Modifying LACP Mode and Parameters on an Existing vLAG Configuration

You can modify the LACP mode as part of an existing vLAG configuration using the following command to change parameters like LACP mode or timeout:

CLI (network-admin@switch) > vlag-modify

Configuring a (v)LAG in LACP fallback mode individual (vs. bundle) allows it to operate as individual ports in the absence of proper LACP negotiation with a network peer. This configuration is useful with hosts with multiple network interfaces that for example need to boot from a server on the network prior to booting the operating system on the local hard drive (this is known as PXE boot, based on the Pre-Boot Execution Environment). In this scenario the hosts would have to use individual ports until they can boot the operating system and start using LACP.

Once LACP is running and port members receive LACP PDUs from their peers, then the port members of the configured vLAG can get bundled to operate as a trunk.

With this configuration, Netvisor ONE logically prepares the trunk on the switch but does not add any of the port members to it. The ports continue to operate individually until LACP PDUs are heard on them. At that point, the dynamic negotiation process is started, proper compatibility and communication is verified between the peers and the bundling process is carried out if all conditions are met. Only then all member ports cease to operate individually and are aggregated together as an operational trunk.

To give hosts enough time to PXE boot, a fallback timeout interval parameter is used (with a default value of 50 seconds). If no LACP PDUs are received for the number of seconds configured as the fallback timeout, the LACP logic checks if the LACP negotiation interval (lacp-timeout) has expired. If it has, then the port members fall back to individual mode. If it has not, another fallback timer is scheduled with a value equal to the fallback timeout.

For example:

• The LACP fallback timeout is set to 50 seconds and the LACP negotiation interval is set to 90 seconds (default).

• After 50 seconds, the fallback timer is rescheduled because the LACP negotiation interval has not expired yet.

• After an additional 40 seconds (90 seconds total), the LACP negotiation interval expires.

• Another 10 seconds pass (100 seconds total) when the fallback timer expires, no LACP PDUs have been received (for example due to the host still booting), then the member ports fall back to individual ports.

Both the negotiation/bundling and the fallback cases described above represent the on-demand characteristic of LACP-based port aggregation process (applicable to both vLAGs and normal trunks).