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FlexFabric-20/40 F8 Module Stacking active/active help?

Occasional Advisor

FlexFabric-20/40 F8 Module Stacking active/active help?

Hi everyone,

I've configured what I thought was an active/active setup from side A and B, but when testing failures, I've found that my F8 modules are in active/standby mode which causes an issue with chassis that have one QSFP from side A and one QSFP from side B to my 5940 switches.

Just for a little overview, I have two 5940's in a IRF stack, which I'll refer to as switch 1 and switch 2, but it's important to note they are a single fabric. So in the above exmaple I have chassis side A F8 module connected to switch 1, and chassis side B F8 module connected to switch 2. Side A F8 module is currently active, and side B F8 module is currently in standby mode. VC is in full stacking mode.

When I simulate a power failure on switch 1 in the above scenario, because there is now only a single link between chassis side B F8 module and switch 2, my servers now can't talk. Within the shared uplink set it looks like everything is ok, the links are in an active state, but traffic is not being passed. I'm assuming is because of this active/standby module scenario.

This leads ot my question; should I be configuring external stacking links between the modules to facilitate the configuration I want, or should I change VC to horizontal stacking mode?

My shared uplink sets are in a active/active configuration. My ideal scenario is to have internal chassis server communication to happen across the modules in the chassis, and chassis to chassis comminucation to go to my 5940s. I have 6 chassis, but possibly I should be daisy chaining these modules together so inter-chassis comms don't even go to my 5940s? Also my chassis are all going to be part of their own domains. 

Potentially this isn't even my problem. I've played around with stacking now and I still can't get one side to work. The config is identical to a chassis I do have working, although that has multiple QSFP's from each F8 module to switch 1 and switch 2, so when one switch does down each module still has a path to the remaining switch, where in the above scenario there isn't.

Help :)



Thomas Martin
Trusted Contributor

Re: FlexFabric-20/40 F8 Module Stacking active/active help?


have you defined both Uplink ports to the same Uplink network? This is necessary for switch over. The traffic goes normaly from server nic1 to Interconnect Bay1 and then to the external switch. If this uplink fails, the the traffic goes this way:

Nic1 -> interconnect Bay1 -> crossover to interconnect Bay2 -> external Switch

Please check if you have set the connection mode to "failover". This is very import in an active/standby configuration. Dont let it set to "auto".

Otherwise you can define 2 Uplinknetworks (Uplink1/Uplink2) with the same VLANs. Each Uplink has a separte uplink port. Then you have to present both networks to the serverprofile. Network from Interconnect Bay1 to server nic port 1 and Network fromInterconnect Bay2 to server nic port 2. Dont forget to activate the "Smart link" option in such a configuration. The server blade will the detect the "Link down" information and switch over to the other nic.


Occasional Advisor

Re: FlexFabric-20/40 F8 Module Stacking active/active help?

Hi Thomas,

Thank you for taking the time to reply. I ran through your suggested checks, and everytihng was looking good. What I found upon further investigation was a I had a configuration issue in the uplink switch ports. I hadn't configure them into a bridge because I was only using single links.

Then it dawned on me that shared uplinks sets are just basically LACP trunks, so without LACP correctly configured it was never going to work. What threw me is one side came up, and one side didn't, I think I would have come to my conclusion a lot faster had  the links just failed to establish at all.

Now I have my single QSFP uplinks configured properly everything is working fine.