[SOLVED] Mapping SNMP ASN.1 to C++ Datatypes

Mapping SNMP ASN.1 to C++ Datatypes

I am adding SNMP EtherLike MIB variables to our existing SNMP C++ codebase and doing it for very first time.

The difficulty I am facing is understanding the data types of MIB variables and map it to C++ data types - for example dot3StatsIndex MIB variable syntax is InterfaceIndex so what is it equivalent data type in C++.

Since I am implementing for very first time or rather is in learning phase - please let me know what are the different ASN.1 data types and whether the types all are listed above and how they are mapped to C++ datatypes?

Also how to derive from RFC the data type of the MIB variable?

Solution

I think if you just follow the type inheritance chain, you end up with a base SNMP type which should map to the types you have.

For InterfaceIndex, see from which MIB it's imported (it's IF-MIB):

IMPORTS
    MODULE-IDENTITY, OBJECT-TYPE, OBJECT-IDENTITY,
    Integer32, Counter32, Counter64, mib-2, transmission
        FROM SNMPv2-SMI
    MODULE-COMPLIANCE, OBJECT-GROUP
        FROM SNMPv2-CONF
    TruthValue
        FROM SNMPv2-TC
    ifIndex, InterfaceIndex
        FROM IF-MIB;

Then find its definition which should reference a base type (it's Integer32 which probably maps to ASN1_INT).

InterfaceIndex ::= TEXTUAL-CONVENTION
    DISPLAY-HINT "d"
    STATUS       current
    DESCRIPTION
        "A unique value, greater than zero, for each interface or ...
        network management system to the next re-initialization."
    SYNTAX       Integer32 (1..2147483647)