Administrator Guide

Link Aggregation Control Protocol (LACP)
Introduction to Dynamic LAGs and LACP
The Dell Networking OS uses LACP to create dynamic LAGs. LACP provides a standardized means of exchanging information between
two systems (also called Partner Systems) and automatically establishes the LAG between the systems.
The benefits and constraints of a LAG are basically the same as a port channel, as described in Port Channel Interfaces in the Interfaces
chapter. The unique benefit of a dynamic LAG is that its ports can toggle between participating in the LAG or acting as dedicated ports,
whereas ports in a static LAG must be removed from the LAG in order to act alone.
LACP permits the exchange of messages on a link to allow their LACP instances to:
• Reach an agreement on the identity of the LAG to which the link belongs.
• Move the link to that LAG.
• Enable the transmission and reception functions in an orderly manner.
The Dell Networking implementation of LACP is based on the standards specified in the IEEE 802.3: “Carrier sense multiple access with
collision detection (CSMA/CD) access method and physical layer specifications.”
LACP functions by constantly exchanging custom MAC protocol data units (PDUs) across local area network (LAN) Ethernet links. The
protocol packets are only exchanged between ports that are configured as LACP capable.
Important Points to Remember
• LACP allows you to add members to a port channel (LAG) as long as it has no static members. Conversely, if the LAG already contains
a statically defined member (the channel-member command), the port-channel mode command is not permitted.
• A static LAG cannot be created if a dynamic LAG using the selected number exists.
• No dual membership in static and dynamic LAGs:
• If a physical interface is a part of a static LAG, the port-channel-protocol lacp command is rejected on that interface.
• If a physical interface is a part of a dynamic LAG, it cannot be added as a member of a static LAG. The channel-member
tengigabitethernet x/y command is rejected in the static LAG interface for that physical interface.
• A dynamic LAG can be created with any type of configuration.
• There is a difference between the shutdown and no interface port-channel commands:
• The shutdown command on LAG “xyz” disables the LAG and retains the user commands. However, the system does not allow
the channel number “xyz” to be statically created.
• The no interface port-channel channel-number command deletes the specified LAG, including a dynamically created
LAG. This command removes all LACP-specific commands on the member interfaces. The interfaces are restored to a state that is
ready to be configured.
NOTE:
There is no configuration on the interface because that condition is required for an interface to be part of
a LAG.
• You can configure link dampening on individual members of a LAG.
LACP Modes
Three LACP configuration modes are supported — Off, Active, and Passive.
• Off — In this state, an interface is not capable of being part of a dynamic LAG. LACP does not run on any port that is configured to
be in this state.
• Active — In this state, the interface is said to be in the “active negotiating state.” LACP runs on any link that is configured to be in
this state. A port in Active state also automatically initiates negotiations with other ports by initiating LACP packets.
• Passive — In this state, the interface is not in an active negotiating state, but LACP runs on the link. A port in Passive state also
responds to negotiation requests (from ports in Active state). Ports in Passive state respond to LACP packets.
LAGs are supported in the following cases:
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