EtherChannel over 802.1Q Tunneling

In this tutorial we will take a look how you can create an Etherchannel link over 802.1Q tunneling. If you have no idea how 802.1Q tunneling works, it’s best to read my previous tutorial first that covers the basics of 802.1Q tunneling.

Here’s the topology that I will use:

SW2 and SW3 are the service provider network. SW1 and SW4 belong to the customer and present two different sites. The idea is that we want to create an Etherchannel between SW1 and SW4 over the service provider network. First we will configure the trunk between SW2 and SW3:

SW2(config)#interface fastEthernet 0/21
SW2(config-if)#switchport trunk encapsulation dot1q 
SW2(config-if)#switchport mode trunk

SW3(config)#interface fastEthernet 0/21
SW3(config-if)#switchport trunk encapsulation dot1q 
SW3(config-if)#switchport mode trunk 

Our next move is to configure the interfaces pointing towards the customer switches. To “simulate” that our FastEthernet 0/23 +/24 interfaces on SW1 and SW4 are directly connected to each other we have to use a separate “transit” VLAN for each interface pair. Traffic on the FastEthernet 0/23 interface will flow in service provider VLAN 100 and traffic for FastEthernet 0/24 will use VLAN 200. Take a look at the picture below to visualize this:

If we would use a single transit VLAN for all traffic on the FastEthernet 0/23 and 24 interfaces then we run into issues with our Etherchannel because FastEthernet 0/23 could talk to 0/24 or vice versa.

Here’s the configuration for SW2:

SW2(config)#interface fastEthernet 0/23
SW2(config-if)#switchport access vlan 100
SW2(config-if)#switchport mode dot1q-tunnel 
SW2(config-if)#l2protocol-tunnel point-to-point pagp

SW2(config)#interface fastEthernet 0/24
SW2(config-if)#switchport access vlan 200
SW2(config-if)#switchport mode dot1q-tunnel 
SW2(config-if)#l2protocol-tunnel point-to-point pagp 

The magic bullet that makes the etherchannel possible is the l2protocol-tunnel command and specifying PAgP or LACP. The configuration for SW3 is similar:

SW3(config)#interface fastEthernet 1/0/23
SW3(config-if)#switchport access vlan 100
SW3(config-if)#switchport mode dot1q-tunnel 
SW3(config-if)#l2protocol-tunnel point-to-point pagp

SW3(config)#interface fastEthernet 0/24
SW3(config-if)#switchport access vlan 200
SW3(config-if)#switchport mode dot1q-tunnel
SW3(config-if)#l2protocol-tunnel point-to-point pagp

Our service provider switches are now ready, the configuration on the customer switches is just a regular Etherchannel configuration:

SW1(config)#interface range fastEthernet 0/23 - 24
SW1(config-if-range)#switchport trunk encapsulation dot1q 
SW1(config-if-range)#switchport mode trunk 
SW1(config-if-range)#channel-group 14 mode desirable 
Creating a port-channel interface Port-channel 14

And something similar for SW4:

SW4(config)#interface range fastEthernet 0/23 - 24
SW4(config-if-range)#switchport trunk encapsulation dot1q 
SW4(config-if-range)#switchport mode trunk 
SW4(config-if-range)#channel-group 14 mode desirable 
Creating a port-channel interface Port-channel 14

If everything went OK you should see a message on the console that the port channel interface is “up”. We can also verify it with the show etherchannel command:

SW1#show etherchannel summary 
Flags:  D - down        P - bundled in port-channel
        I - stand-alone s - suspended
        H - Hot-standby (LACP only)
        R - Layer3      S - Layer2
        U - in use      f - failed to allocate aggregator

        M - not in use, minimum links not met
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port

Number of channel-groups in use: 1
Number of aggregators:           1

Group  Port-channel  Protocol    Ports
------+-------------+-----------+-----------------------------------------------
14     Po14(SU)        PAgP      Fa0/23(P)   Fa0/24(P)   

SW4#show etherchannel summary 
Flags:  D - down        P - bundled in port-channel
        I - stand-alone s - suspended
        H - Hot-standby (LACP only)
        R - Layer3      S - Layer2
        U - in use      f - failed to allocate aggregator

        M - not in use, minimum links not met
        u - unsuitable for bundling
        w - waiting to be aggregated
        d - default port

Number of channel-groups in use: 1
Number of aggregators:           1

Group  Port-channel  Protocol    Ports
------+-------------+-----------+-----------------------------------------------
14     Po14(SU)        PAgP      Fa0/23(P) Fa0/24(P)

Looking good, we have an etherchannel between SW1 and SW4! That’s all we have for now…

If you have any questions, feel free to leave a comment!