MNS-BB
Software User Guide
-82-
15.0 Port-Based
Virtual LANs (Static VLANs)
A VLAN is a group of ports designated by the switch as belonging to the same broadcast domain.
(That is, all ports carrying traffic for a particular subnet address would normally belong to the same
VLAN.)
Note:
This section describes
static
VLANs, which are VLANs you manually configure with a name,
VLAN ID (VID), and port assignments. Using a VLAN, you can group users by logical function
instead of physical location. This helps to control bandwidth usage by allowing you to group high-
bandwidth users on low-traffic segments and to organize users from different LAN segments
according to their need for common resources.
By default, the LE2425A and LEV2525 switches are VLAN (Port based) enabled and allow up to 32
VLANs. The port-based nature of the configuration allows interoperation with older switches that
require a separate port for each VLAN.
15.1
General Use and Operation
Port-based VLANs are typically used to enable broadcast traffic reduction and to increase security. A
group of network users assigned to a VLAN form a broadcast domain that is separate from other
VLANs that may be configured on a switch. Packets are forwarded only between ports that are
designated for the same VLAN. Thus, all ports carrying traffic for a particular subnet address should
be configured to the same VLAN. Cross-domain broadcast traffic in the switch is eliminated and
bandwidth is saved by not allowing packets to flood out all ports. An external router is required to
enable separate VLANs on a switch to communicate with each other.
15.2
VLAN Support and the Default VLAN
In the factory default configuration, VLAN support is enabled and all ports on the switch belong to
the default VLAN (named DEFAULT-VLAN). This places all ports in the switch into one physical
broadcast domain.
You can partition the switch into multiple virtual broadcast domains by adding one or more additional
VLANs and moving ports from the default VLAN to the new VLANs. (The switch supports up to 32
VLANs.) You can change the name of the default VLAN, but you cannot change the default VLAN’s
VID (which is always “1”). Although you can remove all ports from the default VLAN, this VLAN is
always present.
The LE2425A and LEV2525A Switches Port Based VLAN operate by restricting the broadcast and
multicast traffic between the ports. A packet with a broadcast address or with an unknown destination
address is forwarded only to ports that share VLAN membership with the source port. Unnecessary
repeating of broadcast packets is thus avoided, conserving bandwidth. Packets destined to known
addresses are forwarded normally.
Note:
Always start all VLANs before editing the default Vlan.
Syntax:
start vlan=all
Then,
edit id=<vlan Id> [name=<vlan name>] port=<number|list|range>
To display the current VLAN, use the CLI
show vlan
command.
Syntax: show vlan type=port
15.3
General Steps for Using VLANs
1. Plan your VLAN strategy and create a map of the logical topology that will result from configuring
VLANs. Include consideration for the interaction between VLANs.
2. Configure at least one VLAN in addition to the default VLAN.
3. Assign the desired switch ports to the new VLAN(s).
