Link Aggregation Overview
Link Aggregation Control Protocol (LACP) is part of the IEEE specification (802.3az) that allows you to bundle several physical ports together to form a single logical channel (LAG). LAGs multiply the bandwidth, increase port flexibility, and provide link redundancy between two devices.
Two types of LAGs are supported:
- Static--A LAG is static if the LACP is disabled on it. The group of ports assigned to a static LAG are always active members.
- Dynamic--A LAG is dynamic if LACP is enabled on it. The group of ports assigned to dynamic LAG are candidate ports. LACP determines which candidate ports are active member ports. The non-active candidate ports are standby ports ready to replace any failing active member ports.
Load Balancing
Traffic forwarded to a LAG is load-balanced across the active member ports, thus achieving an effective bandwidth close to the aggregate bandwidth of all the active member ports of the LAG.
Traffic load balancing over the active member ports of a LAG is managed by a hash-based distribution function that distributes Unicast and Multicast traffic based on Layer 2 or Layer 3 packet header information.
The switch supports two modes of load balancing:
LAG Management
In general, a LAG is treated by the system as a single logical port. In particular, the LAG has port attributes similar to a regular port, such as state and speed.
The switch supports eight LAGs.
Every LAG has the following characteristics:
- All ports in a LAG must be of the same media type.
- To add a port to the LAG, it cannot belong to any VLAN except the default VLAN.
- Ports in a LAG must not be assigned to another LAG.
- No more than eight ports are assigned to a static LAG and no more than 16 ports can be candidates for a dynamic LAG.
- All the ports in a LAG must have auto-negotiation disabled, although the LAG can have auto-negotiation enabled.
- When a port is added to a LAG, the configuration of the LAG is applied to the port. When the port is removed from the LAG, its original configuration is reapplied.
- Protocols, such as Spanning Tree, consider all the ports in the LAG to be one port.