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- So here we are at the last video
for this particular CCNA EIGRP lab
where we're gonna do some path manipulation.
So at present,
when Router one is pinging the loop back of Router four,
I can expect that it's gonna
take this fast Ethernet link.
How would I actually prove that?
Well, here's what we're gonna do.
Let's go ahead and start the routers up.
And let's go into Router one,
and what we're gonna do is,
we're gonna look at his routing table.
And then we're gonna see, according to his routing table
if he was gonna route packets
to the 44.44.44 network,
what would his egress interface be?
Where would he send those packets?
Show IP route.
And we can see he's learned of that network
and he would route them out the fast Ethernet link,
just like we thought.
Okay, now we also saw previously we did
sho ip eigrp topol all-links
We did see that he had learned about that route
via the slow-speed serial.
So what we need to do
is we need to ultimately make EIGRP follow the top link.
We have to trick it, or fool it, into thinking
that the top link is actually the better path.
Well let me ask you a question.
By default, when EIGRP is coming up with its metric,
that big long number that we call distance,
what are the variables that it plugs into the formula
to come up with its distance value?
What are the default variables,
otherwise known as vector metrics?
Well hopefully you quickly answered, bandwidth and delay.
Bandwidth and delay are part of that formula,
the default formula.
Now it's recommended that you do not touch
the bandwidth on an interface
because bandwidth is used by other things as well.
So ideally, if you wanna manipulate EIGRP,
you're gonna manipulate the delay variable.
So, let's go ahead and start by doing this.
Let's go ahead and in here,
let's try to take this interface right here,
Serial two/zero, and let's lower the delay.
Actually, let's lower to the minimum value
and see if that works to get our desired result.
Alright, so let's go into Router one.
Actually, I'm not sure if when I took my last snapshot
I had the routers turned off or not.
So, I'm gonna go ahead and retake that snapshot
because I suspect I did not.
Okay, so now let's turn them all back on
and let's go into Router one and go onto a Serial two/zero
and reduce the delay to the minimum possible value
to make it look like there's hardly any delay
on that interface at all.
Interface Serial two/zero and we'll say delay
and the lowest number I can select is one,
which actually because it's tens of microseconds
means I'm telling him the delay
on that interface is 10 microseconds.
Save my config,
sho ip eigrp topology,
and remember the way this works is that
after your prefix or your network,
what you'll see first in this output
is the successor, or if you have more than one successor,
the successors, followed by the feasible successors.
Okay so in this particular case
it's still using fastethernet zero/zero.
Nothing has changed.
Okay, that being the case, let's go back to our topology now
and try lowering the delay on this upstream interface
and see if that will also work.
So that is, what is that?
That is Serial two/one on Router two.
We'll minimize this.
Actually we'll maximize it, and let's go back to Router two.
Interface Serial two/one delay of one
Save that, we're not gonna need Router two anymore.
Close him down, alright,
did that make Router one switch over?
Nope, still using the fast Ethernet.
Okay, now before we resort to modifying bandwidth values,
is there anything else we can do with delay?
Well, in our topology here, we lowered the delay of these
as far as we can possibly go.
Why don't we take the reverse approach now?
And why don't we go to Router one's upstream interface
and increase the delay to some really horrible number?
So he thinks that anything going out that interface
will experience a lot of delay.
So let's go back to Router one.
We're still there.
Interface fast Ethernet zero/zero, delay,
and let's give him some delay of like 55555.
So 55 and that's tens of microseconds,
so that'll actually be 555,550.
Okay, did that make him change?
Nope, still using that fast Ethernet.
Hasn't switched over yet.
Oh, there we go, it did work. Look at that.
Now the 44 network, the next line which is the successor,
is showing as Serial two/zero.
Now we do sho ip route
We can now see that the 44 network is indeed
going across the top path, the serial link.
Now I can verify that by doing trace 44.44.44.4
And we can see the first hop was 1.2.1.2
which was right here, Router two,
and then the next hop was 2.4.2.4
which was this address right here.
Now as of this point, I'm gonna go ahead
and stop the video at this point.
We're not entirely done, so if you're doing this
on your own, you're almost there.
We've got packets from Router one going to Router four,
taking the top link.
But, that's not going to affect the return traffic.
Router four is still gonna believe
that to get back to Router one,
he should go across this bottom path.
So right now what we have
is what's called asymmetric routing,
where packets going in one direction take one path,
and the reply packets take another.
How can we verify that?
Well, let's go to Router four
and let's see if he was to ping back to the 11 network,
what path would he take?
And we can see that right now,
he's still taking the lower link.
So in order to complete this lab,
you're gonna have to continue manipulating metrics
until Router four also believes
that he should take the upstream serial link.
And just in case you get stuck with that,
what you're gonna do is sort of the reverse
of what we just did, so you're going to,
on Router four, decrease, minimize the delay
on this interface down to one,
minimize the delay on this interface down to one,
and then you're gonna wanna maximize
or really increase the delay on the fast Ethernet interface
to make it look like it's just horrible
and you don't wanna go that direction.
And that will allow Router four to take the top link.
And that concludes this video series on
our CCNA EIGRP lab using GNS3.
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