Cisco Catalyst 3550 Command Reference Manual page 626
Multilayer switch
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Also See for Catalyst 3550:
- Command reference manual (662 pages) ,
- Installation manual (154 pages) ,
- Hardware installation manual (106 pages)
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switchport trunk
Allowed VLAN:
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Trunk pruning:
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Examples
This example shows how to cause a port interface configured as a switched interface to encapsulate in
IEEE 802.1Q trunking format regardless of its default trunking format in trunking mode:
Switch(config-if)# switchport trunk encapsulation dot1q
This example shows how to configure VLAN 3 as the default port to send all untagged traffic:
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-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-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
Catalyst 3550 Multilayer Switch Command Reference
2-600
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. This is known as VLAN 1
minimization. VLAN 1 minimization disables VLAN 1 (the default VLAN on all Cisco switch trunk
ports) on an individual VLAN trunk link. As a result, no user traffic, including spanning-tree
advertisements, is sent or received on VLAN 1.
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.
Chapter 2 Catalyst 3550 Switch Cisco IOS Commands
OL-8566-01
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