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4.14. IEEE 802.1Q VLANs
In large networks, routers are used to isolate broadcast traffic for each subnet into separate
domains. This switch provides a similar service at Layer 2 by using VLANs to organize any
group of network nodes into separate broadcast domains. VLANs confine broadcast traffic to
the originating group, and can eliminate broadcast storms in large networks. This also
provides a more secure and cleaner network environment.
An IEEE 802.1Q VLAN is a group of ports that can be located anywhere in the network, but
communicate as though they belong to the same physical segment.
VLANs help to simplify network management by allowing you to move devices to a new
VLAN without having to change any physical connections. VLANs can be easily organized to
reflect departmental groups (such as Marketing or R&D), usage groups (such as e-mail), or
multicast groups (used for multimedia applications such as videoconferencing).
VLANs provide greater network efficiency by reducing broadcast traffic, and allow you to
make network changes without having to update IP addresses or IP subnets. VLANs
inherently provide a high level of network security since traffic must pass through a
configured Layer 3 link to reach a different VLAN.
This switch supports the following VLAN features:
◆ Up to 256 VLANs based on the IEEE 802.1Q standard
◆ Distributed VLAN learning across multiple switches using explicit or implicit tagging
◆ Port overlapping, allowing a port to participate in multiple VLANs
◆ End stations can belong to multiple VLANs
◆ Passing traffic between VLAN-aware and VLAN-unaware devices
◆ Priority tagging
ASSIGNING PORTS TO VLANS
Before enabling VLANs for the switch, you must first assign each port to the VLAN group(s)
in which it will participate. By default all ports are assigned to VLAN 1 as untagged ports. Add
a port as a tagged port if you want it to carry traffic for one or more VLANs, and any
intermediate network devices or the host at the other end of the connection supports VLANs.
Then assign ports on the other VLAN-aware network devices along the path that will carry
this traffic to the same VLAN(s), either manually or dynamically using GVRP. However, if you
want a port on this switch to participate in one or more VLANs, but none of the intermediate
network devices nor the host at the other end of the connection supports VLANs, then you
should add this port to the VLAN as an untagged port.
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