Net::SNMP(3pm) User Contributed Perl Documentation Net::SNMP(3pm)NAMENet::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").
SUBROUTINESoid_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.
perl v5.26.0 2017-08-22 Net::SNMP(3pm)
