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air flow

we have 5020 and 2148 switches - we have them in the top of racks with the port side in the rear of cabinet (makes cableing to and from servers more managable) but the fans are drawing air in from the rear of cabinet and that is my hot air exhaust from my servers - my question is can I turn the fans around to pull cold air in from the rear of the switch (which would be from my server cabinet cold aisle?

Cisco Employee

Hi Chris,

The airflow on Nexus 5020 switch is front to back.

We support reversed airflow (back-to-front) only on nexus 55xx UP (Universal port) models, such as the 5548UP and 5596UP. It is not available on the original Nexus 5010/5020 switches or on the Nexus 5548P.

Nexus 5000 Switch - Air Flow

Hope this helps to clarify things for you.




Does not help it is a sad design ports are most commonly mounted to back of server cabinets for ease of cabling installation but these switches suck air in from that direction – very poor design not to mention your big switches that pull air from side to side – thanks but unless I can turn the fans around it is no help


So back-to-front airflow is supported by the 55xxUP models.  Is this acheived by a simple cli command or by replacing the fans?


Replacing of fan trays, so the fans turn in the opposite direction and power supply ( as those have fans too).


Thanks good info.


The nice part is that the SW detects it automatically and you don't have anything to configure on NX-OS.



Cisco Employee

The air-flow is Front-to-Back, but the back is considered where the ports are. "Air enters the chassis through the fan trays and power supplies mounted at the front of the chassis and exits the chassis through perforations on the rear of the chassis."

Could you past a 'sh environment fan detail' It should show something similar to this below. If it does, then the airflow is blowing air 'out' the ports and 'in' from the power supplies.

switch5k(config)# sh environment fan detail



Module  Fan  Airflow        Speed(%)  Speed(RPM)



1       1    Front-to-Back  40        6699

1       2    Front-to-Back  40        6708

2       1    Front-to-Back  40        6569

2       2    Front-to-Back  40        6585

3       1    Front-to-Back  40        6650

3       2    Front-to-Back  40        6569

4       1    Front-to-Back  40        6666

4       2    Front-to-Back  40        6666


This is the switch we use along with the 2148 we install the port side to rear of our server cabinets – they blow hot air towards the front of our cabinets (cold aisle) I want to know if I can turn the fans around so they suck cold air in the rear which would be my cold side of cabinet


That is very strange, because the 5Ks blow hot air out the port side, not the power supply side. This is by design, for the very reason you are stating. I am very curious to how your 5020 is blowing hot air out the port side, as this is the first time I've heard of it. If you have ports facing the back of the servers, hot isle, this should be fine. If you don't then it would need to be reversed mounted.

The side where the power cords plug in, where cords are, that is facing the hot isle?

Front = fans/power supplies

Back = port side

As stated earlier, we support reversed airflow (back-to-front) only on nexus 55xx UP (Universal port) models, such as the 5548UP and 5596UP. It is not available on the original Nexus 5010/5020 switches or on the Nexus 5548P.


I was mistaken the cisco 5020 and 2148s are blowing air the corrct way – sorry . The Cisco 4520 is blowing side to side but we can install a 2U APC fan to fix it’s side to side air flow

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