Cisco Systems 3750E Manual De Usuario
13-21
Catalyst 3750-E and 3560-E Switch Software Configuration Guide
OL-9775-02
Chapter 13 Configuring VLANs
Configuring VLAN Trunks
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.
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 IEEE 802.1Q trunk. The example assumes that the
neighbor interface is configured to support IEEE 802.1Q trunking.
neighbor interface is configured to support IEEE 802.1Q trunking.
Switch# configure terminal
Enter configuration commands, one per line. End with CNTL/Z.
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.
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.
Note
VLAN 1 is the default VLAN on all trunk ports in all Cisco switches, and it has previously been a
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.
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.
Step 4
switchport mode {dynamic {auto |
desirable} | trunk}
desirable} | trunk}
Configure the interface as a Layer 2 trunk (required only if the interface
is a Layer 2 access port or tunnel port or to specify the trunking mode).
is a Layer 2 access port or tunnel port or 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.
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.
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.
to convert the link to a trunk link even if the neighboring interface is
not a trunk interface.
Step 5
switchport access vlan vlan-id
(Optional) Specify the default VLAN, which is used if the interface stops
trunking.
trunking.
Step 6
switchport trunk native vlan vlan-id
Specify the native VLAN for IEEE 802.1Q trunks.
Step 7
end
Return to privileged EXEC mode.
Step 8
show interfaces interface-id switchport Display the switchport configuration of the interface in the Administrative
Mode and the Administrative Trunking Encapsulation fields of the
display.
display.
Step 9
show interfaces interface-id trunk
Display the trunk configuration of the interface.
Step 10
copy running-config startup-config
(Optional) Save your entries in the configuration file.
Command
Purpose