancing with EIGRP,
and that's the topic for our next video.
So I'll see you there in just a moment.
Meanwhile, I hope this has been informative for you, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Meanwhile, I hope this has been informative for you,
and I'd like to thank you for viewing.