DTP sends out adverisments every 30 seconds and ports can become a trunk either by configuration or dynamically. A port can be in one of five modes:
ACCESS: A user port in a single clan.
TRUNK: A port has negotiated its a trunk with its peer.
NON-NEGOTIATE: The port is a trunk and does not negotiate with any peers.
DYNAMIC DESIRABLE: Dynamically negotiates with its peer and will become a trunk if the other end is set to trunk,dynamic desirable or dynamic auto.
DYNAMIC AUTO: Passively waits to negotiate DTP with its peer. The peer must be configured as a trunk or dynamic desirable.