PAgP EtherChannel

1. Introduction to PAgP EtherChannel

In this course, we will go step by step through the configuration of PAgP EtherChannel. Unlike LACP, which is an open standard, PAgP (Port Aggregation Protocol) is a Cisco proprietary protocol used for link aggregation.

Interfaces are dynamically grouped using desirable or auto modes. This configuration will also include setting up interfaces as trunks and allowing VLAN 50 on the trunk.

🛠️ Prerequisites for Configuration

Before starting, ensure the following conditions are met:

✅ Interface Consistency: All interfaces in the EtherChannel must have the same speed, duplex, and interface type.

✅ VLAN and Trunking: For Layer 2 links, interfaces must be in the same VLAN or have identical trunk settings.

✅ Active Links: Ensure that each physical link is operational.

EtherChannel Caracteristics 2

📌 For this configuration, we will use GigabitEthernet interfaces in full-duplex mode, and we will allow VLAN 50 on the trunk link.

2. Steps to Configure PAgP EtherChannel

Here, we will configure EtherChannel using the Cisco-proprietary Port Aggregation Protocol (PAgP). This allows us to bundle multiple physical links between two switches into a single logical link to provide redundancy and increased bandwidth.

Afterward, we will configure the ports as trunks and ensure that VLAN 50 is allowed on the trunk.

Configuring EtherChannel using PAgP

🔹 Enter Interface Configuration Mode

Start by selecting the interfaces that will form the EtherChannel on both switches.

  • On SW1:
SW1(config)# interface range g0/0 - 1
  • On SW2:
SW2(config)# interface range g0/0 - 1

🔹 Set PAgP Mode

Next, configure the PAgP mode for each switch. On SW1, we’ll set it to Auto, meaning the switch will passively wait for a PAgP negotiation request. On SW2, we’ll set it to Desirable, so it actively initiates the negotiation.

  • SW1 (Auto Mode):
SW1(config-if-range)# channel-group 1 mode auto
  • SW2 (Desirable Mode):
SW2(config-if-range)# channel-group 1 mode desirable

The channel-group command assigns the selected interfaces to an EtherChannel group (group 1 in this case), creating the EtherChannel between SW1 and SW2 using PAgP.

🔹 Configure Trunking and Allow VLAN

After the EtherChannel is established, we configure it as a trunk to allow VLAN traffic across the link. This includes setting the 802.1q encapsulation and allowing VLAN 50.

  • SW1:
SW1(config)# interface port-channel 1
SW1(config-if)# switchport trunk encapsulation dot1q
SW1(config-if)# switchport mode trunk 
SW1(config-if)# switchport trunk allowed vlan 50
  • SW2:
SW2(config)# interface port-channel 1 
SW2(config-if)# switchport trunk encapsulation dot1q 
SW2(config-if)# switchport mode trunk 
SW2(config-if)# switchport trunk allowed vlan 50

These commands configure Port-Channel 1 as a trunk, enable 802.1q encapsulation for VLAN tagging, and allow VLAN 50 to pass through the trunk.

3. 🔍 Verifying the Configuration

Verify the EtherChannel PAgP Formation

To ensure that the EtherChannel has formed correctly, use the show etherchannel summary command on both switches.

  • SW1:
SW1# show etherchannel summary
Flags:  D - down        P - in port-channel
        I - stand-alone  S - suspended
        H - Hot-standby (LACP only)
        R - Layer3      S - Layer2
        U - in use       N - not in use, no aggregation
        f - failed to allocate aggregator
        M - not in use, minimum links not met
        m - not in use, port not aggregated due to minimum links not met
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port

Group  Port-channel  Protocol    Ports
------ ------------- ----------- ----------------------------------------------
1      Po1(SU)       PAgP        Gi0/0(P) Gi0/1(P)

The output confirms that Port-Channel 1 (Po1) is active and operational in Layer 2 mode (S, U) using the PAgP protocol, with interfaces Gi0/0 and Gi0/1 successfully included in the EtherChannel.

  • SW2:
SW2# show etherchannel summary
Flags:  D - down        P - in port-channel
        I - stand-alone  S - suspended
        H - Hot-standby (LACP only)
        R - Layer3      S - Layer2
        U - in use       N - not in use, no aggregation
        f - failed to allocate aggregator
        M - not in use, minimum links not met
        m - not in use, port not aggregated due to minimum links not met
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port

Group  Port-channel  Protocol    Ports
------ ------------- ----------- ----------------------------------------------
1      Po1(SU)       PAgP        Gi0/0(P) Gi0/1(P)

The output verifies that Port-Channel 1 (Po1) is active in Layer 2 mode (S, U) using the PAgP protocol, with interfaces Gi0/0 and Gi0/1 successfully included in the EtherChannel.

🔍 Verify the Trunk Configuration

To confirm the trunk is correctly configured and that VLAN 50 is allowed, use the show interfaces trunk command.

  • SW1:
SW1# show interfaces trunk
Port        Mode         Encapsulation  Status        Native vlan
Po1         on           802.1q         trunking      1

Port        Vlans allowed on trunk
Po1         50
  • SW2:
SW2# show interfaces trunk
Port        Mode         Encapsulation  Status        Native vlan
Po1         on           802.1q         trunking      1

Port        Vlans allowed on trunk
Po1         50

The output verifies that Port-Channel 1 (Po1) is active as a trunk with 802.1q encapsulation, and VLAN 50 is successfully permitted on the trunk.

4. Conclusion

📢 Summary

Verify the EtherChannel PAgP Formation 1

The PAgP EtherChannel configuration is complete. Both switches are now using Port-Channel 1, which aggregates the two physical interfaces into one logical link !

Static Route