2009/3/30 Tanisha Kashyap <[email protected]>:
> What's the difference between a dynamically loaded module and a subagent.
Whenever you're working with SNMP, you'll always have an "agent" - a process
that is running all of the time, and will respond to requests for information.
The question is how this agent know what information to return for any
given request.
Some information will be handled within the agent itself, so can be
returned directly.
There's no need for it to look elsewhere.
But some information may not be available to this agent process, so
the agent needs
to be extended to be able to handle those requests.
One approach is to write a new chunk of code, and include it within the agent
(by recompiling the agent, and restarting it). So you've essentially got a new
agent, that knows a bit more than before. This is the most efficient approach,
but does involve a (hopefully short) break in service.
A related approach is to write the same new chunk of code, but compile it into
a .so file, and have the main agent load this dynamically. That way,
it now knows
about the new information, and can respond to request - but it's never actually
stopped running. This is known as a "dynamically loaded module".
Both of these end up with a single agent process running on the system.
The idea of a subagent is to take the same new chunk of code, but compile
it into a separate application ("subagent") which runs as a separate process.
This then connects to the main ("master") agent, and offers to handle requests
for this new information.
So here you now have *two* processes running at the same time.
Typically, the MIB code itself is likely to be more-or-less the same
in each case.
The differences are in how these MIB modules are plugged into the overall agent
framework - are they included within a single SNMP agent (either statically or
dynamically), or are they run as part of a separate subagent.
Dave
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