VLAN Types
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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: |
- 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.
- 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.
- 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.
- 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.
Examples:
| IP Subnet |
VLAN |
| 192.23.160.0 |
1 |
| 192.23.161.0 |
2 |
| 112.18.0.0 |
3 |
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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