FAQ:Applications 17

What quotes should I use for string index values?

There's one other aspect of string-indexed tables that can cause problems - the difference between implicit- and explicit-length strings, and how to represent these when making an SNMP query.

The most common style of string index uses an explicit length, followed by the individual ASCII character values:

     "dave"  =  4.'d'.'a'.'v'.'e' 

(as shown in the previous entry).

However if the string index is defined in the MIB file as IMPLIED (or if it has a fixed length, such as a physical ethernet address), then the length subidentifier is omitted, and the index simply consists of the character values:

     "dave"  =  'd'.'a'.'v'.'e'

Note that IMPLIED index objects can only appear as the *last* index for a table.

The Net-SNMP library uses double quotes (i.e. "dave") to indicate an explicit length string index value, and single quotes (i.e. 'dave') to indicate an implicit length one. If you use the wrong style of quotes, then the resulting OID will be incorrect, and you'll get confusing results to your query.

   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?