Add doc for SNMP debug tips (#1831)

plugins/inputs/snmp/DEBUGGING.md

@@ -0,0 +1,53 @@
+# Debugging & Testing SNMP Issues
+
+### Install net-snmp on your system:
+
+Mac:
+
+```
+brew install net-snmp
+```
+
+### Run an SNMP simulator docker image to get a full MIB on port 161:
+
+```
+docker run -d -p 161:161/udp xeemetric/snmp-simulator
+```
+
+### snmpget:
+
+snmpget corresponds to the inputs.snmp.field configuration.
+
+```bash
+$ # get an snmp field with fully-qualified MIB name.
+$ snmpget -v2c -c public localhost:161 system.sysUpTime.0
+DISMAN-EVENT-MIB::sysUpTimeInstance = Timeticks: (1643) 0:00:16.43
+
+$ # get an snmp field, outputting the numeric OID.
+$ snmpget -On -v2c -c public localhost:161 system.sysUpTime.0
+.1.3.6.1.2.1.1.3.0 = Timeticks: (1638) 0:00:16.38
+```
+
+### snmptranslate:
+
+snmptranslate can be used to translate an OID to a MIB name:
+
+```bash
+$ snmptranslate .1.3.6.1.2.1.1.3.0
+DISMAN-EVENT-MIB::sysUpTimeInstance
+```
+
+And to convert a partial MIB name to a fully qualified one:
+
+```bash
+$ snmptranslate -IR sysUpTime.0
+DISMAN-EVENT-MIB::sysUpTimeInstance
+```
+
+And to convert a MIB name to an OID:
+
+```bash
+$ snmptranslate -On -IR system.sysUpTime.0
+.1.3.6.1.2.1.1.3.0
+```
+