I can think of a lot of jokes about auto,
like with auto negotiation, auto work.
Well, auto summary is a feature that
is not on by default anymore with iOS
regarding routing protocols including EIGRP.
And in this video, I'd like to talk with you
about the concept of auto summarization
so you can be aware of it, and then
give you a hands-on lab opportunity to see it
in action.
So here's our lab topology.
I've got R3, R2, and R1.
Between R1 and R3, it's 10.0.13.
Over here on R3, we have dot three, and R1 one has dot one. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Over here on R3, we have dot three, and R1 one has dot one.
Then between R1 and R2 is 10.0.12.1 24-bit mask.
That one here, dot there.
And then, what I'd like us to do in the lab,
let's create a loopback interface
on R3 with 172.16.3.3 with a 24-bit mask,
and over here on R2, we'll create loopback to
with 172.16.2.2.
slash 24.
Then if we enable EIGRP across the board, and--
let's do it two ways.
Let's enable EIGRP for all networks, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Let's enable EIGRP for all networks,
and basically it's going to work great
because R2's going to say, oh, to get
to 172.16.3, that 24-bit network, I need to go that way.
And R3 is going to say, oh, to get to this network,
it's going to go that way.
Life is good.
So if we turned on EIGRP normally,
and which is where auto summarization is off,
everything would be advertised normally.
However, in this topology, we have the 172.16.3 network here
and then a different last network here, the 10.0.13
network here.
If we turned on auto summarization, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
If we turned on auto summarization,
R3 would say, whoa, I'm going over this other network.
I'm going to summarize the 172.16.3 with its class
full of boundaries.
Because it's a class B, it would be advertised
as 172.16 and over here on R2, it
would be advertised as it goes this way as 172.16.0.0
with a 16-bit mask.
And unfortunately, R1 is going to say, hey, I got two routes.
And they're equal cost to get to 172.16. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
And they're equal cost to get to 172.16.
But at the other day is only one of those
paths is going to be correct based on the actual destination
that R1 is trying to reach.
So let's set this up.
I'll walk you through it with basic EIGRP
with auto summarization disabled, which is the default,
then we'll enable it, and we can see all heck
break loose in our lab network.
Let's go to the lab.
All right, so to do this, I'm going
to open up a new little Notepad document to make
this a little bit easier.
And from a fresh Notepad document,
let's do this do config t router eigrp 1, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
let's do this do config t router eigrp 1,
and then we'll just bring all the networks in.
And that'll do it, and end.
And by default, auto summary is off by default,
so let's go ahead and put this on R1, R2, and R3,
gonna Copy, Paste.
There's two, there's three.
Then in R2, we'll make the loop back.
We'll go configuration mode interface
loopback 2 based on our plan, IP address,
172.16.2.2 with a 24-bit mask. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
172.16.2.2 with a 24-bit mask.
Great.
And then we'll go to R3, big T interface loopback 3.
Just help remind us where we're at, an IP address, 172.16.3.3
with a 24-bit mask.
Awesome.
All right, and then we've already
got our neighbor adjacency.
So if we go to R1, which is in the middle between because R2
and R3, and we do a show IP route,
let's just look for the 172.16 networks.
There we go, that'll be great. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
There we go, that'll be great.
Though I've got two 172.16 networks, one
that is the next hop according to R2, one that
has the next hop going to R3, life is good,
and that's because auto summary is not enabled on R2 and R3
for EIGRP.
We can verify that by going to R2,
and let's do a show IP protocols,
and that should reveal it.
So right here, auto summarization disabled.
Fantastic.
So let's tweak this a little bit.
Let's enable it.
So let's go back to our Notepad document, WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
So let's go back to our Notepad document,
and we'll go to router EIGRP 1, and we
will say auto, which is short for auto summarization,
and that'll be enough.
So config t router eigrp 1 auto.
Great, I'm going to copy that, and I'm just
going to paste it into R1, R2, and R3.
So EIGRP is so fast to converge, it's done.
If we go back to R1 and hit the Up arrow key a few times,
do a show IP route for 172.16, it says, great.
I'll actually show you the routing table too.
Show IP. WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
Show IP.
We have two equal cost paths, or so it believes.
Show IP route for EIGRP learned routes would be great,
and there we have it, right there.
Two equal cost routes for 172.16 with a 16-bit mask.
One goes to R2, one goes to R3.
Though this is not a desirable situation, and that's
probably why auto summary has been turned off by default
for protocols like EIGRP.
So now that we've taken a look at auto summary
and how we probably don't want to use auto summary,
in the next video, let's take a look WEBVTT X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:900000
in the next video, let's take a look
at using manual summarization at the interfaces in an EIGRP
network.
So I'll see in that video in just a moment.
Meanwhile, I hope this has been informative for you,
and I'd like to thank you for viewing.