Listen traps with pysnmp

Question

Hello I'm trying to listen for traps with this code from pysnmp doc:

from pysnmp.carrier.asynsock.dispatch import AsynsockDispatcher
from pysnmp.carrier.asynsock.dgram import udp, udp6
from pyasn1.codec.ber import decoder
from pysnmp.proto import api

def cbFun(transportDispatcher, transportDomain, transportAddress, wholeMsg):
    print('cbFun is called')
    while wholeMsg:
    print('loop...')
        msgVer = int(api.decodeMessageVersion(wholeMsg))
        if msgVer in api.protoModules:
            pMod = api.protoModules[msgVer]
        else:
            print('Unsupported SNMP version %s' % msgVer)
            return
        reqMsg, wholeMsg = decoder.decode(
            wholeMsg, asn1Spec=pMod.Message(),
            )
        print('Notification message from %s:%s: ' % (
            transportDomain, transportAddress
            )
        )
        reqPDU = pMod.apiMessage.getPDU(reqMsg)
        if reqPDU.isSameTypeWith(pMod.TrapPDU()):
            if msgVer == api.protoVersion1:
                print('Enterprise: %s' % (
                    pMod.apiTrapPDU.getEnterprise(reqPDU).prettyPrint()
                    )
                )
                print('Agent Address: %s' % (
                    pMod.apiTrapPDU.getAgentAddr(reqPDU).prettyPrint()
                    )
                )
                print('Generic Trap: %s' % (
                    pMod.apiTrapPDU.getGenericTrap(reqPDU).prettyPrint()
                    )
                )
                print('Specific Trap: %s' % (
                    pMod.apiTrapPDU.getSpecificTrap(reqPDU).prettyPrint()
                    )
                )
                print('Uptime: %s' % (
                    pMod.apiTrapPDU.getTimeStamp(reqPDU).prettyPrint()
                    )
                )
                varBinds = pMod.apiTrapPDU.getVarBindList(reqPDU)
            else:
                varBinds = pMod.apiPDU.getVarBindList(reqPDU)
            print('Var-binds:')
            for oid, val in varBinds:
                print('%s = %s' % (oid.prettyPrint(), val.prettyPrint()))
    return wholeMsg

transportDispatcher = AsynsockDispatcher()

transportDispatcher.registerRecvCbFun(cbFun)

# UDP/IPv4
transportDispatcher.registerTransport(
    udp.domainName, udp.UdpSocketTransport().openServerMode(('localhost', 162))
)

# UDP/IPv6
transportDispatcher.registerTransport(
    udp6.domainName, udp6.Udp6SocketTransport().openServerMode(('::1', 162))
)

transportDispatcher.jobStarted(1)

try:
    # Dispatcher will never finish as job#1 never reaches zero
    print('run dispatcher')
    transportDispatcher.runDispatcher()
except:
    transportDispatcher.closeDispatcher()
    raise

But when I test it with this command:

$ snmptrap -v1 -c public 127.0.0.1 1.3.6.1.4.1.20408.4.1.1.2
127.0.0.1 1 1 123 1.3.6.1.2.1.1.1.0 s test

Nothing is displayed. Could someone help me ? Everything I want is to display traps received by this receiver.

EDIT: I added some prints and this is what I get when I run the program:

C:\user\snmp\test>python fonction.py
rundispatcher
_

When I send a trap, nothing displays. When I press Ctrl+C I get:

C:\user\snmp\test>python fonction.py
rundispatcher
Traceback (most recent call last):
  File "fonction.py", line 73, in <module>
    transportDispatcher.runDispatcher()
  File "C:\user\snmp\test\pysnmp\carrier\asyncore\dispatch.py", line 37, in runDispatcher
    use_poll=True, map=self.__sockMap, count=1)
  File "C:\Python27\lib\asyncore.py", line 220, in loop
    poll_fun(timeout, map)
  File "C:\Python27\lib\asyncore.py", line 145, in poll
    r, w, e = select.select(r, w, e, timeout)
KeyboardInterrupt

Answer 1

On Windows I found I had to change the listener address from 'localhost' to ''.

netstat -a then shows it bound as 0.0.0.0:162 instead of 127.0.0.0:162 and it works correctly:

C:\>netstat -a | find ":162"
  UDP    0.0.0.0:162            *:*