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.