SNMP - Man Page

 use SNMP;
 ...
 $sess = new SNMP::Session(DestHost => localhost, Community => public);
 $val = $sess->get('sysDescr.0');
 ...
 $vars = new SNMP::VarList([sysDescr,0], [sysContact,0], [sysLocation,0]);
 @vals = $sess->get($vars);
 ...
 $vb = new SNMP::Varbind();
 do {
    $val = $sess->getnext($vb);
    print "@{$vb}\n";
 } until ($sess->{ErrorNum});
 ...
 $SNMP::save_descriptions = 1;
 SNMP::initMib(); # assuming mib is not already loaded
 print "$SNMP::MIB{sysDescr}{description}\n";

Note: The perl SNMP 5.0 module which comes with net-snmp 5.0 and higher is different than previous versions in a number of ways.  Most importantly, it behaves like a proper net-snmp application and calls init_snmp properly, which means it will read configuration files and use those defaults where appropriate automatically parse MIB files, etc.  This will likely affect your perl applications if you have, for instance, default values set up in your snmp.conf file (as the perl module will now make use of those defaults).  The documentation, however, has sadly not been updated yet (aside from this note), nor is the read_config default usage implementation fully complete.

The basic operations of the SNMP protocol are provided by this module through an object oriented interface for modularity and ease of use. The primary class is SNMP::Session which encapsulates the persistent aspects of a connection between the management application and the managed agent. Internally the class is implemented as a blessed hash reference. This class supplies 'get', 'getnext', 'set', 'fget', and 'fgetnext' method calls. The methods take a variety of input argument formats and support both synchronous and asynchronous operation through a polymorphic API (i.e., method behaviour varies dependent on args passed - see below).

$sess = new SNMP::Session(DestHost => 'host', ...)

The following arguments may be passed to new as a hash.

$sess = new SNMP::Session(DestHost => 'host', ...)

supports all applicable fields from SNMP::Session (see above)

<vars> may be one of the following forms:

SNMP::VarList

represents an array of MIB objects to get or set, implemented as a blessed reference to an array of SNMP::Varbinds, (e.g., [<varbind1>, <varbind2>, ...])

SNMP::Varbind

represents a single MIB object to get or set, implemented as a blessed reference to a 4 element array; [<obj>, <iid>, <val>, <type>].

<obj>

one of the following forms:

1)

leaf identifier (e.g., 'sysDescr') assumed to be unique for practical purposes

2)

fully qualified identifier (e.g., '.iso.org.dod.internet.mgmt.mib-2.system.sysDescr')

3)

fully qualified, dotted-decimal, numeric OID (e.g., '.1.3.6.1.2.1.1.1')

<iid>

the dotted-decimal, instance identifier. for scalar MIB objects use '0'

<val>

the SNMP data value retrieved from or being set to the agents MIB. for (f)get(next) operations <val> may have a variety of formats as determined by session and package settings. However for set operations the <val> format must be canonical to ensure unambiguous translation. The canonical forms are as follows:

OBJECTID

dotted-decimal (e.g., .1.3.6.1.2.1.1.1)

OCTETSTR

perl scalar containing octets

INTEGER

decimal signed integer (or enum)

NETADDR

dotted-decimal

IPADDR

dotted-decimal

COUNTER

decimal unsigned integer

COUNTER64

decimal unsigned integer

GAUGE

decimal unsigned integer

UINTEGER

decimal unsigned integer

TICKS

decimal unsigned integer

OPAQUE

perl scalar containing octets

NULL

perl scalar containing nothing

<type>

SNMP data type (see list above), this field is populated by 'get' and 'getnext' operations. In some cases the programmer needs to populate this field when passing to a 'set' operation. this field need not be supplied when the attribute indicated by <tag> is already described by loaded Mib modules. for 'set's, if a numeric OID is used and the object is not currently in the loaded Mib, the <type> field must be supplied

simple string

light weight form of <var> used to 'set' or 'get' a single attribute without constructing an SNMP::Varbind. stored in a perl scalar, has the form '<tag>.<iid>', (e.g., 'sysDescr.0'). for 'set' operations the value is passed as a second arg. Note: This argument form is not updated in get[next] operations as are the other forms.

<callback> may be one of the following forms:

without arguments

\&subname

sub { ... }

or with arguments

[ \&subname, $arg1, ... ]

[ sub { ... }, $arg1, ... ]

[ "method", $obj, $arg1, ... ]

callback will be called when response is received or timeout occurs. the last argument passed to callback will be a SNMP::VarList reference. In case of timeout the last argument will be undef.

&SNMP::MainLoop([<timeout>, [<callback>]])

to be used with async SNMP::Session calls. MainLoop must be called after initial async calls so return packets from the agent will be processed. If no args supplied this function enters an infinite loop so program must be exited in a callback or externally interrupted. If <timeout(sic)

&SNMP::finish()

This function, when called from an SNMP::MainLoop() callback function, will cause the current SNMP::MainLoop() to return after the callback is completed.  finish() can be used to terminate an otherwise-infinite MainLoop.  A new MainLoop() instance can then be started to handle further requests.

$SNMP::VERSION

the current version specifier (e.g., 3.1.0)

$SNMP::auto_init_mib

default '1', set to 0 to disable automatic reading of the MIB upon session creation. set to non-zero to call initMib at session creation which will result in MIB loading according to Net-SNMP env. variables (see man mib_api)

$SNMP::verbose

default '0', controls warning/info output of SNMP module, 0 => no output, 1 => enables warning/info output from SNMP module itself (is also controlled by SNMP::debugging - see below)

$SNMP::use_long_names

default '0', set to non-zero to enable the use of longer Mib identifiers. see translateObj. will also influence the formatting of <tag> in varbinds returned from 'getnext' operations. Can be set on a per session basis (UseLongNames)

$SNMP::use_sprint_value

default '0', set to non-zero to enable formatting of response values using the snmp libraries snprint_value function. can also be set on a per session basis (see UseSprintValue) Note: returned values may not be suitable for 'set' operations

$SNMP::use_enums

default '0',set non-zero to return values as enums and allow sets using enums where appropriate. integer data will still be accepted for set operations. can also be set on a per session basis (see UseEnums)

$SNMP::use_numeric

default to '0',set to non-zero to have <tags> for 'get' methods returned as numeric OID's rather than descriptions. UseLongNames will be set so that the entire OID will be returned.  Set on a per-session basis (see UseNumeric).

$SNMP::best_guess

default '0'.  This setting controls how <tags> are parsed.  Setting to 0 causes a regular lookup.  Setting to 1 causes a regular expression match (defined as -Ib in snmpcmd) and setting to 2 causes a random access lookup (defined as -IR in snmpcmd).  Can also be set on a per session basis (see BestGuess)

$SNMP::save_descriptions

default '0',set non-zero to have mib parser save attribute descriptions. must be set prior to mib initialization

$SNMP::debugging

default '0', controls debugging output level within SNMP module and libsnmp

1. enables 'SNMP::verbose' (see above)
2. level 1 plus snmp_set_do_debugging(1)
3. level 2 plus snmp_set_dump_packet(1)

$SNMP::dump_packet

default '0', set [non-]zero to independently set snmp_set_dump_packet()

SNMP::register_debug_tokens()

Allows to register one or more debug tokens, just like the -D option of snmpd. Each debug token enables a group of debug statements. An example: SNMP::register_debug_tokens("tdomain,netsnmp_unix");

a tied hash to access parsed MIB information. After the MIB has been loaded this hash allows access to to the parsed in MIB meta-data(the structure of the MIB (i.e., schema)). The hash returns blessed references to SNMP::MIB::NODE objects which represent a single MIB attribute. The nodes can be fetched with multiple 'key' formats - the leaf name (e.g.,sysDescr) or fully/partially qualified name (e.g., system.sysDescr) or fully qualified numeric OID. The returned node object supports the following fields:

objectID

dotted decimal fully qualified OID

label

leaf textual identifier (e.g., 'sysDescr')

subID

leaf numeric OID component of objectID (e.g., '1')

moduleID

textual identifier for module (e.g., 'RFC1213-MIB')

parent

parent node

children

array reference of children nodes

nextNode

next lexico node (BUG!does not return in lexico order)

type

returns application type (see getType for values)

access

returns ACCESS (ReadOnly, ReadWrite, WriteOnly, NoAccess, Notify, Create)

status

returns STATUS (Mandatory, Optional, Obsolete, Deprecated)

syntax

returns 'textualConvention' if defined else 'type'

textualConvention

returns TEXTUAL-CONVENTION

TCDescription

returns the TEXTUAL-CONVENTION's Description field.

units

returns UNITS

hint

returns HINT

enums

returns hash ref {tag => num, ...}

ranges

returns array ref of hash ref [{low => num, high => num}, ...]

description

returns Description ($SNMP::save_descriptions must be set prior to MIB initialization/parsing)

reference

returns the REFERENCE clause

indexes

returns the objects in the INDEX clause

implied

returns true if the last object in the INDEX is IMPLIED

&SNMP::setMib(<file>)

allows dynamic parsing of the mib and explicit specification of mib file independent of environment variables. called with no args acts like initMib, loading MIBs indicated by environment variables (see Net-SNMP mib_api docs). passing non-zero second arg forces previous mib to be freed and replaced (Note: second arg not working since freeing previous Mib is more involved than before).

&SNMP::initMib()

calls library init_mib function if Mib not already loaded - does nothing if Mib already loaded. will parse directories and load modules according to environment variables described in Net-SNMP documentations. (see man mib_api, MIBDIRS, MIBS, MIBFILE(S), etc.)

&SNMP::addMibDirs(<dir>,...)

calls library add_mibdir for each directory supplied. will cause directory(s) to be added to internal list and made available for searching in subsequent loadModules calls

&SNMP::addMibFiles(<file>,...)

calls library read_mib function. The file(s) supplied will be read and all Mib module definitions contained therein will be added to internal mib tree structure

&SNMP::loadModules(<mod>,...)

calls library read_module function. The module(s) supplied will be searched for in the current mibdirs and and added to internal mib tree structure. Passing special <mod>, 'ALL', will cause all known modules to be loaded.

&SNMP::unloadModules(<mod>,...)

*Not Implemented*

&SNMP::translateObj(<var>[,arg,[arg]])

will convert a text obj tag to an OID and vice-versa. Any iid suffix is retained numerically.  Default behaviour when converting a numeric OID to text form is to return leaf identifier only (e.g.,'sysDescr') but when $SNMP::use_long_names is non-zero or a non-zero second arg is supplied it will return a longer textual identifier.  An optional third argument of non-zero will cause the module name to be prepended to the text name (e.g. 'SNMPv2-MIB::sysDescr').  When converting a text obj, the $SNMP::best_guess option is used.  If no Mib is loaded when called and $SNMP::auto_init_mib is enabled then the Mib will be loaded. Will return 'undef' upon failure.

&SNMP::getType(<var>)

return SNMP data type for given textual identifier OBJECTID, OCTETSTR, INTEGER, NETADDR, IPADDR, COUNTER GAUGE, TIMETICKS, OPAQUE, or undef

&SNMP::mapEnum(<var>)

converts integer value to enumertion tag defined in Mib or converts tag to integer depending on input. the function will return the corresponding integer value *or* tag for a given MIB attribute and value. The function will sense which direction to perform the conversion. Various arg formats are supported

$val = SNMP::mapEnum($varbind);

where $varbind is SNMP::Varbind or equiv. note: $varbind will be updated

$val = SNMP::mapEnum('ipForwarding', 'forwarding');

$val = SNMP::mapEnum('ipForwarding', 1);

Note: utility functions do not support async operation yet.

&snmp_get()

takes args of SNMP::Session::new followed by those of SNMP::Session::get

&snmp_getnext()

takes args of SNMP::Session::new followed by those of SNMP::Session::getnext

&snmp_set()

takes args of SNMP::Session::new followed by those of SNMP::Session::set

&snmp_trap()

takes args of SNMP::TrapSession::new followed by those of SNMP::TrapSession::trap

If problems occur there are number areas to look at to narrow down the possibilities.

The first step should be to test the Net-SNMP installation independently from the Perl5 SNMP interface.

Try running the apps from the Net-SNMP distribution.

Make sure your agent (snmpd) is running and properly configured with read-write access for the community you are using.

Ensure that your MIBs are installed and enviroment variables are set appropriately (see man mib_api)

Be sure to remove old net-snmp installations and ensure headers and libraries from old CMU installations are not being used by mistake.

If the problem occurs during compilation/linking check that the snmp library being linked is actually the Net-SNMP library (there have been name conflicts with existing snmp libs).

Also check that the header files are correct and up to date.

Sometimes compiling the Net-SNMP library with 'position-independent-code' enabled is required (HPUX specifically).

If you cannot resolve the problem you can post to comp.lang.perl.modules or net-snmp-users@net-snmp-users@lists.sourceforge.net

please give sufficient information to analyze the problem (OS type, versions for OS/Perl/Net-SNMP/compiler, complete error output, etc.)

Many thanks to all those who supplied patches, suggestions and feedback.

 Joe Marzot (the original author)
 Wes Hardaker and the net-snmp-coders
 Dave Perkins
 Marcel Wiget
 David Blackburn
 John Stofell
 Gary Hayward
 Claire Harrison
 Achim Bohnet
 Doug Kingston
 Jacques Vidrine
 Carl Jacobsen
 Wayne Marquette
 Scott Schumate
 Michael Slifcak
 Srivathsan Srinivasagopalan
 Bill Fenner
 Jef Peeraer
 Daniel Hagerty
 Karl "Rat" Schilke and Electric Lightwave, Inc.
 Perl5 Porters
 Alex Burger

Apologies to any/all who's patch/feature/request was not mentioned or included - most likely it was lost when paying work intruded on my fun. Please try again if you do not see a desired feature. This may actually turn out to be a decent package with such excellent help and the fact that I have more time to work on it than in the past.

bugs, comments, questions to net-snmp-users@lists.sourceforge.net

     Copyright (c) 1995-2000 G. S. Marzot. All rights reserved.
     This program is free software; you can redistribute it and/or
     modify it under the same terms as Perl itself.

     Copyright (c) 2001-2002 Networks Associates Technology, Inc.  All
     Rights Reserved.  This program is free software; you can
     redistribute it and/or modify it under the same terms as Perl
     itself.