Link aggregation vs. fault tolerance

Customers with fault-tolerant Fast Ethernet adapters in full-duplex operation can theoretically accrue performance benefits from either link aggregation or load balancing. However, the two technologies operate very differently. Network administrators need to understand these differences if they are planning to integrate adapter fault tolerance in their network.

Link aggregation and load balancing both leverage the additional throughput provided by redundant server-to-switch connections to improve performance. While link aggregation provides a standard method to distribute traffic evenly in both directions, load balancing is proprietary. Not surprisingly, because load-balancing solutions are proprietary, they use a variety of schemes for distributing traffic across available links.

Several load-balancing solutions offer a combination of 1) unidirectional or 2) unidirectional and bidirectional links, to and from the system. Although the links are full-duplex, if traffic is only transmitted unidirectionally, the link theoretically supports a half-duplex connection. However, a product that supports bidirectional traffic on all links will achieve the best throughput benefits.

The other main difference between the two technologies is that, with a load-balancing solution, each adapter retains a unique media access control (MAC) address. Link aggregation, on the other hand, requires that all network interface cards logically combine to form one adapter, and therefore, all assume the same MAC address. Because of this MAC scheme, a link aggregation solution mandates that products attached to both ends of the link support link aggregation, and therefore, associate the same remote MAC address with several links. A load-balancing solution requires no such support and can theoretically interoperate with any device.

Customers with fault-tolerant adapters who deploy link aggregation at the adapter may achieve high throughput but will need to purchase switches that support link aggregation. However, if those customers use load balancing, instead, they can achieve high throughput rates without purchasing new switches.

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