Hello David
You have some great questions regarding EtherChannel and PAGP. Let’s dive into them:
PAGP Priority: The PAGP priority is used to determine which end of the EtherChannel will become the master. The device with the lower priority value will become the master. The master device is responsible for sending PAGP packets to its partner device to negotiate EtherChannel formation. While it’s true that all ports should be transmitting PAGP messages, the priority is used to decide which end takes the active role in the formation of the EtherChannel.
PAGP Timer: The pagp timer command is used to determine after how long PAgP informational packets are considered valid.
The age value indicates the time in seconds since the last PAgP packet was received from the neighbor. Now it does seem strange that your Age value should exceed the PAgP timer. I labbed this up and did some experimentation and in no case did the value exceed 30 seconds. And this makes sense, because there is another value that is involved here, which is the hello timer. This has a value of 30 seconds, and cannot be changed. You can see this value in the output of the show pagp internal command. Can you share with us the full configuration of the physical interfaces and the portchannel interface of your configuration? For your reference, here is the command reference for the pagp timer command:
PAGP Learning Modes: You’re correct in your understanding of the two learning modes. In physical mode, MAC addresses are learned on the physical port, while in aggregate mode, MAC addresses are learned on the Port-Channel interface. I tried recreating your scenario by configuring the learning to physical on the interfaces in CML and found I got the same results as you. I don’t know why, but I’d be interested to try this out on real devices at some point.
I wish I could have been more helpful with your questions, but in the meantime, I hope this helped you to further understand the technology of EtherChannel.
I hope this has been helpful!
Laz