title: How to check port is up or down with SNMP
body: <p>I develop a app which discovers a network topology and draw it programmaticly with java and SNMP4j
  I send CDP and LLDP requests to devices and analyze result of this. However there are devices which has not support CDP or LLDP(like Access Point) therefor I cannot discover it. I must show it as unkown device.
  Thanks to CDP and LLDP I know which device is on which port. To understand unknown device is on which port, 
  I need a oid  to learn up and down ports of the Switch with SNMP  or another method.</p>
  
  <p>I use SNMP4J</p>