# Transport tweaks

## SNMPv2c, custom timeout

Send a SNMP GET request:

- with SNMPv2c, community ‘public’

- over IPv4/UDP

- to an Agent at 104.236.166.95:161

- wait 3 seconds for response, retry 5 times (plus one initial attempt)

- for an OID in tuple form

This script performs similar to the following Net-SNMP command:

$ snmpget -v2c -c public -ObentU -r 5 -t 1 104.236.166.95 1.3.6.1.2.1.1.1.0

    from pysnmp.entity import engine, config
    from pysnmp.carrier.asyncore.dgram import udp
    from pysnmp.entity.rfc3413 import cmdgen

    # Create SNMP engine instance
    snmpEngine = engine.SnmpEngine()

    #
    # SNMPv2c setup
    #

    # SecurityName <-> CommunityName mapping
    config.addV1System(snmpEngine, 'my-area', 'public')

    # Specify security settings per SecurityName (SNMPv1 - 0, SNMPv2c - 1)
    config.addTargetParams(snmpEngine, 'my-creds', 'my-area', 'noAuthNoPriv', 1)

    #
    # Setup transport endpoint and bind it with security settings yielding
    # a target name
    #

    # UDP/IPv4
    config.addTransport(
        snmpEngine,
        udp.domainName,
        udp.UdpSocketTransport().openClientMode()
    )
    config.addTargetAddr(
        snmpEngine, 'my-router',
        udp.domainName, ('104.236.166.95', 161),
        'my-creds',
        timeout=300,  # in 1/100 sec
        retryCount=5
    )

    # Error/response receiver
    # noinspection PyUnusedLocal,PyUnusedLocal,PyUnusedLocal
    def cbFun(snmpEngine, sendRequestHandle, errorIndication,
              errorStatus, errorIndex, varBinds, cbCtx):
        if errorIndication:
            print(errorIndication)
        elif errorStatus:
            print('%s at %s' % (errorStatus.prettyPrint(),
                                errorIndex and varBinds[int(errorIndex) - 1][0] or '?'))
        else:
            for oid, val in varBinds:
                print('%s = %s' % (oid.prettyPrint(), val.prettyPrint()))

    # Prepare and send a request message
    cmdgen.GetCommandGenerator().sendVarBinds(
        snmpEngine,
        'my-router',
        None, '',  # contextEngineId, contextName
        [((1, 3, 6, 1, 2, 1, 1, 1, 0), None)],
        cbFun
    )

    # Run I/O dispatcher which would send pending queries and process responses
    snmpEngine.transportDispatcher.runDispatcher()

`Download` script.

## Send packets from specific local interface

Send a series of SNMP GETNEXT requests with the following options:

- with SNMPv2c, community ‘public’

- over IPv4/UDP

- to an Agent at 104.236.166.95:161

- sending packets from primary local interface 0.0.0.0, local port 61024

- for two OIDs in tuple form

- stop on end-of-mib condition for both OIDs

This script performs similar to the following Net-SNMP command:

$ snmpwalk -v2c -c public -ObentU 104.236.166.95 1.3.6.1.2.1.1 1.3.6.1.4.1.1

    from pysnmp.entity import engine, config
    from pysnmp.carrier.asyncore.dgram import udp
    from pysnmp.entity.rfc3413 import cmdgen

    # Create SNMP engine instance
    snmpEngine = engine.SnmpEngine()

    #
    # SNMPv1/2c setup (if you use SNMPv1 or v2c)
    #

    # SecurityName <-> CommunityName mapping
    config.addV1System(snmpEngine, 'my-area', 'public')

    # Specify security settings per SecurityName (SNMPv1 - 0, SNMPv2c - 1)
    config.addTargetParams(snmpEngine, 'my-creds', 'my-area', 'noAuthNoPriv', 0)

    #
    # Setup transport endpoint and bind it with security settings yielding
    # a target name
    #

    # UDP/IPv4
    config.addTransport(
        snmpEngine,
        udp.domainName,
        udp.UdpSocketTransport().openClientMode(('0.0.0.0', 61024))
    )
    config.addTargetAddr(
        snmpEngine, 'my-router',
        udp.domainName, ('104.236.166.95', 161),
        'my-creds'
    )

    # Error/response receiver
    # noinspection PyUnusedLocal,PyUnusedLocal,PyUnusedLocal
    def cbFun(snmpEngine, sendRequestHandle, errorIndication,
              errorStatus, errorIndex, varBindTable, cbCtx):
        if errorIndication:
            print(errorIndication)
            return
        if errorStatus:
            print('%s at %s' % (errorStatus.prettyPrint(),
                                errorIndex and varBindTable[-1][int(errorIndex) - 1][0] or '?'))
            return  # stop on error
        for varBindRow in varBindTable:
            for oid, val in varBindRow:
                print('%s = %s' % (oid.prettyPrint(), val.prettyPrint()))
        return 1  # signal dispatcher to continue

    # Prepare initial request to be sent
    cmdgen.NextCommandGenerator().sendVarBinds(
        snmpEngine,
        'my-router',
        None, '',  # contextEngineId, contextName
        [((1, 3, 6, 1, 2, 1, 1), None),
         ((1, 3, 6, 1, 2, 1, 11), None)],
        cbFun
    )

    # Run I/O dispatcher which would send pending queries and process responses
    snmpEngine.transportDispatcher.runDispatcher()

`Download` script.

## Spoof source address

Send a SNMP GET request * with SNMPv2c, community ‘public’ * over IPv4/UDP * to an Agent at 104.236.166.95:161 * from a non-local, spoofed IP 1.2.3.4 (root and Python 3.3+ required) * for an OID in tuple form

This script performs similar to the following Net-SNMP command:

$ snmpget -v2c -c public -ObentU 104.236.166.95 1.3.6.1.2.1.1.1.0

But unlike the above command, this script issues SNMP request from a non-default, non-local IP address.

It is indeed possible to originate SNMP traffic from any valid local IP addresses. It could be a secondary IP interface, for instance. Superuser privileges are only required to send spoofed packets. Alternatively, sending from local interface could also be achieved by binding to it (via openClientMode() parameter).

    from pysnmp.entity import engine, config
    from pysnmp.carrier.asyncore.dgram import udp
    from pysnmp.entity.rfc3413 import cmdgen

    # Create SNMP engine instance
    snmpEngine = engine.SnmpEngine()

    #
    # SNMPv1 setup
    #

    # SecurityName <-> CommunityName mapping
    config.addV1System(snmpEngine, 'my-area', 'public')

    # Specify security settings per SecurityName (SNMPv1 - 0, SNMPv2c - 1)
    config.addTargetParams(snmpEngine, 'my-creds', 'my-area', 'noAuthNoPriv', 0)

    #
    # Setup transport endpoint and bind it with security settings yielding
    # a target name
    #

    # Initialize asyncore-based UDP/IPv4 transport
    udpSocketTransport = udp.UdpSocketTransport().openClientMode()

    # Use sendmsg()/recvmsg() for socket communication (required for
    # IP source spoofing functionality)
    udpSocketTransport.enablePktInfo()

    # Enable IP source spoofing (requires root privileges)
    udpSocketTransport.enableTransparent()

    # Register this transport at SNMP Engine
    config.addTransport(
        snmpEngine,
        udp.domainName,
        udpSocketTransport
    )

    # Configure destination IPv4 address as well as source IPv4 address
    config.addTargetAddr(
        snmpEngine, 'my-router',
        udp.domainName, ('104.236.166.95', 161),
        'my-creds',
        sourceAddress=('1.2.3.4', 0)
    )

    # Error/response receiver
    # noinspection PyUnusedLocal,PyUnusedLocal,PyUnusedLocal
    def cbFun(snmpEngine, sendRequestHandle, errorIndication,
              errorStatus, errorIndex, varBinds, cbCtx):
        if errorIndication:
            print(errorIndication)
        # SNMPv1 response may contain noSuchName error *and* SNMPv2c exception,
        # so we ignore noSuchName error here
        elif errorStatus and errorStatus != 2:
            print('%s at %s' % (errorStatus.prettyPrint(),
                                errorIndex and varBinds[int(errorIndex) - 1][0] or '?'))
        else:
            for oid, val in varBinds:
                print('%s = %s' % (oid.prettyPrint(), val.prettyPrint()))

    # Prepare and send a request message
    cmdgen.GetCommandGenerator().sendVarBinds(
        snmpEngine,
        'my-router',
        None, '',  # contextEngineId, contextName
        [((1, 3, 6, 1, 2, 1, 1, 1, 0), None)],
        cbFun
    )

    # Run I/O dispatcher which would send pending queries and process responses
    snmpEngine.transportDispatcher.runDispatcher()

`Download` script.

## Walk Agent over IPv6

Send a series of SNMP GETNEXT requests with the following options:

- with SNMPv3 with user ‘usr-md5-none’, MD5 auth and no privacy protocols

- over IPv6/UDP

- to an Agent at [::1]:161

- for two OIDs in tuple form

- stop on end-of-mib condition for both OIDs

This script performs similar to the following Net-SNMP command:

$ snmpwalk -v3 -l authNoPriv -u usr-md5-none -A authkey1 -ObentU udp6:[::1]:161 1.3.6.1.2.1.1 1.3.6.1.4.1.1

    from pysnmp.entity import engine, config
    from pysnmp.carrier.asyncore.dgram import udp6
    from pysnmp.entity.rfc3413 import cmdgen

    # Create SNMP engine instance
    snmpEngine = engine.SnmpEngine()

    #
    # SNMPv3/USM setup
    #

    # user: usr-md5-des, auth: MD5, priv NONE
    config.addV3User(
        snmpEngine, 'usr-md5-none',
        config.usmHMACMD5AuthProtocol, 'authkey1'
    )
    config.addTargetParams(snmpEngine, 'my-creds', 'usr-md5-none', 'authNoPriv')

    #
    # Setup transport endpoint and bind it with security settings yielding
    # a target name
    #

    # UDP/IPv6
    config.addTransport(
        snmpEngine,
        udp6.domainName,
        udp6.Udp6SocketTransport().openClientMode()
    )
    config.addTargetAddr(
        snmpEngine, 'my-router',
        udp6.domainName, ('::1', 161),
        'my-creds'
    )

    # Error/response receiver
    # noinspection PyUnusedLocal,PyUnusedLocal,PyUnusedLocal
    def cbFun(snmpEngine, sendRequestHandle, errorIndication,
              errorStatus, errorIndex, varBindTable, cbCtx):
        if errorIndication:
            print(errorIndication)
            return
        if errorStatus:
            print('%s at %s' % (errorStatus.prettyPrint(),
                                errorIndex and varBindTable[-1][int(errorIndex) - 1][0] or '?'))
            return  # stop on error
        for varBindRow in varBindTable:
            for oid, val in varBindRow:
                print('%s = %s' % (oid.prettyPrint(), val.prettyPrint()))
        return True  # signal dispatcher to continue

    # Prepare initial request to be sent
    cmdgen.NextCommandGenerator().sendVarBinds(
        snmpEngine,
        'my-router',
        None, '',  # contextEngineId, contextName
        [((1, 3, 6, 1, 2, 1, 1), None),
         ((1, 3, 6, 1, 4, 1, 1), None)],
        cbFun
    )

    # Run I/O dispatcher which would send pending queries and process responses
    snmpEngine.transportDispatcher.runDispatcher()

`Download` script.

See also: library-reference.