Cisco WS-C2950T-24 User Manual

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Catalyst 2900 Series XL and Catalyst 3500 Series XL Software Configuration Guide
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Chapter 8 Configuring VLANs
How VLAN Trunks Work
Disabling a Trunk Port
You can disable trunking on a port by returning it to its default static-access mode.
Beginning in privileged EXEC mode, follow these steps to disable trunking on a port:
Defining the Allowed VLANs on a Trunk
By default, a trunk port sends to and receives traffic from all VLANs in the VLAN database. All VLANs,
1 to 1005, 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 remove vlan-list parameter to remove specific VLANs from the allowed list.
A trunk port can become a member of a VLAN if the VLAN is enabled, if VTP knows of the VLAN,
and if the VLAN is in the allowed list for the port. When VTP detects a newly enabled VLAN and the
VLAN is in the allowed list for a trunk port, the trunk port automatically becomes a member of the
enabled VLAN. When VTP detects a new VLAN and the VLAN is not in the allowed list for a trunk
port, the trunk port does not become a member of the new VLAN.
Beginning in privileged EXEC mode, follow these steps to modify the allowed list of a ISL or 802.1Q
trunk:
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface_id Enter the interface configuration mode and the port to be added to the
VLAN.
Step 3
no switchport mode Return the port to its default static-access mode.
Step 4
end Return to privileged EXEC.
Step 5
show interface interface-id
switchport
Verify your entries.
In the display, check the Negotiation of Trunking field.
Command Purpose
Step 1
configure terminal Enter global configuration mode.
Step 2
interface interface_id Enter interface configuration mode and the port to be added to the VLAN.
Step 3
switchport mode trunk Configure VLAN membership mode for trunks.
Step 4
switchport trunk allowed vlan
remove vlan-list
Define the VLANs that are not allowed to send and receive on the port.
The vlan-list parameter is a range of VLAN IDs Separate nonconsecutive
VLAN IDs with a comma and no spaces; use a hyphen to designate a range
of IDs. Valid IDs are from 2 to 1001.
Step 5
end Return to privileged EXEC.
Step 6
show interface interface-id
switchport allowed-vlan
Verify your entries.
Step 7
copy running-config startup-config Save the configuration.

Cisco WS-C2950T-24 Specifications

General

Brand	Cisco
Model	WS-C2950T-24
Category	Switch
Language	English