CSC 2773 LAN Technologies PDF

CSC 2773 LAN TECHNOLOGIES 1.0 LAN TECHNOLOGIES 1.2.1 VLANS 1.2.2 802.1 Q FRAME TAGGING 1.2.3 VTP VLANs  Overview of VLANs VLAN Definitions VLANs can segment LAN devices without regard for the physical location of the user or device. ◦ In the figure, IT users on the first, second, and third f...

CSC 2773 LAN TECHNOLOGIES 1.0 LAN TECHNOLOGIES 1.2.1 VLANS 1.2.2 802.1 Q FRAME TAGGING 1.2.3 VTP VLANs  Overview of VLANs VLAN Definitions VLANs can segment LAN devices without regard for the physical location of the user or device. ◦ In the figure, IT users on the first, second, and third floors are all on the same LAN segment. The same is true for HR and Sales users. A VLAN is a logical partition of a Layer 2 network. ◦ Multiple partitions can be created and multiple VLANs can co- exist. ◦ The partitioning of the Layer 2 network takes place inside a Layer 2 device, usually via a switch. ◦ Each VLAN is a broadcast domain that can span multiple physical ▪ VLANs are mutually isolated and packets can LAN segments. only pass between VLANs via a router. ◦ Hosts on the same VLAN are unaware of the VLAN’s existence.  Overview of VLANs Benefits of VLANs Benefits Description Smaller Dividing the LAN reduces the number of broadcast Broadcast domains Domains Improved Only users in the same VLAN can communicate Security together Improved IT VLANs can group devices with similar Efficiency requirements, e.g. faculty vs. students Reduced Cost One switch can support multiple groups or VLANs Better Small broadcast domains reduce traffic, improving Performance bandwidth Simpler Similar groups will need similar applications and Management other network resources  Overview of VLANs Types of VLANs Default VLAN Assignment Common types of VLANs: ◦ Default VLAN – Also known as VLAN 1. All switch ports are members of VLAN 1 by default. ◦ Data VLAN – Data VLANs are commonly created for specific groups of users or devices. They carry user generated traffic. ◦ Native VLAN – This is the VLAN that carries all untagged traffic. This is traffic that does not originate from a VLAN port (e.g., STP BPDU traffic exchanged between STP enabled switches). The Initially, all switch ports are members of VLAN 1. native VLAN is VLAN 1 by default. ◦ Management VLAN – This is a VLAN that is created to carry network management traffic including SSH, SNMP, Syslog, and more. VLAN 1 is the default VLAN used for network management. Overview of VLANs Creating a VLAN VLAN details are stored in the vlan.dat file. You create VLANs in the global configuration mode. Task IOS Command Enter global configuration mode. Switch# configure terminal Create a VLAN with a valid ID number. Switch(config)# vlan vlan-id Specify a unique name to identify the VLAN. Switch(config-vlan)# name vlan-name Return to the privileged EXEC mode. Switch(config-vlan)# end Enter global configuration mode. Switch# configure terminal  Overview of VLANs Creating a VLAN If the Student PC is going to be in VLAN 20, we will create the VLAN first and then name it. If you do not name it, the Cisco IOS will give it a default name of vlan and the four digit number of the VLAN. E.g. Prompt Command vlan0020 for VLAN 20. S1# Configure terminal S1(config)# vlan 20 S1(config-vlan)# name student S1(config-vlan)# end  Overview of VLANs Assigning Ports to VLANs Once the VLAN is created, we can then assign it to the correct interfaces. Task Command Enter global configuration mode. Switch# configure terminal Enter interface configuration mode. Switch(config)# interface interface-id Set the port to access mode. Switch(config-if)# switchport mode access Switch(config-if)# switchport access vlan Assign the port to a VLAN. vlan-id Return to the privileged EXEC mode. Switch(config-if)# end  Overview of VLANs Assigning Ports to VLANs If the Student PC is going to be in VLAN 20, we will create the VLAN first and then name it. If you do not name it, the Cisco IOS will give it a default name of vlan and the four digit number of the VLAN. E.g. vlan0020 for VLAN 20. Prompt Command S1# Configure terminal S1(config)# vlan 20 S1(config-vlan)# name student S1(config-vlan)# end  Overview of VLANs Verify VLANs Information Command Task Option Display VLAN name, status and its ports one VLAN Show vlan per line Display VLAN name, status, and its ports one VLAN show vlan brief per line. Display information about the identified VLAN ID show vlan id number. vlan-id Display information about the identified VLAN name. show vlan name The vlan-name is an ASCII string from 1 to 32 vlan-name characters. Overview of VLANs Packet Tracer – Who Hears the Broadcast? 802.1Q FRAME TAGGING / TRUNK  VLANs in a Multi-Switched Environment VLAN Trunks A VLAN trunk is a point-to-point link that carries more than one VLAN. ◦ Usually established between switches to support intra VLAN communication. ◦ A VLAN trunk or trunk ports are not associated to any VLANs. Cisco IOS supports IEEE 802.1q, a The links between switches S1 and S2, and S1 and S3 are popular VLAN trunk protocol. configured to transmit traffic coming from VLANs 10, 20, 30, and 99 across the network.  VLANs in a Multi-Switched Environment Controlling Broadcast Domains with VLANs If a switch port receives a broadcast frame, it forwards it out all ports except the originating port. ◦ Eventually the entire network receives the broadcast because the network is one broadcast domain. VLANs can be used to limit the reach of broadcast frames because each VLAN is a broadcast domain. ◦ VLANs help control the reach of broadcast frames and their impact in the network. ▪ In the figure, PC1 on VLAN 10 sends a broadcast frame. Trunk links between S2 - S1 and S1 - S3 propagate the broadcast to other devices in VLAN 10. Only devices in the same VLAN receive the broadcast therefore, PC4 would receive the broadcast.  VLANs in a Multi-Switched Environment Tagging Ethernet Frames for VLAN Identification Before a frame is forwarded across a trunk link, it must be tagged with its VLAN information. ◦ Frame tagging is the process of adding a VLAN identification header to the frame. ◦ It is used to properly transmit multiple VLAN frames through a trunk link. IEEE 802.1Q is a vey popular VLAN trunking protocol that defines the structure of the tagging header added to the frame. Switches add VLAN tagging information after the Source MAC address field. The fields in the 802.1Q VLAN tag includes VLAN ID (VID). Trunk links add the tag information before sending the frame and then remove the tags before forwarding frames through non-trunk ports.  VLANs in a Multi-Switched Environment Native VLANs and 802.1Q Tagging Control traffic sent on the native VLAN should not be tagged. Frames received untagged, remain untagged and are placed in the native VLAN when forwarded. If there are no ports associated to the native VLAN and no other trunk links, an untagged frame is dropped. When configuring a switch port on a Cisco switch, configure devices so that they do not send tagged frames on the native VLAN. In Cisco switches, the native VLAN is VLAN 1, by default. VLANs in a Multi-Switched Environment Packet Tracer – Investigating a VLAN Implementation Trunking and Inter-VLAN Routing Trunks Ports Trunking and Inter-VLAN Routing Trunks Ports Trunking and Inter-VLAN Routing Trunks Ports Trunk ◦A physical and logical connection between two switches across which network traffic travels ◦A single transmission channel between two points (usually switching centers) ◦A point-to-point link that supports several VLANs  Trunking and Inter-VLAN Routing Trunks Ports Switch ports can be configured for two different roles: ◦Access port ◦Trunk port. Access Port ◦Belongs to only one VLAN example PCs or servers ◦If a hub connects multiple PCs to the single access port, each device connected to the hub is a member of the same VLAN. Trunk Port ◦Point-to-point link ◦Carry multiple-VLAN traffic over single link Trunking and Inter-VLAN Routing Trunks Ports Support for frame tagging ◦VLAN trunking uses tagged frames to allow multiple VLANs to be carried throughout a large switched network over shared backbones Two trunking protocols: ◦IEEE 802.1Q (widely implemented) ◦Cisco’s Inter-Switch Link (ISL) - a proprietary trunking protocol that can be implemented in Cisco networks Higher-end switches, such as the Catalyst 6500 series, still support both tagging protocols; however, most LAN switches, such as the 2960, support only 802.1Q. Trunking and Inter-VLAN Routing Trunks Ports To configure a switch port as a trunk port, use the following commands: ◦Switch(config)#interface fa0/port_number ◦Switch(config-if)#switchport mode trunk ◦Switch(config-if)#switchport trunk encapsulation {dot1q | isl | negotiate} Trunking and Inter-VLAN Routing Trunks Ports In desirable mode, the port becomes a trunk port if the other end is set to either trunk, desirable, or auto. In auto mode, the port becomes a trunk port if the other end is set to either trunk or desirable. To return a trunk port to an access port: –Switch(config)#interface fa0/port_number –Switch(config-if)#no switchport mode trunk or –Switch(config-if)#switchport mode access Trunking and Inter-VLAN Routing Extending VLANs across Switches Trunking enables VLANs to forward traffic between switches using only a single port. A trunk link configured with 802.1Q on both ends allows traffic that has a 4- byte tag field added to the frame. This frame tag contains the VLAN ID. When a switch receives a tagged frame on a trunk port, it removes the tag before sending it out an access port. The switch forwards the frame only if the access port is a member of the same VLAN as the tagged frame. Some traffic however, needs to cross the 802.1Q configured link without VLAN ID. Traffic with no VLAN ID is called untagged. Examples of untagged traffic are Cisco Discovery Protocol (CDP), VTP, and certain types of voice traffic. Untagged traffic minimizes the delays associated with inspection of the VLAN ID tag. Trunking and Inter-VLAN Routing Extending VLANs across Switches Trunking and Inter-VLAN Routing Extending VLANs across Switches Trunking and Inter-VLAN Routing Extending VLANs across Switches Trunking and Inter-VLAN Routing Extending VLANs across Switches Trunking and Inter-VLAN Routing Extending VLANs across Switches Trunking and Inter-VLAN Routing Extending VLANs across Switches To accommodate untagged traffic, a special VLAN called a native VLAN is available. Untagged frames received on the 802.1Q trunk port will become members of the native VLAN. On Cisco Catalyst switches, VLAN 1 is the native VLAN by default. On an 802.1Q trunk, use the following command to assign the native VLAN ID on a physical interface: ◦Switch(config-if)#dot1q native vlan vlan-idConfiguring a native VLAN Trunking and Inter-VLAN Routing Extending VLANs across Switches Trunking and Inter-VLAN Routing Inter-VLAN Routing ❑In switched environment, only members of the same VLAN can communicate. ❑A Layer 3 device provides connectivity between different VLANs. ❑This arrangement enables the network administrator to strictly control the type of traffic that flows from one VLAN to another.  Trunking and Inter-VLAN Routing Inter-VLAN Routing Connectivity between different VLANs Subinterfaces Router-on-a-stick Trunking and Inter-VLAN Routing. Inter-VLAN Routing Connectivity between different VLANs Requirements: ◦Subinterfaces - logically divide one physical interface into multiple logical pathways ◦Router-on-a-stick To support inter-VLAN communication using subinterfaces requires configuration on both the switch and the router. Switch ◦Configure the switch interface as an 802.1Q trunk link. Router ◦Select a router interface with a minimum of a 100Mbps FastEthernet ◦Configure subinterfaces that support 802.1Q encapsulation. ◦Configure one subinterface for each VLAN. A subinterface allows each VLAN to have its own logical pathway and default gateway into the router. Trunking and Inter-VLAN Routing Inter-VLAN Routing To configure inter-VLAN routing, use the following steps: 1. Configure a trunk port on the switch. ◦Switch(config)#interface fa0/2 ◦Switch(config-if)#switchport mode trunk 2. On the router, configure a FastEthernet interface with no IP address or subnet mask. ◦Router(config)#interface fa0/1 ◦Router(config-if)#no ip address ◦Router(config-if)#no shutdown Trunking and Inter-VLAN Routing Inter-VLAN Routing 3. On the router, configure one subinterface with an IP address and subnet mask for each VLAN. Each subinterface has an 802.1Q encapsulation. ◦Router(config)#interface fa0/0.10 ◦Router(config-subif)#encapsulation dot1q 10 ◦Router(config-subif)#ip address 192.168.10.1 255.255.255.0 4. Use the following commands to verify the inter-VLAN routing configuration and functionality. ◦Switch#show trunk ◦Router#show ip interfaces ◦Router#show ip interfaces brief ◦Router#show ip route VTP Maintaining VLANs on an Enterprise Network VLAN Trunking Protocol (VTP) VLAN Trunking Protocol (VTP) purpose and goals If there is no automated way to manage an enterprise network with hundreds of VLANs, manual configuration of each VLAN on each switch is necessary. Any change to the VLAN structure requires further manual configuration. One incorrectly keyed number causes inconsistencies in connectivity throughout the entire network. To resolve this issue, Cisco created VTP to automate many of the VLAN configuration functions. VTP ensures that VLAN configuration is consistently maintained across the network and reduces the task of VLAN management and monitoring. Maintaining VLANs on an Enterprise Network VLAN Trunking Protocol (VTP) Two different versions of VTP exist. Version 1 is the default and it is not compatible with Version 2. All switches must be configured with the same version. ◦Version 1 and Version 2. VTP modes: server, client, transparent Maintaining VLANs on an Enterprise Network VLAN Trunking Protocol (VTP) VTP modes: server, client, transparent Maintaining VLANs on an Enterprise Network VLAN Trunking Protocol (VTP) VLAN database – keep in NVRAM ◦ based on revision number (use latest version) Configuration revision number ◦Return revision number to 0 Maintaining VLANs on an Enterprise Network VLAN Trunking Protocol (VTP) Maintaining VLANs on an Enterprise Network VLAN Trunking Protocol (VTP) VTP messages ◦Summary advertisements issue every 5 minutes or whenever a change to the VLAN database occurs. Contain the current VTP domain name and the configuration revision number. ◦Subset advertisements contains a list of VLAN information based on the summary advertisement. I if there are several VLANs, they require more than one subset advertisement. ◦Advertisement requests switches use advertisement requests to ask for VLAN information. required if the switch has been reset or the VTP domain name has been changed. Summary ❑A VLAN is a way to group hosts on the same logical network even though they may be physically separated ❑Frame tagging allows a switch to identify the source VLAN of an Ethernet frame. ❑A Layer 3 device is needed to move traffic between different VLANs. ❑Subinterfaces allow router interfaces to support multiple VLANs. ❑VLAN Trunking Protocol provides centralized control, distribution and maintenance of VLANs. EXERCISE Explain the purpose of VLANs in a switched network. Explain how a switch forwards frames based on VLAN configuration in a multi-switch environment. Configure a switch port to be assigned to a VLAN based on requirements. Configure a trunk port on a LAN switch.