Port Aggregation Protocol (PAgP)

Port Aggregation Protocol (PAgP) is a Cisco priority standard that allows multiple physical interfaces to be aggregated into one logical link.
Each logical link can contain up-to 8 physical members. All member ports within the bundle must have the same physical settings such as port type, speed and duplex.

Modes

Within PAgP there are 2 modes available, Desirable and Auto.

  • Desirable – Enables PAgP unconditionally ; Actively sends packets to its neighbor in order to negotiate PAgP.
  • Auto – Awaits PAgP packets from its neighbor before initiating PAgP

In addition to these modes the are 2 forms of operation, Non-Slient and Slient.

  • Non-Silent – The bundle is not initiated until bidirectional traffic is detected. Non-Slient provides the ability to protect against unidirectional failures on fibre based connections.
  • Silent – Default on the majority of copper based switches. With this form of operation the bundle is initiated even if no traffic is seen.

Create PAgP Bundle

Creating an LACP bundle is simple, you define the port-channel number onto each of the interfaces.

Switch(config-if)#interface range gi0/1-3
Switch(config-if-range)#channel-group 33 mode desirable
Creating a port-channel interface Port-channel 33

Learning Method

There are 2 methods for learning, physical and aggregated.

  • aggregation-port – Default. The switch learns the addresses on the aggregated port. Traffic is sent back to the source using any of the ports within the bundle.
  • physical-port – The switch learns the source MAC address on the physical port the packet has come in on. Traffic is then sent back out the same physical port.

Note : This is configured within the interface configuration.

Switch(config-if)# pagp learn-method physical-port

Show Commands

In addition to the show pagp …. commands you can also review the status of the portchannel via the command below,

Switch#show etherchannel 33 summary

 

Rick Donato
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