Chapter 19
| VLAN Commands
Displaying VLAN Information
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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 27 and 28 to establish a
path across the switch for unknown VLAN groups:
Console(config)#interface ethernet 1/27
Console(config-if)#vlan-trunking
Console(config-if)#interface ethernet 1/28
Console(config-if)#vlan-trunking
Console(config-if)#
Displaying VLAN Information
This section describes commands used to display VLAN information.
show vlan This command shows VLAN information.
Syntax
show vlan [id vlan-id | name vlan-name]
id - Keyword to be followed by the VLAN ID.
vlan-id - ID of the configured VLAN. (Range: 1-4094)
Table 98: Commands for Displaying VLAN Information
Command Function Mode
show interfaces status vlan Displays status for the specified VLAN interface NE, PE
show interfaces switchport Displays the administrative and operational status of an
interface
NE, PE
show vlan Shows VLAN information NE, PE
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