Cisco Systems RJ-45-to-AUX manual Mapping VLANs to a Trunk Port, 107

Mapping VLANs to a Trunk Port

In the last example, we assigned port 2/1 as a trunk port using ISL encapsulation. Notice that we did not specify the VLANs to trunk. By default, all VLANs would be trunked. You can assign only VLANs 1 through

200 to be trunked across this configured trunk link, as shown here:

Console> (enable) set trunk 2/1 on 1−200 isl Adding vlans 1−1005 to allowed list.

Please use the Ôclear trunk’ command to remove vlans from allowed list. Port(s) 2/1 allowed vlans modified to 1−1005.

Port(s) 2/1 trunk mode set to on. Port(s) 2/1 trunk type set to isl.

Configuring a Trunk Port on a Cisco 1900EN Series

To configure a trunk on a 1900EN series switch, you use the trunk command. The 1900 switch has the same port negotiation options as the 5000 series, but only runs the DISL encapsulation method. You can see the syntaxes available for configuring a 1900EN series switch by using the trunk option from Interface Configuration mode:

1912(config)#int f0/26
1912(config−if)#trunk		?
auto	Set DISL	state to AUTO
desirable	Set DISL	state to DESIRABLE
nonegotiate Set DISL		state to NONEGOTIATE
off	Set DISL	state to OFF
on	Set DISL	state to ON

trunk is the only command needed to trunk a port once you are in Interface Configuration mode for the port that needs to be trunked. You can set the trunked port to always be a trunk link, using the following command:

1900EN(config−if)#trunk on

Clearing VLANs from Trunk Links on a Cisco 5000 Series

All VLANs are configured on a trunk by default. They remain configured unless cleared by an administrator. If you want a trunk link not to carry certain VLAN information—perhaps because you want to stop broadcasts on a certain VLAN from traversing the trunk link, or you want to stop topology change information from being sent across a link where a VLAN is not supported—use the clear trunk command:

5000> (enable) clear trunk 2/1 4−1005 Removing Vlan(s) 4−1005 from allowed list.

Clearing VLANs from Trunk Links on a Cisco 1900EN Series

To remove VLANs from a trunk port on a 1900, use the no trunk−vlan command in Interface Configuration mode. First, to view the possible options for the command, use the following:

1912(config−if)#no trunk−vlan ? <1−1005> ISL VLAN index

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