Cisco Switch
S(config-if)#switchport mode dynamic auto Default on a lot of Cisco switches but
is changing to dynamic desirable on most new switches.
S(config-if)#switchport
mode dynamic desirable Makes the interface actively attempt to convert the link
to a trunk link.
S(config-if)#switchport mode trunk Puts the interface into
permanent trunking mode and negotiates to convert the neighboring link into a
trunk link. The interface becomes a trunk interface even if the neighboring
interface is in access mode.
S(config-if)#switchport nonegotiate Prevents the
interface from generating DTP (Dynamic Trunk Protocol, the protocol that
negotiates trunking modes) frames. Interface must first be set to either trunk
or access.
access + dynamic auto = access
access + dynamic desirable = access
access + trunk = traffic in the native VLAN will cross the link successfully but other VLAN’s traffic will not
dynamic auto + dynamic auto = access
dynamic auto + dynamic desirable = trunk
dynamic auto + trunk = trunk