Port Aggregation Protocol (PAgP) is a Cisco proprietary link aggregation protocol that enables the automatic creation of EtherChannels. By default, PAgP packets are sent between EtherChannel-capable ports in order to negotiate the forming of an EtherChannel. These packets are sent to the destination Multicast MAC address 01-00-0C-CC-CC-CC, which is also the same Multicast address that is used by CDP, UDLD, VTP, and DTP. Figure 33.2 below shows the fields contained within a PAgP frame as seen on the wire: