Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc From Hubs to VLANs

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Using Hubs Layer 1 devices Inexpensive In one port, out the others One collision domain One broadcast domain

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc This is fine for small workgroups, but does not scale well for larger workgroups or heavy traffic. Hub Single Hub  One Network (IP Network Address - usually)  One Collision Domain  One Broadcast Domain

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc What if the computers were on two different subnets? Could they communicate within their own subnet? Yes Between subnets? No, need a router. Single Hub - Two subnets  Two subnets  One Collision Domain  One Broadcast Domain Hub

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Same issues as before, with more of an impact on the network. All Hubs  One Network Address  One Collision Domain  One Broadcast Domain Hub Hub

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Using Switches Layer 2 devices Moderate expense for common access switches, but can be very expensive. Layer 2 filtering based on Destination MAC addresses and Source Address Table One collision domain per port One broadcast domain

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Switch and Hub Network  One Network  Several Collision Domains  One per switch port  One for the entire Hub  One Broadcast Domain Hub Switch Two virtual circuits: (complete SAT tables) Data traffic from to and from to

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Switch and Hub Network  One Network  Several Collision Domains  One per switch port  One for the entire Hub  One Broadcast Domain Hub Switch As opposed to the Hub: Data traffic from to and from to Collision!

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Switch and Hub Network  One Network  Several Collision Domains  One per switch port  One for the entire Hub  One Broadcast Domain Hub Switch Collisions and Switches: What happens when two devices on a switch, send data to another device on the switch to and to

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Switch and Hub Network  One Network  Several Collision Domains  One per switch port  One for the entire Hub  One Broadcast Domain Hub Switch The switch keeps the frames in buffer memory, and queues the traffic for the host This means that the sending hosts do not know about the collisions and do not have to re-send the frames. Frames in buffer

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Other Switching Features Review Asymmetric ports: 10 Mbps and 100 Mbps Full-duplex ports Cut-through versus Store-and-Forward switching

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Ports between switches and server ports are good candidates for higher bandwidth ports (100 Mbps) and full-duplex ports. All Switched Network  One Network  Several Collision Domains  One per switch port  One Broadcast Domain Switch Switch

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Introducing Multiple Subnets/Networks without Routers Switches are Layer 2 devices Router are Layer 3 devices Data between subnets/networks must pass through a router.

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc All Switched Network - Two Networks  Two Subnets  Several Collision Domains  One per switch port  One Broadcast Domain Switch Switch A Switched Network with two subnets: What are the issues? Can data travel within the subnet? Yes Can data travel between subnets? No, need a router! What is the impact of a layer 2 broadcast, like an ARP Request? ARP Request

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc All Switched Network - Two Networks  Two Subnets  Several Collision Domains  One per switch port  One Broadcast Domain Switch Switch All devices see the ARP Request. One broadcast domain means the switches flood all broadcast out all ports, except the incoming port. Switches have no idea of the layer 3 information contained in the ARP Request. This consumes bandwidth on the network and processing cycles on the hosts.

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc One Solution: Physically separate the subnets. But still no data can travel between the subnets. How can we get the data to travel between the two subnets? Two Switched Networks  Two Subnets  Several Collision Domains  One per switch port  Two Broadcast Domain Switch Switch

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Introducing Multiple Subnets/Networks with Routers Switches are Layer 2 devices Router are Layer 3 devices Data between subnets/networks must pass through a router.

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Routed Networks  Two Subnets  Several Collision Domains  One per switch port  Communication between subnets Switch Switch Router Routed Network: Two separate broadcast domains, because the router will not forward the layer 2 broadcasts such as ARP Requests.

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Switches with multiple subnets So far this should have been a review. Let’s see what happens when we have two subnets on a single switch and we want to route between the two subnets.

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Routed Networks  Two Subnets  Communication between subnets Switch Router sec Router-on-a-stick: When a single interface is used to route between subnets or networks, this is known as a router-on-a-stick. To assign multiple ip addresses to the same interface, secondary addresses or subinterfaces are used. interface e 0 ip address ip address secondary

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Router-on-a-stick Advantages Useful when there are limited Ethernet interfaces on the router. Disadvantage Because a single link is used to connect multiple subnets, one link is having to carry the traffic for multiple subnets. Be sure this is link can handle the traffic. You may wish to use a high-speed link (100 Mbps) and full-duplex.

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Gotcha’s 1. Remember to have the proper default gateway set for each host hosts - default gateway is hosts - default gateway is The router must still route between subnets, so you must include: Router (config)# router rip Router (config-router)# network

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Routed Networks  Two Subnets  Communication between subnets Switch Router Multiple interfaces: Two Ethernet router ports may be used instead of one. However this may be difficult if you do not have enough Ethernet ports on your router. E0E1

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc One switch two subnets: Good News: Data can travel between subnets and we have two separate broadcast domains. Bad News: Hosts are on different subnets but on a single layer 2 broadcast domain. Routed Networks  Two Subnets  Communication between subnets Switch Router sec ARP Request

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc An ARP Request from for will still be seen by all hosts on the switch. The switch is a layer 2 device and will flood broadcast traffic out all ports, except the incoming port. Routed Networks  Two Subnets  Communication between subnets Switch Router sec

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Introducing VLANs VLANs create separate broadcast domains Routers are needed to pass information between different VLANs VLANs are not necessary to have separate subnets on a switched network, but as we will see they give us more advantages when it comes to things like data link (layer 2) broadcasts.

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Two VLANs  Two Subnets Switch VLAN VLAN VLAN VLAN 2 Layer 2 broadcast control: An ARP Request from for will only be seen by hosts on that VLAN. The switch will flood broadcast traffic out only those ports belonging to that particular VLAN, in this case VLAN 1.

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Port-centric VLAN Switches Remember, as the Network Administrator, it is your job to assign switch ports to the proper VLAN. This assignment is only done at the switch and not at the host. Note: The following diagrams show the VLAN below the host, but it is actually assigned within the switch Port VLAN

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Catalyst VLAN Membership Configuration [M] Membership type [V] VLAN assignment [R] Reconfirm dynamic membership[X] Exit to previous menu Enter Selection: PortVLANMembership Type 11Static Static 111Static 122Static AUI1Static A1 B1

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Layer 2 broadcast control: Without VLANs, the ARP Request would be seen by all hosts. Again, consuming unnecessary network bandwidth and host processing cycles. No VLANs  Same as a single VLAN  Two Subnets Switch 1

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Two VLANs  Two Subnets Switch VLAN VLAN VLAN VLAN 2 With VLANs: Data will only travel within the VLAN. Remember that switches are Layer 2 devices and they can only pass traffic within the VLAN.

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Port VLAN Switch Port: VLAN ID

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Two VLANs  Two Subnets Switch VLAN VLAN VLAN VLAN 2 With VLANs: A switch cannot route data between different VLANs. Example: Data from to X Switch Port: VLAN ID

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Gotcha’s 1.Remember that VLAN IDs (numbers) are assigned to the switch port and not to the host. (Port-centric VLAN switches) 2.Be sure to have all of the hosts on the same subnet belong to the same VLAN, or you will have problems. Hosts on subnet /24 - VLAN 1 Hosts on subnet /24 - VLAN 2 etc.

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Routing and VLANs In the previous example data could travel within the VLAN, but not between VLANs. Just like subnets, a router is needed to route information between different VLANs. The advantage is the switch propagates broadcast traffic only within the VLAN.

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc VLANs  Two Subnets  Communication between VLANs  NOTE : VLANs assigned only to the ports Switch VLAN VLAN VLAN VLAN 2 Router VLAN VLAN 2 Data between VLANs is routed through the router. Data from to

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Gotcha’s 1. Remember to have the proper default gateway set for each host hosts - default gateway is hosts - default gateway is The router must still route between subnets, so you must include: Router (config)# router rip Router (config-router)# network The switch ports to the router must have the corresponding VLAN ID to that subnet. Switch port to must be on VLAN 1 Switch port to must be on VLAN 2

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Switch Port: VLAN ID Router (VLAN 1) (VLAN 2) (VLAN ID not set at router.)

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc So, what’s the difference? One of the main differences between subnets with VLANs and subnets without VLANs on switched networks, is that VLANs offer layer 2 broadcast control.

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Here is an ARP Request example without VLANs. Routed Networks  Two Subnets  Communication between subnets Switch Router ARP Request

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Here is an ARP Request example with VLANs. Notice that the broadcast is isolated only to the VLAN that it came from, in this case VLAN 1. VLANs  Two Subnets  Communication between VLANs  NOTE : VLANs assigned only to the ports Switch VLAN VLAN VLAN VLAN 2 Router VLAN VLAN 2 ARP Request

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Can I use the Router-on-a-stick method with multiple VLANs? Can you remind me what Router-on-a-stick is?

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Routed Networks  Two Subnets  Communication between subnets Switch Router sec What is Router-on-a-stick? When a single interface is used to route between subnets or networks, this is know as a router-on-a-stick. To assign multiple ip addresses to the same interface, secondary addresses or subinterfaces are used. interface e 0 ip address ip address secondary

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc With Router-on-a-stick, ISL or 802.1Q trunking is needed. We will talk about tagging and trunking in the next section. VLANs  Two Subnets  Communication between VLANs using trunking  NOTE: VLANs assigned only to the ports Switch VLAN VLAN VLAN VLAN 2 Router secondary Trunking ISLor 802.1Q

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Non-tagging Switches Lets first see how multiple VLANs are interconnected using switches that do not have the tagging capability.

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc BaseT Ports Port 1 = VLAN 1 & Port 2 = VLAN 2 Moe Larry VLAN 1: Port 1 on switch Moe is connected to Port 1 on Switch Larry. VLAN 2: Port 2 on switch Moe is connected to Port 2 on Switch Larry. Non-tagging Switches For each VLAN, there must be a link between the two switches. One link per VLAN. Be sure the switch ports on the switches are configured for the proper VLAN. 1 2 Port 1 = VLAN 1 & Port 2 = VLAN 2

Hubs to VLANs Cisco Networking Academy Program © Cisco Systems, Inc Advantages Each VLAN gets its own dedicated link with its own bandwidth. Disadvantages This requires a separate link for each VLAN. There may not be enough ports on the switch to accommodate a lot of different VLANs.