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Catalyst 6500 Series Switch Command Reference—Release8.4
OL-6244-01
Chapter2 Catalyst 6500 Series Switch and ROM Monitor Commands
set trunk
The following usage guidelines apply when using the set trunk command:
•If a trunk-type keyword (isl, dot1q, negotiate) is not specified when configuring an EtherChannel
trunk, the current trunk type is not affected.
•To return a trunk to its default trunk type and mode, enter the clear trunk mod/port command.
•Trunking capabilities are hardware-dependent. Refer to the Catalyst6500 Series Module
Installation Guide to determine the trunking capabilities of your hardware, or enter the show port
capabilities command.
•Catalyst 6500 series switches use DTP to negotiate trunk links automatically on EtherChannel ports.
Whether or not a port will negotiate to become a trunk port depends on both the m ode and th e tr unk
type specified for that port. Refer to the Catalyst 6500 Series Switch Switch Software Configuration
Guide for detailed information on how trunk ports are negotiated.
•DTP is a point-to-point protocol. However, some internetworking devices might improperly forward
DTP frames. You can avoid this problem by ensuring that trunking is turned off on ports connected
to non-Catalyst 6500 series switch devices if you do not intend to t runk a cros s t hos e l inks. Wh en
enabling trunking on a link to a Cisco router, enter the noneg keyword to cause the port to become
a trunk but not generate DTP frames.
•To remove VLANs from the allowed list for a trunk, e nter the clear t runk mod/port vlans command.
When you first configure a port as a trunk, the set trunk command always adds all VLANs to the
allowed VLAN list for the trunk, even if you specify a VLAN range. (The specified VLAN range is
ignored.)
•To remove VLANs from the allowed list, enter the clear trunk mod/port vlans command. To later
add VLANs that were removed, enter the set trunk mod/port vlans command.
•You cannot change the allowed VLAN range on the MSM port. The MSM port can be configured
only as an IEEE 802.1Q-type trunk.
•For trunking to be negotiated on EtherChannel ports, the ports must be in the same VTP domain.
However, you can use the on or noneg mode to force a port to become a trunk, even if it is in a
different domain.
•When you configure a trunk, all VLANs are active on the trunk by default. If y ou do not want a ny
active VLANs on the trunk, enter the none keyword. The none keyword clears all VLANs from the
trunk.
Examples This example shows how to set port 2 on module 1 as a trunk port:
Console> (enable) set trunk 1/2 on
Port(s) 1/2 trunk mode set to on.
Console> (enable)
This example shows how to add VLANs 5 through 50 to the allowed VLAN list for a trunk port (VLANs
were previously removed from the allowed list with the clear trunk command):
Console> (enable) set trunk 1/1 5-50
Adding vlans 5-50 to allowed list.
Port(s) 1/1 allowed vlans modified to 1,5-50,101-1005.
Console> (enable)
This example shows how to set port 5 on module 4 as an 802.1Q trunk port in desirable mode:
Console> (enable) set trunk 4/5 desirable dot1q
Port(s) 4/5 trunk mode set to desirable.
Port(s) 4/5 trunk type set to dot1q.
Console> (enable)