Technology: Switching
Area: Link aggregation
Vendor: Cisco
Software: 12.X , 15.X
Platform: Catalyst platforms

Port Aggregation Protocol (PAgP) is a Cisco proprietary protocol which is used for the automated, logical aggregation of Ethernet switch ports, known as an Ether Channel. There are two modes of PAgP:

• Auto mode: it passively negotiates PAgP aggregation. If the remote end of the link is also configured with Auto mode, a PAgP EtherChannel will not form. Auto side is waiting for negotiation to start from the other end.
• Desirable mode: that actively negotiates PAgP. The remote end must be configured in Auto or Desirable mode for a PAgP EtherChannel to form.

To configure interface to talk actively with PAgP packects (desirable mode):

Switch#configure terminal
Switch(configure)#interface range f0/1 - 2
Switch(configure-if-range)#channel-group 1 mode desirable
Switch(configure-if-range)#end



To verify if the ether channel is formed use following show command:

Switch# show ethernet channel summary

To configure interface to wait with PAgP to respond to PAgP packets from other end (auto mode):

Switch#configure terminal
Switch(configure)#interface range f0/1 - 2
Switch(configure-if-range)#channel-group 1 mode auto
Switch(configure-if-range)#end


To verify if the ether channel is formed use following show command:

Switch# show ethernet channel summary