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What is link aggregation?

Link aggregation is a feature available in managed switches to have multiple physical ports act as a single virtual port with the aggregated capacity of all of the physical ports. It is commonly deployed for backhaul between the MDF and IDF(s) in networks requiring very high local data capacity, such as when using storage area networks (SANs) or in networks consisting of several surveillance IP cameras streaming data to a network video recorder (NVR) or in the MDF. An example application is shown in Figure 1. An aggregated link can also serve to provide redundancy (at reduced capacity) in case one of the connections should be broken.

Figure 1: Example of Link Aggregation to connect a switch to a storage area network (SAN).

 

On any EnGenius switch, a link aggregation group (LAG) can be established under L2 Features   Link Aggregation   Port Trunking, as shown in Figure 2. Up to eight link aggregation groups can be defined on a particular switch, and are referred to as “trunk groups” with port numbers t1 – t8. A physical port can be a member of only one trunk group. The ports that make up a group need not be sequential, though it is often convenient to use sequential ports from a wiring perspective. There is also no limit as to how many physical ports can be aggregated into a single group, until one physically runs out of ports on the switch.

There are two modes defined for establishing a trunk group. In “static” mode, the ports are always considered part of the trunk group, and the switch will always load balance outbound traffic on the trunk port across all of the physical ports. In “LACP” mode, the switch uses Link Aggregation Control Protocol (LACP) to periodically verify that each physical link is established end-to-end, so LACP must be running on both sides of the link (i.e. both switches connected via an aggregated link). It is best practice to use LACP mode to establish an aggregated link between two switches.

Figure 2: Setting up a link aggregation group on an EnGenius managed switch.