Hello folks, as we know, LACP and PagP are both used to form the eth-trunk between the devices, in this post, I will introduce briefly what's is the difference between them.

LACP, knows as link aggregation control protocol, is used to control the links to form the eth-trunk, which could helps to enrich the link bandwidth. lt's based on the standard IEEE 802.3ad, so that the LACP could allow the eth-trunk established between the devices of the different vendors.

PAgP, the abbreviation of aggregation protocol, is a private protocol developed by Cisco. As LACP, PAgP also helps to check the link parameters to form the eth-trunk, while the eth-trunk is called port aggregation in Cisco. Because of the PAgP is a private protocol, so it cannot be used to establish the eth-trunk between different vendors' devices.

In LACP, the device send out the LACPDU to negotiate with the remote device. In the LACPDU packets, the system priority, MAC address and port priority are included, those information are used to select the ports to join the eth-trunk.

There are three interface modes in both LACP and PagP.

For LACP, when the interface are set to passive mode, the LACPDU packets wouldn't be sent out from this interface, while it will listen to the remote device, if LACPDU packets are received on these passive interface, it will start calculating to figure out if it will be selected as an active interface to forward traffic flow. If the active mode is configured, the interface will send LACPDU packets spontaneously.

For PagP there are the corresponding interface modes. The PagP interface work mode auto is same as the passive mode in LACP, while desiable mode is same as the active mode in LACP.