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Cisco VSS L3 MEC Question in regards to connections to an ISR

I see in the design guide that Cisco recommends the following:

Do not use on and off

options with PAgP or LACP or Trunk protocol negotiation.

PAgP     Run Desirable−Desirable with MEC links.

LACP     Run Active−Active with MEC links.

Trunk     Run Desirable−Desirable with MEC links.

My issue is this, I would like to connect a Cisco 3925 router using a L3 EtherChannel on the router and adding two of the embedded links into it and then connecting this to the VSS Switch Pair using a L3 MEC connection. My problem is the 3900 series router supports only Mode On for the EtherChannel connections.

In our lab environment, I've configured it as I mentioned (no negotation) just a forced EtherChannel and it seems to be working fine. Right now I'm debating on using this as an alternative to ECMP routing which we have in our current 6500 to 6500 legacy setup. If I can get away with using no negotiated EtherChannel to the router I would prefer that, it seems to work well in the lab we have setup so far.

New Member

Cisco VSS L3 MEC Question in regards to connections to an ISR

Hi Mike,

It should work fine as long as you don't have a transparent IPS or something simillar between the VSS and the ISR. I had this setup working for a long time with a MEC between a VSS and a Nexus pair configured with ON option.



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