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

9.2. Application of Link Aggregation

Figure 9-1 depicts a number of situations where link aggregation is commonly deployed. These include:

• Switch-to-switch connections

• Switch-to-station (server or router) connections

• Station-to-station connections

Figure 9.1. Aggregated links

9.2.1. Switch-to-Switch Connections

In Figure 9-1, the capacity of each of the workgroup-to-campus switch connections has been increased by aggregating two 100 Mb/s links, effectively creating a 200 Mb/s channel. Network availability has been increased as well; the failure of either of the physical links comprising the aggregate will not sever communications to the backbone. The capacity of the channel may be reduced in this case, but connectivity is not lost.

Note that the workgroup switches in this catenet are 24-port, 100 Mb/s–only devices, a common and popular configuration for bounded switches. These units have no high-speed uplink port for connecting to servers or backbone switches. By aggregating multiple links, you can create higher-speed connections without a hardware upgrade. Aggregation thus implies a tradeoff between port usage and additional capacity for a given device pair; link aggregation reduces the number of ports available for connection to other devices.

Of course, the switch itself must be designed to support link aggregation. Depending on the internal architecture (both hardware and ...