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(electronic music)

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- So here we are at the last video

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for this particular CCNA EIGRP lab

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where we're gonna do
some path manipulation.

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So at present,

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when Router one is pinging
the loop back of Router four,

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I can expect that it's gonna

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take this fast Ethernet link.

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How would I actually prove that?

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Well, here's what we're gonna do.

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Let's go ahead and start the routers up.

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And let's go into Router one,

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and what we're gonna do is,

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we're gonna look at his routing table.

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And then we're gonna see,
according to his routing table

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if he was gonna route packets

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to the 44.44.44 network,

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what would his egress interface be?

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Where would he send those packets?

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Show IP route.

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And we can see he's
learned of that network

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and he would route them
out the fast Ethernet link,

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just like we thought.

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Okay, now we also saw previously we did

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sho ip eigrp topol all-links

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We did see that he had
learned about that route

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via the slow-speed serial.

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So what we need to do

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is we need to ultimately make
EIGRP follow the top link.

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We have to trick it, or
fool it, into thinking

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that the top link is
actually the better path.

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Well let me ask you a question.

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By default, when EIGRP is
coming up with its metric,

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that big long number
that we call distance,

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what are the variables that
it plugs into the formula

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to come up with its distance value?

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What are the default variables,

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otherwise known as vector metrics?

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Well hopefully you quickly
answered, bandwidth and delay.

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Bandwidth and delay are
part of that formula,

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the default formula.

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Now it's recommended that you do not touch

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the bandwidth on an interface

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because bandwidth is used
by other things as well.

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So ideally, if you wanna manipulate EIGRP,

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you're gonna manipulate
the delay variable.

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So, let's go ahead and
start by doing this.

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Let's go ahead and in here,

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let's try to take this
interface right here,

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Serial two/zero, and
let's lower the delay.

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Actually, let's lower to the minimum value

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and see if that works to
get our desired result.

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Alright, so let's go into Router one.

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Actually, I'm not sure if
when I took my last snapshot

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I had the routers turned off or not.

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So, I'm gonna go ahead
and retake that snapshot

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because I suspect I did not.

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Okay, so now let's turn them all back on

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and let's go into Router one
and go onto a Serial two/zero

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and reduce the delay to
the minimum possible value

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to make it look like
there's hardly any delay

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on that interface at all.

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Interface Serial two/zero
and we'll say delay

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and the lowest number I can select is one,

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which actually because
it's tens of microseconds

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means I'm telling him the delay

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on that interface is 10 microseconds.

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Save my config,

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sho ip eigrp topology,

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and remember the way this works is that

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after your prefix or your network,

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what you'll see first in this output

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is the successor, or if you
have more than one successor,

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the successors, followed
by the feasible successors.

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Okay so in this particular case

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it's still using fastethernet zero/zero.

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Nothing has changed.

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Okay, that being the case, let's
go back to our topology now

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and try lowering the delay
on this upstream interface

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and see if that will also work.

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So that is, what is that?

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That is Serial two/one on Router two.

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We'll minimize this.

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Actually we'll maximize it, and
let's go back to Router two.

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Interface Serial two/one delay of one

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Save that, we're not gonna
need Router two anymore.

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Close him down, alright,

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did that make Router one switch over?

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Nope, still using the fast Ethernet.

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Okay, now before we resort to
modifying bandwidth values,

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is there anything else
we can do with delay?

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Well, in our topology here,
we lowered the delay of these

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as far as we can possibly go.

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Why don't we take the
reverse approach now?

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And why don't we go to Router
one's upstream interface

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and increase the delay to
some really horrible number?

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So he thinks that anything
going out that interface

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will experience a lot of delay.

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So let's go back to Router one.

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We're still there.

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Interface fast Ethernet zero/zero, delay,

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and let's give him some
delay of like 55555.

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So 55 and that's tens of microseconds,

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so that'll actually be 555,550.

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Okay, did that make him change?

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Nope, still using that fast Ethernet.

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Hasn't switched over yet.

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Oh, there we go, it
did work. Look at that.

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Now the 44 network, the next
line which is the successor,

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is showing as Serial two/zero.

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Now we do sho ip route

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We can now see that the
44 network is indeed

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going across the top
path, the serial link.

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Now I can verify that by
doing trace 44.44.44.4

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And we can see the first hop was 1.2.1.2

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which was right here, Router two,

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and then the next hop was 2.4.2.4

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which was this address right here.

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Now as of this point, I'm gonna go ahead

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and stop the video at this point.

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We're not entirely done,
so if you're doing this

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on your own, you're almost there.

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We've got packets from Router
one going to Router four,

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taking the top link.

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But, that's not going to
affect the return traffic.

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Router four is still gonna believe

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that to get back to Router one,

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he should go across this bottom path.

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So right now what we have

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is what's called asymmetric routing,

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where packets going in one
direction take one path,

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and the reply packets take another.

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How can we verify that?

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Well, let's go to Router four

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and let's see if he was to
ping back to the 11 network,

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what path would he take?

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And we can see that right now,

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he's still taking the lower link.

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So in order to complete this lab,

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you're gonna have to
continue manipulating metrics

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until Router four also believes

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that he should take the
upstream serial link.

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And just in case you get stuck with that,

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what you're gonna do
is sort of the reverse

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of what we just did, so you're going to,

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on Router four, decrease,
minimize the delay

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on this interface down to one,

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minimize the delay on this
interface down to one,

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and then you're gonna wanna maximize

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or really increase the delay
on the fast Ethernet interface

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to make it look like it's just horrible

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and you don't wanna go that direction.

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And that will allow Router
four to take the top link.

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And that concludes this video series on

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our CCNA EIGRP lab using GNS3.

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(electronic music)