User-Configured Port-Based Vlans; Important Considerations - 3Com 4007 Implementation Manual

270 C 14: V
HAPTER IRTUAL
User-Configured
Port-based VLANs
LAN (VLAN )
S S
You can explicitly configure port-based VLAN interfaces on the Layer 2
and Multilayer switching modules as well as the switch fabric module.

Important Considerations

When you create this type of VLAN interface, review these guidelines:
When you select the bridge ports that you want to be part of the
VLAN, the bridge ports that you specify as part of the VLAN are the
same as your physical ports, unless you have created trunks.
If you define trunks, a single bridge port called the anchor port (the
lowest-numbered port in the trunk) represents all ports that are part
of the trunk. Only the anchor bridge port for the trunk is selectable
when you are creating VLANs; the other bridge ports in the trunk are
not selectable. For more information, see Chapter 12.
Decide whether you want the ports that you are specifying for the
VLAN interface to be shared by any other VLAN interface. Shared
ports produce overlapped VLANs; ports that are not shared produce
nonoverlapped VLANs.
The per-port tagging options are IEEE 802.1Q tagging or no tagging.
The IEEE 802.1Q tagging option embeds explicit VLAN membership
information in each frame.
Overlapped VLANs require tagging; that is, two port-based VLAN
interfaces may contain the same bridge port if one of the VLAN
interfaces defines the shared port to use IEEE 802.1Q tagging. This
rule is true for either allOpen or allClosed mode. For example, a shared
bridge port is set to tagging none for one VLAN and IEEE 802.1Q
tagging for the other VLAN, or IEEE 802.1Q tagging for each VLAN.
Multiple VLANs can span several modules, which may or may not
overlap on the front-panel ports of the modules. However, they do
overlap on the backplane ports. When multiple VLANs span modules,
only one VLAN (usually, the default VLAN) can be untagged. Because
all VLAN traffic flow between modules takes place through the GEN
Switch Fabric Module by way of the backplane ports (regardless of the
front-panel port configurations), the backplane ports for additional
overlapping VLANs require explicit 802.1Q tagging.
On Multilayer Switching Modules, port-based VLANs use the protocol
type unspecified. This setting is implicit on a Layer 2 module. On a
Multilayer Switching Module, you must specify the protocol type
unspecified to create a port-based VLAN.