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New Member

Layer 3 Etherchannel and Flex Link

I would wondering if Flex Link would be supported on a layer 3 Etherchannel? The document states that is works on layer 2 ports or port channels and not vlan or layer 3 interfaces. Since I am defining my layer 3 on the sub-interfaces i was wondering if it is still supported on the layer 2 port channel.

My configuration on a 7606 will be as follows:

interface port-channel 1

switchport backup interface port-channel 2

interface port-channel 1.10

ip add

interface port-channel 1.20

ip add

interface port-channel 2


interface port-channel 2.10

ip add

interface port-channel 2.20

ip add

We are trying to eliminate the need to create SVI because of the restrictions of 4000 vlans per 7606. We are connected this 7606 to a pair of 6500 and another pair of 6509 (not tied together) and our vlan tags may duplicate between the two (2) pair of 6500 switches.We do not at this time have VSS installed in either of our 6509 pairs but would like to provide redundancy from our 7606 to the 6509 until we can get VSS or a Nexus 7k.

Your input is appreciated.

Everyone's tags (2)
Cisco Employee

Re: Layer 3 Etherchannel and Flex Link

In the example you give, flex link is not supported on Po1.  Po1 isn't a layer 2 interface in this case since you have the subinterfaces configured with layer 3.  This feature is only supported for layer 2 interfaces, like access or trunk ports.

See the output from my lab device.  When Portchannel1 has layer 3 subinterfaces it won't let you configure the flex link because Po1 is not a switchport:

Switch(config-if)#switch backup int g2/28

Command rejected: Po1 not a switching port.

If you try to make Po1 a switchport, it will delete your subinterfaces:
Switch(config-if-range)#int po1
Subinterfaces configured on this interface will not be available after switchport.
Proceed with the command? [confirm]
So flex link is NOT supported on layer 3 etherchannel.

New Member

Re: Layer 3 Etherchannel and Flex Link

Great information. Thank you very much.

Do you know anyway I can have some redundant links between a single 7606 layer 3 switch and (2) 6509 switches NOT in VSS mode?

Cisco Employee

Re: Layer 3 Etherchannel and Flex Link

Looking more at your original post, you should know that using a subinterface on a 7600 is the same as using a Vlan like an SVI.  Two subinterfaces cannot use the same Vlan ID.

7609(config)#int port-channel 1.1

7609(config-subif)#encapsulation dot1Q 200

7609(config-subif)#int port-channel 2.1

7609(config-subif)#encapsulation dot1Q 200

Command rejected: VLAN 200 not available

Using layer 2 interfaces and an SVI would allow you to create a routing protocol adjacency between the 3 boxes on the same subnet.  Then you can use load balancing with ECMP.  If one box goes down it will route through the other.