C
HAPTER
34
| VLAN Commands
Configuring VLAN Interfaces
– 794 –
vlan-trunking This command allows unknown VLAN groups to pass through the specified
interface. Use the no form to disable this feature.
SYNTAX
[no] vlan-trunking
DEFAULT SETTING
Disabled
COMMAND MODE
Interface Configuration (Ethernet, Port Channel)
COMMAND USAGE
◆ Use this command to configure a tunnel across one or more
intermediate switches which pass traffic for VLAN groups to which they
do not belong.
The following figure shows VLANs 1 and 2 configured on switches A and
B, with VLAN trunking being used to pass traffic for these VLAN groups
across switches C, D and E.
Figure 293: 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.
◆ The following restrictions apply to this feature:
■
VLAN trunking can only be enabled on Gigabit Ethernet ports or
trunks.
■
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.
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