Cisco Catalyst 3750 Command Reference Manual page 617

Chapter 2 Catalyst 3750 Switch Cisco IOS Commands
Allowed VLAN:
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Trunk pruning:
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Examples
This example shows how to cause a port configured as a switched interface to encapsulate in 802.1Q
trunking format regardless of its default trunking format in trunking mode:
Switch(config)# interface gigabitethernet1/0/2
Switch(config-if)# switchport trunk encapsulation dot1q
This example shows how to configure VLAN 3 as the default for the port to send all untagged traffic:
Switch(config)# interface gigabitethernet1/0/2
Switch(config-if)# switchport trunk native vlan 3
This example shows how to add VLANs 1, 2, 5, and 6 to the allowed list:
Switch(config)# interface gigabitethernet1/0/2
Switch(config-if)# switchport trunk allowed vlan add 1,2,5,6
This example shows how to remove VLANs 3 and 10 to 15 from the pruning-eligible list:
Switch(config)# interface gigabitethernet1/0/2
Switch(config-if)# switchport trunk pruning vlan remove 3,10-15
You can verify your settings by entering the show interfaces interface-id switchport privileged EXEC
command.
Related Commands Command
show interfaces
switchport mode
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To reduce the risk of spanning-tree loops or storms, you can disable VLAN 1 on any individual
VLAN trunk port by removing VLAN 1 from the allowed list. When you remove VLAN 1 from a
trunk port, the interface continues to send and receive management traffic, for example, Cisco
Discovery Protocol (CDP), Port Aggregation Protocol (PAgP), Link Aggregation Control Protocol
(LACP), Dynamic Trunking Protocol (DTP), and VLAN Trunking Protocol (VTP) in VLAN 1.
The no form of the allowed vlan command resets the list to the default list, which allows all VLANs.
The pruning-eligible list applies only to trunk ports.
Each trunk port has its own eligibility list.
If you do not want a VLAN to be pruned, remove it from the pruning-eligible list. VLANs that are
pruning-ineligible receive flooded traffic.
VLAN 1, VLANs 1002 to 1005, and extended-range VLANs (VLANs 1006 to 4094) cannot be
pruned.
switchport
Description
Displays the administrative and operational status of a switching
(nonrouting) port, including port blocking and port protection settings.
Configures the VLAN membership mode of a port.
Catalyst 3750 Switch Command Reference
switchport trunk
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