PAgP
The PAgP or Port Aggregation Protocol is a network protocol for dynamic bundling of multiple physical Ethernet connections at Cisco .
The functional principle of the proprietary PAgP is similar to the open LACP . By sending out so-called Hello packets, the PAgP recognizes whether two switches are directly connected via more than one physical connection. If this is the case and PAgP is configured on both sides, these multiple physical connections are combined to form a new logical connection, the so-called Etherchannel .
PAgP should only be used in conjunction with a variant of the Spanning Tree Protocol so that there are no unwanted loops in the network.