Links on a Switch
Video Activity
Now that we've created Access Ports, we review the steps to create Access Ports, and move on to explain the concepts for the second type of link that exits on a switch, Trunk Links. We define and diagraph what a Trunk Link is and demonstrate the process flow for how it works.
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Time
27 hours 46 minutes
Difficulty
Intermediate
CEU/CPE
31
Video Description
Links on a Switch Now that we've created Access Ports, we review the steps to create Access Ports, and move on to explain the concepts for the second type of link that exits on a switch, Trunk Links. We define and diagraph what a Trunk Link is and demonstrate the process flow for how it works. You'll learn how many VLANs can live on a trunk Link and see the interrelationships with end devices. For this lesson we also review some important standards and explain their relevance to CCNA and the VLAN system.
Video Transcription
00:04
we're done with access ports.
00:06
The two steps to create an access port.
00:09
Our creative Ellen, Step one and Step two is assigning that villain to a port.
00:16
And as soon as
00:19
that port becomes part of that one villain,
00:22
it becomes an access port, especially the command switch. Port Mod Access unconditionally sets that port to access mode. And then the camp command, transport, access villain and the villain I d in this case, it being 1 50 So switch port access. Villain 1 50 puts that port in Villain 1 50
00:42
So that was the first type of link
00:44
we covered
00:45
that can exist on a switch, Which is your access ling.
00:49
The second type
00:50
off link that can exist on a switch is your trunk link. A trunk link can carry more than one villain at a time. Why would that be needed? Oh, go to our little box diagram. Again, this is switch one on the link between them on this is switch
01:08
two.
01:11
Both of these are connected to each other on faster than a zero slash 24
01:15
report 24. And let's say
01:19
we have
01:22
PC one envy lan.
01:26
So I'm gonna shorten the land to be l 10 in pc to on switch to in villain 10 then PC three on switch one in Villain 20 and P. C. Four on switch to and villain 20 if this link between switch one and switch to
01:45
this port 24.
01:47
If we were to put that in
01:51
real and 10
01:55
then on Lee PC one, which is in Bill, and 10 NPC to which is in Bill and 10 can talk to each other. Remember I said that villains can transfer switches well,
02:05
at this point, we are only transfers England 10 across this link, connecting the two switches
02:10
on Port 24
02:14
pc three and P C. Four, and they can't talk to each other.
02:19
If I were to put this link
02:22
in Villain 20
02:27
then BC three NBC four would be able to talk to each other. But
02:30
BC one and two. No, there wouldn't be able to talk to each other.
02:36
I have another option.
02:40
I could create another link between these two devices
02:44
as zero slash 23 abs, you know slash 23 on both ends
02:50
and have one carry villain 10 and the other one carry villain 20.
02:55
But then again, that's a waste of ports. What if you have 10 villains purse, which you're gonna use up 10 ports on each switch just to carry the villain across?
03:07
So Cisco came up with a better idea.
03:09
How about we have one link between the switches? Let's keep it AB zero slash 24 0 slash 24
03:20
and allow it to carry both villain 10
03:23
and 20.
03:27
And now you're not wasting ports
03:30
because or one port you carrying multiple villains more than one villain in the trunk Link is a link that carries more than one villain at a time.
03:38
But how does this happen
03:40
when PC one tries to talk to PC TO and PC three tries to talk to P C. Four at the same time? Remember, this is full duplex. The sending switch sends all its frames on for 24 out tour. Switch to
03:55
how will switch to know which frame belongs to rich villain. How will switch to differentiate between frames coming from PC one, which is in Bill and 10 and frames coming from PC three, which is in the land? 20.
04:11
And the answer is
04:13
frame telling
04:15
switch. One will actually
04:17
put an identify on the frame
04:21
telling
04:23
the frame that, Okay, you're part of Dilantin.
04:26
And another frame from PC three, for example, will have a tag put in it, saying that you're this frame is from villain 20.
04:33
So each frame coming from Bill PC one or PC three when the switch sends it out towards which one sends it out to our switch to,
04:42
well, haven't identify inside off it identifying
04:46
the villain that the frame belongs to.
04:49
So when sweets to receives a frame coming from PC one, the frame will have an idea that says, this friend belongs to be lon 10. So that way, switch to will know to Ford this frame out to PC to
05:03
ah, frame from PC three. Switch one bill at a tag to it, saying this friend belongs to be land 20.
05:12
So when switch to receives the frame from PC three, which one would have already tagged it within villain, I d off 20 so switch to will know this frame goes to be land 20 or in this case, P. C four.
05:27
Now, how is this done? This frame tagging
05:30
is done using one of two protocols,
05:34
the 1st 1
05:36
So this is a subheading frame tagging or trunk ing protocols. The 1st 1
05:45
is Inter Switch Link. Now what interest Wish Link does
05:50
and interest rates. Linkous, Cisco proprietary So you cannot run interest. Which link are the short
05:57
form I sl
05:59
on a non Cisco device? I s Ellis Cisco. Proprietary.
06:03
Now what I SL does is it takes the original frame, for example, frame coming from Bill and 10
06:11
and it encapsulate. Or it surrounds the original frame in a new header. Or, in a new frame.
06:19
A new 26 bite frame with the 26 bite header and a four bite footer. So a total of 30 bites.
06:29
So I SL puts a new frame around the original frame, and this new friend has a field in it that identifies the villain the frame belongs to.
06:40
So you take the frame.
06:43
Think of the frame original frame as a as a letter,
06:46
and you put it in a new envelope or you put the on look in another bigger on bullet.
06:51
That new frame, the isil frame has a field inside off it.
06:57
That says villain I D. Is 10 or villain ideas? 20. So
07:01
the isil frame as an identifying field for the villains that's being carried inside.
07:09
The other one is the open standard, which is I Triple E 802.1 q. By open standard, I mean, all networking devices are all switches can use this. It is not Siskel proprietary.
07:26
What in, 2.1 q or
07:29
the short form
07:30
0.1 Q.
07:32
Does
07:33
is insert a four bite field.
07:36
Justin takes a four bite feel that inserts it in the original frame, and that four bite field is a tag identifying what the land this frame belongs to.
07:46
So if the frame belongs to be land 10. Attagirl, save the land. 10. It's just inserted into the original frame.
07:55
Keep in mind, though, that the maximum transmission unit for Ethernet is 1500 bytes.
08:01
When you add four bites
08:03
off a 0.1 Q
08:07
drunk
08:09
to it,
08:09
you get a frame that is 15 04 bites.
08:13
This little tidbit of information come in will come in handy when you get to your CCN piece.
08:20
For now, it's a relevant kind of for CNN, but do remember it also,
08:26
the 802.1 Q Drinking Protocol
08:30
has a feature called the Native Villain. Feature
08:33
the name of villain
08:35
off a 0.1 Q. Trunk
08:39
is the villain that is not tagged or the trump.
08:41
So let's say I have ill and 10 2030 40 and 50
08:48
Real antennas getting tagged real and 20 is getting tagged. So as soon as the frames from Bill and 10
08:56
transfers the trunk, a tag of tennis at it or not, one Q tag of 10 is added
09:01
to those frames for villain 20 attacker twenties added for Villa and 30 attacker Thirties added, Let's say Vienna and 40 I make it the native villain off my trunk.
09:13
There's not going to be a tag that is going to be added to reel and 40.
09:18
So the native villain off a 0.1 q trunk is the villain. That trance verses the trunk without being tagged,
09:28
and you will see this happen on our lab.
09:30
So between I sl and 0.1 Q. Which one's better?
09:35
The answer being the one with less overhead
09:41
I S O or interest rates links as a 26 bite header.
09:46
That's a lot of overhead that's a lot of that. That's a lot more work a switch has to do to process that frame. Ah, four bite field, a little tied four by tag inserted into the original frame is much easier to process. So the sending device as the tag
10:03
and identifies the frame
10:05
with the villain it belongs to, and the receiving switch reads The tag Say is okay. This frame belongs to be Land 10 for example, and then removes the tag and forwards the frame out to be land 10 before we get to the configuration part off the trunk ing. Take note that you can manually configure trunks
10:24
and eventually we're gonna end up manually configuring trunks.
10:26
But there is a protocol called dynamic Trunk ING Protocol, which is my next topic. So Pro Call call dynamic drunk ING or D T P For short, dynamic trucking, Torre call performs automatic trunk negotiation between switches that are connected on ports
10:46
so ifs, which is connected to
10:50
switch be on Port 24. Dynamic trucking protocol under certain circumstances will automatically bring up a trunk on those ports,
11:01
so dynamic trucking protocol can run in one of three modes. The first mode is dynamic desirable. The switch port.
11:11
If it isn't dynamic, desirable mode,
11:16
it will send
11:18
DTP frames,
11:20
and it will respond to DTP frames.
11:24
So every boat send and respond to DTP frames from the other end of the link,
11:31
as the name say's, a trunk is desirable.
11:35
So if the other side is sending me dynamic drinking protocol frames, I will respond to them. If the other side is quiet, I'm going to send it. DTP frames, basically the poor on the local side and the port on the remote side are trying their best to bring up the trunk, so they're negotiating with each other,
11:54
talking DTP with each other,
11:56
trying to bring up a trunk
11:58
when it's in dynamic, desirable mode.
12:01
Take note
12:03
that switch models in the Cisco genre of the Cisco World
12:09
switch models that end with the number
12:13
50. So, for example, a switch model 35 50 which I have at home we'll have by default all its ports in dynamic, desirable mode. If two switches that are both 35 fifties
12:28
are connected back to back with each other with the cable
12:33
across over cable. If you remember to similar devices use a crossover cable. So if I just connect to 35 50 switches to each other,
12:41
a trunk is automatically going to come up
12:43
because they're gonna talk. DTP and both sides are gonna be in dynamic, desirable mode. Both sides are going to send DTP frames and respond to frames from the other side, and the trunk will automatically come up.
12:56
The second mode is your dynamic Otto mood In dynamic auto mode,
13:03
the port
13:05
will respond to DTP frames from the other end from the remote side,
13:11
but it will not send.
13:15
It will not send DTP friends so n dynamic, desirable mode. The port initiates trunk ing.
13:22
It wants to create a truck and it starts sending DTP frames and also responding to DTP frames from the other side. But basically the port initiates the trunk.
13:33
In dynamic autumn owed, a port will not initiate trunk ing.
13:37
Yes, it will respond to DTP frames from the other end.
13:43
So if the other end is dynamic desirable,
13:46
it will respond to DTB frames from the other side and the trunk will come up.
13:50
But it will in itself not initiate trunk ing by sending DTP frames
13:58
now switch models
14:01
that end in the number 60
14:03
like the switch model 35 60 automatically have all their ports in dynamic auto mode, by default have all the airports in dynamic auto mode.
14:16
So if you connect to 35 60 switches back to back with each other with a crossover cable with a trunk, come up.
14:24
Nope,
14:24
because both sides will sit there and wait for the other side to initiate trunk ing
14:30
in Dynamic Otto, you respond to DTB Frames. You don't send them, so both sides will sit there and there's basically no trunk will come up.
14:39
So for our labs, did I pick the type of switches where a trunk will come up automatically? Or did that pick one where you will have to configure a trunk? Well, of course, I picked 35 sixties because I don't want my trunks to come up automatic me because I want us to do the work.
14:56
The third mood is simply mode on.
15:01
This says
15:03
I don't care what the other side is.
15:05
I want to consent my side unconditionally to a trunk,
15:11
so sets the local port
15:13
to trunk ing unconditionally.
15:16
Now,
15:16
mode on will also
15:20
send
15:22
and respond to DTP frames. You'll set your side
15:26
two on,
15:26
and then if the other side
15:30
sends you DTB frames, you will respond to him, and you all will also send GT three frames to the other side.
15:35
So if you have two sides and both of whom are desirable, desirable yes, trunk comes on desirable auto
15:43
drunk comes on desirable on trunk comes on auto, and on Trump comes on. The only time the trunk doesn't come up automatically
15:54
is when you have both sides as auto. So if you have out on one side and out on the other side, you won't automatically get a truck,
16:02
which is ideal, actually.
16:04
So we're done with the charity part of this lecture. Let's get on the lab, and I will show you the commands to configure trunks.
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