3Com TR - Manual (Page 102)

7-4 C HAPTER 7: V IRTUAL LAN S
Connecting Common VLANs Between Switch Units
In the Switch 2000 TR, you typically connect VLANs to
other Switch 2000 TRs and units using backbone
ports. This allows the Switch to forward all frames
with an unknown address to the rest of the network,
and it also stops the Switch Database from becoming
full if there are more than 500 addresses in the net-
work. Note that you normally require one backbone
port per VLAN.
In addition, to make the Switch-to-Switch connec-
tions more cost-effective, the Switch 2000 TR allows
you to specify that one port forms part of a Virtual
LAN Trunk (VLT). A VLT is a connection that carries
traffic for multiple VLANs between Switch units. If
you configure both ends of a Switch-to-Switch con-
nection as part of a VLT, you only need that one con-
nection for all the VLANs.
NOTE: VLTs can only be used for links between
SuperStack II Switch 2000 TR units. You cannot use
VLTs for Switch-router links.
If you specify that a backbone port on one VLAN is
part of a VLT, that backbone port becomes a back-
bone port for all the VLANs on the Switch, even if
they had no backbone port before. If you subse-
quently disable the VLT function on that port, the port
becomes the backbone port for the Default VLAN
(VLAN 1) and all other VLANs lose their backbone
ports.
Using Non-routable Protocols
If you are running non-routable protocols on your
network (for example, DEC LAT or NETBIOS), devices
within one VLAN will not be able to communicate
with devices in a different VLAN.
Using Unique MAC Addresses
If you connect a server with multiple network adapt-
ers to the Switch, we recommend that you configure
each network adapter with a unique MAC address.
Extending VLANs into an ATM Network
If the Switch has an ATM OC-3c Module installed, you
can extend the VLANs you have defined in your exist-
ing network into an ATM network. For more informa-
tion, see the SuperStack II Switch ATM OC-3c
Module User Guide.
Example 1
The example shown in Figure 7-2 illustrates a simple
VLAN configuration with a single Switch 2000 TR
whose ports are divided between two VLANs. VLAN 1
is able to talk to VLAN 2 using the connection
between each VLAN and the router.
To set up this configuration:
1 Use the VT100 screens or VLAN Server database to:
a Place ports 1-6 in VLAN 1.
b Place ports 7-12 in VLAN 2.
2 Connect a port in VLAN 1 to the router.
3 Repeat steps 2 and 3 for VLAN 2.