Cisco CCNA ICND2 640-816

Switch VLANs: Understanding VLANs

by Jeremy Cioara

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Video Title Duration

Review: Rebuilding the Small Office Network, Part 1

Review: Rebuilding the Small Office Network, Part 2

Review: Rebuilding the Small Office Network, Part 3

Switch VLANs: Understanding VLANs

00:00:00 - We're now moving out of the review and into our first major
00:00:04 - topic of this series which is VLANs. Nothing can be bigger
00:00:08 - in the network world in the last decade than VLANs and
00:00:12 - how they've reshape our entire landscape of the network.
00:00:16 - So, to start things off will take a look at what normal switches
00:00:19 - do. Some of the challenges that we experience even in normal
00:00:22 - switch network, then we'll see how VLANs and trunks address
00:00:26 - those issues will define what VLANs are, and then we'll
00:00:29 - talk about the counterpart that goes right with them and that
00:00:31 - is trunk connections. Finally will look at the flexibility
00:00:35 - of VLANs and I present the design option of what VLANs
00:00:39 - can do for business or an organization giving you flexibility
00:00:43 - with how you use your network.
00:00:46 - With that foundation in place let me be the first to welcome
00:00:49 - you to the world of VLANs. I kind of think of VLANs like I think
00:00:53 - about my microwave oven. About two weeks ago my microwave broke
00:00:58 - down and we called the repair guy and he said my first availability is
00:01:03 - in a week and half and I was like oh yea go ahead and put us on the calendar and my
00:01:07 - wife said we'll be without a microwave oven. I said, microwave oven, who needs them
00:01:11 - right? You now we got a stove. So it's just a laziness factor. I'm telling you after about
00:01:17 - 3 days without a microwave oven, I need a microwave oven.
00:01:20 - I couldn't handle it. I called the repair guy, said don't worry about it,
00:01:23 - we're going to get a new one. we were that desperate for a microwave
00:01:26 - oven and we have a little infant to warm up to the food where to
00:01:29 - put on. It was horrible, horrible. So it's not like you can't
00:01:33 - survive without microwave ovens. In the same way it's not
00:01:36 - like networks don't work without VLANs, but they're so convenient
00:01:41 - and so powerful.
00:01:43 - you see the tie in there. That everybody uses them. What a
00:01:46 - VLAN does is logically group users. Let's get to the official information
00:01:50 - right here, it logically groups our users together.
00:01:55 - So, over here imagine that we had two groups of users in
00:01:58 - our organization, the marketing group, surrounded by pink, and
00:02:02 - the sales group surrounded by blue. So, what I can do with
00:02:07 - VLANs is actually group those people together where the blue
00:02:10 - ports are now isolated to the blue ports in that and this is
00:02:14 - the most accurate statement here. It's segments their broadcast
00:02:17 - domain. So, if a sales PC sends a broadcast it's only going to
00:02:21 - come out of the blue ports you can see we've got some blue
00:02:24 - ports on some other switches as well that will receive the
00:02:27 - broadcast and this guy down here gets to broadcast. It does
00:02:30 - not affect the pink ports and if the pink computers sends a
00:02:32 - broadcast only the pink PCs lined up receiving that. So, you completely
00:02:37 - isolate all of those broadcasts domain into two separate groups.
00:02:42 - Now, as a side note, before we get too deep into VLANs. If the
00:02:47 - blue users send a broadcast it comes out of the blue ports right?
00:02:51 - So, pink users send a broadcast it comes out all the pink ports. If that's
00:02:55 - the case? What VLAN do these ports belong to?
00:03:03 - You're probably thinking the answer is both, and that is absolutely
00:03:06 - correct that is what CISCO calls a trunk port. A trunk
00:03:12 - just think of it like the trunk of your car. If it's like mine you get everything
00:03:15 - in there, you know, and everything goes across the trunk port. So, when
00:03:19 - you were using VLANs the trunk will carry all VLAN
00:03:22 - traffic between your switches and that's what allows your VLANs
00:03:26 - to span beyond just a single switch, otherwise without
00:03:29 - trunk ports we would have a separate VLAN on all our switches
00:03:32 - that couldn't communicate. So, the VLAN segment broadcast domains
00:03:36 - it also correlates to a subnet. Actually saw a statement
00:03:41 - on CISCO's website when I was looking for some the VLAN
00:03:44 - information I thought it was great. They said a VLAN equals
00:03:47 - a broadcast domain equals a subnet.
00:03:51 - Meaning all of those things are equal terms. So, for our marketing
00:03:57 - group we would be 172.16.1.0/24
00:04:01 - And our sales group may be 172.16.2.0/24
00:04:05 - They are on separate subnets
00:04:08 - even though all you see here is a switch. Now keep in mind
00:04:13 - that when you setup VLANs and we use our VLANs in this this
00:04:16 - kind of design. These people cannot reach each other. Marketing
00:04:20 - people cannot reach sales people and vice versa and that provides
00:04:25 - a great level of access control if that's what we want. Now
00:04:28 - we'll talk about routing between VLANs and some of the
00:04:32 - upcoming videos which is something that you need to do and if
00:04:35 - you want sales people to be able to be able to talk to marketing people,
00:04:37 - you would have to get a router that's able to route between
00:04:41 - those two separate VLANs. The blue people would come in the
00:04:44 - router and exit on to the red VLANs and so on and that that's
00:04:47 - a big topic, we'll talk more about that later. The last thing that
00:04:51 - VLANs are used for is quality of service. So, I can separate
00:04:56 - the prioritize traffic from the not so prioritize. For example
00:05:01 - flush the sales and marketing picture out of your mind and imagine
00:05:05 - that the pink VLAN represented the PCs and the blue
00:05:10 - VLAN represented
00:05:12 - phones. Phones you say? Phones I say. We have nowadays
00:05:18 - IP phones that plug into a network so these IP phones
00:05:23 - have traffic that, I mean, it comes out it's very small, IP phones
00:05:27 - don't generate much traffic but that traffic has to be protected
00:05:31 - from everything else. All of the computers will step all over
00:05:35 - your IP phone traffic, I mean think, think
00:05:38 - of that IP phones traffic as a delicate little flower.
00:05:43 - it's so small and pretty and it comes into this switch and is just
00:05:46 - kind of floating along trying to get to another IP phone that's
00:05:49 - on the network somewhere and these PCs here are these football
00:05:53 - players, I can't draw that. And you know they're running all over
00:05:56 - the network trying to gobble up as much bandwidth as they can.
00:05:59 - When you pit a football player against the flower if you don't
00:06:02 - do something about it that poor flower is going to get crashed.
00:06:05 - Where am I going with this? Quality of service sometimes I lose
00:06:09 - myself. Quality of service allows me to say the flower
00:06:14 - that the VOIP or wherever my priority traffic is gets carried
00:06:18 - above all the rushing football players running around my network
00:06:22 - which is the pink VLAN, the PCs in this case. So, VLANs
00:06:25 - will allow me to logically separate them and isolate
00:06:28 - them from each other.
00:06:31 - Before we can truly understand and appreciate the benefits
00:06:34 - of VLANs we need a hit some key points of the normal switching
00:06:38 - world, review some of those key concepts. First of, if we just
00:06:41 - have this usual switch here you know any switch so you can
00:06:44 - pick up from Best Buy or any electronics store, you're automatically
00:06:49 - going to get one collision domain per port and that's a good
00:06:52 - thing, that means that every computer that's plugged into that
00:06:55 - switch can send and recive at the same time if they're operating
00:06:59 - in full duplex mode as any other. So this computer could be
00:07:03 - sending or receiving along with this one and that's okay that's
00:07:06 - a huge stride forward from the hub world where only one device
00:07:10 - plugged into the hub could send or receive at a time. Notice I said send
00:07:14 - or receive that's the half duplex world. Second piece of the
00:07:18 - switch world is that we have broadcast sent to all ports by design.
00:07:23 - when this computer sends a broadcast in the switch, the switch
00:07:26 - will send it out every single port except the port it received it
00:07:29 - on and all the devices will receive it, and that's great because
00:07:33 - broadcasts are necessary they help us locate services it helps
00:07:37 - computers advertise services and there's a whole other plethora
00:07:41 - of uses for broadcasts. But as this network grows and we plug
00:07:45 - in another switch here and another one here and link one
00:07:48 - of here, you just start getting more and more clients attach those
00:07:52 - broadcast start becoming a problem. They cause a network slowdown
00:07:57 - where everybody receives these broadcasts and starts becoming too overwhelming.
00:08:01 - Now different people will tell you different guidelines
00:08:03 - for how big the network can get. CISCO rule of thumb is once
00:08:07 - you reach 500 PCs or 500 devices on a network
00:08:11 - that's where it's time to divide up in separate networks. That's
00:08:15 - a pretty liberal amounts I've seen most people in practical
00:08:18 - use somewhere around two to three hundred PCs will segmented
00:08:22 - of and start another network. Because the broadcast will start
00:08:25 - slowing down the network and all devices that are plugged
00:08:28 - into it.
00:08:29 - Now down below that you see one subnet per LAN, meaning
00:08:32 - in the normal switching world if we have all these switches
00:08:35 - daisy chained together and I said this is the 172.16.1.0
00:08:39 - network that means all the PCs plugged
00:08:44 - into there have to start with 172.16.1.
00:08:47 - something, that's one might be.50 here, this might be.51.
00:08:50 - So, If I were to go of a lim and just say well let's let's go
00:08:54 - out and make this one 172.17.1.50
00:08:57 - or 51 slash 24 and so let's just
00:09:02 - to that that immediately this computer would be isolated from
00:09:05 - the rest even though it's plugged in to the same switch, it
00:09:09 - could not reach any one because logically speaking it thinks it's
00:09:13 - on a separate network then everybody else. So it's going to try
00:09:16 - and go to its default gateway to reach things that are in
00:09:19 - the subnet.
00:09:20 - Finally, in the normal switching world we have very limited
00:09:25 - access control, and what that means is that it's very difficult
00:09:29 - for me to restrict this computer from reaching that computer.
00:09:33 - There is virtual well, there's, there's ways to do it
00:09:37 - but they are extremely painful and involves assigning access list
00:09:41 - to a each individual port, we'll talk about access lists later
00:09:44 - on but it's just not something that's practically done. So,
00:09:48 - in a flat switch network meaning a single broadcast domain
00:09:52 - where one broadcast can reach everybody it's a very difficult
00:09:56 - nearly impossible to prevent devices from accessing each other
00:10:00 - fully. Before we go on let me just mention that a lot of
00:10:04 - the analogies you hear me use, I don't really plan they just kind of
00:10:08 - come to me as an talking. I pause the video between this
00:10:12 - and the slide in the in the last An I thought, flowers where did that come
00:10:16 - from. Hopefully it helped demonstrate the purpose of VLANs. So let's talk
00:10:21 - more about the flexibility of VLANs and why they're so powerful. With
00:10:25 - VLANs you get segmentation of users without routers, without
00:10:30 - without routers before VLANs there is just no way to separate
00:10:34 - uses apart and also one of the problems of routers is that
00:10:38 - you were limited to physical location. Let me give you an example
00:10:42 - let's say this was a network of yester year we had building A,
00:10:45 - building B and building C, and let's say it's college campus
00:10:49 - well if that were the case we would have to have routers going between
00:10:53 - these buildings that will allow them to connect together and
00:10:56 - still allow the users to be separate meaning i've got one subnet
00:11:00 - of people in this building and one subnet of people over
00:11:02 - here, if we didn't have routers between the buildings and
00:11:06 - everybody just linked up. One broadcast would flood the whole
00:11:10 - network so we were just tie routers together. Well with
00:11:15 - VLANs, we can segment our users between the buildings without even
00:11:21 - needing routers in place. I can say building B is isolated
00:11:24 - to the blue users. Building A is isolated to pink users.
00:11:28 - Now, you might see well what that blue guy doing there that some more
00:11:32 - of the flexibility of VLANs. Before if we had a blue user that
00:11:37 - was in this building, I mean maybe building A faced a flowing
00:11:42 - river, and the blue users here
00:11:47 - represents it's a college right? So it's the college of art.
00:11:50 - So let's say that one of the users from from this blue network
00:11:54 - said you know I just feel inspired when I look out the window
00:11:58 - and I see the water flowing to paint the beautiful paintings
00:12:02 - and he said I can't sit and be inspired in building B
00:12:06 - I wanna sit in building A. Well if we were in the old routed
00:12:10 - world and we wanted this user to stay on the building B subnet
00:12:13 - because maybe the red VLAN over here or the red
00:12:17 - users represent the administration and there's been some you
00:12:21 - know college of art users hacking into the administration so we wanted
00:12:24 - separate them. You see where I'm going with this? The point is that if we had
00:12:28 - the router the world the only way to get the that user in the
00:12:32 - building A on building B's network would be to run an
00:12:36 - extra long the ethernet cable, remember they go hundred meters. An extra
00:12:39 - long ethernet cable between the two buildings and plug that user in.
00:12:43 - Now that we have VLANs I can assign one port in building A
00:12:48 - to the college of art VLAN and allow that user to connect.
00:12:53 - So even though he's sitting right next to one of the college
00:12:56 - administrators he can not access their PC.
00:13:00 - The user can look out the window be inspired and be on the
00:13:03 - college of art network without having to be physically plugged
00:13:07 - into the college of art building. So that's what I mean when
00:13:10 - I see no longer limited to the physical location. You can see
00:13:13 - over here and building C we also have an IP phone that
00:13:16 - might be on you know some other VLAN that separated
00:13:19 - from everybody else and we isolate those, and we could put IP
00:13:22 - phones in every single building
00:13:25 - that everybody uses and allow those to be all on the same network
00:13:29 - that cannot be touched by the PC. That's really good because
00:13:33 - there's already programs out there that will allow you to sniff
00:13:37 - the network like tap into the network and capture the VOIP
00:13:41 - packets and assembled them into a normal WAVE file or
00:13:45 - mp3 file so I can actually it's kind of like if you come from
00:13:49 - the telephone background it's like a but set where you tap
00:13:52 - into the wires and you can hear the conversations that are
00:13:54 - going on but people can just do it from their own computers unless
00:13:59 - you separate those phones from the rest the network and that's
00:14:03 - one of the powers of VLANs. So with VLANs you also
00:14:07 - have tighter control of broadcast. One broadcast within the
00:14:10 - blue VLANs stays within the blue VLANs. Broadcast in the
00:14:14 - red VLAN or pink VLAN stays in the pink VLAN.
00:14:18 - Because of their importance to the network world all I wanted
00:14:21 - to do is we start off into the world of switch VLANs was
00:14:24 - give you a base understanding of what of a VLAN is and what
00:14:27 - trunks do will expose more of the technical details as we dig
00:14:31 - deeper in this this content. So let's review. We first saw
00:14:36 - the view of a normal switch where every single port is its own
00:14:39 - collision domain. The entire switch in all the switches that
00:14:43 - are plugged in with crossover cables are one broadcast
00:14:47 - domain. So one broadcast will go through them all and that
00:14:49 - can cause a lot of congestion the bigger it gets. Its also very difficult to
00:14:53 - control access into those normal switches of what devices can
00:14:57 - access each other is everybody's one subnet. So as we get into
00:15:01 - VLANs we see those problems solved. The VLANs are our way
00:15:05 - of segmenting the switches into separate broadcast domains
00:15:09 - or separate subnets. That gives us more control over where
00:15:12 - the broadcasts go. Gives is the ability to do quality of service
00:15:15 - and prioritize traffic and it gives us the ability to do access
00:15:19 - control as we divide people in separate subnets. The trunks
00:15:23 - are the links that are going between the switches that carry
00:15:27 - all VLAN traffic.
00:15:29 - That's where every VLAN will be allowed to traverse that trunk
00:15:32 - and that's what allows us to have multiple VLANs on one switch
00:15:36 - that can span down to VLANs on another switch. Now last
00:15:40 - but not least, we talked about the flexibility of VLANs and
00:15:43 - saw some of the possible design options where with VLANs
00:15:46 - you can actually span between buildings and have people in
00:15:49 - separate buildings that are normally on different subnets.
00:15:53 - Be a part of the same subnet. Because we've used VLANs to do our segmentation.
00:15:58 - It gives us ultimate flexibility with where our users are located
00:16:02 - because we're no longer limited to the physical location.
00:16:06 - I hope this is that informative for you and I like to thank you for viewing.

Switch VLANs: Understanding Trunks and VTP

Switch VLANs: Configuring VLANs and VTP, Part 1

Switch VLANs: Configuring VLANs and VTP, Part 2

Switch STP: Understanding the Spanning-Tree Protocol

Switch STP: Configuring Basic STP

Switch STP: Enhancements to STP

General Switching: Troubleshooting and Security Best Practices

Subnetting: Understanding VLSM

Routing Protocols: Distance Vector vs. Link State

Routing Protocols: OSPF Concepts

Routing Protocols: OSPF Configuration and Troubleshooting

Routing Protocols: EIGRP Concepts and Configuration

Access-Lists: The Rules of the ACL

Access-Lists: Configuring ACLs

Access-Lists: Configuring ACLs, Part 2

NAT: Understanding the Three Styles of NAT

NAT: Command-line NAT Configuration

WAN Connections: Concepts of VPN Technology

WAN Connections: Implementing PPP Authentication

WAN Connections: Understanding Frame Relay

WAN Connections: Configuring Frame Relay

IPv6: Understanding Basic Concepts and Addressing

IPv6: Configuring, Routing, and Interoperating

Certification: Some Last Words for Test Takers

Advanced TCP/IP: Working with Binary

Advanced TCP/IP: IP Subnetting, Part 1

Advanced TCP/IP: IP Subnetting, Part 2

Advanced TCP/IP: IP Subnetting, Part 3

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Jeremy Cioara

Jeremy Cioara

CBT Nuggets Trainer

Certifications:
Cisco CCNA, CCDA, CCNA Security, CCNA Voice, CCNP, CCSP, CCVP, CCDP, CCIE R&S; Amazon Web Services CSA; Microsoft MCP, MCSE, Novell CNA, CNE; CompTIA A+, Network+, iNet+

Area Of Expertise:
Cisco network administration and development. Author or coauthor of numerous books, including: CCNA Voice 640-461 Official Cert Guide; CCNA Voice Official Exam Certification Guide (640-460 IIUC); CCENT Exam Prep (Exam 640-822); CCNA Exam Cram (Exam 640-802) 3rd Edition; and CCNA Voice 640-461 Official Cert Guide.


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