Determining with Enabled VLANs from SNMP with Python

Similar to this thread, I wanted to see what VLANs were allowed for a trunked port as reported by SNMP with Python.

With the help of a couple of colleagues, I made some progress.

>>> vlan_value = '000000000020000000000000000000000000200000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000000'
>>> for key,value in enumerate(format(int(vlan_value, 16), "0100b").rjust(len(vlan_value) * 4, '0')):
...     if value == '1':
...         print key
...
...
...
42
146
  • Convert the string returned to Hex
  • Convert that to Binary
  • Right fill 0s to the appropriate length to give offset (determined by the size of the string)
  • Loop through the resulting value and each character that is a 1 is an enabled VLAN on the port

In conjunction with LLDP, I’m able to query each switch/port and interface is connected to and determine if the VLANs are set properly on the port.

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