LACP fallback in a VLT configuration allows VLT peers to control member ports of a port-channel. It includes the following characteristics:
- The LACP fallback feature is applied to support PXE boot from servers with NIC teaming or bonding.
- Use the lacp fallback enable command on the VLT port-channels on both of the VLT nodes that are connected to servers.
- A member port in the VLT port-channel is made active if the LACP PDUs are not received from the server within the LACP fallback timeout period, which is set to 15 seconds by default.
- LACP fallback in VLT allows the PXE boot server to establish a connection over a single port, download the boot image, and continue the boot process.
- After the server boots, it establishes the LACP port-channel, which allows the VLT port-channels to function like a regular VLT port-channel after the LACP PDUs are received.
- PXE boot uses untagged packets. Configure the VLT port-channel as an untagged member in the respective VLAN to reach the PXE/DHCP server.
- During LACP fallback, one VLT port-channel member port is kept active, while other ports are kept in an inactive state.
The active port is selected based on the following order:
- The port with the lowest LACP port priority is kept active.
- The lowest port number is kept active if the port priority is the same or the default port.
- The port on the VLT node with the lowest system MAC address is kept active if the port numbers are the same in both VLT nodes.