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Link Aggregation Control Protocol (LACP)
A link aggregation group (LAG), referred to as a port channel by the Dell Networking OS, can provide both
load-sharing and port redundancy across line cards. You can enable LAGs as static or dynamic.
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:
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Link Aggregation Control Protocol (LACP)