Re: Communication between Master-agent and Sub-agent

On 29/05/07, Shivani Garg <shivanigarg02@gmail.com> wrote:
> a) Say I am writing a MIB .my for an object by the name of myObject. I
> believe a var_myObject() function will be created by mib2c.

Either var_myObject() (if using the old v4 UCD module API), or
myObject_handler() (if using the newer v5 API). The precise details
are somewhat different, but the basic idea is much the same.


> I wanted to know
> how this function is called by the master agent when it receives a snmpget
> for an OID corresponding to myObject.

The agent keeps a registry of all the OIDs that various MIB modules have
told it about. When a request comes in, the main agent framework uses
this registry to decide which module to pass the request on to.
For a GET (or SET) request, there will only be one module that's relevant.
For a GETNEXT request, the agent will work through the registry, calling
each module in turn until it gets a value it can use.

> What is the flow of communication
> between master-agent and sub-agent in this respect.

The above description holds true for both master/subagent communication,
and for MIB modules implemented within the master agent itself.
The only difference for a master/subagent version is that this involves an
AgentX GET (or GETNEXT) request, followed by a RESPONSE message.
(Rather than a simple internal function call).

Things are a bit more complex for SET processing, but don't worry about
that just yet.


> b) Also, agent_check_and_process() will listen for events on internal FDs
> from master-agent (for both GET and SET). Can we send traps also these FDs
> or is there any way to register our own external FDs through
> agent_check_and_process()?? If yes, then how are these handled by netSNMP.

The external FD mechanism is not limited to the standard SNMP GET/SET/etc
model. You'd supply a routine to be called whenever there's something waiting
to be read from that FD. The agent isn't bothered what this data is, or what
it means - that's all left to your code.

Dave

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