[Cisco] Secondary Aggregator Ports Po1A or Po2A are Created

Refer: h**p://www.ciscosystems.org.ro/en/US/tech/tk389/tk213/technologies_configuration_example09186a0080094470.shtml#tshoot
Secondary Aggregator Ports Po1A or Po2A are Created

A secondary aggregator port will be created in the LACP process when the ports you are bundling are not compatible with each other, or with their remote peers. The secondary aggregator port will have the ports which are compatible with others.

Switch#show etherchannel summary
Flags: D - down P - in port-channel
I - stand-alone s - suspended
H - Hot-standby (LACP only)
R - Layer3 S - Layer2
U - in use f - failed to allocate aggregator

u - unsuitable for bundling
Number of channel-groups in use: 6
Number of aggregators: 8

Group Port-channel Protocol Ports
------+-------------+-----------+-----------------------------------------
1 Po1(SU) LACP Gi1/16(P) Gi10/1(P) Gi10/2(P)
2 Po2(SD) LACP
2 Po2A(SU) LACP Gi1/15(P) Gi10/3(P) Gi10/4(P)
3 Po3(SU) LACP Gi1/14(P) Gi10/5(P) Gi10/6(P)
4 Po4(SD) LACP
4 Po4A(SU) LACP Gi1/13(P) Gi10/7(P) Gi10/8(P)
5 Po5(SU) LACP Gi1/12(P) Gi10/9(P) Gi10/10(P)
6 Po6(SU) LACP Gi1/11(P) Gi10/11(P) Gi10/12(P)
Configure all LAN ports in an EtherChannel to operate at the same speed and in the same duplex mode. LACP does not support half-duplex. Half-duplex ports in an LACP EtherChannel are put in the suspended state.

If you configure an EtherChannel from trunking LAN ports, verify that the trunking mode is the same on all the trunks. LAN ports in an EtherChannel with different trunk modes can operate unpredictably.

LAN ports with different STP port path costs can form an EtherChannel as long they are compatibly configured with each other. If you set different STP port path costs, the LAN ports are not incompatible for the formation of an EtherChannel.