Time
15 hours 34 minutes
Difficulty
Intermediate
CEU/CPE
16

Video Description

Serial Link Lab We return out our simulation lab to demonstrate Serial Links and how they work. From this lesson you'll learn how to execute serial interface commands, and why the default Encapsulation type is HDLC is and what that means. For example, you'll learn that there is no MAC address on a serial interface and why that's important to note, what happens when you make a change to the serial interface from both ends of the transmission, how to assess the display output after launching the running configuration such as clock rate, and how that component is affected by change.

Video Transcription

00:04
As you see, we're back to our lab. And the link that I drew on the board was this link between router to one
00:12
and rather one. So router to one serial 010 interface is connected to a router. One serial 000000 interface.
00:22
Let's
00:23
go ahead and log into router to one
00:28
and let's look at the serial 010 interface.
00:39
So I'm gonna execute the command show interfaces serial 010
00:45
A few things I want you to notice about this interface.
00:49
Now, we already know that by default, serial interface is or all interfaces on a router, for that matter are administratively shut down
01:00
again. The maximum transmission unit is 1500 bytes,
01:03
and the band with is 100 and 28 kilobits per second.
01:08
I also want you to notice that the encapsulation
01:11
is high level data link layer control once again, high level data link Clear Control or H D l c.
01:22
So the default encapsulation type for a serial interface is h d l C.
01:27
I also want you to notice that there is no Mac address on a serial interface.
01:34
So serial interface is do not have Mac addresses.
01:38
So let's go ahead and assign this interface an I P address.
01:45
Before I do that show, I'd be interface brief
01:51
just to show you that cereal
01:56
010 by default is down.
02:00
Now, let's go into serial 010
02:02
and assigning an I p address.
02:06
So we configure
02:07
terminal takes, meet your config mode.
02:12
Then I go into the interface by saying interface serial 010
02:20
And now I have signed it tonight P address I P address. And we picked the 200
02:25
about 202 100 range and router to one. I'm gonna make 10.2 and my mask is going to be 255255255252 Which is the same as slash 30.
02:40
A total of 30 bits on into sub net mask. So
02:46
eight,
02:46
eight,
02:47
eight, which makes 24
02:51
and then six,
02:52
which makes 30.
02:53
I'm gonna bring the interface up by executing the no shutdown command.
02:59
Now, I'm going to go to Router One
03:01
and do the same.
03:06
So, in a bull
03:08
configure terminal,
03:13
I'm gonna go into serial zero
03:15
interface serial 000
03:22
signing tonight. Be address.
03:24
Okay,
03:28
This side. I'm going to keep as 0.1. 200. 202 100.1
03:34
And the mass is going to be 255255255252
03:39
And I'm gonna execute the no shutdown command.
03:45
And as you see,
03:46
Interface Serial 000 has been changed to up our link. Should have gone green. Let's check.
03:53
Yep, it is green.
03:57
Let's go.
03:59
Make sure this interface is up.
04:00
Show I P interface
04:04
breathe,
04:06
and it stays up. Up.
04:10
Let me ping the other end and make sure this is up. Ping
04:15
200
04:18
202 100.2. Which is the i P address over Outer to a one,
04:24
and it pings. Now you might be tempted to ask me, Junaid,
04:29
you did not set a clock rate. You just told us that one side is going to be a D c. East Side and the other side's going to be a d t side.
04:36
And you have to set a clock rate on the D. C. Eastside.
04:41
Well, first order of business. Let's figure out which side is the D C. Eastside
04:46
for this should not have worked yet.
04:48
So to figure out which side is the D C Eastside and which side is the D E T E side,
04:55
we execute the command show
04:58
controllers and then the interface I D which is on this end this cereal
05:02
000
05:06
and on top here, if you look it says D. C.
05:10
The readout 35 is the cable type,
05:15
and the D. C Eastside has an automatic clock rate set,
05:19
which is why this link went up.
05:21
Nowadays, Cisco routers come
05:25
with an auto clock rate on the D. C. M.
05:28
So the clock grade, I believe it set to 20 million.
05:30
What is that? Two million?
05:32
Well, two with 123456 years.
05:39
Let's check the other end
05:45
on router to one. If I execute the same command
05:48
with the interface I d. Serial 010
05:53
Show controllers serial 010
05:58
You will see that this end is the D T E end
06:03
and clocks are detected, which means, in detects clocking being set from the other end.
06:12
So let's look at
06:14
the running configuration for outer one.
06:17
So I'm gonna go back to my d C Eastside
06:21
and say shoe
06:25
running config.
06:29
As you see under cereal
06:31
interface Serial 000 It is an automatic clock rate set
06:36
already.
06:40
What if I want to change this clock rate for if I look at my
06:45
interface with the show interface serial 010000 command
06:51
on rather one sided interfere 000
06:57
You will see that the band with all this link is 128 k.
07:01
So this link cannot support a bit transfer rate
07:05
whoever won 28 k.
07:09
So we might as well set the clock rate to match our band with. For you can't go any faster than that.
07:16
So configure terminal.
07:20
I won't go into my interface serial 000
07:26
and execute
07:28
Say clock
07:30
rate.
07:31
And if execute the help feature of this point,
07:34
you will see all the different clock rates available.
07:38
But the one that matters to us is this guy. 100 and 28
07:43
1000 bits per second or 1 28 K
07:47
type and one to a 000 and hit Enter. Let's make sure the clocking exchanged on the interface. So do show interface serial 000
08:00
And now Oh, no, it's doo show controllers. You show
08:07
serial 000
08:11
and now we will see that the clock rate has changed you. 128000
08:18
Now, at this point, if we look at our new show, I p interferes Brief command.
08:24
I see that the interface is up. Up
08:30
now What happens
08:31
if I change the encapsulation type on one end? That's what I meant earlier by mismatch Encapsulation
08:37
on router to one which is the other side we already know by default than encapsulation is HDL See
08:46
And on router one Also the encapsulation by default
08:52
is HDL. See right here under the show into faces serial 000 command you see on both sides on router to one and rather one encapsulation by default is set to HDL. See what happens
09:07
if I change router one to something else.
09:11
Well, let's see.
09:13
I will change the encapsulation type to the three options here.
09:18
Frame relay H T l C and P p p gonna change it to frame. Really?
09:26
Let's look at our show i p i n t brief command again.
09:31
And you see that the interface has changed state two up, down.
09:37
So that is our first layer to issue.
09:41
Now. I can't really get rid of the clocking on this interface because it's there by default. So if I get rid off, if I say no clock space rate 128000
09:52
So if I do this
09:54
well, let me change encapsulation tight back for us too,
09:58
HDL. See? And you see that the link went back up immediately.
10:05
Now, if I try to take the clock, read away by saying no clock rate
10:11
and and then check do show
10:13
controllers serial 000
10:20
If I can spell and type,
10:26
we will just leave it at s 000
10:30
See, I cannot take away the clock rate.
10:33
It is set by default.
10:35
It should have actually gone back to two million.
10:37
But
10:39
on Packet tracer or even on real rounders, you really can't take away the clock raped.
10:43
If I look at my running config,
10:52
the clock rate does not go away once it's set.
10:56
So if I weren't you take away the clock rate.
11:03
If I were to take it with a clock rate, you would again see an up down situation in the show i p interface Brief command.
11:11
The last option is that if router one stops sending keeper lives,
11:16
so if I execute the no keep alive command,
11:20
the link should go down
11:22
in a little bit. But we're not gonna wait five minutes for this to go down.
11:26
You just take my word for it. That if I turn off keeper lives or if there is an error Oh, see, it did go down, actually. So let's test that out again. No, keep alive unless execute to do show I p interface
11:46
Brief command. Well, it shows up up,
11:50
but the link is technically down.
11:52
If I see keep alive command again,
11:56
do they keep alive command again? It shows that lying to recall came back up
12:01
so which meant it was down previously.
12:05
So if you see an up down situation in the show I p interface brief command there, three possible reasons and all three are layer two issues
12:16
keeper lives and missing because the interface is malfunctioning for some reason, Or there is a mismatch encapsulation between your side and the other end
12:26
or the D. C E side has no clock rate set.
12:30
I'm going to save my work
12:33
on Router One and router to So we do not lose it
12:43
and we're going to move on to I p routing. Terry. This concludes the lab.

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Cisco CCNA

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Instructed By

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Junaid Memon
Instructor