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Link Aggregation

A Link Aggregation Group (LAG) optimizes the usage of switch ports by linking a group of ports to form a single, logical, higher-bandwidth link. Aggregating ports multiply the bandwidth and increase port flexibility for Sophos Switch.

Link Aggregation is used most commonly to link high-bandwidth devices, such as servers, to the backbone of a network.

The participating ports form a port trunk group. Because you must configure all ports of the trunk group to operate in the same manner, the configuration of one port of the trunk group is applied to all ports of the trunk group. Thus, you'll only need to configure any one port in the group. A specific data communication packet is always transmitted over the same port in a trunk group. This ensures the delivery of individual frames of a data communication packet will be received in the correct order. The traffic of the LAG is balanced among the ports according to aggregate arithmetic. If the connections of one or several ports are broken, the traffic of these ports will be transmitted on the normal ports to guarantee connection reliability.

When aggregating ports, the ports and LAG must meet the following conditions:

  • All ports within a LAG must be the same media/format type.
  • The port can't have VLAN configured.
  • The port isn't assigned to another LAG.
  • The port doesn't have auto-negotiation mode configured.
  • The port must be in full-duplex mode.
  • The LAG ports must use the same ingress filtering and tagged modes.
  • All ports in the LAG must have the same priority.
  • You can only configure ports as LACP ports when the ports aren't part of a previously configured LAG.

LACP is a dynamic protocol that helps automate the configuration and maintenance of LAGs. Its main purpose is to configure individual links automatically to an aggregate bundle while adding new links, and to help recover from link failures if needed. LACP monitors links to verify if they're connected to the authorized group. You must turn on LACP on the switch's trunk ports initially for devices that support the protocol.