Overview of Link Aggregation

Link aggregation allows you to bundle multiple physical Ethernet links to form a single logical trunk providing enhanced performance and redundancy. The aggregated trunk is referred to as a Link Aggregation Group (LAG). The LAG is viewed as a single logical link by connected devices, the Spanning Tree Protocol, IEEE 802.1Q VLANs, and so on. When one physical link in the LAG fails, the other links stay up. A small drop in traffic is experienced when the link carrying the traffic fails.

To configure links to form a LAG, the physical links must be of the same speed. Link aggregation can be done by statically configuring the LAG, or by dynamically configuring the LAG using the IEEE 802.1AX Link Aggregation Control Protocol (LACP).

When queuing traffic from multiple input sources to the same output port, all input sources are given the same weight, regardless of whether the input source is a single physical link or a trunk with multiple member links.

Link aggregation maintains the following benefits:

  • Increased bandwidth (The logical bandwidth can be dynamically changed as the demand changes.)
  • Increased availability
  • Load sharing
  • Rapid configuration and reconfiguration

You can use a single interface to configure any of the following LAG types:

  • Static LAGs: These LAGs are manually-configured aggregate links containing multiple ports. In static link aggregation, links are added into a LAG without exchanging any control packets between the partner systems. The distribution and collection of frames on static links is determined by the operational status and administrative state of the link.
  • Dynamic LAGs: A dynamic LAG type uses the Link Aggregation Control Protocol (LACP), to maintain aggregate links over multiple ports. Typically, two partner systems sharing multiple physical Ethernet links can aggregate a number of those physical links using LACP. LACP creates a LAG on both partner systems and identifies the LAG by the LAG ID. All links with the same administrative key and all links that are connected to the same partner switch become members of the LAG. LACP PDUs are exchanged between ports on each device to determine if the connection is active. The LAG shuts down ports if their connections are no longer active.
  • Keep-alive LAGs: In a keep-alive LAG, a single connection between a single port on two RUCKUS devices is established. In a keep-alive LAG, LACP PDUs are exchanged between the two ports to determine if the connection between the devices is still active. If it is determined that the connection is no longer active, the ports are blocked.
    Note: In earlier releases, the keep-alive LAG functionality was referred to as Single Link LACP.
Beginning with FastIron release 08.0.61, new LAG configuration procedures supersede any prior configurations procedures for LAGs and Dynamic Link Aggregation. When a RUCKUS device is upgraded to FastIron 08.0.61 or later, any configurations for LAGs or Dynamic Link Aggregation defined in releases prior to FastIron 08.0.61 are converted to a FastIron 08.0.61-compatible (or later) LAG configuration.

In this section:

  1. LAG Virtual Interface
  2. LAG Formation Rules
  3. Error Disable
    LAG ports with operational speeds that do not match the LAG virtual interface are error-disabled with the "lag-oper-speed-mismatch" reason. Error-disabled ports can be recovered if the operational speed is adjusted to match the LAG virtual interface speed.
  4. Error Disable Recovery
    The error disable auto-recovery mechanism is used to bring the ports out of the error-disabled state. You can use the speed-duplex command to change the configured speed of the member ports, which will result in an operational speed change implicitly. Depending on the peer speed duplex setting, either the port will come up in a negotiated operational speed or the port will remain down if the speed does not match the peer speed configuration. Using the speed-duplex command on VLAG interfaces flaps the LAG member ports; all member ports that come up will subsequently have the same operational speed.
  5. LAG Virtual Anchor Speed
    The LAG interface retains the reference operational speed as long as the member port is up. When the last port goes down, the operational speed is reset. Depending on the subsequent sequence of ports coming up, the LAG interface reference speed is used.
  6. Use Cases
    Some ports become error-disabled if their operational speeds differ. Use the speed-duplex command to align speeds and select appropriate ports for aggregation to achieve optimal bandwidth.
  7. Configuration Notes for FastIron Devices in a Traditional Stack
  8. Maximum number of LAGs
  9. Upgrade and Downgrade Notes
  10. LAG Load Sharing
  11. LAG Hashing on Stacking Products
  12. Symmetric Load Balancing
    Symmetric load balancing is a mechanism of interchanging the source and destination addresses to ensure that bidirectional traffic specific to a particular source and destination address pair flows out of the same member of a trunk group.
Parent topic: Link Aggregation Group