Link Redundancy

Although a failed network card might not actually stop the server or a system, it might as well. A network server that cannot be used on the network makes for server downtime. Although the chances of a failed network card are relatively low, our attempts to reduce the occurrence of downtime have led to the development of a strategy that provides fault tolerance for network connections.

Through a process called adapter teaming, groups of network cards are configured to act as a single unit. The teaming capability is achieved through software, either as a function of the network card driver or through specific application software. The process of adapter teaming is not widely implemented; though the benefits it offers are many, so it's likely to become a more common sight. The result of adapter teaming is increased bandwidth, fault tolerance, and the ability to manage network traffic more effectively. These features are broken down into three sections:

  • Adapter fault tolerance The basic configuration enables one network card to be configured as the primary device and others as secondary. If the primary adapter fails, one of the other cards can take its place without the need for intervention. When the original card is replaced, it resumes the role of primary controller.

  • Adapter load balancing Because software controls the network adapters, workloads can be distributed evenly among the cards so that each link is used to a similar degree. This distribution allows for a more responsive server because one card is not overworked while another is under worked.

  • Link aggregation This provides vastly improved performance by allowing more than one network card's bandwidth to be aggregatedcombined into a single connection. For example, through link aggregation, four 100MBps network cards can provide a total of 400MBps bandwidth. Link aggregation requires that both the network adapters and the switch being used support it. In 1999, the IEEE ratified the 802.3ad standard for link aggregation, allowing compatible products to be produced.