variables


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 indi-
       vidual 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  representa-
       tion 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:
       ably  compact form.  It also makes it relatively easy to find the defi-
       nition of the MIB object.

       This is the default format for displaying  OIDs  in  Net-SNMP  applica-
       tions.   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 circum-
       stances),  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  pre-
       fix  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.
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