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Josh Harmacinski

Fex Deployment Best Practices

I am going to be replacing old Nexus 5020's with new Nexus 9300s and there are dual-homed fexs on the old 5020s. What are the current best practices for deploying FEXs in new deployments? 


I feel like dual-homing them just causes issues because of how upgrading the parent switch effects them - and single homing them would be the better choice. I understand I lose path redundancy, but I also don't have to worry about future upgrades either.Nexus 2000, Nexus 9000, Best Practices


Hello Josh, 


The link below contains all supported and unsupported topologies.


My prefered topology is "Host VPC (Single Link) and FEX Single Homed (Port Channel Mode) Straight through Design".

  1. If server are running VMware, just connect the cable from server to FEX and configure the vSwitch manage load balance and redundancy.
  2. Physical server or other hypervisor, do a LAG with both fex.

In case one switch or fex go down, you lost only bandwidth.



Remi Astruc

Hi Josh,


In fact there is not a Best solution. There is a Best solution for each situation...


If the servers you will connect are all dual-attached to 2 FEXs using Port-channel, then go for Straight-through FEXs. Dual-homed FEXs would bring only more constraints.

If some servers will be single-attached, Dual-homed FEXs will bring the redundancy they need in case of 1 FEX, Uplink or 1 N9K failure. Straight-through FEXs would not.

Regarding the drawback of having all FEXs upgrading at the same time in case of Dual-homed FEX, that can be avoided during the operation by shuting 1 of the 2 Uplinks on all your FEXs so that each odd FEX has only 1 Uplink to N9K A and even FEX 1 Uplink to N9K B. I did that a couple of times without issue.


Does that answer your question?


And be sure to read 9300 release notes re: FEX compatibilty before you make your purchase!

Good day all, 


İ would like to ask that is there any design practise that fex switches located several km away from spine switch? We have 16 connection point with direct fiber link and i would like to implement nexus spine leaf fex solution. But the point is connection points is 5-10km away from main data center room. Please advice.


Yashar Mammadov.