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Virtual LANs (VLANs) 5-3
VLANs and the Switch
The Switch 1000 supports VLANs which consist of
a set of switch ports. Each switch port can only
belong to one VLAN at a time, regardless of the
device to which it is attached.
Each Switch 1000 can support up to 16 VLANs.
However, you can have more than 16 VLANs in your
entire network by connecting the 16 Switch VLANs
to other VLANs using a router.
The Default VLAN and Moving Ports From the
Default VLAN
On each Switch, VLAN 1 is the Default VLAN of the
Switch; it has two properties:
■
It contains all the ports on a new or initialized
Switch
■
It is the only VLAN which allows an SNMP Net-
work Manager to access the management agent
of the unit
By default, if a device is attached to a port in the
Default VLAN and you want to move the device into
another VLAN, you need to use the VLAN Setup
screen to place the port in that VLAN. For more
information about the VLAN Setup screen, refer to
“
Setting Up VLANs on the Switch” on page 5-8.
Connecting VLANs to a Router
If the devices in a VLAN need to talk to devices in a
different VLAN, each VLAN requires a connection to
a router. Communication between VLANs can only
take place if they are all connected to the router. A
VLAN not connected to a router is an isolated
VLAN. You need one port for each VLAN connected
to the router.
Connecting Common VLANs Between Switch
Units
If you want to connect the VLANs on the Switch
1000 with the same VLANs on another Switch unit,
you can set up one link per VLAN. Alternatively,
you can set up a single link for all the VLANs by cre-
ating a
Virtual LAN Trunk
(VLT). A VLT is a
Switch-to-Switch link which carries traffic for all the
VLANs on each Switch. To set up a VLT, you config-
ure the port at each end of the link.
VLTs can only be used for links between Super-
Stack
®
II Switch 1000, Switch 3000 and Desktop
Switch units. You cannot use VLTs for Switch–router
links.
If you specify that a port on one VLAN is a VLT port,
that port carries traffic for all the VLANs on the
Switch. If you then disable the VLT function on that
port, the port only carries traffic for the Default
VLAN (VLAN 1).
Using AutoSelect VLAN Mode
By default, all ports on the Switch use Port VLAN
Mode — where each switch port is
manually
placed in the required VLAN. The Switch allows
some ports to use another mode, AutoSelect VLAN
Mode. In this mode, the ports are
automatically
placed in the required VLAN by referring to a VLAN
Server database in 3Com’s Transcend Enterprise
Manager v6.0 for Windows.