TUT:snmptable

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

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