Manual Reference Pages  - SNMP (3)


SNMP - The Perl5 SNMP Extension Module for the Net-SNMP SNMP package.



 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 docmuentation, 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 syncronous and asyncronous 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.
DestHost default ’localhost’, hostname or ip addr of SNMP agent
Community default ’public’, SNMP community string (used for both R/W)
Version default taken from library configuration - probably 3 [1, 2 (same as 2c), 2c, 3]
RemotePort default ’161’, allow remote UDP port to be overriden
Timeout default ’1000000’, micro-seconds before retry
Retries default ’5’, retries before failure
RetryNoSuch default ’0’, if enabled NOSUCH errors in ’get’ pdus will be repaired, removing the varbind in error, and resent - undef will be returned for all NOSUCH varbinds, when set to ’0’ this feature is disabled and the entire get request will fail on any NOSUCH error (applies to v1 only)
SecName default ’initial’, security name (v3)
SecLevel default ’noAuthNoPriv’, security level [noAuthNoPriv, authNoPriv, authPriv] (v3)
SecEngineId default <none>, security engineID, will be probed if not supplied (v3)
ContextEngineId default <SecEngineId>, context engineID, will be probed if not supplied (v3)
Context default ’’, context name (v3)
AuthProto default ’MD5’, authentication protocol [MD5, SHA] (v3)
AuthPass default <none>, authentication passphrase
PrivProto default ’DES’, privacy protocol [DES, AES] (v3)
PrivPass default <none>, privacy passphrase (v3)
PrivLocalizedKey Directly specified SNMPv3 USM user keys (used if you want to specify the keys instead of deriving them from a password as above).
VarFormats default ’undef’, used by ’fget[next]’, holds an hash reference of output value formatters, (e.g., {<obj> => <sub-ref>, ... }, <obj> must match the <obj> and format used in the get operation. A special <obj>, ’*’, may be used to apply all <obj>s, the supplied sub is called to translate the value to a new format. The sub is called passing the Varbind as the arg
TypeFormats default ’undef’, used by ’fget[next]’, holds an hash reference of output value formatters, (e.g., {<type> => <sub-ref>, ... }, the supplied sub is called to translate the value to a new format, unless a VarFormat mathces first (e.g., $sess->{TypeFormats}{INTEGER} = \&mapEnum(); although this can be done more efficiently by enabling $SNMP::use_enums or session creation param ’UseEnums’)
UseLongNames defaults to the value of SNMP::use_long_names at time of session creation. set to non-zero to have <tags> for ’getnext’ methods generated preferring longer Mib name convention (e.g., system.sysDescr vs just sysDescr)
UseSprintValue defaults to the value of SNMP::use_sprint_value at time of session creation. set to non-zero to have return values for ’get’ and ’getnext’ methods formatted with the libraries snprint_value function. This will result in certain data types being returned in non-canonical format Note: values returned with this option set may not be appropriate for ’set’ operations (see discussion of value formats in <vars> description section)
UseEnums defaults to the value of SNMP::use_enums at time of session creation. set to non-zero to have integer return values converted to enumeration identifiers if possible, these values will also be acceptable when supplied to ’set’ operations
UseNumeric defaults to the value of SNMP::use_numeric at time of session creation. 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 full OID is returned to the caller.
BestGuess defaults to the value of SNMP::best_guess at time of session creation. 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).
ErrorStr read-only, holds the error message assoc. w/ last request
ErrorNum read-only, holds the snmp_err or staus of last request
ErrorInd read-only, holds the snmp_err_index when appropriate
Private variables:
DestAddr internal field used to hold the translated DestHost field
SessPtr internal field used to cache a created session structure

SNMP::Session methods

$sess->update(<fields>) Updates the SNMP::Session object with the values fields passed in as a hash list (similar to new(<fields>)) (WARNING! not fully implemented)
$sess->get(<vars> [,<callback>]) do SNMP GET, multiple <vars> formats accepted. for syncronous operation <vars> will be updated with value(s) and type(s) and will also return retrieved value(s). If <callback> supplied method will operate asyncronously
$sess->fget(<vars> [,<callback>]) do SNMP GET like ’get’ and format the values according the handlers specified in $sess->{VarFormats} and $sess->{TypeFormats}
$sess->getnext(<vars> [,<callback>]) do SNMP GETNEXT, multiple <vars> formats accepted, returns retrieved value(s), <vars> passed as arguments are updated to indicate next lexicographical <obj>,<iid>,<val>, and <type>

Note: simple string <vars>,(e.g., ’sysDescr.0’) form is not updated. If <callback> supplied method will operate asyncronously

$sess->fgetnext(<vars> [,<callback>]) do SNMP GETNEXT like getnext and format the values according the handlers specified in $sess->{VarFormats} and $sess->{TypeFormats}
$sess->set(<vars> [,<callback>]) do SNMP SET, multiple <vars> formats accepted. the value field in all <vars> formats must be in a canonical format (i.e., well known format) to ensure unambiguous translation to SNMP MIB data value (see discussion of canonical value format <vars> description section), returns snmp_errno. If <callback> supplied method will operate asyncronously
$sess->getbulk(<non-repeaters>, <max-repeaters>, <vars>) do an SNMP GETBULK, from the list of Varbinds, the single next lexico instance is fetched for the first n Varbinds as defined by <non-repeaters>. For remaining Varbinds, the m lexico instances are retrieved each of the remaining Varbinds, where m is <max-repeaters>.
$sess->bulkwalk(<non-repeaters>, <max-repeaters>, <vars> [,<callback>]) Do a bulkwalk of the list of Varbinds. This is done by sending a GETBULK request (see getbulk() above) for the Varbinds. For each requested variable, the response is examined to see if the next lexico instance has left the requested sub-tree. Any further instances returned for this variable are ignored, and the walk for that sub-tree is considered complete.

If any sub-trees were not completed when the end of the responses is reached, another request is composed, consisting of the remaining variables. This process is repeated until all sub-trees have been completed, or too many packets have been exchanged (to avoid loops).

The bulkwalk() method returns an array containing an array of Varbinds, one for each requested variable, in the order of the variable requests. Upon error, bulkwalk() returns undef and sets $sess->ErrorStr and $sess->ErrorNum. If a callback is supplied, bulkwalk() returns the SNMP request id, and returns immediately. The callback will be called with the supplied argument list and the returned variables list.

Note: Because the client must discover that the tree is complete by comparing the returned variables with those that were requested, there is a potential gotcha when using the max-repeaters value. Consider the following code to print a list of interfaces and byte counts:

    $numInts = $sess->get(’ifNumber.0’);
    ($desc, $in, $out) = $sess->bulkwalk(0, $numInts,
                  [[’ifDescr’], [’ifInOctets’], [’ifOutOctets’]]);

    for $i (0..($numInts - 1)) {
        printf "Interface %4s: %s inOctets, %s outOctets\n",
                  $$desc[$i]->val, $$in[$i]->val, $$out[$i]->val;

This code will produce *two* requests to the agent — the first to get the interface values, and the second to discover that all the information was in the first packet. To get around this, use ’$numInts + 1’ for the max_repeaters value. This asks the agent to include one additional (unrelated) variable that signals the end of the sub-tree, allowing bulkwalk() to determine that the request is complete.

$results = $sess->gettable(<TABLE OID>, <OPTIONgt) This will retrieve an entire table of data and return a hash reference to that data. The returned hash reference will have indexes of the OID suffixes for the index data as the key. The value for each entry will be another hash containing the data for a given row. The keys to that hash will be the column names, and the values will be the data.



  use SNMP;
  use Data::Dumper;

  my $s = new SNMP::Session(DestHost => ’localhost’);

  print Dumper($s->gettable(’ifTable’));

On my machine produces:

  $VAR1 = {
            ’6’ => {
                     ’ifMtu’ => ’1500’,
                     ’ifPhysAddress’ => ’PV’,
                     # ...
                     ’ifInUnknownProtos’ => ’0’
            ’4’ => {
                     ’ifMtu’ => ’1480’,
                     ’ifPhysAddress’ => ’’,
                     # ...
                     ’ifInUnknownProtos’ => ’0’
            # ...

By default, it will try to do as optimized retrieval as possible. It’ll request multiple columns at once, and use GETBULK if possible. A few options may be specified by passing in an OPTIONS hash containing various parameters:
noindexes => 1 Instructs the code not to parse the indexes and place the results in the second hash. If you don’t need the index data, this will be faster.
columns => [ colname1, ... ] This specifies which columns to collect. By default, it will try to collect all the columns defined in the MIB table.
repeat => COUNT Specifies a GETBULK repeat COUNT. IE, it will request this many varbinds back per column when using the GETBULK operation. Shortening this will mean smaller packets which may help going through some systems. By default, this value is calculated and attepmts to guess at what will fit all the results into 1000 bytes. This calculation is fairly safe, hopefully, but you can either raise or lower the number using this option if desired. In lossy networks, you want to make sure that the packets don’t get fragmented and lowering this value is one way to help that.
nogetbulk => 1 Force the use of GETNEXT rather than GETBULK. (always true for SNMPv1, as it doesn’t have GETBULK anyway). Some agents are great implementers of GETBULK and this allows you to force the use of GETNEXT oprations instead.


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

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

SNMP::TrapSession methods

$sess->trap(enterprise, agent, generic, specific, uptime, <vars>)

    $sess->trap(enterprise=>’.’, # or ’ucdavis’ [default]
                agent => ’’, # or ’localhost’,[dflt 1st intf on host]
                generic => specific,  # can be omitted if ’specific’ supplied
                specific => 5,        # can be omitted if ’generic’ supplied
                uptime => 1234,       # dflt to localhost uptime (0 on win32)
                [[ifIndex, 1, 1],[sysLocation, 0, "here"]]); # optional vars
                                                             # always last

trap(oid, uptime, <vars>) - v2 format

    $sess->trap(oid => ’snmpRisingAlarm’,
                uptime => 1234,
                [[ifIndex, 1, 1],[sysLocation, 0, "here"]]); # optional vars
                                                             # always last

Acceptable variable formats:

<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., ’’)
3) fully qualified, dotted-decimal, numeric OID (e.g., ’.’)
<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., .
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.

Acceptable callback formats

<callback> may be one of the following forms:
without arguments
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 not be processed. If no args suplied this function enters an infinite loop so program must be exited in a callback or externally interupted. 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 package variables and functions

$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 UCD 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’, controlls 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()


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

MIB Functions

&SNMP::setMib(<file>) allows dynamic parsing of the mib and explicit specification of mib file independent of enviroment variables. called with no args acts like initMib, loading MIBs indicated by environment variables (see ucd 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 UCD 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);

Exported SNMP utility functions

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

Trouble Shooting

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

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

Try running the apps from the UCD 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 ucd-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 UCD 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 UCD 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

please give sufficient information to analyze the problem (OS type, versions for OS/Perl/UCD/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


     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

perl v5.8.8 SNMP (3) 2008-06-18
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