Difference between revisions of "TUT:snmptable"

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Although [[TUT:snmpwalk|snmpwalk]] can be used to retrieve the contents of a table,
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Although [[snmpwalk|snmpwalk]] can be used to retrieve the contents of a table,
 
it will list the results for each column in turn.  This is not how most people
 
it will list the results for each column in turn.  This is not how most people
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would naturally expect to see a table displayed, which is where <tt>snmptable</tt> comes in.
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would naturally expect to see a table displayed, which is where <tt>[[snmptable]]</tt> comes in.
  
 
== Basic Example ==
 
== Basic Example ==
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== Holes in Tables ==
 
== Holes in Tables ==
  
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The [[TUT:snmpget|snmpgetnext tutorial]] includes a discussion of the idea of
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The [[TUT:snmpgetnext|snmpgetnext tutorial]] includes a discussion of the idea of
 
"holes" in a table, illustrated by an (artificially) missing value for
 
"holes" in a table, illustrated by an (artificially) missing value for
 
<tt>sysORDescr.4</tt>.  The <tt>snmptable</tt> command will handle such holes
 
<tt>sysORDescr.4</tt>.  The <tt>snmptable</tt> command will handle such holes

Latest revision as of 16:13, 23 December 2014

Although snmpwalk can be used to retrieve the contents of a table, it will list the results for each column in turn. This is not how most people would naturally expect to see a table displayed, which is where snmptable comes in.

Basic Example

The snmptable command retrieves the contents of an SNMP table, and displays it in the usual manner - one row at a time: 

  % snmptable -v 2c -c demopublic -Os test.net-snmp.org sysORTable
  SNMP table: sysORTable
    sysORID                                         sysORDescr   sysORUpTime
    snmpMIB                The Mib module for SNMPv2 entities.  0:0:00:00.82
      ifMIB   generic objects for network interface sub-layers  0:0:00:00.81
         ip            The MIB module for managing IP and ICMP  0:0:00:00.83
     udpMIB    The MIB module for managing UDP implementations  0:0:00:00.82

The headings for the table columns (and the name of the table itself) can be omitted using the -Ch flag.

Wide Tables

This particular table only has a few columns (and the description strings shown here have been deliberately shortened). In practise, the output for many tables can be too wide to be handled sensibly.

Fortunately, snmptable can apply a maximum width to the output, splitting the table into several chunks if necessary: 

  % snmptable -v 2c -c demopublic -Os -Cw 70 test.net-snmp.org sysORTable
  SNMP table: sysORTable
    sysORID                                         sysORDescr
    snmpMIB                The Mib module for SNMPv2 entities.
      ifMIB   generic objects for network interface sub-layers
         ip            The MIB module for managing IP and ICMP
     udpMIB    The MIB module for managing UDP implementations
  

  SNMP table: sysORTable, part 2
     sysORUpTime
    0:0:00:00.82
    0:0:00:00.81
    0:0:00:00.83
    0:0:00:00.82


Table Indexes

One thing missing from the tables above, is any indication of the index values for each row. The earliest MIB tables (and some more recent, but poorly designed tables) did define the indexes as accessible objects, which would therefore appear in the snmptable output. But current MIB design has recognised that the index values are included in the instance OIDs, so it is not necessary to explicitly retrieve them as a separate column object.

By default, the snmptable command ignores these index values, but it will display them if invoked with the -Ci option: 

  % snmptable -v 2c -c demopublic -Os -Cw 70 -Ci test.net-snmp.org sysORTable
  SNMP table: sysORTable
   index    sysORID                                         sysORDescr
       1    snmpMIB                The Mib module for SNMPv2 entities.
       2      ifMIB   generic objects for network interface sub-layers
       4         ip            The MIB module for managing IP and ICMP
       5     udpMIB    The MIB module for managing UDP implementations
  

  SNMP table: sysORTable, part 2
   index   sysORUpTime
       1  0:0:00:00.82
       2  0:0:00:00.81
       4  0:0:00:00.83
       5  0:0:00:00.82

Note that the index is listed for each block of a width-limited (and hence multi-sectioned) table display.

Holes in Tables

The snmpgetnext tutorial includes a discussion of the idea of "holes" in a table, illustrated by an (artificially) missing value for sysORDescr.4. The snmptable command will handle such holes automatically, filling in any such missing values: 

  % snmptable -v 2c -c demopublic -Os test.net-snmp.org sysORTable
  SNMP table: sysORTable
    sysORID                                         sysORDescr   sysORUpTime
    snmpMIB                The Mib module for SNMPv2 entities.  0:0:00:00.82
      ifMIB   generic objects for network interface sub-layers  0:0:00:00.81
         ip                                                  ?  0:0:00:00.83
     udpMIB    The MIB module for managing UDP implementations  0:0:00:00.82


Specifying the Table OID

Unlike the other command line applications (snmpget, snmpgetnext, snmpwalk etc), snmptable can only be used with a MIB table object. If this command is given any other OID (including the tableEntry object, one of the table columns, or a particular instance within a table), then this will be rejected: 

   % snmptable -v 2c -c demopublic -Os test.net-snmp.org sysOREntry
   Was that a table? sysOREntry
   % snmptable -v 2c -c demopublic -Os test.net-snmp.org sysORID
   Was that a table? sysORID
   % snmptable -v 2c -c demopublic -Os test.net-snmp.org sysORID.3
   Was that a table? sysORID.3
   % snmptable -v 2c -c demopublic -Os test.net-snmp.org system
   Was that a table? system

Also, snmptable relies on having the relevant MIB file available (and loaded), in order to know which columns to retrieve. It is not possible to run it without this MIB - even if numeric OIDs are used (which would otherwise be fine): 

   % snmptable -v 2c -c demopublic -m ' ' test.net-snmp.org .1.3.6.1.2.1.1.9
   Was that a table? iso.3.6.1.2.1.1.9
   % snmptable -v 2c -c demopublic        test.net-snmp.org .1.3.6.1.2.1.1.9
   SNMP table: SNMPv2-MIB::sysORTable
       etc, etc


Tutorial Sections

About the SNMP Protocol

These tutorial links talk about SNMP generically and how the protocol itself works. They are good introductory reading material and the concepts are important to understand before diving into the later tutorials about Net-SNMP itself.

Net-SNMP Command Line Applications

These tutorial pages discuss the command line tools provided in the Net-SNMP suite of tools. Nearly all the example commands in these tutorials works if you try it yourself, as they're all examples that talk to our online Net-SNMP test agent. Given them a shot!

Application Configuration

All of our applications support configuration to allow you to customize how they behave.

Net-SNMP Daemons

Net-SNMP comes with two long-running daemons: a SNMP agent (snmpd) for responding to management requests and a notification receiver (snmptrapd) for receiving SNMP notifications.

Coding Tutorials

Net-SNMP comes with a highly flexible and extensible API. The API allows you to create your own commands, add extensions to the agent to support your own MIBs and perform specialized processing of notifications.

Debugging SNMP Applications and Agents

All our tools and applications have extensive debugging output. These tutorials talk about how the debugging system works and how you can add your own debugging statements to you code:

Operating System Specific Tutorials

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