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Get PoE Information via SNMP on Stacked 3850 Switchs



I am trying to read PoE Information via SNMP from stacked 3850 Switchs.

I manage to do it on non-stacked 3850, on 3750 Stacked or not, and 3560 Switchs.

The stacked 3850 are running IOS-XE 03.03.01SE.

The Problem I meet is not to read the PoE Information, but to correlate the PoE-Port-Index, with de physical index.

I use

$MibcpeExtPsePortEntPhyIndex = ""; # The entPhysicalIndex that identifies the Port


$MibentPhysicalDescr = ""; # A textual description of physical entity

to do the corelation.

On stacked Switchs, the SNMP request for MibcpeExtPsePortEntPhyIndex Returns the same value for all Interfaces of Switch#1 and another one, for all Interfaces of Switch#2.

Example on a non stacked device :  PoE-Index 1.1 refers Physical 1008, ... etc. OK

[jur466@nocu07 ~]$ snmpwalk -c toto lish01

. = INTEGER: 1008

. = INTEGER: 1009


On stacked devices: All PoE Indexes refers to physical Index 57 for Switch#1 and physical Index 113 for the Switch#2

[jur466@nocu07 ~]$ snmpwalk -c toto monr02

. = INTEGER: 57

. = INTEGER: 57

. = INTEGER: 57

skipped lines

. = INTEGER: 57

. = INTEGER: 57

. = INTEGER: 113

. = INTEGER: 113

. = INTEGER: 113

skipped lines

. = INTEGER: 113

Has it to do with the IOS Version ?

Best regards


4 Replies 4

LJ Gabrillo

Dude you are not a computer, use an NMS software that will translate that for you.
Solarwinds NPM is a good one, w/c has 30 days free trial.
PRTG has free 10 sensors as well

If you want to be a computer, you need to reference the OID Table on the MIB file and that SNMP message you get

Shure I am not a computer,... I am much cleverer than that.

The Problem lies not in saying

 iso. org. dod. internet. private. enterprises. cisco. ciscoMgmt. ciscoPowerEthernetExtMIB. cpeExtMIBObjects. cpeExtPsePortTable. cpeExtPsePortEntry. cpeExtPsePortEntPhyIndex.cpeExtPsePortEntPhyIndex


. .

I can cope with both representation.

The Problem is that the retuned value is always the same, wich is simply impossible.

No Computer will tell you that.

What I am saying is  that if the SNMP query Returns that :

Interface Gi1/0/1 delivers 15.4 W and that

Interface Gi1/0/1 delivers 7.2 W and that

Interface Gi1/0/1 delivers 30 W and that... and so on

 , even the best NMS will just "translate that for me".

So my question is : is there a known bug  in the IOS my devices are running, explaining this behaviour ?

Best regards


Oh I get you
apologies, I thought you were trying to verify with is if your interpretation is correct

Anyway, note that the values displayed/given by an OID there DOES NOT NECESSARILY MEAN that will be the value in Watts

Example, one of our switch here(non Cisco) temperature OID reports a value of 90. If we translated that literally then our switch is close to boiling point, 90 deg. Celsius haha, but checking the details of the OID, the actual value needs to be divided first by 2 in order to get the temperature in celsius, meaning our switch temp is actually 45 deg. Celisius

That might also be your case there: 
Kindly check the details (if you can) of OID . and how it is translated

I used a software built-in our Solarwinds NMS to get the description/details of the example OID that I gave you (the one we need first to divide by 2)

If you cant, then probably we can estimate what formula you need, 
The best way we can do this is to compare your MIB Walk values, and the actual values using the "show commands" on the switch

Kindly do the ff.
1. While doing your MIB/OID Walk to get those integers, do in tandem a "#show power inline"
    -Let's try to smartly guess how your the PoE usage is computed

Oh yeah, do you have an NMS server out there? If so, why not actually poll the device and verify the value

also, don't forget to cofigure "snmp-server ifindex persist" 

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