FAQ:Coding 10

Are there any examples, or documentation for developing MIB modules?

Many of the MIB modules shipped with the Net-SNMP agent still use the v4 "traditional" MIB module API, but an increasing number use one of the newer v5 helper-based handlers. All of these can be found under agent/mibgroup

The tdata helper is used in the new DisMan Event, Expression and Schedule MIB modules (see disman/{event,expr,schedule}/*). The similar dataset helper is used in the older DisMan Event MIB implementation (see disman/mteEvent*) and the Notification Log MIB (see notification-log-mib/*), used by snmptrapd to log incoming traps.

The basic iterator handler is used in the TCP and UDP table implementations (mibII/tcpTable & mibII/udpTable), VACM context handling (mibII/vacm_context) and various tables relating to agent internals (agent/*). These show a number of different approaches to using the iterator helper, so it's worth comparing them.

The two examples/netSnmpHostsTable* modules provide a contrast between the iterator and iterator_access helpers.

There are several examples based on the MfD framework (see {if,ip,tcp,udp}-mib/). Much of this code is not intended to be viewed directly, but individual files are clearly commented to distinguish between internal implementation and public code.

The Net-SNMP agent does not currently include any MIB modules using the array-user container-based helper. The best examples of this are to be found in the net-policy project. See http://net-policy.sourceforge.net/

   FAQ:Coding
   

1. How do I write C code to integrate with the agent?
2. How does the agent fetch the value of a MIB variable from the system?
3. Mib2c complains about a missing "mib reference" - what does this mean?
4. Mib2c complains about not having a "valid OID" - what does this mean?
5. Why doesn't mib2c like the MIB file I'm giving it?
6. Mib2c ignores my MIB and generates a pair of 'mib-2' code files. Why?
7. What's the difference between the various mib2c configuration files?
8. Which mib2c configuration file should I use?
9. How can I have mib2c generate code for both scalars and tables?
10. Are there any examples, or documentation for generating MIB modules?
11. Where should I put the files produced by 'mib2c'?
12. Why doesn't my new MIB module report anything?
13. Why does the iterator call my get_{first,next} routines so often?
14. How can I get the agent to generate a trap (or inform)?
15. How can I get an AgentX sub-agent to generate a trap (or inform)?
16. How can I get the agent to send an SNMPv1 (or SNMPv2c) trap?
17. How can I get the agent to include varbinds with an SNMPv1 trap?
18. How can I get the agent to send an SNMPv1 enterprise-specific trap?
19. How can I get the agent to send an SNMPv3 trap (or inform)?
20. Why does calling 'send_v2trap' generate an SNMPv1 trap (or vice versa)?
21. How can I register a MIB module in a different (SNMPv3) context?