Inlet temperatur on cisco 3850

[as00001111]

Hey guys,

I would like to monitor the temperature in my rack, but I don't have a temperature sensor.

So I thought to use the value of the cisco 3850 switches.

Is the inlet temperature value exactly the same value as the rack temperature?

Is that reliable?

[Ben Walters]

I would say it is a pretty good indicator of the rack temperature if you don't have a separate sensor in the rack itself, it wouldn't be exactly the same but probably close enough to know if something was wrong with the cooling.

I just checked our 3850s we have deployed and found the inlet temperature was within a degree or so of the room/rack temperature.  

[as00001111]

Thank you!

May I ask you which value does your rack temperature have and when you get alarmed?

[Ben Walters]

Our rack temp is around 25 degrees and we use the Cisco values for warning and critical temperatures, 46 for warning and 60 for critical on the 3850s.

[as00001111]

do you know which maximum temperature a cisco switch is able to cope with?

Don't you think 46 degrees is already far too hot?

[Ben Walters]

If you are talking about ambient room operating temperature yes 46 degrees is quite warm and if our datacenter ever got to that point there would be bigger concerns.

Basically at 46 degrees you are probably looking at manually shutting down your equipment to stop overheating, at 60 degrees the switch will shut itself down to prevent damage.  

[as00001111]

@Ben Walters

Ben, can you tell me where the sensor for the inlet temperature does sit?

I placed an ATEN temperature sensor directly infront of my cisco switch.

ATEN temperature sensor: 25°

cisco inlet temperature: 30°

That's a huge difference.

---

@Ben Walters wrote:
I just checked our 3850s we have deployed and found the inlet temperature was within a degree or so of the room/rack temperature.  

---

Where does your temperature sensor sit?

[Ben Walters]

We have our 3850s in a single rack in a smaller room, the wall thermostat is set to 25 reads 25 and the 3850 inlet temp is 26 degrees.  

In our situation it seems to match up but I would agree that a 5 degree difference is too much.

[as00001111]

@Ben Walters

I put a temperature sensor behind the cisco switch and now it shows me 30°.

As well as the cisco inlet temperature.

Is it possible that the cisco inlet temperature sensor is placed at the back of the switch?

[Ben Walters]

Honestly it is hard to tell on the switches since they give terrible descriptions of the sensors when using SNMP.

Although when you SNMP walk the 3850 you get 3 different temp sensors which should be inlet, exhaust and CPU. When you use the show env temp commands though it only shows the 2 sensors.