VLANs logically segment LANs into broadcast domains by using switches to assign ports and their attached devices to VLAN groups based on their MAC address, IP subnet, or switch port. This allows devices that are physically located on different floors or buildings to belong to the same logical LAN segment while preventing Layer 2 broadcasts from crossing VLAN boundaries. VLAN trunk links between switches allow multiple VLANs to be transmitted over the same physical link.

2. LAN A Local Area Network (LAN) was originally defined as a network of computers located within the same area Local Area Networks are defined as a single broadcast domain. This means that if a user broadcasts information on his/her LAN, the broadcast will be received by every other user on the LAN. Broadcasts are prevented from leaving a LAN by using a router. The disadvantage of this method is routers usually take more time to process incoming data compared to a bridge or a switch

3. VLAN A VLAN is a logical group of network devices that appears to be on the same LAN Configured as if they are attached to the same physical connection even if they are located on a number of different LAN segments. Logically segment LAN into different broadcast domains.

4. VLAN VLANs can logically segment users into different subnets (broadcast domains) Broadcast frames are only switched on the same VLAN ID. This is a logical segmentation and not a physical one, workstations do not have to be physically located together. Users on different floors of the same building, or even in different buildings can now belong to the same LAN.

5. LAN VS VLAN By using switches, we can assign computer on different floors to VLAN1, VLAN2, and VLAN3 Now, logically, a department is spread across 3 floors even though they are physically located on different floors

7. VLAN Configurations

8. STATIC VLANS Static membership VLANs are called port-based and port-centric membership VLANs. This is the most common method of assigning ports to VLANs. As a device enters the network, it automatically assumes the VLAN membership of the port to which it is attached. There is a default VLAN , on Cisco switches that is VLAN 1. Default VLAN 1 Default VLAN 1 ConfiguredVlan 10

9. DYNAMIC VLANS Dynamic membership VLANs are created through network management software Dynamic VLANs allow for membership based on the MAC address of the device connected to the switch port. As a device enters the network, it queries a database within the switch for a VLAN membership

10. CONFIGURING PORTS Access ports are used when: Only a single device is connected to the port Multiple devices (hub) are connected to the port, all belonging to the same VLAN Another switch is connected to this interface, but this link is only carrying a single VLAN (non-trunk link). Trunk ports are used when: Another switch is connected to this interface, and this link is carrying multiple VLANs(trunk link).

11. Switch(config-if)switchport mode [access|trunk] An access port means that the port (interface) can only belong to a single VLAN.

12. Switch(config-if)switchport mode access Switch(config-if)switchport mode trunk ACCESS PORTS TRUNK PORT

13. VLAN TRUNKING In a switched network, a trunk is a point-to-point link that supports several VLANs. The purpose of a trunk is to conserve ports when a link between two devices that implement VLANs is created .

14. VLAN TECHNIQUES Two techniques Frame Filtering --examines particular information about each frame (MAC address or layer 3 protocol type) Frame Tagging --places a unique identifier in the header of each frame as it is forwarded throughout the network backbone.

15. FRAME FILTERING Users can be logically group via software based on: port number MAC address Ip subnet protocol being used

17. Membership by Port Membership by MAC Address Membership by IP Subnet Address port vlan 1 1 2 1 3 2 4 1 disadvantage of this method is that it does not allow for user mobility.

18. Membership by Port Membership by MAC Address Membership by IP Subnet Address Advantage : no reconfiguration needed Disadvantage : VLAN membership must be assigned initially. performance degradation as members of different VLANs coexist on a single switch port MAC Address vlan 1212354145121 1 2389234873743 1 3045834758445 2 5483573475843 1

19. Membership by Port Membership by MAC Address Membership by IP Subnet Address Advantage: Good for application-based VLAN strategy User can move workstations eliminate the need for frame tagging IP Subnet vlan 23.2.24 1 26.21.35 2

20. VLAN TAGGING VLAN frame tagging was specifically developed for switched communications. Frame tagging places a unique identifier in the header of each frame as it is forwarded throughout the network backbone. The identifier is understood and examined by each switch before any broadcasts or transmissions are made to other switches, routers, or end stations. When the frame exits the network backbone, the switch removes the identifier before the frame is transmitted to the target end station.

21. The two most common tagging schemes for Ethernet segments are ISL (Inter-Switch Link) 802.1Q – An IEEE standard

22. ISL (Frame Encapsulation) An Ethernet frame is encapsulated with a header that transports VLAN IDs. The ISL encapsulation is added by the switch before sending across the trunk.

23. The switch removes the ISL encapsulation before sending it out a non trunk link. It adds overhead to the frame as a 26-byte header containing a 10-bit VLAN ID . In addition, a 4-byte cyclic redundancy check (CRC) is appended to the end of each frame. This CRC is in addition to any frame checking that the Ethernet frame requires.

24. IEEE 802.1Q Significantly less overhead than the ISL. 802.1Q inserts only an additional 4 bytes into the Ethernet frame. The 802.1Q tag is inserted by the switch before sending across the trunk. The switch removes the 802.1Q tag before sending it out a non trunk link.

27. Trunking protocols were developed to effectively manage the transfer of frames from different VLANs on a single physical link. The trunking protocols establish agreement for the distribution of frames to the associated ports at both ends of the trunk. VLAN tagging information is added by the switch before it is sent across the trunk and removed by the switch before it is sent down a non-trunk link

28. CONFIGURING TRUNKING

29. SwitchA(config-if) switchport mode trunk SwitchB(config-if)switchport mode trunk encapsulation dot1q SwitchB(config-if)switchport mode trunk If SwitchA can only be a 802.1.Q trunk and SwitchB can be either ISL or 802.1Q trunk, configure SwitchB to be 802.1Q. On switches that support both 802.1Q and ISL, the switchport trunk encapsulation command must be done BEFORE the switchport mode trunk command.

30. VLAN Configuration Configuring VLANs under Linux is a process similar to configuring regular Ethernet interfaces. The main difference is you first must attach each VLAN to a physical device. This is accomplished with the vconfig utility. If the trunk device itself is configured, it is treated as native. For example, these commands define VLANs 2-4 on device eth0: vconfig add eth0 2 vconfig add eth0 3 vconfig add eth0 4

31. Switch Configuration Before you begin configuration, make sure the IP address of the switch falls within the new management subnet. The IP configuration is associated with a virtual interface. This is normally VLAN1. interface VLAN1 ip address 10.0.0.2 255.255.255.224

32. Enabling the Trunk interface FastEthernet 0/1 switchport trunk encapsulation dot1q switchport mode trunk

33. Moving the Ports interface FastEthernet0/2 switchport access vlan 2 interface FastEthernet0/3 switchport access vlan 2 interface FastEthernet0/4 switchport access vlan 3 interface FastEthernet0/5 switchport access vlan 3 Once your changes are complete, you can see which ports are in which VLAN by using the show vlan command.

34. BENEFITS OF VLAN Performance Formation of Virtual Workgroups Simplified Administration Reduced Cost Security

35. REFERENCES David Passmore, John Freeman, ``The Virtual LAN Technology Report,'‘ Paul Frieden,” VLANS on LINUX “ cisco

41. TPID - defined value of 8100 in hex. When a frame has the EtherType equal to 8100, this frame carries the tag IEEE 802.1Q / 802.1P. TCI - Tag Control Information field including user priority, Canonical format indicator and VLAN ID. User Priority - Defines user priority, giving eight (2^3) priority levels. IEEE 802.1P defines the operation for these 3 user priority bits. CFI - Canonical Format Indicator is always set to zero for Ethernet switches. CFI is used for compatibility reason between Ethernet type network and Token Ring type network. If a frame received at an Ethernet port has a CFI set to 1, then that frame should not be forwarded as it is to an untagged port. VID - VLAN ID is the identification of the VLAN, which is basically used by the standard 802.1Q. It has 12 bits and allow the identification of 4096 (2^12) VLANs. Of the 4096 possible VIDs, a VID of 0 is used to identify priority frames and value 4095 (FFF) is reserved, so the maximum possible VLAN configurations are 4,094.

42. Switch Model Number of Supported VLANs Catalyst 2950-12 64 Catalyst 2950-24 64 Catalyst 2950C-24 250 Catalyst 2950G-12-EI 250 Catalyst 2950G-24-EI 250 Catalyst 2950G-48-EI 250 Catalyst 2950G-24-EI-DC 250 Catalyst 2950T-24 250