Link Aggregation, also called trunking or port trunking, is a technique of combining physical network links into a single logical link for increased bandwidth, achieving load balancing and increase fault tolerance. Link aggregation may be used to improve access to public networks by aggregating modem links or digital lines. Link aggregation may also be used in the enterprise network to build multigigabit backbone links between Gigabit Ethernet switches.
Networking vendors have long offered a functionality for aggregating bandwidth across multiple physical links to a switch. This allows a machine (frequently a server) to treat multiple physical connections to switch units as a single logical link.
The standard for this technology is IEEE 802.3ad. The standard lists the following main goals and objectives for Link Aggregation:
- Increased bandwidth
- Increased availability
- Linearly incremental bandwidth
- Load sharing
- Automatic configuration
- Rapid configuration and reconfiguration
- Deterministic behavior
- Low risk of duplication or mis-ordering of frames
There are a number of situations where Link Aggregation is commonly deployed:
- Switch-to-switch connections: In this scenario, multiple workgroups are joined to form one aggregated link. By aggregating multiple links, the higher speed connections can be achieved without hardware upgrade.
- Switch-to-station (server or router) connections: In this case the higher performance channel is created without having to upgrade to higher-speed LAN hardware.
Station-to-station connections: In this case, no switches are involved at all. In some cases, higher-speed NICs may not even be available for a particular server platform, making link aggregation the only practical choice for improved performance.
Link Aggregation and Trunking
Related Terms: Port Trunking, IEEE 802.3ad, Load Balancing