- The asyncore-based transport subsystem extended to support POSIX

  sendmsg()/recvmsg() based socket communication what could be used,
  among other things, in the context of a transparent SNMP proxy
  application. Technically, the following features were brought
  into pysnmp with this update:
  * Sending SNMP packets from a non-local IP address
  * Receiving IP packets for non-local IP addresses
  * Responding to SNMP requests from exactly the same IP address
    the query was sent to. This proves to be useful when listening
    on both primary and secondary IP interfaces.

1 files changed, 87 insertions, 0 deletions

diff --git a/examples/v1arch/asyncore/manager/cmdgen/spoof-source-address.py b/examples/v1arch/asyncore/manager/cmdgen/spoof-source-address.py
new file mode 100644
index 00000000..28f2190e
--- /dev/null
+++ b/examples/v1arch/asyncore/manager/cmdgen/spoof-source-address.py
@@ -0,0 +1,87 @@
+from pysnmp.carrier.asynsock.dispatch import AsynsockDispatcher
+from pysnmp.carrier.asynsock.dgram import udp
+from pysnmp.proto import api
+from pyasn1.codec.ber import encoder, decoder
+from time import time
+
+# Send request message to this address
+transportAddress = udp.UdpTransportAddress(('195.218.195.228', 161))
+
+# Send request message from this non-local (!) IP address
+transportAddress.setLocalAddress(('1.2.3.4', 0))
+
+# Protocol version to use
+#pMod = api.protoModules[api.protoVersion1]
+pMod = api.protoModules[api.protoVersion2c]
+
+# Build PDU
+reqPDU =  pMod.GetRequestPDU()
+pMod.apiPDU.setDefaults(reqPDU)
+pMod.apiPDU.setVarBinds(
+    reqPDU, ( ('1.3.6.1.2.1.1.1.0', pMod.Null('')),
+              ('1.3.6.1.2.1.1.3.0', pMod.Null('')) )
+    )
+
+# Build message
+reqMsg = pMod.Message()
+pMod.apiMessage.setDefaults(reqMsg)
+pMod.apiMessage.setCommunity(reqMsg, 'public')
+pMod.apiMessage.setPDU(reqMsg, reqPDU)
+
+startedAt = time()
+
+class StopWaiting(Exception): pass
+
+def cbTimerFun(timeNow):
+    if timeNow - startedAt > 3:
+        raise StopWaiting()
+    
+def cbRecvFun(transportDispatcher, transportDomain, transportAddress,
+              wholeMsg, reqPDU=reqPDU):
+    while wholeMsg:
+        rspMsg, wholeMsg = decoder.decode(wholeMsg, asn1Spec=pMod.Message())
+        rspPDU = pMod.apiMessage.getPDU(rspMsg)
+        # Match response to request
+        if pMod.apiPDU.getRequestID(reqPDU)==pMod.apiPDU.getRequestID(rspPDU):
+            # Check for SNMP errors reported
+            errorStatus = pMod.apiPDU.getErrorStatus(rspPDU)
+            if errorStatus:
+                print(errorStatus.prettyPrint())
+            else:
+                for oid, val in pMod.apiPDU.getVarBinds(rspPDU):
+                    print('%s = %s' % (oid.prettyPrint(), val.prettyPrint()))
+            transportDispatcher.jobFinished(1)
+    return wholeMsg
+
+transportDispatcher = AsynsockDispatcher()
+
+transportDispatcher.registerRecvCbFun(cbRecvFun)
+transportDispatcher.registerTimerCbFun(cbTimerFun)
+
+# Initialize 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()
+
+transportDispatcher.registerTransport(udp.domainName, udpSocketTransport)
+
+# Pass message to dispatcher
+transportDispatcher.sendMessage(
+    encoder.encode(reqMsg), udp.domainName, transportAddress
+)
+
+# We might never receive any response as we sent request with fake source IP
+transportDispatcher.jobStarted(1)
+
+# Dispatcher will finish as all jobs counter reaches zero
+try:
+    transportDispatcher.runDispatcher()
+except StopWaiting:
+    transportDispatcher.closeDispatcher()
+else:
+    raise