How to add the Hardware Serial and query it via SNMP?
On the Config->Licensing page there is a field called "Hardware Serial Number" which by default is blank.
You can put there a the Hardware Serial Number of the actual device.
It is also possible to add any other UTF8 string of your choice
Please note, once you put a value in that field it cannot be changed again.
Once the "Hardware Serial Number" is set you can query its value via SNMP on OID=.126.96.36.199.4.1.104188.8.131.52.2.0