How a Switch distinguishes between VLANs? This is done by associating the work stations to a specific VLAN using specified format. This is known as VLAN membership. Four prominent VLAN membership methods are by port, MAC address, protocol type, and subnet address. Each of these are discussed below:
1. VLAN membership by Port:
Here, you define which ports of a Switch belong to which VLAN. Any work station connected to a particular port will automatically be assigned that VLAN. For example, in a Switch with eight ports, ports 1-4 may be configured with VLAN 1, and ports 5-8 may be configured with VLAN2.
One of the disadvantages of this method is that it requires Switch port reconfiguration whenever a user (of course, with associated workstation) moves from one place to another. VLANs by port association operates at Layer 1 of the OSI model.
2. VLAN membership by MAC Address:
Here, membership in a VLAN is based on the MAC address of the user workstation. A Switch that participates in VLAN, uses the MAC addresses to assign a VLAN to each workstation. When a workstation moves to another place, the corresponding switch automatically discovers the VLAN association based on the MAC address of the workstation. Since the MAC address is normally inseparable from that of the workstation, this method of VLAN membership is more amenable to workstation moves.
This type of VLAN works at Layer 2 of the OSI model.
3. Membership by Protocol Type:
Layer 2 header contains the protocol type field. You can use this information to decide on the VLAN association. For example, all IP traffic may be associated with VLAN 1 and all IPX traffic may be associated with VLAN 2.
4. Membership by IP Subnet Address
In this type of VLAN association, membership is based on the Layer 3 header. The Switch reads the Layer 3 IP address and associates a VLAN membership. Note that even though the Switch accesses Layer 3 information, it still works at Layer 2 of OSI model only. A VLAN Switch doesn't do any routing based on IP address.
IP Subnet addresses assignment to different VLAN's.
IP address based VLANs allow user moves. However, it is likely to take more time to forward a packet by a Switch because it has to read Layer 3 information. Hence the latency rates may be relatively more using this type of VLAN membership.
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