# Getting peer address information

17. How do I find out peer transport address or security information within my receiving app (CommandResponder or Notification Receiver)?

1. SNMP architecture forces you to distinguish communicating entities only on the basis of their community names (SNMPv1/v2c) or ContextEngineId/ContextName pair (SNMPv3).

   In other words, if one SNMP Manager should anyhow differ from another, then they should use distinct community names or SNMP contexts. Transport information should never be used for the identification purposes, as in some cases it proves to be unreliable (cases include NAT device or a proxy in the middle, not to mention address spoofing).

   As practice reveals, even perfect design does not always cope well with the imperfect world. So we had to pinch a logic hole from the scope of an SNMP app down to transport layer. Now with the getTransportInfo(stateReference) method call you could get peer transport information upon receiving its SNMP message.

    # Callback function for receiving notifications
    def cbFun(snmpEngine,
              stateReference,
              contextEngineId, contextName,
              varBinds,
              cbCtx):
        transportDomain, transportAddress = snmpEngine.msgAndPduDsp.getTransportInfo(stateReference)