I need help with winsnmp to emulate a agent device

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C++

SNMP

I am trying to write some code to emulate a number of agent devices on the network. These uses the SNMP protocol to communicate with a host computer. I have successfully used the SnmpListen function within winSNMP to read the requests sent by the host. My problems so far are:

1) When I send a response the SnmpSendMsg call succeeds but sometimes the port number instead of being 161 (as I set it) is some random number.

2) When I send messages I specify a source entity by using SnmpStrToEntity and specifying the IP address of the emulated device. My network setting have all the devices specified. However when I examine the packets with Wireshark they always have the same sourceIP address and not what I specified in the SnmpSendMsg call.

3) SnmpSendMsg is an asynchronous call. Can I reuse the PDU immediately or do I have to wait for the send to complete first. In other words, does the call make a copy of the PDU and entities, or does it use them directly. I suspect this is what is causing issue 1 above.

4) Is there an alternative SNMP library that I can use?

This is the environment that I am trying to use:

Language : C++ (unmanaged)
Operating system : Windows 7 and 10
SNMP version : v2c

What I have tried:

Tried declaring PDU as a member variable.
Tried explicitly specifying the source entity.
Tried creating a different session for the receiver and sender.