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Chapter 11
Configuring VLAN Trunks on Fast Ethernet and Gigabit Ethernet Ports
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•
Default Trunk Configuration
Table 11-5
Table 11-5 Default Fast Ethernet and Gigabit Ethernet Trunk Configuration
Feature
Trunk mode
Trunk encapsulation
Allowed VLAN range
Configuring a Trunk Link
These sections describe how to configure a trunk link on Fast Ethernet and Gigabit Ethernet ports and
how to define the allowed VLAN range on a trunk:
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•
•
Configuring an 802.1Q Trunk
Some hardware does not support 802.1Q encapsulation. To determine whether your hardware supports
Note
802.1Q, see your hardware documentation or use the show port capabilities command.
Caution
You must configure the ports on both ends of the trunk link as 802.1Q trunks using the set trunk
command with the nonegotiate and dot1q keywords. Expect Spanning Tree Protocol (STP) to block the
port on the other end of the trunk link until you configure that end of the link as an 802.1Q trunk as well.
Do not configure one end of a trunk as an 802.1Q trunk and the other end as an ISL trunk or a nontrunk
port. Errors will occur and no traffic can pass over the link. For more information, see the
Modes and Encapsulation Types" section on page
78-12647-02
Make sure that the native VLAN is the same on ALL of the 802.1Q trunks connecting the Cisco
switches to the non-Cisco 802.1Q cloud.
If you are connecting multiple Cisco switches to a non-Cisco 802.1Q cloud, all of the connections
MUST be through 802.1Q trunks. You CANNOT connect Cisco switches to a non-Cisco 802.1Q
cloud through ISL trunks or through access ports. Doing so will cause the switch to place the ISL
trunk port or access port into the spanning-tree "port inconsistent" state and no traffic will pass
through the port.
shows the default Fast Ethernet and Gigabit Ethernet trunk configuration.
Configuring an 802.1Q Trunk, page 11-5
Defining the Allowed VLANs on a Trunk, page 11-6
Disabling a Trunk Port, page 11-7
Software Configuration Guide—Catalyst 4000 Family, Catalyst 2948G, Catalyst 2980G, Releases 6.3 and 6.4
Default Configuration
auto
dot1q (on hardware supporting 802.1Q only)
VLANs 1–1005
11-2.
Default Trunk Configuration
"Trunking
11-5
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Troubleshooting
