bionic (5) variables.5.gz

Provided by: libsnmp-base_5.7.3+dfsg-1.8ubuntu3.8_all bug

NAME

           variables - Format of specifying variable names to SNMP tools.

DESCRIPTION

       The  syntax  and  semantics of management information in SNMP is given by the definitions of MIB objects,
       loaded from one or more MIB files (or "MIB modules").  These definitions are not  strictly  required  for
       the  SNMP  protocol to operate correctly, but are typically needed by SNMP client applications to display
       information in a meaningful manner.

       The MIB file also serves as a design document when developing an SNMP agent (or sub-agent) that  provides
       this  information,  and ensures that client and server share a common understanding about what management
       information represents.

OIDs

       MIB objects are specified using Object Identifiers (OIDs), which can take a number of forms.   Note  that
       all of the examples in this section refer to the same MIB object.

   Numeric OIDs
       The fundamental format of an OID is a sequence of integer values (or "subidentifiers"), typically written
       using dots to separate the individual subidentifiers.
               .1.3.6.1.2.1.1.1
       This is the format that is used within the SNMP protocol itself, in the packets that are  sent  over  the
       network.

       This  form  of  representing an OID does not require MIB files or MIB object definitions to be available.
       However it does rely on the client application and/or network administrator knowing what a given  numeric
       OID refers to.  As such, it is not a particularly helpful representation to anyone just starting out with
       SNMP.

       This format can be obtained by giving the command-line option -On to most Net-SNMP commands.

   Full OID path
       A similar (but somewhat more informative) format uses the same dotted list representation, but  with  the
       numeric subidentifiers replaced by names, taken from the relevant MIB file(s).
               .iso.org.dod.internet.mgmt.mib-2.system.sysDescr
       This  uniquely identifies a particular MIB object (as with the numeric OID), but the list of names should
       hopefully give some indication as to what information this object represents.  However it  does  rely  on
       the  relevant MIB files being available (as do all formats other than the purely numeric OID).  Such OIDs
       also tend to be fairly long!

       This format can be obtained by giving the command-line option -Of to most Net-SNMP commands.

       A variant of this (typically used when writing OIDs in descriptive text, rather than  running  programs),
       is to combine the name and numeric subidentifier:
               .iso(1).org(3).dod(6).internet(1).mgmt(2).mib-2(1).system(1)
               .sysDescr(1)

   Module-qualified OIDs
       An  alternative  way  to  (more-or-less)  uniquely specify an OID, is to give the name of the MIB object,
       together with the MIB module where it is defined.
              SNMPv2-MIB::sysDescr
       MIB object names are unique within a given module, so as long as there are not two MIB modules  with  the
       same  name  (which  is  unusual,  though  not  unheard of), this format specifies the desired object in a
       reasonably compact form.  It also makes it relatively easy to find the definition of the MIB object.

       This is the default format for displaying OIDs in  Net-SNMP  applications.   It  can  also  be  specified
       explicitly by giving the command-line option -OS to most Net-SNMP commands.

   Object name
       Possibly  the most common form for specifying MIB objects is using the name of the object alone - without
       the full path or the name of the module that defines it.
              sysDescr
       This is by far the shortest and most convenient way to refer to a MIB object.  However the danger is that
       if  two  MIB  modules  each  define  a  MIB  object  with the same name (which is perfectly legal in some
       circumstances), then it's not necessarily clear which MIB object is actually meant.  For day-to-day  use,
       particularly  when  using  standard MIB objects, this is probaby safe.  But it's important to be aware of
       the potential ambiguities.

       This format can be obtained by giving the command-line option -Os to most Net-SNMP commands.

   UCD-format
       Previous versions of the code (UCD v4.x and earlier) used a simple approach to shortening  the  way  OIDs
       were specified.  If the full path of the OID began with .iso.org.dod.internet.mgmt.mib-2 then this prefix
       was removed from the OID before displaying it.  All other OIDs were displayed in full.

       Similarly, if an OID was passed to the UCD library that did not begin with  a  dot  (and  wasn't  in  the
       module::name format), then the same prefix was prepended.   The example OID from the formats listed above
       would therefore be given or displayed as
              system.sysDescr
       The inconsistent handling of OIDs, depending on their location within the OID tree,  proved  to  be  more
       trouble than it was worth, and this format is no longer recommended.

       The  previous behaviour can be obtained by giving the command-line option -Ou (for displaying output), or
       -Iu (for interpreting input OIDs without a leading dot) to most Net-SNMP commands.

SEE ALSO

       snmpcmd(1)

BUGS

       The parser of the MIB files file is not expected to handle bizarre (although correct) interpretations  of
       the ASN.1 notation.