Specifications

CHAPTER 2
VLAN Implementation
Using the trunk keyword with the show interfaces command gives information about the trunk link:
# show interfaces fastethernet 0/1 trunk
Port Mode Encapsulation Status Native vlan
Fa0/1 desirable n-802.1q trunking 1
Port Vlans allowed on trunk
Fa0/1 1-150
<further output omitted>
Best Practices for Trunking
n Change the Native VLAN to one not assigned to any users.
n On links that should be trunks, turn off trunking negotiation by setting the mode to trunk, specifying the encapsula-
tion type, and adding the nonnegotiate command.
n On links that should never be trunks, turn off trunking negotiation by setting the switchport mode to host. This sets
it as an access port, enables Portfast, and disables EtherChannel negotiation.
n Limit the VLAN traffic carried by the trunk to only those VLANs it needs to carry.
VLAN Trunking Protocol
VLAN Trunking Protocol (VTP) is a Cisco-proprietary protocol that runs over trunk links and synchronizes the VLAN
databases of all switches in the VTP domain. A VTP domain is an administrative group; all switches within that group
must have the same VTP domain name configured, or they do not synchronize databases.
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CCNP SWITCH 642-813 Quick Reference by Denise Donohue