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:

etherchannel over 8021q tunneling 4 switches

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:

etherchannel over 8021q tunneling dedicated path

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:

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Forum Replies

  1. Hi Srini,

    I used routers just to have some “customer” device that could do tagging for me in this example. In a real network, you would use customer switches instead.

    The tag on the left side is the tag from the ISP, I should probably have used the same color for the customer tag.


  2. Hi Rene,

    Could you please explain Jumbo Frame in plain English :slight_smile:

    who uses it and why someone will use it ? Is it configurable ? Where this has to be configured ?


  3. Hello Abhishek

    In order to clearly answer your question, you’ll have to understand the following terminology:

    MTU - Maximum transmission unit - this is the largest physical packet size measured in bytes that a network can transmit. Any packet larger than this MTU is divided or fragmented into smaller packets before transmission. The standard MTU on an Ethernet network is 1500 bytes plus the size of the L2 header and frame check sequence which is an additional 18 bytes. So standard MTU size for Ethernet is 1518.

    Jumbo frame - A frame that is larger than the s

    ... Continue reading in our forum

  4. What happen if we have two customers, customer X and Y and use the same SVLAN (outer vlan) 123 and we segregate traffic using different cvlans (cvlan 12 for customer x and cvlan 13 for customer y). So, we have customer x site 1 and site 2, both sites using lan switches connected to the metro ethernet service provider lan switch and the same for customer y.
    If customer X Lan Switch sends a BPDU towards the ISP, this BPDU will be carried on the inner vlan ? or should I have to configure the “l2protocol stp” on the interface configuration mode on the ISP edge inte

    ... Continue reading in our forum

  5. Hi Lagapides,

    Your response was definitely helpful.


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