- 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, 99 insertions, 0 deletions

diff --git a/examples/v3arch/manager/cmdgen/get-v2c-spoof-source-address.py b/examples/v3arch/manager/cmdgen/get-v2c-spoof-source-address.py
new file mode 100644
index 0000000..036cf3f
--- /dev/null
+++ b/examples/v3arch/manager/cmdgen/get-v2c-spoof-source-address.py
@@ -0,0 +1,99 @@
+#
+# GET Command Generator
+#
+# Send a SNMP GET request
+#     with SNMPv2c, community 'public'
+#     over IPv4/UDP
+#     to an Agent at 195.218.195.228:161
+#     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 195.218.195.228 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.asynsock.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, ('195.218.195.228', 161),
+    'my-creds',
+    sourceAddress=('1.2.3.4', 0)
+)
+
+# Error/response receiver
+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()