Use the option that provides the greatest variety in your configuration. For example, if the traffic on a channel is going only to a single MAC address, using the destination-MAC address always chooses the same link in the channel. Using source addresses or IP addresses might result in better load-balancing. EtherChannel and Switch Stacks If a stack member that has ports participating in an EtherChannel fails or leaves the stack, the active switch removes the failed stack member switch ports from the EtherChannel. The remaining ports of the EtherChannel, if any, continue to provide connectivity.
When a switch is added to an existing stack, the new switch receives the running configuration from the active switch and updates itself with the EtherChannel-related stack configuration. The stack member also receives the operational information (the list of ports that are up and are members of a channel). When two stacks merge that have EtherChannels configured between them, self-looped ports result. Spanning tree detects this condition and acts accordingly. Any PAgP or LACP configuration on a winning switch stack is not affected, but the PAgP or LACP configuration on the losing switch stack is lost after the stack reboots.
Switch Stack and Port Aggregation Protocol With PAgP, if the active switch fails or leaves the stack, the standby switch becomes the new active switch. The new active switch synchronizes the configuration of the stack members to that of the active switch. The PAgP configuration is not affected after an active switch change unless the EtherChannel has ports residing on the old active switch. Switch Stacks and Link Aggregation Control Protocol With LACP, the system ID uses the stack MAC address from the active switch. When an active switch fails or leaves the stack and the standby switch becomes the new active switch, the LACP system ID is unchanged.
By default, the LACP configuration is not affected after the active switch changes. Default EtherChannel Configuration The default EtherChannel configuration is described in this table. Table 3: Default EtherChannel Configuration Configuring EtherChannels EtherChannel and Switch Stacks Feature Default Setting Channel groups None assigned. Port-channel logical interface None defined. PAgP mode No default. PAgP learn method Aggregate-port learning on all ports. PAgP priority 128 on all ports. LACP mode No default. LACP learn method Aggregate-port learning on all ports. Configuring EtherChannels 10