Understanding LAG Path Selection and Load Balancing

For Layer 2 back-to-back connectivity, Pluribus Netvisor ONE software supports the standard link aggregation technology in order to combine multiple network connections into a logical pipe called a Link Aggregation Group (LAG), or ‘(port) trunk’, which can provide redundancy in case of single or multiple link failure.

Figure4-1: Two-port LAG Example

Netvisor ONE also supports link aggregation across two redundant chassis to implement multi-pathing without requiring the creation of Layer 2 loops and the use of the Spanning Tree protocol. This feature is called vLAG (Virtual Link Aggregation Group) on a switch cluster.

Figure4-2: Two-port vLAG Example

Both the aforementioned technologies perform path selection in hardware using a high-performance technology called packet field hashing.

What that means is that the hardware extracts a number of packet fields and with them performs a special calculation to generate a hardware index. Such index is then used to select an egress physical port for a (v)LAG.