FAQ:Agent 14

How can I combine two copies of the 'mib2' tree from separate subagents?

This is the purpose of the SNMPv3 'context' field. Register the MIB module a second time in a non-default context (see the relevant entry in the CODING section for details), and specify this context when querying the agent. The MIB module can use this context information to determine which set of information to report.

Or you could register two completely different handlers for the same OID (using different contexts), and the agent will invoke the appropriate code. This holds for both MIB modules implemented within the main agent, or AgentX subagents - the same approach will work for both.

Contexts can also be used with proxied SNMP requests - just specify the option '-Cn {context}' as part of the "proxy" entry. See the 'snmpd.conf(5)' man page for details.

It's currently not possible to support parallel MIB trees when using SNMPv1 or SNMPv2c. In principle, it should be possible to use the community string in a similar way, but this has not (yet) been implemented.

This mechanism is only available with the v5 Net-SNMP agent. The v4 UCD agent does not support contexts at all. Sorry about that.

Another way to handle this would be to tweak one of the subagents to use a different set of (non-standard) OID assignments - perhaps by relocating the whole of the subtree to another (private) OID. This is not ideal, but should work with all configurations.

   FAQ:Agent
   

1. What MIBs are supported?
2. What protocols are supported?
3. How do I configure the agent?
4. How do I remove a MIB from the agent?
5. I've installed a new MIB file. Why can't I query it?
6. How do I add a MIB to the agent?
7. What's the difference between 'exec', 'sh', 'extend' and 'pass'?
8. What's the difference between AgentX, SMUX and proxied SNMP?
9. What is the purpose of 'dlmod'?
10. Which extension mechanism should I use?
11. Can I use AgentX when running under Windows?
12. How can I run AgentX with a different socket address?
13. How can I turn off SMUX support?
14. How can I combine two copies of the 'mib2' tree from separate subagents?
15. What traps are sent by the agent?
16. Where are these traps sent to?
17. How can I send a particular trap to selected destinations?
18. When I run the agent it runs and then quits without staying around. Why?
19. After a while the agent stops responding, and starts eating CPU time. Why?
20. How can I stop other people getting at my agent?
21. How can I listen on just one particular interface?
22. The agent is complaining about 'snmpd.conf'. Where is this?
23. Why does the agent complain about 'no access control information'?
24. How do I configure access control?
25. How do I configure SNMPv3 users?
26. The 'createUser' line disappears when I start the agent. Why?
27. What's the difference between /var/net-snmp and /usr/local/share/snmp?
28. My new agent is ignoring the old snmpd.conf file. Why?
29. Where should the snmpd.conf file go?
30. Why am I getting "Connection refused"?
31. Why can't I see values in the UCDavis 'extensible' or 'disk' trees?
32. Why can't I see values in the UCDavis 'memory' or 'vmstat' tree?
33. What do the CPU statistics mean - is this the load average?
34. How do I get percentage CPU utilization using ssCpuRawIdle?
35. What about multi-processor systems?
36. The speed/type of my network interfaces is wrong - how can I fix it?
37. The interface statistics for my subinterfaces are all zero - why?
38. Does the agent support the RMON-MIB?
39. What does "klread: bad address" mean?
40. What does "nlist err: wombat not found" (or similar) mean?
41. What does "Can't open /dev/kmem" mean?
42. The system uptime (sysUpTime) returned is wrong!
43. Can the agent run multi-threaded?
44. Can I use AgentX (or an embedded SNMP agent) in a threaded application?