lowed vlan remove 200 3550-I0S(config-if)# switchport trunk allowed vlan remove 300 show interface trunk now shows that all VLANs-except 100, 200, and 300-are allowed on the trunk: 3550-IOS# sho int trunk Encapsulation Status Native vlan Fao/15 802.1q trunking Vlans allowed on trunk Fa0/15 1-99,101-199,201-299,301-4094 Vlans allowed and active in management domain Fao/15 1,3-4,10 Vlans in spanning tree forwarding state and not pruned Fao/15 1,3-4,10 CatOS Configuring a trunk on a CatOS switch is done via the set trunk command. Options for the set trunk command are as follows: Switch1-CatOS# (enable) set trunk 3/1 ? No vlans <mode> Trunk mode (on, off, desirable, auto, nonegotiate) <type> Trunk type dot1q, dot10, lane, negotiate) <vlan> VLAN number The mode on indicates that the port has been hardcoded to be a trunk, and the mode off indicates that the port will never be a trunk. The modes desirable and auto are both dynamic, and refer to the method in which DTP will operate on the port. desirable indicates that the port will initiate negotiations, and try to make the link a trunk. auto indicates that the port will listen for DTP, but will not actively attempt to become a port. You can use the mode nonegotiate to turn off DTP in the event that either on or off has been chosen as the mode on the opposing port. The trunk types isl and dotq1 specify ISL and 802.1Q as the protocols, respectively; negotiate indicates that DTP should be used to determine the protocol. The trunk types dot10 and lane are for technologies such as ATM, and will not be covered here. Chapter 5: Trunking One of the nice features of CatOS is that it allows you to stack multiple arguments in a single command. This command sets the port to mode desirable, and the protocol to 802.1Q: Switch1-Catos# (enable) set trunk 3/5 desirable dot1q Port(s) 3/1 trunk mode set to desirable. Port(s) 3/1 trunk type set to dot1q. Switch1-Cat0S# (enable) 2006 May 23 11:29:31 6ETHC-5-PORTFROMSTP:I Port 3/5 left bridge port 3/5 2006 May 23 11:29:34 %DTP-5-TRUNKPORTON