Overview:
Port Aggregation Protocol (PAgP) is another option when configuring EtherChannels
Study Notes:
- PAgP is a Cisco proprietary protocol
- It uses the multicast address of 01-00-0C-CC-CC-CC
- Channel mode must be set to "auto" or "desirable" to specify a PAgP port-channel
- Auto - Enable PAgP only if a PAgP device is detected
- Desirable - Enable PAgP unconditionally
- In other words, desirable sends requests and auto does not. If both sides are auto than a PAgP link will not form.
- At least one side or both must be desirable for a PAgP link to form
- During PAgP negotiation, it ensures all links are configured the same with the same speed and duplex else they aren't allowed to participate in the PAgP channel. This prevents loops.
- Maximum number of links in port-channel is 8
- It is recommended to configure 1, 2, 4 or 8 ports in the EtherChannel
- A drawback to PAgP is that it doesn't support participating interfaces being on different physical switches. If you are using VSS, or stacked switches, or device redundancy through virtualization, then PAgP won’t work.
PacketTracer Lab: CCNA-2.9.b-How-to-configure-PAgP-Port-Channels.pkt
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