what is EtherCahannel? | Link Aggregation Control Protocol (LACP) | Port Aggregation Protocol (LAgP)

EtherChannel technology enables you, to bundle multiple physical interfaces into one logical channel to increase the bandwidth on point-to-point links. In addition, EtherChannel provides a way to prevent the need for Spanning Tree Protocol (STP) convergence when only a single port or cable failure occurs.
EtherChannel, a technology that Cisco developed, can bundle up to eight equal-speed links.
Most configuration tasks can be done on the EtherChannel interface instead of, on each individual port.
 EtherChannel relies on the existing switch ports to increase bandwidth. No hardware upgrades are needed.
 Load balancing is possible between links that are part of the same EtherChannel.
 EtherChannel creates an aggregation that STP recognizes as one logical link.
 EtherChannel provides redundancy. The loss of one physical link does not create a change in the topology.
Port Aggregation Protocol (LAgP):
PAgP is a Cisco-proprietary protocol that automatic creation of EtherChannel links. PAgP checks for configuration consistency and manages link additions and failures between two switches. It ensures that when an EtherChannel is created, all ports have the same type of configuration. PAgP uses ON mode:
■ On: This mode forces the interface to channel without PAgP.
■ Desirable mode: The interface initiates negotiations with other interfaces by sending PAgP packets.
■ Auto mode: The interface responds to the PAgP packets that it receives but does not initiate PAgP negotiation.
Link Aggregation Control Protocol (LACP):
The Link Aggregation Control Protocol (LACP) is an IEEE protocol (802.3ad) that allows a switch to negotiate an automatic bundle by sending LACP packets to the peer.
It performs a function similar to PAgP with Cisco EtherChannel. Cisco devices support both PAgP and LACP.
LACP uses the ON mode,
■ On: This mode forces the interface to channel without LACP.
■ Active mode: The interface initiates negotiations with other interfaces by sending LACP packets.
Passive mode: The interface responds to the LACP packets that it receives but does not initiate LACP negotiation.
As with PAgP, the LACP modes must be compatible on the two sides of the EtherChannel.