156 | Link Aggregationw w w . d e l l . c o m | s u p p o r t . d e l l . c o m Server-Facing LAGsServer-facing ports are configured as individual ports by default. If a server NIC is configured forLACP-based NIC teaming, server-facing ports are automatically configured as part of dynamic LAGs. TheLAG range 1 to127 is reserved for server-facing LAGs.Once the Aggregator receives LACPDU from server-facing ports, the information embedded in theLACPDU (remote-system ID and port key) is used to form a server-facing LAG. The LAG/port-channelnumber is assigned based on the first available number in the range 1 to 127. For each unique remotesystem-id and port-key combination, a new LAG is formed and the port automatically becomes a memberof the LAG.All ports with the same combination of system ID and port key automatically become members of thesame LAG. Ports are automatically removed from the LAG if the NIC teaming configuration on aserver-facing port changes or if the port goes operationally down. Also, a server-facing LAG is removedwhen the last port member is removed from the LAG.The benefit of supporting a dynamic LAG is that the Aggregator's server-facing ports can toggle betweenparticipating in the LAG or acting as individual ports based on the dynamic information exchanged with aserver NIC. LACP supports the exchange of messages on a link to allow their LACP instances to:• Reach agreement on the identity of the LAG to which the link belongs.• Attach the link to that LAG.• Enable the transmission and reception functions in an orderly manner.• Detach the link from the LAG if one of the partner stops responding.LACP ModesThe Aggregator supports only LACP active mode as the default mode of operation. In active mode, a portinterface is considered to be not part of a LAG but rather in an active negotiating state.A port in active mode automatically initiates negotiations with other ports by sending LACP packets. Ifserver-facing ports are configured for LACP-based NIC teaming, LACP negotiations will take place toaggregate the port in a dynamic LAG. If server-facing ports are not configured for LACP-based NICteaming, a port will be treated as an individual port in the active negotiating state.Auto-Configured LACP TimeoutLACPDUs are exchanged between port channel (LAG) interfaces to maintain LACP sessions. LACPDUsare transmitted at either at a slow or fast transmission rate, depending on the LACP timeout valueconfigured on the partner system.The timeout value is the amount of time that a LAG interface waits for a PDU from the partner systembefore bringing the LACP session down. The default timeout is long-timeout (30 seconds) and is notuser-configurable on the Aggregator.
