FAQ:Applications 08

Requesting an object fails with "Unknown Object Identifier" Why?

If a general snmpwalk shows the entry, but asking for it more specifically gives a "sub-identifier not found:" or "Unknown Object Identifier" error, then that's a problem with the tool, rather than the agent.

Firstly, make sure that you're asking for the object by the right name. Object descriptors are case-sensitive, so asking for 'sysuptime' will not be recognised, but 'sysUpTime' will.

Secondly, the object may be defined in a MIB that hasn't been loaded. Try loading in all the MIB files:

       snmpget -m ALL -v1 -c public localhost sysUpTime.0

(though if snmpwalk displays the object by name, this is unlikely to be the cause).

Thirdly, earlier versions of the UCD software expected "full" paths for object names, either based at the root of the whole MIB tree (".iso.org.dod.internet.mgmt.mib-2.system.sysUpTime") or the 'mib-2' subtree ("system.sysUpTime"). Try:

       snmpget -v1 -c public myhost system.sysUpTime.0

These earlier versions of the tools may take a command-line option '-R' or '-IR' (depending on vintage) to invoke this "random-access" mode. Note that snmptranslate still requires "random-access" to be specified explicitly - all other command tools now use this mode by defaults.

All versions of the UCD and Net-SNMP tools accept the syntax

       snmpget -v1 -c public myhost RFC1213-MIB::sysUpTime.0

to denote a particular object in a specific MIB module. Note that this uses the name of the module, not the name of the file. See the second question in this section for the distinction.

   FAQ:Applications

1. How do I add a MIB?
2. How do I add a MIB to the tools?
3. Why can't I see anything from the agent?
4. Why doesn't the agent respond?
5. I can see the system group, but nothing else. Why?
6. Why can't I see values in the <ENTERPRISE> tree?
7. The agent worked for a while, then stopped responding. Why?
8. Requesting an object fails with "Unknown Object Identifier" Why?
9. Why do I get "noSuchName" when asking for "sysUpTime" (or similar)?
10. Why do I sometimes get "End of MIB" when walking a tree, and sometimes not?
11. How do I use SNMPv3?
12. Why can't I set any variables in the MIB?
13. Variables seem to disappear when I try to set them. Why?
14. Why can't I change sysLocation (or sysContact)?
15. I get an error when trying to set a negative value - why?
16. I get an error when trying to query a string-indexed table value - why?
17. How should I specify string-index table values?
18. How do I send traps and notifications?
19. How do I receive traps and notifications?
20. How do I receive SNNMPv1 traps?
21. Why don't I receive incoming traps?
22. My traphandler script doesn't work when run like this - why not?
23. How can the agent receive traps and notifications?
24. How big can an SNMP request (or reply) be?
25. How can I monitor my systems (disk, memory, etc)?
26. Applications complain about entries in your example 'snmp.conf' file. Why?
27. OK, what should I put in snmp.conf?
28. How do I specify IPv6 addresses in tools command line arguments?