Brocade 6910 Ethernet Access Switch Configuration Guide (Supporting R2.2.0.0) - Manual (Page 439)

Brocade 6910 Ethernet Access Switch Configuration Guide 383
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Configuring VLAN Interfaces
FIGURE 3 Configuring VLAN Trunking
Without VLAN trunking, you would have to configure VLANs 1 and 2 on all intermediate
switches – C, D and E; otherwise these switches would drop any frames with unknown VLAN
group tags. However, by enabling VLAN trunking on the intermediate switch ports along the
path connecting VLANs 1 and 2, you only need to create these VLAN groups in switches A and
B. Switches C, D and E automatically allow frames with VLAN group tags 1 and 2 (groups that
are unknown to those switches) to pass through their VLAN trunking ports.
• VLAN trunking is mutually exclusive with the “access” switchport mode (see the switchport
mode command). If VLAN trunking is enabled on an interface, then that interface cannot be
set to access mode, and vice versa.
• To prevent loops from forming in the spanning tree, all unknown VLANs will be bound to a
single instance (either STP/RSTP or an MSTP instance, depending on the selected STA mode).
• If both VLAN trunking and ingress filtering are disabled on an interface, packets with unknown
VLAN tags will still be allowed to enter this interface and will be flooded to all other ports where
VLAN trunking is enabled. (In other words, VLAN trunking will still be effectively enabled for the
unknown VLAN).
Example
The following example enables VLAN trunking on ports 9 and 10 to establish a path across the
switch for unknown VLAN groups:
Console(config)#interface ethernet 1/9
Console(config-if)#vlan-trunking
Console(config-if)#interface ethernet 1/10
Console(config-if)#vlan-trunking
Console(config-if)#
A
V1
B
C
D
E
V2 V1 V2