Defining The Allowed Vlans On A Trunk - Cisco WS-C3750-48PS-S Software Configuration Manual

Chapter 13 Configuring VLANs
Command
Step 4 switchport mode {dynamic {auto |
desirable} | trunk}
Step 5 switchport access vlan vlan-id
Step 6 switchport trunk native vlan vlan-id
Step 7
end
Step 8 show interfaces interface-id switchport Display the switchport configuration of the interface in the Administrative
Step 9 show interfaces interface-id trunk
Step 10 copy running-config startup-config
To return an interface to its default configuration, use the default interface interface-id interface
configuration command. To reset all trunking characteristics of a trunking interface to the defaults, use
the no switchport trunk interface configuration command. To disable trunking, use the switchport
mode access interface configuration command to configure the port as a static-access port.
This example shows how to configure a port as an 802.1Q trunk. The example assumes that the neighbor
interface is configured to support 802.1Q trunking.
Switch# configure terminal
Enter configuration commands, one per line.
Switch(config)# interface gigabitethernet1/0/2
Switch(config-if)# switchport mode dynamic desirable
Switch(config-if)# switchport trunk encapsulation dot1q
Switch(config-if)# end

Defining the Allowed VLANs on a Trunk

By default, a trunk port sends traffic to and receives traffic from all VLANs. All VLAN IDs, 1 to 4094,
are allowed on each trunk. However, you can remove VLANs from the allowed list, preventing traffic
from those VLANs from passing over the trunk. To restrict the traffic a trunk carries, use the switchport
trunk allowed vlan remove vlan-list interface configuration command to remove specific VLANs from
the allowed list.
VLAN 1 is the default VLAN on all trunk ports in all Cisco switches, and it has previously been a
Note
requirement that VLAN 1 always be enabled on every trunk link. You can use the VLAN 1 minimization
feature to disable VLAN 1 on any individual VLAN trunk link so that no user traffic (including spanning
tree advertisements) is sent or received on VLAN 1.
78-16180-02
Purpose
Configure the interface as a Layer 2 trunk (required only if the interface
is a Layer 2 access port to specify the trunking mode).
dynamic auto—Set the interface to a trunk link if the neighboring
•
interface is set to trunk or desirable mode. This is the default.
dynamic desirable—Set the interface to a trunk link if the
•
neighboring interface is set to trunk, desirable, or auto mode.
trunk—Set the interface in permanent trunking mode and negotiate
•
to convert the link to a trunk link even if the neighboring interface is
not a trunk interface.
(Optional) Specify the default VLAN, which is used if the interface stops
trunking.
Specify the native VLAN for 802.1Q trunks.
Return to privileged EXEC mode.
Mode and the Administrative Trunking Encapsulation fields of the
display.
Display the trunk configuration of the interface.
(Optional) Save your entries in the configuration file.
End with CNTL/Z.
Catalyst 3750 Switch Software Configuration Guide
Configuring VLAN Trunks
13-21