Provided by: libnet-snmp-perl_6.0.1-7_all 
NAME
Net::SNMP - Object oriented interface to SNMP
SYNOPSIS
The Net::SNMP module implements an object oriented interface to the Simple Network
Management Protocol. Perl applications can use the module to retrieve or update
information on a remote host using the SNMP protocol. The module supports SNMP version-1,
SNMP version-2c (Community-Based SNMPv2), and SNMP version-3. The Net::SNMP module assumes
that the user has a basic understanding of the Simple Network Management Protocol and
related network management concepts.
DESCRIPTION
The Net::SNMP module abstracts the intricate details of the Simple Network Management
Protocol by providing a high level programming interface to the protocol. Each Net::SNMP
object provides a one-to-one mapping between a Perl object and a remote SNMP agent or
manager. Once an object is created, it can be used to perform the basic protocol exchange
actions defined by SNMP.
A Net::SNMP object can be created such that it has either "blocking" or "non-blocking"
properties. By default, the methods used to send SNMP messages do not return until the
protocol exchange has completed successfully or a timeout period has expired. This
behavior gives the object a "blocking" property because the flow of the code is stopped
until the method returns.
The optional named argument -nonblocking can be passed to the object constructor with a
true value to give the object "non-blocking" behavior. A method invoked by a non-blocking
object queues the SNMP message and returns immediately, allowing the flow of the code to
continue. The queued SNMP messages are not sent until an event loop is entered by calling
the "snmp_dispatcher()" method. When the SNMP messages are sent, any response to the
messages invokes the subroutine defined by the user when the message was originally
queued. The event loop exits when all messages have been removed from the queue by either
receiving a response, or by exceeding the number of retries at the Transport Layer.
Blocking Objects
The default behavior of the methods associated with a Net::SNMP object is to block the
code flow until the method completes. For methods that initiate a SNMP protocol exchange
requiring a response, a hash reference containing the results of the query is returned.
The undefined value is returned by all methods when a failure has occurred. The "error()"
method can be used to determine the cause of the failure.
The hash reference returned by a SNMP protocol exchange points to a hash constructed from
the VarBindList contained in the SNMP response message. The hash is created using the
ObjectName and the ObjectSyntax pairs in the VarBindList. The keys of the hash consist of
the OBJECT IDENTIFIERs in dotted notation corresponding to each ObjectName in the
VarBindList. The value of each hash entry is set equal to the value of the corresponding
ObjectSyntax. This hash reference can also be retrieved using the "var_bind_list()"
method.
Non-blocking Objects
When a Net::SNMP object is created having non-blocking behavior, the invocation of a
method associated with the object returns immediately, allowing the flow of the code to
continue. When a method is invoked that would initiate a SNMP protocol exchange requiring
a response, either a true value (i.e. 0x1) is returned immediately or the undefined value
is returned if there was a failure. The "error()" method can be used to determine the
cause of the failure.
The contents of the VarBindList contained in the SNMP response message can be retrieved by
calling the "var_bind_list()" method using the object reference passed as the first
argument to the callback. The value returned by the "var_bind_list()" method is a hash
reference created using the ObjectName and the ObjectSyntax pairs in the VarBindList. The
keys of the hash consist of the OBJECT IDENTIFIERs in dotted notation corresponding to
each ObjectName in the VarBindList. The value of each hash entry is set equal to the
value of the corresponding ObjectSyntax. The undefined value is returned if there has been
a failure and the "error()" method may be used to determine the reason.
METHODS
When named arguments are expected by the methods, two different styles are supported. All
examples in this documentation use the dashed-option style:
$object->method(-argument => $value);
However, the IO:: style is also allowed:
$object->method(Argument => $value);
Non-blocking Objects Arguments
When a Net::SNMP object has been created with a "non-blocking" property, most methods
that generate a SNMP message take additional arguments to support this property.
Callback
Most methods associated with a non-blocking object have an optional named argument
called -callback. The -callback argument expects a reference to a subroutine or
to an array whose first element must be a reference to a subroutine. The
subroutine defined by the -callback option is executed when a response to a SNMP
message is received, an error condition has occurred, or the number of retries for
the message has been exceeded.
When the -callback argument only contains a subroutine reference, the subroutine
is evaluated passing a reference to the original Net::SNMP object as the only
parameter. If the -callback argument was defined as an array reference, all
elements in the array are passed to subroutine after the reference to the
Net::SNMP object. The first element, which is required to be a reference to a
subroutine, is removed before the remaining arguments are passed to that
subroutine.
Once one method is invoked with the -callback argument, this argument stays with
the object and is used by any further calls to methods using the -callback option
if the argument is absent. The undefined value may be passed to the -callback
argument to delete the callback.
NOTE: The subroutine being passed with the -callback named argument should not
cause blocking itself. This will cause all the actions in the event loop to be
stopped, defeating the non-blocking property of the Net::SNMP module.
Delay
An optional argument -delay can also be passed to non-blocking objects. The
-delay argument instructs the object to wait the number of seconds passed to the
argument before executing the SNMP protocol exchange. The delay period starts
when the event loop is entered. The -delay parameter is applied to all methods
associated with the object once it is specified. The delay value must be set back
to 0 seconds to disable the delay parameter.
SNMPv3 Arguments
A SNMP context is a collection of management information accessible by a SNMP entity.
An item of management information may exist in more than one context and a SNMP entity
potentially has access to many contexts. The combination of a contextEngineID and a
contextName unambiguously identifies a context within an administrative domain. In a
SNMPv3 message, the contextEngineID and contextName are included as part of the
scopedPDU. All methods that generate a SNMP message optionally take a
-contextengineid and -contextname argument to configure these fields.
Context Engine ID
The -contextengineid argument expects a hexadecimal string representing the
desired contextEngineID. The string must be 10 to 64 characters (5 to 32 octets)
long and can be prefixed with an optional "0x". Once the -contextengineid is
specified it stays with the object until it is changed again or reset to default
by passing in the undefined value. By default, the contextEngineID is set to
match the authoritativeEngineID of the authoritative SNMP engine.
Context Name
The contextName is passed as a string which must be 0 to 32 octets in length using
the -contextname argument. The contextName stays with the object until it is
changed. The contextName defaults to an empty string which represents the
"default" context.
session() - create a new Net::SNMP object
($session, $error) = Net::SNMP->session(
[-hostname => $hostname,]
[-port => $port,]
[-localaddr => $localaddr,]
[-localport => $localport,]
[-nonblocking => $boolean,]
[-version => $version,]
[-domain => $domain,]
[-timeout => $seconds,]
[-retries => $count,]
[-maxmsgsize => $octets,]
[-translate => $translate,]
[-debug => $bitmask,]
[-community => $community,] # v1/v2c
[-username => $username,] # v3
[-authkey => $authkey,] # v3
[-authpassword => $authpasswd,] # v3
[-authprotocol => $authproto,] # v3
[-privkey => $privkey,] # v3
[-privpassword => $privpasswd,] # v3
[-privprotocol => $privproto,] # v3
);
This is the constructor for Net::SNMP objects. In scalar context, a reference to a new
Net::SNMP object is returned if the creation of the object is successful. In list
context, a reference to a new Net::SNMP object and an empty error message string is
returned. If a failure occurs, the object reference is returned as the undefined value.
The error string may be used to determine the cause of the error.
Most of the named arguments passed to the constructor define basic attributes for the
object and are not modifiable after the object has been created. The -timeout, -retries,
-maxmsgsize, -translate, and -debug arguments are modifiable using an accessor method.
See their corresponding method definitions for a complete description of their usage,
default values, and valid ranges.
Transport Domain Arguments
The Net::SNMP module uses UDP/IPv4 as the default Transport Domain to exchange SNMP
messages between the local and remote devices. The module also supports UDP/IPv6,
TCP/IPv4, and TCP/IPv6 as alternative Transport Domains. The -domain argument can be
used to change the Transport Domain by setting the value to one of the following
strings: 'udp6', 'udp/ipv6'; 'tcp', 'tcp4', 'tcp/ipv4'; 'tcp6', or 'tcp/ipv6'. The
-domain argument also accepts the strings 'udp', 'udp4', or 'udp/ipv4' which
correspond to the default Transport Domain of UDP/IPv4.
The transport address of the destination SNMP device can be specified using the
-hostname argument. This argument is optional and defaults to "localhost". The
destination port number can be specified as part of the transport address or by using
the -port argument. Either a numeric port number or a textual service name can be
specified. A numeric port number in parentheses can optionally follow the service
name. This port number will be used if the service name cannot be resolved. If the
destination port number is not specified, the well-known SNMP port number 161 is used.
By default the source transport address and port number are assigned dynamically by
the local device on which the Net::SNMP module is being used. This dynamic assignment
can be overridden by using the -localaddr and -localport arguments. These arguments
accept the same values as the -hostname and -port arguments respectively. The
resolved address must correspond to a valid address of an interface on the local
device.
When using an IPv4 Transport Domain, the transport address can be specified as either
an IP network hostname or an IPv4 address in standard dotted notation. The port
information can be optionally appended to the hostname or address delimited by a
colon. The accepted IPv4 transport address formats are "address", "address:port",
"hostname", and "hostname:port".
When using an IPv6 Transport Domain, the transport address can be specified as an IP
hostname (which will be looked up as a DNS quad-A record) or an IPv6 address in
presentation format. The port information can optionally be included following a
colon after the hostname or address. When including this information after an IPv6
address, the address must be enclosed in square brackets. The scope zone index
(described in RFC 4007) can be specified after the address as a decimal value
delimited by a percent sign. The accepted transport address formats for IPv6 are
"address", "address%zone", "[address]:port", "[address%zone]:port", "hostname", and
"hostname:port".
Security Model Arguments
The -version argument controls which other arguments are expected or required by the
"session()" constructor. The Net::SNMP module supports SNMPv1, SNMPv2c, and SNMPv3.
The module defaults to SNMPv1 if no -version argument is specified. The -version
argument expects either a digit (i.e. '1', '2', or '3') or a string specifying the
version (i.e. 'snmpv1', 'snmpv2c', or 'snmpv3') to define the SNMP version.
The Security Model used by the Net::SNMP object is based on the SNMP version
associated with the object. If the SNMP version is SNMPv1 or SNMPv2c a Community-
based Security Model will be used, while the User-based Security Model (USM) will be
used if the version is SNMPv3.
Community-based Security Model Argument
If the Security Model is Community-based, the only argument available is the
-community argument. This argument expects a string that is to be used as the
SNMP community name. By default the community name is set to 'public' if the
argument is not present.
User-based Security Model Arguments
The User-based Security Model (USM) used by SNMPv3 requires that a securityName be
specified using the -username argument. The creation of a Net::SNMP object with
the version set to SNMPv3 will fail if the -username argument is not present. The
-username argument expects a string 1 to 32 octets in length.
Different levels of security are allowed by the User-based Security Model which
address authentication and privacy concerns. A SNMPv3 Net::SNMP object will
derive the security level (securityLevel) based on which of the following
arguments are specified.
By default a securityLevel of 'noAuthNoPriv' is assumed. If the -authkey or
-authpassword arguments are specified, the securityLevel becomes 'authNoPriv'.
The -authpassword argument expects a string which is at least 1 octet in length.
Optionally, the -authkey argument can be used so that a plain text password does
not have to be specified in a script. The -authkey argument expects a hexadecimal
string produced by localizing the password with the authoritativeEngineID for the
specific destination device. The "snmpkey" utility included with the distribution
can be used to create the hexadecimal string (see snmpkey).
Two different hash algorithms are defined by SNMPv3 which can be used by the
Security Model for authentication. These algorithms are HMAC-MD5-96 "MD5" (RFC
1321) and HMAC-SHA-96 "SHA-1" (NIST FIPS PUB 180-1). The default algorithm used
by the module is HMAC-MD5-96. This behavior can be changed by using the
-authprotocol argument. This argument expects either the string 'md5' or 'sha' to
be passed to modify the hash algorithm.
By specifying the arguments -privkey or -privpassword the securityLevel associated
with the object becomes 'authPriv'. According to SNMPv3, privacy requires the use
of authentication. Therefore, if either of these two arguments are present and
the -authkey or -authpassword arguments are missing, the creation of the object
fails. The -privkey and -privpassword arguments expect the same input as the
-authkey and -authpassword arguments respectively.
The User-based Security Model described in RFC 3414 defines a single encryption
protocol to be used for privacy. This protocol, CBC-DES "DES" (NIST FIPS PUB
46-1), is used by default or if the string 'des' is passed to the -privprotocol
argument. The module also supports RFC 3826 which describes the use of
CFB128-AES-128 "AES" (NIST FIPS PUB 197) in the USM. The AES encryption protocol
can be selected by passing 'aes' or 'aes128' to the -privprotocol argument. By
working with the Extended Security Options Consortium
<http://www.snmp.com/protocol/eso.shtml>, the module also supports CBC-3DES-EDE
"Triple-DES" (NIST FIPS 46-3) in the User-based Security Model. This is defined
in the draft <http://www.snmp.com/eso/draft-reeder-snmpv3-usm-3desede-00.txt>.
The Triple-DES encryption protocol can be selected using the -privprotocol
argument with the string '3des' or '3desede'.
close() - clear the Transport Domain associated with the object
$session->close();
This method clears the Transport Domain and any errors associated with the object. Once
closed, the Net::SNMP object can no longer be used to send or receive SNMP messages.
snmp_dispatcher() - enter the non-blocking object event loop
$session->snmp_dispatcher();
This method enters the event loop associated with non-blocking Net::SNMP objects. The
method exits when all queued SNMP messages have received a response or have timed out at
the Transport Layer. This method is also exported as the stand alone function
"snmp_dispatcher()" by default (see "EXPORTS").
get_request() - send a SNMP get-request to the remote agent
$result = $session->get_request(
[-callback => sub {},] # non-blocking
[-delay => $seconds,] # non-blocking
[-contextengineid => $engine_id,] # v3
[-contextname => $name,] # v3
-varbindlist => \@oids,
);
This method performs a SNMP get-request query to gather data from the remote agent on the
host associated with the Net::SNMP object. The message is built using the list of OBJECT
IDENTIFIERs in dotted notation passed to the method as an array reference using the
-varbindlist argument. Each OBJECT IDENTIFIER is placed into a single SNMP GetRequest-PDU
in the same order that it held in the original list.
A reference to a hash is returned in blocking mode which contains the contents of the
VarBindList. In non-blocking mode, a true value is returned when no error has occurred.
In either mode, the undefined value is returned when an error has occurred. The "error()"
method may be used to determine the cause of the failure.
get_next_request() - send a SNMP get-next-request to the remote agent
$result = $session->get_next_request(
[-callback => sub {},] # non-blocking
[-delay => $seconds,] # non-blocking
[-contextengineid => $engine_id,] # v3
[-contextname => $name,] # v3
-varbindlist => \@oids,
);
This method performs a SNMP get-next-request query to gather data from the remote agent on
the host associated with the Net::SNMP object. The message is built using the list of
OBJECT IDENTIFIERs in dotted notation passed to the method as an array reference using the
-varbindlist argument. Each OBJECT IDENTIFER is placed into a single SNMP GetNextRequest-
PDU in the same order that it held in the original list.
A reference to a hash is returned in blocking mode which contains the contents of the
VarBindList. In non-blocking mode, a true value is returned when no error has occurred.
In either mode, the undefined value is returned when an error has occurred. The "error()"
method may be used to determine the cause of the failure.
set_request() - send a SNMP set-request to the remote agent
$result = $session->set_request(
[-callback => sub {},] # non-blocking
[-delay => $seconds,] # non-blocking
[-contextengineid => $engine_id,] # v3
[-contextname => $name,] # v3
-varbindlist => \@oid_value,
);
This method is used to modify data on the remote agent that is associated with the
Net::SNMP object using a SNMP set-request. The message is built using a list of values
consisting of groups of an OBJECT IDENTIFIER, an object type, and the actual value to be
set. This list is passed to the method as an array reference using the -varbindlist
argument. The OBJECT IDENTIFIERs in each trio are to be in dotted notation. The object
type is an octet corresponding to the ASN.1 type of value that is to be set. Each of the
supported ASN.1 types have been defined and are exported by the package by default (see
"EXPORTS").
A reference to a hash is returned in blocking mode which contains the contents of the
VarBindList. In non-blocking mode, a true value is returned when no error has occurred.
In either mode, the undefined value is returned when an error has occurred. The "error()"
method may be used to determine the cause of the failure.
trap() - send a SNMP trap to the remote manager
$result = $session->trap(
[-delay => $seconds,] # non-blocking
[-enterprise => $oid,]
[-agentaddr => $ipaddress,]
[-generictrap => $generic,]
[-specifictrap => $specific,]
[-timestamp => $timeticks,]
-varbindlist => \@oid_value,
);
This method sends a SNMP trap to the remote manager associated with the Net::SNMP object.
All arguments are optional and will be given the following defaults in the absence of a
corresponding named argument:
• The default value for the trap -enterprise is "1.3.6.1.4.1", which corresponds to
"iso.org.dod.internet.private.enterprises". The enterprise value is expected to be an
OBJECT IDENTIFER in dotted notation.
• When the Transport Domain is UDP/IPv4 or TCP/IPv4, the default value for the trap
-agentaddr is the IP address associated with the interface on which the trap will be
transmitted. For other Transport Domains the -agentaddr is defaulted to "0.0.0.0".
When specified, the agent-addr is expected to be an IpAddress in dotted notation.
• The default value for the -generictrap type is 6 which corresponds to
"enterpriseSpecific". The generic-trap types are defined and can be exported upon
request (see "EXPORTS").
• The default value for the -specifictrap type is 0. No pre-defined values are
available for specific-trap types.
• The default value for the trap -timestamp is the "uptime" of the script. The "uptime"
of the script is the number of hundredths of seconds that have elapsed since the
script began running. The time-stamp is expected to be a TimeTicks number in
hundredths of seconds.
• The default value for the trap -varbindlist is an empty array reference. The
variable-bindings are expected to be in an array format consisting of groups of an
OBJECT IDENTIFIER, an object type, and the actual value of the object. This is
identical to the list expected by the "set_request()" method. The OBJECT IDENTIFIERs
in each trio are to be in dotted notation. The object type is an octet corresponding
to the ASN.1 type for the value. Each of the supported types have been defined and are
exported by default (see "EXPORTS").
A true value is returned when the method is successful. The undefined value is returned
when a failure has occurred. The "error()" method can be used to determine the cause of
the failure. Since there are no acknowledgements for Trap-PDUs, there is no way to
determine if the remote host actually received the trap.
NOTE: When the object is in non-blocking mode, the trap is not sent until the event loop
is entered and no callback is ever executed.
NOTE: This method can only be used when the version of the object is set to SNMPv1.
get_bulk_request() - send a SNMP get-bulk-request to the remote agent
$result = $session->get_bulk_request(
[-callback => sub {},] # non-blocking
[-delay => $seconds,] # non-blocking
[-contextengineid => $engine_id,] # v3
[-contextname => $name,] # v3
[-nonrepeaters => $non_reps,]
[-maxrepetitions => $max_reps,]
-varbindlist => \@oids,
);
This method performs a SNMP get-bulk-request query to gather data from the remote agent on
the host associated with the Net::SNMP object. All arguments are optional except
-varbindlist and will be given the following defaults in the absence of a corresponding
named argument:
• The default value for the get-bulk-request -nonrepeaters is 0. The non-repeaters
value specifies the number of variables in the variable-bindings list for which a
single successor is to be returned.
• The default value for the get-bulk-request -maxrepetitions is 0. The max-repetitions
value specifies the number of successors to be returned for the remaining variables in
the variable-bindings list.
• The -varbindlist argument expects an array reference consisting of a list of OBJECT
IDENTIFIERs in dotted notation. Each OBJECT IDENTIFER is placed into a single SNMP
GetBulkRequest-PDU in the same order that it held in the original list.
A reference to a hash is returned in blocking mode which contains the contents of the
VarBindList. In non-blocking mode, a true value is returned when no error has occurred.
In either mode, the undefined value is returned when an error has occurred. The "error()"
method may be used to determine the cause of the failure.
NOTE: This method can only be used when the version of the object is set to SNMPv2c or
SNMPv3.
inform_request() - send a SNMP inform-request to the remote manager
$result = $session->inform_request(
[-callback => sub {},] # non-blocking
[-delay => $seconds,] # non-blocking
[-contextengineid => $engine_id,] # v3
[-contextname => $name,] # v3
-varbindlist => \@oid_value,
);
This method is used to provide management information to the remote manager associated
with the Net::SNMP object using an inform-request. The message is built using a list of
values consisting of groups of an OBJECT IDENTIFIER, an object type, and the actual value
to be identified. This list is passed to the method as an array reference using the
-varbindlist argument. The OBJECT IDENTIFIERs in each trio are to be in dotted notation.
The object type is an octet corresponding to the ASN.1 type of value that is to be
identified. Each of the supported ASN.1 types have been defined and are exported by the
package by default (see "EXPORTS").
The first two variable-bindings fields in the inform-request are specified by SNMPv2 and
should be:
• sysUpTime.0 - ('1.3.6.1.2.1.1.3.0', TIMETICKS, $timeticks)
• snmpTrapOID.0 - ('1.3.6.1.6.3.1.1.4.1.0', OBJECT_IDENTIFIER, $oid)
A reference to a hash is returned in blocking mode which contains the contents of the
VarBindList. In non-blocking mode, a true value is returned when no error has occurred.
In either mode, the undefined value is returned when an error has occurred. The "error()"
method may be used to determine the cause of the failure.
NOTE: This method can only be used when the version of the object is set to SNMPv2c or
SNMPv3.
snmpv2_trap() - send a SNMP snmpV2-trap to the remote manager
$result = $session->snmpv2_trap(
[-delay => $seconds,] # non-blocking
-varbindlist => \@oid_value,
);
This method sends a snmpV2-trap to the remote manager associated with the Net::SNMP
object. The message is built using a list of values consisting of groups of an OBJECT
IDENTIFIER, an object type, and the actual value to be identified. This list is passed to
the method as an array reference using the -varbindlist argument. The OBJECT IDENTIFIERs
in each trio are to be in dotted notation. The object type is an octet corresponding to
the ASN.1 type of value that is to be identified. Each of the supported ASN.1 types have
been defined and are exported by the package by default (see "EXPORTS").
The first two variable-bindings fields in the snmpV2-trap are specified by SNMPv2 and
should be:
• sysUpTime.0 - ('1.3.6.1.2.1.1.3.0', TIMETICKS, $timeticks)
• snmpTrapOID.0 - ('1.3.6.1.6.3.1.1.4.1.0', OBJECT_IDENTIFIER, $oid)
A true value is returned when the method is successful. The undefined value is returned
when a failure has occurred. The "error()" method can be used to determine the cause of
the failure. Since there are no acknowledgements for SNMPv2-Trap-PDUs, there is no way to
determine if the remote host actually received the snmpV2-trap.
NOTE: When the object is in non-blocking mode, the snmpV2-trap is not sent until the event
loop is entered and no callback is ever executed.
NOTE: This method can only be used when the version of the object is set to SNMPv2c.
SNMPv2-Trap-PDUs are supported by SNMPv3, but require the sender of the message to be an
authoritative SNMP engine which is not currently supported by the Net::SNMP module.
get_table() - retrieve a table from the remote agent
$result = $session->get_table(
[-callback => sub {},] # non-blocking
[-delay => $seconds,] # non-blocking
[-contextengineid => $engine_id,] # v3
[-contextname => $name,] # v3
-baseoid => $oid,
[-maxrepetitions => $max_reps,] # v2c/v3
);
This method performs repeated SNMP get-next-request or get-bulk-request (when using
SNMPv2c or SNMPv3) queries to gather data from the remote agent on the host associated
with the Net::SNMP object. The first message sent is built using the OBJECT IDENTIFIER in
dotted notation passed to the method by the -baseoid argument. Repeated SNMP requests
are issued until the OBJECT IDENTIFIER in the response is no longer a child of the base
OBJECT IDENTIFIER.
The -maxrepetitions argument can be used to specify the max-repetitions value that is
passed to the get-bulk-requests when using SNMPv2c or SNMPv3. If this argument is not
present, a value is calculated based on the maximum message size for the Net::SNMP object.
If the value is set to 1 or less, get-next-requests will be used for the queries instead
of get-bulk-requests.
A reference to a hash is returned in blocking mode which contains the contents of the
VarBindList. In non-blocking mode, a true value is returned when no error has occurred.
In either mode, the undefined value is returned when an error has occurred. The "error()"
method may be used to determine the cause of the failure.
WARNING: Results from this method can become very large if the base OBJECT IDENTIFIER is
close to the root of the SNMP MIB tree.
get_entries() - retrieve table entries from the remote agent
$result = $session->get_entries(
[-callback => sub {},] # non-blocking
[-delay => $seconds,] # non-blocking
[-contextengineid => $engine_id,] # v3
[-contextname => $name,] # v3
-columns => \@columns,
[-startindex => $start,]
[-endindex => $end,]
[-maxrepetitions => $max_reps,] # v2c/v3
);
This method performs repeated SNMP get-next-request or get-bulk-request (when using
SNMPv2c or SNMPv3) queries to gather data from the remote agent on the host associated
with the Net::SNMP object. Each message specifically requests data for each OBJECT
IDENTIFIER specified in the -columns array. The OBJECT IDENTIFIERs must correspond to
column entries for a conceptual row in a table. They may however be columns in different
tables as long as each table is indexed the same way. The optional -startindex and
-endindex arguments may be specified to limit the query to specific rows in the table(s).
The -startindex can be specified as a single decimal value or in dotted notation if the
index associated with the entry so requires. If the -startindex is specified, it will be
include as part of the query results. If no -startindex is specified, the first request
message will be sent without an index. To insure that the -startindex is included, the
last sub-identifier in the index is decremented by one. If the last sub-identifier has a
value of zero, the sub-identifier is removed from the index.
The optional -endindex argument can be specified as a single decimal value or in dotted
notation. If the -endindex is specified, it will be included as part of the query
results. If no -endindex is specified, repeated SNMP requests are issued until the
response no longer returns entries matching any of the columns specified in the -columns
array.
The -maxrepetitions argument can be used to specify the max-repetitions value that is
passed to the get-bulk-requests when using SNMPv2c or SNMPv3. If this argument is not
present, a value is calculated based on the maximum message size of the object and the
number of columns specified in the -columns array. If the value is set to 1 or less, get-
next-requests will be used for the queries instead of get-bulk-requests.
A reference to a hash is returned in blocking mode which contains the contents of the
VarBindList. In non-blocking mode, a true value is returned when no error has occurred.
In either mode, the undefined value is returned when an error has occurred. The "error()"
method may be used to determine the cause of the failure.
version() - get the SNMP version from the object
$rfc_version = $session->version();
This method returns the current value for the SNMP version associated with the object.
The returned value is the corresponding version number defined by the RFCs for the
protocol version field (i.e. SNMPv1 == 0, SNMPv2c == 1, and SNMPv3 == 3). The RFC
versions are defined as constant by the module and can be exported by request (see
"EXPORTS").
error() - get the current error message from the object
$error_message = $session->error();
This method returns a text string explaining the reason for the last error. An empty
string is returned if no error has occurred.
hostname() - get the hostname associated with the object
$hostname = $session->hostname();
This method returns the parsed hostname string that is associated with the object. Any
port information and formatting that can be included with the corresponding "session()"
constructor argument will be stripped and not included as part of the returned string.
error_status() - get the current SNMP error-status from the object
$error_status = $session->error_status();
This method returns the numeric value of the error-status contained in the last SNMP
message received by the object.
error_index() - get the current SNMP error-index from the object
$error_index = $session->error_index();
This method returns the numeric value of the error-index contained in the last SNMP
message received by the object.
var_bind_list() - get the hash reference for the VarBindList values
$values = $session->var_bind_list();
This method returns a hash reference created using the ObjectName and the ObjectSyntax
pairs in the VarBindList of the last SNMP message received by the object. The keys of the
hash consist of the OBJECT IDENTIFIERs in dotted notation corresponding to each ObjectName
in the VarBindList. If any of the OBJECT IDENTIFIERs passed to the request method began
with a leading dot, all of the OBJECT IDENTIFIER hash keys will be prefixed with a leading
dot. If duplicate OBJECT IDENTIFIERs are present in the VarBindList they will be padded
with spaces to make them an unique hash key. The value of each hash entry is set equal to
the value of the corresponding ObjectSyntax. The undefined value is returned if there has
been a failure.
var_bind_names() - get the array of the ObjectNames in the VarBindList
@names = $session->var_bind_names();
This method returns an array containing the OBJECT IDENTIFIERs corresponding to the
ObjectNames in the VarBindList in the order that they were received in the last SNMP
message. The entries in the array will map directly to the keys in the hash reference
returned by the methods that perform SNMP message exchanges and by the "var_bind_list()"
and "var_bind_types()" methods. The array returned for the convenience methods
"get_table()" and "get_entries()" will be in lexicographical order. An empty array is
returned if there has been a failure.
var_bind_types() - get the hash reference for the VarBindList ASN.1 types
$types = $session->var_bind_types();
This method returns a hash reference created using the ObjectName and the ASN.1 type of
the ObjectSyntax in the VarBindList of the last SNMP message received by the object. The
keys of the hash consist of the OBJECT IDENTIFIERs in dotted notation corresponding to
each ObjectName in the VarBindList. The value of each hash entry is set equal to the
ASN.1 type of the corresponding ObjectSyntax. Constants for the supported ASN.1 types
have been defined and are exported by the package by default (see "EXPORTS"). The
undefined value is returned if there has been a failure.
timeout() - set or get the current timeout period for the object
$seconds = $session->timeout([$seconds]);
This method returns the current value for the Transport Layer timeout for the Net::SNMP
object. This value is the number of seconds that the object will wait for a response from
the agent on the remote host. The default timeout is 5.0 seconds.
If a parameter is specified, the timeout for the object is set to the provided value if it
falls within the range 1.0 to 60.0 seconds. The undefined value is returned upon an error
and the "error()" method may be used to determine the cause.
retries() - set or get the current retry count for the object
$count = $session->retries([$count]);
This method returns the current value for the number of times to retry sending a SNMP
message to the remote host. The default number of retries is 1.
If a parameter is specified, the number of retries for the object is set to the provided
value if it falls within the range 0 to 20. The undefined value is returned upon an error
and the "error()" method may be used to determine the cause.
max_msg_size() - set or get the current maxMsgSize for the object
$octets = $session->max_msg_size([$octets]);
This method returns the current value for the maximum message size (maxMsgSize) for the
Net::SNMP object. This value is the largest message size in octets that can be prepared
or processed by the object. The default maxMsgSize is 1472 octets for UDP/IPv4, 1452
octets for UDP/IPv6, 1460 octets for TCP/IPv4, and 1440 octets for TCP/IPv6.
If a parameter is specified, the maxMsgSize is set to the provided value if it falls
within the range 484 to 65535 octets. The undefined value is returned upon an error and
the "error()" method may be used to determine the cause.
NOTE: When using SNMPv3, the maxMsgSize is actually contained in the SNMP message (as
msgMaxSize). If the value received from a remote device is less than the current
maxMsgSize, the size is automatically adjusted to be the lower value.
translate() - enable or disable the translation mode for the object
$mask = $session->translate([
$mode |
[ # Perl anonymous ARRAY reference
['-all' => $mode0,]
['-octetstring' => $mode1,]
['-null' => $mode2,]
['-timeticks' => $mode3,]
['-opaque' => $mode4,]
['-nosuchobject' => $mode5,]
['-nosuchinstance' => $mode6,]
['-endofmibview' => $mode7,]
['-unsigned' => $mode8]
]
]);
When the object decodes the GetResponse-PDU that is returned in response to a SNMP
message, certain values are translated into a more "human readable" form. By default the
following translations occur:
• OCTET STRINGs and Opaques containing any octet which is not part of the character set
defined as a DisplayString in RFC 2679 are converted into a hexadecimal representation
prefixed with "0x". The control codes NUL(0x00), BEL(0x07), BS(0x08), HT(0x09),
LF(0x0A), VT(0x0b), FF(0x0C), and CR(0x0D) are part of the character set and will not
trigger translation. The sequence 'CR x' for any x other than LF or NUL is illegal
and will trigger translation.
• TimeTicks integer values are converted to a time format.
• NULL values return the string "NULL" instead of an empty string.
• noSuchObject exception values return the string "noSuchObject" instead of an empty
string.
• noSuchInstance exception values return the string "noSuchInstance" instead of an empty
string.
• endOfMibView exception values return the string "endOfMibView" instead of an empty
string.
• Counter64, Counter, Gauge, and TimeTick values that have been incorrectly encoded as
signed negative values are returned as unsigned values.
The "translate()" method can be invoked with two different types of arguments.
If the argument passed is any Perl variable type except an array reference, the
translation mode for all ASN.1 types is set to either enabled or disabled, depending on
the value of the passed parameter. Any value that Perl would treat as a true value will
set the mode to be enabled for all types, while a false value will disable translation for
all types.
A reference to an array can be passed to the "translate()" method in order to define the
translation mode on a per ASN.1 type basis. The array is expected to contain a list of
named argument pairs for each ASN.1 type that is to be modified. The arguments in the
list are applied in the order that they are passed in via the array. Arguments at the end
of the list supersede those passed earlier in the list. The argument "-all" can be used
to specify that the mode is to apply to all ASN.1 types. Only the arguments for the ASN.1
types that are to be modified need to be included in the list.
The "translate()" method returns a bit mask indicating which ASN.1 types are to be
translated. Definitions of the bit to ASN.1 type mappings can be exported using the
:translate tag (see "EXPORTS"). The undefined value is returned upon an error and the
"error()" method may be used to determine the cause.
debug() - set or get the debug mode for the module
$mask = $session->debug([$mask]);
This method is used to enable or disable debugging for the Net::SNMP module. Debugging
can be enabled on a per component level as defined by a bit mask passed to the "debug()"
method. The bit mask is broken up as follows:
• 0x02 - Message or PDU encoding and decoding
• 0x04 - Transport Layer
• 0x08 - Dispatcher
• 0x10 - Message Processing
• 0x20 - Security
Symbols representing these bit mask values are defined by the module and can be exported
using the :debug tag (see "EXPORTS"). If a non-numeric value is passed to the "debug()"
method, it is evaluated in boolean context. Debugging for all of the components is then
enabled or disabled based on the resulting truth value.
The current debugging mask is returned by the method. Debugging can also be enabled using
the stand alone function "snmp_debug()". This function can be exported by request (see
"EXPORTS").
SUBROUTINES
oid_base_match() - determine if an OID has a specified OID base
$value = oid_base_match($base_oid, $oid);
This function takes two OBJECT IDENTIFIERs in dotted notation and returns a true value
(i.e. 0x1) if the second OBJECT IDENTIFIER is equal to or is a child of the first OBJECT
IDENTIFIER in the SNMP Management Information Base (MIB). This function can be used in
conjunction with the "get-next-request()" or "get-bulk-request()" methods to determine
when a OBJECT IDENTIFIER in the GetResponse-PDU is no longer in the desired MIB tree
branch.
oid_lex_cmp() - compare two OBJECT IDENTIFIERs lexicographically
$cmp = oid_lex_cmp($oid1, $oid2);
This function takes two OBJECT IDENTIFIERs in dotted notation and returns one of the
values 1, 0, -1 if $oid1 is respectively lexicographically greater, equal, or less than
$oid2.
oid_lex_sort() - sort a list of OBJECT IDENTIFIERs lexicographically
@sorted_oids = oid_lex_sort(@oids);
This function takes a list of OBJECT IDENTIFIERs in dotted notation and returns the listed
sorted in lexicographical order.
snmp_type_ntop() - convert an ASN.1 type to presentation format
$text = snmp_type_ntop($type);
This function takes an ASN.1 type octet and returns a text string suitable for
presentation. Some ASN.1 type definitions map to the same octet value when encoded. This
method cannot distinguish between these multiple mappings and the most basic type name
will be returned.
ticks_to_time() - convert TimeTicks to formatted time
$time = ticks_to_time($timeticks);
This function takes an ASN.1 TimeTicks value and returns a string representing the time
defined by the value. The TimeTicks value is expected to be a non-negative integer value
representing the time in hundredths of a second since some epoch. The returned string
will display the time in days, hours, and seconds format according to the value of the
TimeTicks argument.
EXPORTS
The Net::SNMP module uses the Exporter module to export useful constants and subroutines.
These exportable symbols are defined below and follow the rules and conventions of the
Exporter module (see Exporter).
Default
&snmp_dispatcher, INTEGER, INTEGER32, OCTET_STRING, OBJECT_IDENTIFIER, IPADDRESS,
COUNTER, COUNTER32, GAUGE, GAUGE32, UNSIGNED32, TIMETICKS, OPAQUE, COUNTER64,
NOSUCHOBJECT, NOSUCHINSTANCE, ENDOFMIBVIEW
Exportable
&snmp_debug, &snmp_dispatcher, &snmp_type_ntop, &oid_base_match, &oid_lex_cmp,
&oid_lex_sort,&ticks_to_time, INTEGER, INTEGER32, OCTET_STRING, NULL,
OBJECT_IDENTIFIER, SEQUENCE, IPADDRESS, COUNTER, COUNTER32, GAUGE, GAUGE32,
UNSIGNED32, TIMETICKS, OPAQUE, COUNTER64, NOSUCHOBJECT, NOSUCHINSTANCE, ENDOFMIBVIEW,
GET_REQUEST, GET_NEXT_REQUEST, GET_RESPONSE, SET_REQUEST, TRAP, GET_BULK_REQUEST,
INFORM_REQUEST, SNMPV2_TRAP, REPORT, DEBUG_ALL, DEBUG_NONE, DEBUG_MESSAGE,
DEBUG_TRANSPORT, DEBUG_DISPATCHER,DEBUG_PROCESSING, DEBUG_SECURITY, COLD_START,
WARM_START, LINK_DOWN, LINK_UP, AUTHENTICATION_FAILURE, EGP_NEIGHBOR_LOSS,
ENTERPRISE_SPECIFIC, SNMP_VERSION_1, SNMP_VERSION_2C, SNMP_VERSION_3, SNMP_PORT,
SNMP_TRAP_PORT, TRANSLATE_NONE,TRANSLATE_OCTET_STRING, TRANSLATE_NULL,
TRANSLATE_TIMETICKS, TRANSLATE_OPAQUE,TRANSLATE_NOSUCHOBJECT,
TRANSLATE_NOSUCHINSTANCE, TRANSLATE_ENDOFMIBVIEW, TRANSLATE_UNSIGNED, TRANSLATE_ALL
Tags
:asn1
INTEGER, INTEGER32, OCTET_STRING, NULL, OBJECT_IDENTIFIER, SEQUENCE, IPADDRESS,
COUNTER, COUNTER32, GAUGE, GAUGE32, UNSIGNED32, TIMETICKS, OPAQUE, COUNTER64,
NOSUCHOBJECT, NOSUCHINSTANCE, ENDOFMIBVIEW, GET_REQUEST, GET_NEXT_REQUEST,
GET_RESPONSE, SET_REQUEST, TRAP, GET_BULK_REQUEST, INFORM_REQUEST, SNMPV2_TRAP,
REPORT
:debug
&snmp_debug, DEBUG_ALL, DEBUG_NONE, DEBUG_MESSAGE, DEBUG_TRANSPORT,
DEBUG_DISPATCHER, DEBUG_PROCESSING, DEBUG_SECURITY
:generictrap
COLD_START, WARM_START, LINK_DOWN, LINK_UP, AUTHENTICATION_FAILURE,
EGP_NEIGHBOR_LOSS, ENTERPRISE_SPECIFIC
:snmp
&snmp_debug, &snmp_dispatcher, &snmp_type_ntop, &oid_base_match, &oid_lex_cmp,
&oid_lex_sort, &ticks_to_time, SNMP_VERSION_1, SNMP_VERSION_2C, SNMP_VERSION_3,
SNMP_PORT, SNMP_TRAP_PORT
:translate
TRANSLATE_NONE, TRANSLATE_OCTET_STRING, TRANSLATE_NULL, TRANSLATE_TIMETICKS,
TRANSLATE_OPAQUE, TRANSLATE_NOSUCHOBJECT, TRANSLATE_NOSUCHINSTANCE,
TRANSLATE_ENDOFMIBVIEW, TRANSLATE_UNSIGNED, TRANSLATE_ALL
:ALL
All of the above exportable items.
EXAMPLES
1. Blocking SNMPv1 get-request for sysUpTime
This example gets the sysUpTime from a remote host.
#! /usr/local/bin/perl
use strict;
use warnings;
use Net::SNMP;
my $OID_sysUpTime = '1.3.6.1.2.1.1.3.0';
my ($session, $error) = Net::SNMP->session(
-hostname => shift || 'localhost',
-community => shift || 'public',
);
if (!defined $session) {
printf "ERROR: %s.\n", $error;
exit 1;
}
my $result = $session->get_request(-varbindlist => [ $OID_sysUpTime ],);
if (!defined $result) {
printf "ERROR: %s.\n", $session->error();
$session->close();
exit 1;
}
printf "The sysUpTime for host '%s' is %s.\n",
$session->hostname(), $result->{$OID_sysUpTime};
$session->close();
exit 0;
2. Blocking SNMPv3 set-request of sysContact
This example sets the sysContact information on the remote host to "Help Desk x911". The
named arguments passed to the "session()" constructor are for the demonstration of syntax
only. These parameters will need to be set according to the SNMPv3 parameters of the
remote host. The "snmpkey" utility included with the distribution can be used to create
the key values.
#! /usr/local/bin/perl
use strict;
use warnings;
use Net::SNMP;
my $OID_sysContact = '1.3.6.1.2.1.1.4.0';
my ($session, $error) = Net::SNMP->session(
-hostname => 'myv3host.example.com',
-version => 'snmpv3',
-username => 'myv3Username',
-authprotocol => 'sha1',
-authkey => '0x6695febc9288e36282235fc7151f128497b38f3f',
-privprotocol => 'des',
-privkey => '0x6695febc9288e36282235fc7151f1284',
);
if (!defined $session) {
printf "ERROR: %s.\n", $error;
exit 1;
}
my $result = $session->set_request(
-varbindlist => [ $OID_sysContact, OCTET_STRING, 'Help Desk x911' ],
);
if (!defined $result) {
printf "ERROR: %s.\n", $session->error();
$session->close();
exit 1;
}
printf "The sysContact for host '%s' was set to '%s'.\n",
$session->hostname(), $result->{$OID_sysContact};
$session->close();
exit 0;
3. Non-blocking SNMPv2c get-bulk-request for ifTable
This example gets the contents of the ifTable by sending get-bulk-requests until the
responses are no longer part of the ifTable. The ifTable can also be retrieved using the
"get_table()" method. The ifPhysAddress object in the table has a syntax of an OCTET
STRING. By default, translation is enabled and non-printable OCTET STRINGs are translated
into a hexadecimal format. Sometimes the OCTET STRING contains all printable characters
and this produces unexpected output when it is not translated. The example turns off
translation for OCTET STRINGs and specifically formats the output for the ifPhysAddress
objects.
#! /usr/local/bin/perl
use strict;
use warnings;
use Net::SNMP qw(:snmp);
my $OID_ifTable = '1.3.6.1.2.1.2.2';
my $OID_ifPhysAddress = '1.3.6.1.2.1.2.2.1.6';
my ($session, $error) = Net::SNMP->session(
-hostname => shift || 'localhost',
-community => shift || 'public',
-nonblocking => 1,
-translate => [-octetstring => 0],
-version => 'snmpv2c',
);
if (!defined $session) {
printf "ERROR: %s.\n", $error;
exit 1;
}
my %table; # Hash to store the results
my $result = $session->get_bulk_request(
-varbindlist => [ $OID_ifTable ],
-callback => [ \&table_callback, \%table ],
-maxrepetitions => 10,
);
if (!defined $result) {
printf "ERROR: %s\n", $session->error();
$session->close();
exit 1;
}
# Now initiate the SNMP message exchange.
snmp_dispatcher();
$session->close();
# Print the results, specifically formatting ifPhysAddress.
for my $oid (oid_lex_sort(keys %table)) {
if (!oid_base_match($OID_ifPhysAddress, $oid)) {
printf "%s = %s\n", $oid, $table{$oid};
} else {
printf "%s = %s\n", $oid, unpack 'H*', $table{$oid};
}
}
exit 0;
sub table_callback
{
my ($session, $table) = @_;
my $list = $session->var_bind_list();
if (!defined $list) {
printf "ERROR: %s\n", $session->error();
return;
}
# Loop through each of the OIDs in the response and assign
# the key/value pairs to the reference that was passed with
# the callback. Make sure that we are still in the table
# before assigning the key/values.
my @names = $session->var_bind_names();
my $next = undef;
while (@names) {
$next = shift @names;
if (!oid_base_match($OID_ifTable, $next)) {
return; # Table is done.
}
$table->{$next} = $list->{$next};
}
# Table is not done, send another request, starting at the last
# OBJECT IDENTIFIER in the response. No need to include the
# calback argument, the same callback that was specified for the
# original request will be used.
my $result = $session->get_bulk_request(
-varbindlist => [ $next ],
-maxrepetitions => 10,
);
if (!defined $result) {
printf "ERROR: %s.\n", $session->error();
}
return;
}
4. Non-blocking SNMPv1 get-request and set-request on multiple hosts
This example first polls several hosts for their sysUpTime. If the poll of the host is
successful, the sysContact and sysLocation information is set on the host. The sysContact
information is hardcoded to "Help Desk x911" while the sysLocation information is passed
as an argument to the callback.
#! /usr/local/bin/perl
use strict;
use warnings;
use Net::SNMP;
my $OID_sysUpTime = '1.3.6.1.2.1.1.3.0';
my $OID_sysContact = '1.3.6.1.2.1.1.4.0';
my $OID_sysLocation = '1.3.6.1.2.1.1.6.0';
# Hash of hosts and location data.
my %host_data = (
'10.1.1.2' => 'Building 1, Second Floor',
'10.2.1.1' => 'Building 2, First Floor',
'localhost' => 'Right here!',
);
# Create a session for each host and queue a get-request for sysUpTime.
for my $host (keys %host_data) {
my ($session, $error) = Net::SNMP->session(
-hostname => $host,
-community => 'private',
-nonblocking => 1,
);
if (!defined $session) {
printf "ERROR: Failed to create session for host '%s': %s.\n",
$host, $error;
next;
}
my $result = $session->get_request(
-varbindlist => [ $OID_sysUpTime ],
-callback => [ \&get_callback, $host_data{$host} ],
);
if (!defined $result) {
printf "ERROR: Failed to queue get request for host '%s': %s.\n",
$session->hostname(), $session->error();
}
}
# Now initiate the SNMP message exchange.
snmp_dispatcher();
exit 0;
sub get_callback
{
my ($session, $location) = @_;
my $result = $session->var_bind_list();
if (!defined $result) {
printf "ERROR: Get request failed for host '%s': %s.\n",
$session->hostname(), $session->error();
return;
}
printf "The sysUpTime for host '%s' is %s.\n",
$session->hostname(), $result->{$OID_sysUpTime};
# Now set the sysContact and sysLocation for the host.
$result = $session->set_request(
-varbindlist =>
[
$OID_sysContact, OCTET_STRING, 'Help Desk x911',
$OID_sysLocation, OCTET_STRING, $location,
],
-callback => \&set_callback,
);
if (!defined $result) {
printf "ERROR: Failed to queue set request for host '%s': %s.\n",
$session->hostname(), $session->error();
}
return;
}
sub set_callback
{
my ($session) = @_;
my $result = $session->var_bind_list();
if (defined $result) {
printf "The sysContact for host '%s' was set to '%s'.\n",
$session->hostname(), $result->{$OID_sysContact};
printf "The sysLocation for host '%s' was set to '%s'.\n",
$session->hostname(), $result->{$OID_sysLocation};
} else {
printf "ERROR: Set request failed for host '%s': %s.\n",
$session->hostname(), $session->error();
}
return;
}
REQUIREMENTS
• The Net::SNMP module uses syntax that is not supported in versions of Perl earlier
than v5.6.0.
• The non-core modules Crypt::DES, Digest::MD5, and Digest::HMAC are required to support
SNMPv3.
• In order to support the AES Cipher Algorithm as a SNMPv3 privacy protocol, the non-
core module Crypt::Rijndael is needed.
• To use UDP/IPv6 or TCP/IPv6 as a Transport Domain, the non-core module Socket6 is
needed.
AUTHOR
David M. Town <dtown@cpan.org>
ACKNOWLEDGMENTS
The original concept for this module was based on SNMP_Session.pm written by Simon Leinen
<simon@switch.ch>.
The Abstract Syntax Notation One (ASN.1) encode and decode methods were originally derived
by example from the CMU SNMP package whose copyright follows: Copyright (c) 1988, 1989,
1991, 1992 by Carnegie Mellon University. All rights reserved.
LICENSE AND COPYRIGHT
Copyright (c) 1998-2010 David M. Town. All rights reserved.
This program is free software; you may redistribute it and/or modify it under the same
terms as the Perl 5 programming language system itself.