Apple 10.6 manual Link Aggregation

Link Aggregation

Although not common, the failure of a switch, cable, or network interface card can cause your server to become unavailable. To eliminate these single points of failure, you can use link aggregation or trunking. This technology, also known as IEEE 802.3ad, is built into Mac OS X and Mac OS X Server.

Link aggregation allows you to aggregate or combine multiple physical links connecting your Mac to a link aggregation device (a switch or another Mac) into a single logical link. The result is a fault-tolerant link with a bandwidth equal to the sum of the bandwidths of the physical links.

For example, you can set up an Xserve with four 1-Gbit/s ports (en1, en2, en3, and en4) and use the Network pane of System Preferences to create a link aggregate port configuration (bond0) that combines en1, en2, en3, and en4 into one logical link.

The resulting logical link will have a bandwidth of 4 Gbit/s. This link also provides fault tolerance. If a physical link fails, your Xserve’s bandwidth will shrink, but the Xserve can still service requests as long as not all physical links fail at once.

The following illustration shows four Ethernet ports aggregated as a single interface:

server1.example.com

400 Mbit/s bond0

en1 en2 en3 en4

4 x 100 Mbit/s

Switch

Link aggregation also allows you to take advantage of existing or inexpensive hardware to increase the bandwidth of your server. For example, you can form a link aggregate from a combination of multiple 100-Mbit/s links or 1-Gbit/s links.

Chapter 7    Ongoing System Management

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