FAQ:Applications 06

Why can't I see values in the <INSERT ENTERPRISE HERE> tree?

If you can see most of the standard information (not just the system and hrSystem groups), but not in the vendor-specific 'enterprises' tree, then once again there are several possible causes.

Firstly, it's possible that the agent does not implement this particular enterprise tree. Remember that adding a MIB to the client tools does not automatically add support for these object to the agent. See the AGENT section for more information.

Alternatively, it may be that the agent does implement some or all of this enterprise tree, but the access control settings are configured to block access to it.

The simplest way to checks whether the agent implements a given portion of the OID tree is to run

       snmpwalk .... nsModuleName
   

and look for index values that fall in the area of interest. (Always assuming that you have access to this particular section of the Net-SNMP enterprise tree, of course!)

Checking the access control settings can be done by examining the tables vacmAccessTable and vacmViewTreeFamilyTable.
Note that these are used to configure access control for all versions of SNMP - not just SNMPv3.

The third possibility is that simply isn't any information in the specified tree. For example, several of the tables in the UCDavis enterprise tree (such as prTable, extTable, dskTable and fileTable) require explicit configuration in the snmpd.conf file. If you query this particular tables without the necessary configuration entries, then they will be empty.

Finally, if you can't see anything from any enterprise-specific tree, then this may be down to how you are asking for the information. By default, if snmpwalk is run without an explicitly starting OID, then it will display the contents of the 'mib-2' tree, containing most of the IETF-standard management information supported by the agent.

When the agent reaches the end of this tree, it will return the first enterprise-specific value, snmpwalk will recognise that this marks the end of the (implicit) requested tree, and stop. No enterprise-specific information will be displayed.

To walk the whole tree, and see all the information that the agent supports, specify a starting point of '.iso' or '.1'. To walk a specific enterprise subtree, specify the root of this tree as the starting point - e.g:

       snmpwalk -v1 -c public localhost UCD-SNMP-MIB::ucdavis

There is more information about particular UCD-specific subtrees in the AGENT section.

If you're walking a specific tree, but failing to see anything in it, then the most likely cause is that the agent simply does not implement those particular MIB objects. Or if it does, that the access control or other configuration settings mean that there's nothing for you to see there.

However, if you're trying a basic 'snmpwalk' with no explicit OID specified, then this would also explain why you're not seeing any enterprise-specific results.

By default, unless given an explicit starting OID, then the 'snmpwalk' command will display the contents of the 'mib-2' tree, containing most of the IETF-standard management information supported by the agent. When the agent reaches the end of this tree, it will return the first enterprise-specific value, and 'snmpwalk' will recognise that this marks the end of the (implicit) request tree, and stop. No enterprise-specific information will be displayed.

To walk the whole tree, and see all the information that the agent supports, specify a starting point of '.iso' or '.1'.

To walk a specific enterprise subtree, specify the root of this tree as the starting point - e.g:

       snmpwalk -v1 -c public localhost UCD-SNMP-MIB::ucdavis
 

There is more information about particular UCD-specific subtrees in the Agent section.

   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?