Link Aggregation Overview

Link aggregation, or load sharing, is disabled by default. Load sharing allows the switch to use multiple ports as a single logical port, or LAG.



All ports in a LAG must be running at the same speed and duplex setting. Each port can belong to only one LAG.

For example, VLANs see the LAG as a single logical port. And, although you can only reference the master port of a LAG to a Spanning Tree Domain (STPD), all the ports of the LAG actually belong to the specified STPD.

If a port in a load-sharing group (or LAG) fails, traffic is redistributed to the remaining ports in the LAG. If the failed port becomes active again, traffic is redistributed to include that port.



Load sharing must be enabled on both ends of the link, or a network loop may result.
Link aggregation is most useful when:
  • The egress bandwidth of traffic exceeds the capacity of a single link.

  • Multiple links are used for network resiliency.

In both situations, the aggregation of separate physical links into a single logical link multiplies total link bandwidth in addition to providing resiliency against individual link failures.

In modular switches, ExtremeXOS supports LAGs across multiple modules, so resiliency is also provided against individual module failures.

The software supports control protocols across the LAGs, both static and dynamic. If you add the protocols (for example, EAPS, ESRP, and so forth) to the port and then create a LAG on that port, you may experience a slight interruption in the protocol operation. To seamlessly add or delete bandwidth when running control protocols, we recommend that you create a LAG consisting of only one port. Then add your protocols to that port and add other ports as needed.