librenms-librenms/doc/General/MIB-based-polling.md

WARNING

MIB-based polling is experimental. It might overload your LibreNMS server, destroy your data, set your routers on fire, and kick your cat. It has been tested against a very limited set of devices (namely Ruckus ZD1000 wireless controllers, and net-snmp on Linux). It may fail badly on other hardware.

The approach taken is fairly basic and I claim no special expertise in understanding MIBs. Most of my understanding of SNMP comes from reading net-snmp man pages, and reverse engineering the output of snmptranslate and snmpwalk and trying to make devices work with LibreNMS. I may have made false assumptions and probably use wrong terminology in many places. Feel free to offer corrections/suggestions via pull requests or email.

Paul Gear paul@librenms.org

Overview

MIB-based polling is disabled by default; you must set $config['poller_modules']['mib'] = 1; in config.php to enable it.

The components involved in of MIB-based support are:

Discovery

• MIB-based detection is not involved; any work done here would have to be duplicated by the poller and thus would only increase load.

Polling

• The file includes/snmp.inc.php now contains code which can parse MIBs using snmptranslate and use the data returned to populate an array which guides the poller in what to store. At the moment, only OIDs with Unsigned32 and Counter64 data types are parsed.
• includes/polling/mib.inc.php looks for a MIB matching sysObjectID in the MIB directory; if one is found, it:
  • parses it
  • walks that MIB on the device
  • stores any numeric results in individual RRD files
  • updates/adds graph definitions in the previously-unused graph_types database table
• Individual OSes (includes/polling/os/*.inc.php) can poll extra MIBs for a given OS by calling poll_mib(). At the moment, this actually happens before the general MIB polling.
• Devices may be excluded from MIB polling by changing the setting in the device edit screen (/device/device=ID/tab=edit/section=modules/)

Graphing

• For each graph type defined in the database, a graph will appear in: Device -> Graphs -> MIB
• MIB graphs are generated generically by html/includes/graphs/device/mib.inc.php
• At the moment, all units are placed in the same graph. This is probably non-optimal for, e.g., wifi controllers with hundreds of APs attached.

Adding/testing other device types

One of the goals of this work is to help take out the heavy lifting of adding new device types. Even if you want fully customised graphs or tables, you can use the automatic collection of MIBs to make it easy to gather the data you want.

How to add a new device MIB

1. Ensure the manufacturer's MIB is present in the mibs directory. If you plan to submit your work to LibreNMS, make sure you attribute the source of the MIB, including the exact download URL.
2. Check that snmptranslate -Ts -M mibs -m MODULE | grep mibName produces a named list of OIDs. See the comments for snmp_mib_walk() in includes/snmp.inc.php for an example.
3. Check that snmptranslate -Td -On -M mibs -m MODULE MODULE::mibName produces a parsed description of the OID values. An example can be found in the comments for snmp_mib_parse() in includes/snmp.inc.php.
4. Get the sysObjectID from a device, for example: snmpget -v2c -c public -OUsb -m SNMPv2-MIB -M /opt/librenms/mibs -t 30 hostname sysObjectID.0
5. Ensure snmptranslate -m all -M /opt/librenms/mibs OID 2>/dev/null (where OID is the value returned for sysObjectID above) results in a valid name for the MIB. See the comments for snmp_translate() in includes/snmp.inc.php for an example. If this step fails, it means there is something wrong with the MIB and net-snmp cannot parse it.
6. Add any additional MIBs you wish to poll for specific device types to includes/polling/os/OSNAME.inc.php by calling poll_mibs() with the MIB module and name. See includes/polling/os/ruckuswireless.inc.php for an example.
7. That should be all you need to see MIB graphs!

TODO

• Save the most recent MIB data in the database (including string types which cannot be graphed). Display it in the appropriate places.
• Parse and save integer and timetick data types.
• Filter MIBs/OIDs from being polled and/or saved.
• Move graphs from the MIB section to elsewhere. e.g. There is already specific support for wireless APs - this should be utilised, but isn't yet.
• Combine multiple MIB values into graphs automatically on a predefined or user-defined basis.
• Include MIB types in stats submissions.