o turn off DTP in the event that either 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. 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-CatOS# (enable) 2006 May 23 11:29:31 %ETHC-5-PORTFROMSTP: Port 3/5 left bridge port 3/5 2006 May 23 11:29:34 %DTP-5-TRUNKPORTON: Port 3/5 has become dot1q trunk The other side of the link was not configured, but the trunk became active because the default state of the ports on the other side is auto. Chapter 5: Trunking The command to view trunk status on CatOS is show port trunk: Switch1 - CatOS#sho port trunk * - indicates vtp domain mismatch # - indicates dot1q-all-tagged enabled on the port $ - indicates non-default dot1q-ethertype value Encapsulation Status Native vlan desirable dot1q trunking nonegotiate isl trunking nonegotiate isl trunking Vlans allowed on trunk 1-4094 1-4094 1-4094 Vlans allowed and active in management domain 1,10,20 Vlans in spanning tree forwarding state and not pruned 1,10,20 The trunks 15/1 and 16/1 shown in this output are internal trunks. On a 6500 switch running CatOS, trunks exist from the supervisors to the multilayer switch feature cards (MSFCs). The MSFCs are known as slots 15 and 16 when two supervisors are installed. To specify which VLANs can traverse a trunk, use the same set trunk command and append the VLANs you wish to allow. CatOS works a little differently from IOS in that it will not remove all of the active VLANs in favor of ones you specify: Switch-2# (enable)set trunk 3/5 100 Vlan(s) 100 already allowed on th