How to configure EtherChannel Port Aggregation Protocol (PAgP) in Cisco Switches

EtherChannel is a port link aggregation technology developed by Cisco, which provides fault-tolerant high-speed links between Switches, Routers, and Servers. EtherChannel technology allows multiple physical Ethernet links (Fast EtherNet or Gigabit Ethernet) to combine into one logical channel.

There are two protocols used for negotiating EtherChannel and Link Aggregation. We can configure EtherChannel in three ways in Cisco Switches.

1. Port Aggregation Protocol (PAgP) - Cisco Proprietary protocol
2. IEEE Link Aggregation Control Protocol (LACP) - Industry Standard
3. Manual Etherchannel Configuration - Without using any negotiation protocol listed above

Port Aggregation Protocol (PAgP) is a Cisco proprietary protocol. Therefore Port Aggregation Protocol (PAgP) can be used to negotiate EtherChannels only between Cisco switches.

Follow these steps to configure EtherChannel using Port Aggregation Protocol (PAgP) in Cisco Switches. The ports which are going to be in EtherChannel must be in the shutdown state while configuring the EtherChannel to prevent loops and other related problems.

Switch omnisecu.com.SW1

omnisecu.com.SW1>
omnisecu.com.SW1>enable
omnisecu.com.SW1#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
omnisecu.com.SW1(config)#interface range gigabitEthernet 0/1 - 2
omnisecu.com.SW1(config-if-range)#channel-group 1 mode desirable
omnisecu.com.SW1(config-if-range)#channel-protocol pagp 
omnisecu.com.SW1(config-if-range)#exit
omnisecu.com.SW1(config)#exit
omnisecu.com.SW1#

Switch omnisecu.com.SW2

omnisecu.com.SW2>
omnisecu.com.SW2>enable
omnisecu.com.SW2#configure terminal
Enter configuration commands, one per line.  End with CNTL/Z.
omnisecu.com.SW2(config)#interface range gigabitEthernet 0/1 - 2
omnisecu.com.SW2(config-if-range)#channel-group 1 mode desirable
omnisecu.com.SW2(config-if-range)#channel-protocol pagp
omnisecu.com.SW2(config-if-range)#exit
omnisecu.com.SW2(config)#exit
omnisecu.com.SW2#

omnisecu.com.SW1(config-if-range)#channel-group 1 mode desirable specifies the EtherChannel Group Number as 1 and the Port Aggregation Protocol (PAgP) Channel mode as Desirable

Run "show ip interface brief" from Global Configuration mode to find the new EtherChannel virtual interface, Port-channel 1 as shown below.

omnisecu.com.SW2#show ip interface brief 
Interface              IP-Address      OK? Method Status                Protocol
 
<output_omitted>
GigabitEthernet0/1     unassigned      YES unset  up                    up
 
GigabitEthernet0/2     unassigned      YES unset  up                    up
 
Vlan1                  unassigned      YES unset  administratively down down
 
Port-channel 1         unassigned      YES unset  up                    up
omnisecu.com.SW2#