Trunking
119
Clearing VLANs from Trunk Links
As demonstrated in the preceding sections, all VLANs are configured on a
trunk link unless cleared by an administrator. If you want a trunk link to not
carry VLAN information because you want to stop broadcasts on a certain
VLAN from traversing the trunk link, or because you want to stop topology
change information from being sent across a link where a VLAN is not sup-
ported, use the clear trunk command.
This section will show you how to clear VLANs from trunked links on
both the 5000 and 1900 series of switches.
5000 Series
The command to clear a VLAN from a trunked link is clear trunk slot/
port vlans
. Here is an example:
Console> (enable) clear trunk 2/12 5-1005
Removing Vlan(s) 5-1005 from allowed list.
Port 1/2 allowed vlans modified to 1-4
1900 Switch
To delete VLANs from a trunk port on a 1900, use the interface no trunk-
vlan
command:
1900EN(config-if)#no trunk-vlan ?
<1-1005> ISL VLAN index
1900EN(config-if)#no trunk-vlan 5
1900EN(config-if)#
Per Cisco documentation, you can clear up to 10 VLANs at once. The syn-
tax is no trunk-vlan <vlan-list>. The VLANS must be separated by
spaces. Typically, you wouldn't clear more than a few VLANs anyway,
because functionally, it makes no difference if they are turned on or not. If
you have security, broadcast, or routing update issues, you need to consider
clearing VLANs from a trunked link.
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