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200-125 CCNA v3.0 | Day 10: Port Modes and Functions | Free Cisco CCNA


999990000000000000000Cisco Certified Network Associate – Day 10 Welcome back everybody,
I am Imran Rafai, your Trainer for this entire series. Today, we would be dealing
with Switch port modes and different functions of a switch. So, without wasting much time
let’s get straight into this class. Like I said, obvious of Today’s class, we will look at the Switch Port Modes, and we will look at Switch Functions. The Switch has two modes. The first mode is the Access mode. An Access mode is used when you are connecting a
Switch port to an End Device. So, let’s if you want to connect your
computer or your Desktop to a Switch. That particular port we
configure as an Access Port. The configuration or the
command for configuring a port Switch port in Access mode
is switchport mode access, and by this level in our training video
you should be able to identify that when the command the switchport prompt when the switch, the CLI
prompt says config-if this should tell you that this is a command that is been tied inner
interface subcommand. That is, I have used an interface
fa 0/1 or fa 0/something, and that is why the
prompt has changed to -if. So, this is a command in the subcommand
under interface on a switch. So you go into any interface, which interface that you want
to convert with access port, you go there and says
switchport mode access. Typically when you type a command like
switchport mode access there is another vlan command
that we need to give, but at the moment don’t worry about vlan, at the moment only worry about the modes, so like I said, the first mode we’re
talking about is the Access mode, and like I have mentioned here,
this mode is used if you are connecting that particular port to an End Device, like your
computer or your Desktop. The other mode the switch port can
take is known as the trunk port. So what’s a Trunk port? A Trunk port is a port that
is connecting to switches, so if you connecting a port of
a switch to another switch, if you connecting to another port, so basically a switch is
connected to a switch, that particular port through which are
connecting a switch to another switch, should always be a Trunk, right. So Trunk where Trunk is
a very “Cisco” word, normally all other manufacturers
call it “Attack port”, but Cisco calls it a Trunk port, so typically both “Trunk port” or
“Attack port” have same functions, what they do is they make sure that they carry all the traffic
that is there in a switch. So basically they share. So at the moment we haven’t
spoken much about VLANs, but when we talk about
VLAN we will come back more into Trunk and we
will talk big enough. But at the moment you know that Trunk mode is used when a switch
is connected to another switch, Access mode is used when that switch
is connected to an End Device. Here when I say switch, what I literally
mean is that particular port, so these modes are not for the switch, these modes are for the particular
port that we are talking about, so these are the two modes
each switch port can be in, And just like how we’ve discussed with the command for putting
a port in access mode, the command to put a port in the
Trunk mode is switchport mode trunk. So, when we talk about switch port modes, there is another protocol
we need to talk about, and that is the Dynamic Trunking Protocol. Now, this protocol is a
Cisco proprietary protocol, that means to say that you cannot use
this protocol with any other switch, any other switch manufactured
by any other manufacturer. So only if you are using a
Cisco switch you would be able to use this concept, or
this protocol called DTP. Of course, I know there
are some manufacturers because Cisco is such a huge company, and such a well accepted
company in the industry, there are some manufacturers who
make use of the DTP concept of Cisco. But since this video series
about Cisco and CCNA, we are going to stick to Cisco. So in DTP there are three modes,
or rather there are two modes Dynamic Desirable Mode
and Dynamic Auto. And the third that you see in the screen is
No Negotiate, that is a way to disable DTP. So let’s start from the top. When a switchport is in the
Dynamic Desirable mode, what it does is… it immediately
starts sending out DTP packets, and that means it starts sending
DTP packets to negotiate. And what does it negotiating? It’s negotiating a trunk. So you should get a hint
from the protocol name, It’s a dynamic trunking protocol, that means: what does it negotiate?
it negotiates a trunk, so the minute another device
is connected to that port, and if that port is in dynamic
desirable mode, what is it desiring? is desiring to become a trunk. So it’s gonna tell the other port: ok I wuold like to become a trunk,
what do you want to become? Right? And if the other side
also is in dynamic desirable? Pum! Immediately both of them
become trunk ports, right? But let’s assume one side is in
Dynamic Auto, the next command here, so one side is in dynamic auto,
the other side is in dynamic desirable, the dynamic desirable switch will send
a DTP packet to the dynamic auto switch, and the dynamic auto switch say:
fine, I’m configured for auto, that means I can do whatever you want, do you want to become trunk?
fine, let’s become trunk… But, if there is a case where both
these switches are in dynamic auto, then that’s a problem: both
of them auto will do nothing, because dynamic auto is
a very flexible steel, it just waits for DTP negtiation, it will never initiate to
dynamic trunking negotiation, so if you keep both the
sides at the dynamic auto, then it will not work, right? So, if you want to create
trunking automatically, then you need to make one side at
least, or both sides if you want, as dynamic desirable. Now you might say: ok this is good,
you can create automatic trunking, right? you can create automatic trunking, so if you connect another switch, automatically that negotiates a
trunk and the trunk is formed, but come to think effort to keeping
your switchport in dynamic auto or dynamic desirable is
not very desirable, why? because let’s assume in our organization we have kept all our switches in
dynamic auto or dynamic desirable, now, if there is somebody who
wants to hack into our switch, so let’s assume one of our employees,
stands out as a bad guy, and he wants to hack into the system, it’s very easy, all he has
to do is get another switch, configure that port, whichever port
is connected to our office switch, with dynamic desirable, so immediately
it’ll start negotiating trunk with this, and it negotiates a trunk and if this is
in dynamic desirable or dynamic auto, they will actually form a trunk. The problem of forming
a trunk with a switch is that it’ll send all the traffic, a copy of all the traffic to that
switch because it’s a switch, right? so this is how trunks work. If two switches are in trunk or
if three switches are in trunk, they will share the same data, it is like extending your switch, if your switch has got eight ports, you connect another eight ports’ switch
and create a trunk between them, it is as if that the entire switch
is a sixteen ports’ switch. That’s how it is. Basically, by default obviously
there are based of ruling traffic making sure the traffic does not
go from one switch to the other. On a general case, by default if you connect to switches and
form a trunk between them, it is as if those two eight ports’ switches had become one large sixteen
ports’ switch, right? So if our hacker get access to our switch, and creates a trunk with
his hacking switch, then your company switch is actually
sending out all the traffic to his switch, and he can create, like we’ve
discussed on a last video, he can use any packet analysis software and literally analyze the entire
traffic of our organization. So, the ideal situation
would be to switch off, or rather No Negotiate, by using
this third command there, which is switchport nonegotiate, so use that command and disable DTP
if you are not using it, right? so that’s how you disable it, so when you create switchport
access switchport mode access, that disables trunking, that’s you statically configuring the mode,
like we’ve discussing the last slide. So you can statically configure whether
you want mode access or mode trunk, but if you want dynamic,
then may be make use of DTP. So that’s a concept, and I hope
you have understood so far. Next, let’s going to the
switching functions. Basically a switch has three functions. So we’re gonna discuss
three functions today, and that’s the Address Learning
function of the Switch, Forwarding Decision of the
Switch and Loop Avoidance. So let’s start with Address Learning. How does a switch learn addresses? Now, we have discussed many
times in our previous videos, but because we are talking
about switching here, let me talk about how switches
learn addresses once again. Now, like I told you in
one of my old video, when a switch comes on
within 30 to 40 seconds all the devices connected to that
switch literally start chatting, that’s how the computer’s out for, Computers love chatting. Computers send
broadcast every time, they keep sending,
they keep talking, right? So it is: “Hey this is my mac address”, and they achieved any broadcast, so let’s if there are five devices, when the first device sends:
“you know my source addresses?”, he knows that he sends
broadcast, different broadcast, may be ARP broadcast, it may be different servicing that’s running
on your Operating System, towards trying to communicate
with the network, and every time that a device
communicate with the switch, it has to send his Source Mac Address. So if the Switch gets
from the first device, that’s connected to port one, if he gets a broadcast message,
it reads the source mac address of that device and he says: “Ok, my port one is connected
to this Mac Address.”, right? So it creates an entry in its
mac address table or the cam table, at the same time it may the 2nd device,
the 3th device, 4th device, 5th device, all these device treats any broadcast
and everytime it sends a broadcast, it immediately picks the source mac address
and creates an entry in the mac table. Now, if one of those devices wants to
communicate with another mac address, it sends a packet, and the switch looks at the destination
mac address and it looks at the cam table, it knows that at particular mac address
is sitting on one of those ports, so it can immediately make
a switching decision, that’s how the address learning processes. Now, we spoke about Forwarding Decision, so let’s look at a little more. There are two types of switching forwarding
decisions that a layer to switch makes, it can use the “Cut Through” switching or
it can use “Store & Forward” switching. What’s the difference between these? Let’s assume one device wants to
communicate with another device. So what it says? It says OK, this is my
destination mac address, this is my source mac address and all the
other information that follows, right? In Cut-Through Switching,
when the switch receives a frame, it immediately looks at the
destination mac address. So, it just waits for the first
few bytes of information, by which time it has old
information it needs, that is their destination mac address, and it immediately starts sending
that frame out on their interface, so it doesn’t wait to
receive the entire frame. As soon as it receives its
destination mac address detail, it starts forwarding what
of information have get, to type destination port, right? That is how Cut-Through works. Now, let’s look at Store & Forward. What Store & Forward does is: the switch waits until it
receives the entire frame. So, it waits…
it gets the entire frame, it runs through a error detection, it checks if there are any errors, that were induced during transmission, if nothing, it’ll start forwarding
out the destination port. Now, some people might say:
OK Cut-Through is good. And some might say: No, no, no… we need
error detection so Store & Forward is good. But, like I said, there is no right answer. Either of them can be right,
depending on your situation: do you want fast to services? do you want the switch to work faster? then you will go with Cut-Through. Do you want to more
reliable switching? then maybe you’ll go with
Sore & Forward, right? These are the two different
switching methods the switch layer to switches implement. Next we will look at Loop Avoidance. Now, what is loop avoidance? If you remember from my old video, I said that when a switch receives
broadcast, what it does is: it takes that and it sends
out in all the ports. So let me take a bit…
let me try to show it. So this is a switch, OK? and this is a switch, right? I don’t have my pen to this,
so I’ll have to make use of mouse. This is a switch, so when you
see two arrows like these, from on any logical diagram, you need to know that’s a switch, right? So that’s a switch. Let me change the colour. So, normally you will connect one switch
to another switch and this becomes what? Yes, it’s a trunk. You could,
you’re learning very fast. You connect two switches using a trunk.
So now this is your trunk. But, as your network grows, you wouldn’t want to just how one wires, you might say OK, we might
have a discuntion sometimes, so instead of doing the whole wiry, make these two switches
act two different flows, so instead of keeping one wired and
just waiting for that to disconnect or get cut, or I don’t know…
go faulty, and it’s a big dick to rewire,
especially from some two different flows, so what you normally do is,
you would keep two wires, or three wires, it some back of fire, right? So, this is like a backup wire. So again, because it’s connecting
to switches it’s a trunk port. So, you would say: of course we
can disconnect this and keep, unless this goes faulty, and when it
goes faulty you can connect this… Of course, you can do that.
No problem but… I am sure almost all network administrator
would want the wires connected, they don’t want to have headacke of tracing
those cables and putting plug-in it again. So we would connect these two cables. The problem is when you
connect these two cables… and if connect two devices switches, with two cables,
what happens is… If there’s one device here, this is a computer, and if this computer sends
a broadcast, right? it sends a broadcast, and
what is a broadcast do? According to what we know, when the
switch receives a broadcast… it sends that traffic out
on all the switch ports, that means it’ll send
the traffic here, and it’ll send the
traffic here, right? So, it’ll go here,
it’ll go here. Now, when this device
gets this broadcast, it’ll take that and it’ll send it
out on this port. Right? It’s a broadcast. That switch doesn’t know that broadcast
is coming from the same switch, right? But for that switch, it is another port. So it’s gonna sending out here. And the traffic coming
from this port. The switch is gonna
take that there is… OK, you need to go out in this port. Right? The sending happens here.
It comes all the way here. This switch is gonna think: OK that’s another broadcast,
I’m gonna take it and put it on this port. And what of a traffic…
this traffic coming through this port. This switch is gonna take it
and put it back here. And this process will continue. It’ll continue… It’ll go round and
round and round and round and round. And this process is known as
The layer 2 loop. Now, it’s very difficult
to identify a loop. If at all you have a loop in your system,
it’s very difficult to identify… because you wouldn’t know, there is no
indication thing “there is a loop”. I mean, the switch wouldn’t even know
that there is a loop happening, right? Unlike layer 3 traffic. When we reach layer3 we’ll see that layer3
has many loop prevention mechanisms. But a layer2 traffic does not have any loop
prevention, like ‘Time-to-leave’, right? So we don’t have that concept of
‘Time-to-leave’ for layer2 packets. So how to solve this problem, right? An intelligent lady wrote this protocol
known as ‘Spanning Tree Protocol’. You could learn a little bit more about
Spanning Tree Protocol if you want, by doing a Wikipedia search. But just to understand
the concept of Spanning Tree, and, like I said, we will come back to
Spanning Tree little later in the series, but at the moment I just want to
introduce you all to this concept. So what is Spanning Tree Protocol? Spanning Tree Protocol is a protocol that
identifies if there are redundant links. So if it seas that: OK there are two
links connecting to the same switch, right? these two switch, same switch,
and two links connecting to that, it knows that a loop will be formed. So, immediately it does what it has to do. We will discuss that in a later
part of this video when we discuss Spanning Tree in that, right?
I promise we will come back to it. But for now, it has its own protocol. It uses it on rules. It disconnects or logically, I mean physically it’s still connected but logically it disconnects
one side of the second cable, so one pair of both is
going to work perfectly, so that’s gonna be the active link, and then you’ll have a backup link
with one of those ports logically shut, right? so to be shut. Now what happens if for some unforeseen
reason this cable will get disconnected? Immediately STP will know that
this link is stop working. It will enable this port and
this port will start working, and this will become
the active link. This is Spanning Tree Protocol
for you in very very short form. So basically to summarize
Spanning Tree Protocol, is a mechanism to
disconnect a backup line, so that’s how this tree is. I mean, I think about Spanning
Tree Protocol like that. It’s just like a tree fallen on the road
and this road is disconnected, right? So this is Spanning Tree… We will come back. A lot of topics that
we discussed in early stage of CCNA. We will come back later
with much more in depth. So, this is what I keep
telling my students: don’t worry if you don’t understand
too many things, because it’s like building the structure. If you building a tall building,
you don’t start building from ground up, and you don’t paint the walls on the
ground floor and then start building. You just build the frame,
the structure first, from that is floor 0, from the
ground floor… telling maybe… if it’s a fifty-story building,
you build the frame for fifty-story and then you start putting
the walls for that building, right? So, more of things we would be
just brushing through now, right? So once we do the brush, we’ll come
back and construct the walls, right? So at the end of the
series, maybe 40 videos, or 45 videos, or 50 videos…
I don’t know. I’m just doing when I think
there is a good topic that I need to add
and I’ll keep adding. So, when we finish this entire series, trust me, you will have all
the knowledge for your CCNA, and trust me, you’ll have much,
much, much more knowledge, than what is required for your CCNA. So, that’s my promise! All you have to do is stick around
and you will learn. Right? So, I think that’s all that
we want to discuss in today’s video. Thank you so much for watching! Don’t forget to like our facebook page. And don’t forget to subscribe
to our Youtube page. And, like I said, if you go to our
facebook page you will see that… we need more likes, we need
people to share our videos, we need people to like our page. Invite your friend! And I’m gonna set milestones now. If you go to our facebook page,
you will see I’m setting milestones. So if you help us reach a
certain amount number of likes, we will put the next video. And you will see the milestones. So it becomes very easy: if you want
the next video, quickly goes… invite your friends,
invite and share that, get the likes up and automatically
new video will come. So 50 videos can take 50 years… 🙂 🙂 🙂 …I don’t know… …or maybe can take 5 months… …or maybe can take 5 weeks… It all depends on how
you guys support us. How you guys subscribe to our channel, and how you guys share our facebook page… So, start liking, start sharing and…
share the love! Thank you so much for all the love!
Bye Bye!

Reynold King

100 Replies to “200-125 CCNA v3.0 | Day 10: Port Modes and Functions | Free Cisco CCNA”

  1. Mr. Imran you are a good teacher. if i just have money i realy realy want to be your student. i am here in another end of the world beautiful land philippines. you inspired me to study networking again. thank you so much. may allah give you more knowledge to share. 

  2. assalam alaikum Sir 
    i would really like to thanks u , and ur entire team for these all videos
    i also wanted to know that how many videos are are left
    plzz answer it 
    we all are waiting

    thanks again

  3. hello imran i have a query regarding trunk port in a switch how  many ports we could assign as trunk port , can we access three ports as a trunk port ..

    assume i have 24 port switch in which port 1 to 4 connected by a vlan 2, port 5-10 connected by vlan 3 , created a trunk port which access vlan 2 on port 12, another trunk port which allowed vlan 3 and vlan 2 both on port 15, when i access cli
    with show interface trunk i could see only 1 trunk port access,,, why it happen

  4. Hi imaran, THANK YOU SO MUCH and i am waiting for your next (Day 11) class so plsssssssssss post it as soon as possible.

  5. I am planning on writing my ccna this year august ,i already feel save and confident about it..thax a lot Sir

  6. Hello Imran and Team,
    For Past three Month's no videos are uploaded, Atleast please share the status about the further videos, Whether you will upload it or not. How long we have to wait.

  7. Come now Imran you should just upload what you have. As people are become restless with yourself and would like to learn more about CCNA.
    If you make a video telling use how many videos you have and how how long it will take you to upload the whole series it will make it a lot easier.
    You should make a timetable so people will have at lease two videos a week and that way the series will be finished in ten weeks.
    I recommender WEN and FRI

  8. Good stuff. Appreciate your time and effort to get this useful series across. I was looking for a basic networking series and this series just solved that.

  9. Hello Imran Sir 

    I would like to say thanks to you to share Your Fallacious knowledge with us,

    Please Make some more Videos for Us

    i also want to Covert More Topics

    Such as :

    1)Router EIGRP
    2)Router Rip

    and Many more 🙂

  10. Very very interesting Imran i understand your teaching better than my own teacher plz keep it up help us God will pay you.

  11. Hello Imran, i have a cisco 2950 switch, when i connect it to my pc via the serial cable all I get is garbage on the screen, if I press the mode button while plugging in I can get to the CLI but when I type flash_init or boot it fails, do you have any tricks to get this switch working, thanks.

  12. Thank you Imran for your outstanding videos. I felt like that my interest is growing day by day towards networking because of your videos. Earlier I thought of doing CCNA training, but because of the financial problem I did not join any coaching. But now I think something for the better and now I am thinking I am very fortunate to watch the videos uploaded you. I learned a lot till now. Thank you, Thank you,Thank you Thank you……….

  13. please please provide complete ccna course.my interest in network is increased because of your videos only.plesse provide complete course so that I Have to give an exam which does not depend on any other course rather than your videos..Thank you so much 🙂

  14. A trunk port is a port that is assigned to carry traffic for all the VLANs that are accessible by a specific switch, a process known as trunking. Trunk ports mark frames with unique identifying tags – either 802.1Q tags or Interswitch Link (ISL) tags – as they move between switches. Therefore, every single frame can be directed to its designated VLAN.

    An Ethernet interface can either function as a trunk port or as an access port, but not both at the same time. A trunk port is capable of having more than one VLAN set up on the interface. As a result, it is able to carry traffic for numerous VLANs at the same time.

  15. Hi Imran,
    what will happen when a port is directly connects to an another port, that also will create a loop right…..
    how can we identify and prevent such cases.

  16. This is by far the most concise and best method I've come across regarding CCNA. I look forward to your videos after work. Thank you

  17. Off topic, but I just searched my whole house looking for a chirping smoke detector, LOL. I hope you've changed the batteries in yours by now.

  18. I had attended bootcamp CCNA course at training center and also read some CCNA books, but from Mr Imran's ccna video courses here let me grab the understanding much more easier in a very good way of teaching and explaination. Thank you so much for the videos. Keep it up !!!

  19. Hi i love your series i'm learning a lot thank you i just have a question : you said in your previous video that gns3 can act like a real switch .. and if i can connect it to my network (switch ) and allow vtp desirable i will get access to all the trafic ? it might be a dumb question please reply thank's

  20. you are amazing … but the problem is that you show images not related to the subject and you try to explain with your mouse .. (broken tree doesn't explain spanning tree)
    it's better to use layout and packet tracer graph and explain on it

  21. so if video 31 the final video? Or is there more? and where do I donate my money for Imran to continue teaching lol. This is good stuff.

  22. I was insecure at first because I hate reading and people suggested I read the CCNA book. This is interactive and allows me to see the bigger picture. Thank you Imran for all your work.

  23. Hi imran
    i have gone through a looping in my company network and we have some layer 2 switch and some layer 3 switch the question what come to my mind is how layer 3 switch knows that there is a loop in the network …..
    and can u please make a vedio explaing the layer2 and layer 3 stuff
    all your vedio are oosum

    thank you for the help

  24. You are the best Imran Sir
    The way you explain the stuff is unforgettable as you use the real life example or stories..
    Thanks for starting the series.
    Looking forward to more videos.. 🙂

  25. I need help regarding Intranet creating for any company . what things we need require if that is WAN (Intranet).

  26. I have 4 PCs. I connect those 4 by using one single layer 2 switch. switch will learn the 4 PC mac address with in 30 to 50 sec by using the broadcast messages. Now PC1 wants to communicate with PC4. in this case it requires any ARP request or by directly it will send it by using the MAC table.

  27. Hi Imran, in the case I'm connected a Wirelless AP as Bridge on my switch port, will I still set a Port as Access Port?

  28. Hi Mr. Imran, I have already reached video day 10 and I had learned a lot. Thank you so much. I'm going to take a test for ICND1 100-105 soon and my employer will pay for it. Do you have any study materials that I can practice on? Please advise. Thank you

  29. Dear Mr Imran.
    First of all i would like to thank you for the training sessions.your classes are excellent and easy to understand .Very recently i started learning ccna by viewing these videos.So far i covered day 12 video..The way of your teaching makes me understand every concept ..
    Thank you once again…

  30. Hi…
    If i connect 2 switches with a trunk port, it should be with crossover cable or with straight cable. please guide me.

  31. Your a great teacher Imran Rafai. I promised myself to see these videos through, and I'm learning so much! I can't wait to be a CCNA.

  32. Layer 2 loop is also known as a broadcast storm. You will see this term on CCNA . Don’t think it was mentioned in the video.

  33. Can I pass the ccna exam, if I have watched all the videos and learned all the stuffs in your videos??????????

  34. Mr Imran you are the best Sir, I thank you so much I'm Elvis from South Africa, from now on wards i will keep on subscribing to your videos, and a like

  35. This video and this series are still valid. If anything changes, we will update this series accordingly. All the best.

    The full series can be found on this playlist: http://www.youtube.com/playlist?list=PLh94XVT4dq02frQRRZBHzvj2hwuhzSByN

    #FreeCCNA #CiscoCCNA #ImranRafai

  36. Hello Imran Sir & Team,
    Thanks so much to create this series It's help lots of students and learner in Networking field . Sir continue n keep it up make our Future Bright..Sir please upload video if something new coming 😊

  37. Imran sir how to disable switchport mode dynamic desirable and switchport mode dynamic auto once activated…plz inform sir,,waiting 4 ur answer,,,love u lots sir

  38. Kindly help Mr Imran. I am Failing to download this particular lesson (200-125 CCNA v3.0 | Day 10: Port Modes and Functions | Free Cisco CCNA).

  39. All Hail Imrah, the King of Network….. Thank you for your outstanding videos, i am learning a lot from them… You are the best.

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