The All-New Switch Book: The Complete Guide to LAN Switching Technology, Second Edition

9.1. Link Aggregation Benefits

By taking multiple LAN connections and treating them as a unified, aggregated link, you can achieve practical benefits in many applications. In particular, aggregated links can provide:

• Increased link capacity: The total capacity of an aggregated link is the sum of the capacities of the individual links composing the aggregate. This is the primary reason most users deploy aggregation — to improve performance when a traditional individual link is a performance-limiting element or is overwhelmed by a sustained overload condition.

• Incremental capacity increase: While LAN technology offers a variety of data rates, the available options are usually separated by an order-of-magnitude improvement, such as 10 Mb/s, 100 Mb/s, or 1000 Mb/s. Link aggregation can be used to fill in the gaps when an intermediate performance level is more appropriate; a factor of 10 increase may be overkill in some environments.

• Higher link availability: A properly designed link aggregation scheme will prevent the failure of any single component link from disrupting communications between the interconnected devices. For links requiring high availability (for example, backbone connections), this feature may be more important than the concomitant capacity increase. The aggregated link will fail soft; the loss of a link within an aggregation reduces the available capacity but does not disrupt communications entirely. Note that the Spanning Tree Protocol discussed in Chapter 5, "Loop ...