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Proof of Concept

Instead of using canned SSH-based probes for UNIX, we are researching the possibility of using SNMP against unix boxes (and possibly windows). In theory we can . We do this by simply replacing the SSH probes with equivalent SNMP probes which SNMP GET information from extended MIB objects which we apply to all machines we plan to instrument.

...

• SNMP doesn't require us to open up shell access to a broad population of machines
• SNMP is the same protocol used for net devices & printers (2 down, Windows potentially remains the odd man out)

Platforms

Probes to Replace

• ? (will get list when Discovery is available

Proof of Concept

Linux

On Linux/net-snmp 5 here's one way to do extensions (there are several).

• Use "exec" to add an extension to snmpd.conf

  No Format
  exec echotest /bin/cat /etc/motd

• Restart snmpd and do a GET against a view which can see the extended MIBs

  Code Block
  snmpget -v2c localhost -c public 'NET-SNMP-EXTEND-MIB::nsExtendOutputFull."echotest"'

...we may want to use SNMPv3, but the general idea is clear... we can expose arbitrary configuration data through SNMP. Since there are only a few dozen probes (and maybe only a subset of actual interest to Yale) we should be able to leverage SNMP for UNIX discovery instrumentation.

Rewiring of Discovery

• make sure SSH discovery doesn't happen
  • no credentials
  • configure the behavior of the MID server to skip SSH
• Expand the stock Linux classifier for SNMP so that it runs additional Explore-phase probes

Write SNMP Hooks & Custom MIB

• scripts to call from net-snmp extend directives. Put logic in these as opposed to SN... hides information, gives the discovery targets maximum control over the process.
• custom MIB will aid in probe & sensor clarity

Probe Replacement

There are a couple of steps:

• create a probe that gets the desires SNMP object(s)
• add that probe to the "Triggers Probes" section of the Linux SNMP classifier
• write a replacement sensor (next section)

Sensor Replacement

• replace the sensor
  You can probably do this with XML field mapping as well, but here is a very simple scripted sensor that works from an SNMP probe payload:

  Code Block
  /* * sensor for SNMP Distribution discovery (Yale SNMP Discovery) * * william.west@yale.edu */ new DiscoverySensor({ process: function() { // // XML should be in var payload (a global) var element = XMLUtil.getText(payload, '//unk_111'); var rows = element.split('\n'); //expecting multiple lines current.os = rows[0]; current.os_version = rows[1]; }, type: 'DiscoverySensor' });

• list the new sensor in the "Sensors" section of the appropriate probe record

Identifying Which Probes/Sensors to Replace

The most complete approach here is:

• narrow down the sensors to those that apply to our asset types
• look at which ci_ tables are being edited by those and combine sensors with the same function
• generate a list of probes from those sensors
• generate a list of data needed by SNMP
• find out what standard MIBs provide the data
• generate a list of needed extensions for data not covered above