1.2 Configure, verify, and troubleshoot interswitch connectivity

1.2.a Add and remove VLANs on a trunk

By default trunks allow traffic on VLAN’s 1 to 1005 to pass through them with no additional config.
You can also configure trunk ports to allow traffic from only specific VLANs.

Example: Adding a range of interfaces to a port can be done as follows
SW1(config)# interface range fastethernet 0/10 – 15
SW1(config-if)# switchport access vlan 2
SW1(config-if)# switchport mode access
SW1(config-if)# end

1.2.b DTP and VTP (v1&v2)

VTP stands for VLAN Trunking Protocol. It’s a Cisco proprietary protocol on Cisco switches that advertises all of the VLANs configured on a switch. (Something about Vlan number command).
There are three VTP modes that can be used:
Server: This is the mode that a Cisco switch has enabled by default. It is required that at least one switch have server mode switched on in a network is implemented. It allows the user to creat, modify or delete and VLA in the VTP domain. Changes are then advertised out to the VTP domain.
Transparent: VTP can be essentially turned off by running the vtp mode transparent command. When in this mode you can still configure standard and extended range VLANs for the device that’s in transparent mode – but nothing that you implement will be pushed out anywhere else, and you will not accept any VTP information from other switches.
Client: Switches operating in client mode store the same VTP information as switches that are in server mode. They recieve the advertisments that come from server devices, however they are unable to modify any VTP information.

Leaning: Another state in which switch frames that pass through a switch are exammined and MAC addresses are learned. It is not a valid mode for VTP configuration.


DTP stands for Dynamic Trunking Protocol. There are two modes that it can be in when negotiating a trunk connection:

Auto – A port set to Auto will operate in access mode unless a neighbouring interface wants it to be a trunk port
Desirable – Ports set to Desirable will actively negotiate a trunk connection with a neighbouring interface.