> This is the first time I'm answering a question ;-).
> Experts please correct me if I'm wrong.

Sorry, John.
Although most of what you say is strictly correct, it gives a somewhat
misleading impression of the role of the 'netsnmp_session'.   Despite
my current sabbatical from the lists, I can't let this pass uncorrected.


Yes - UDP-based protocols such as SNMP don't typically use the same
sort of "transport session" as you'd see in telnet, ssh, etc.
But the Net-SNMP idea of a "session" is *not* restricted to the
AgentX master<->subagent communication.

Instead, the clue lies in your second comment:

> 2. Each PDU is supposed to have authorization information, if any.


It's this "administrative" information that the SNMP session is concerned
with.   Rather than create the PDU and add the authorization (or community)
settings to it directly, the typical model is to create a 'netsnmp_session'
structure and use *that* to hold the various bits of admin information
(including the address of the remote agent).

Then when it comes to sending the actual request, 'snmp_send' is given
both the PDU and the session structure,  and will fill in any missing
PDU header fields from the session structure.   And if there are a series
of requests to be sent to the same agent, then the same session structure
can be used for each of them.

So it's representing "logical session", rather than an actual network
connection - a "level 7 session" rather than TCP's "level 4/5 session",
if that makes sense.



> There's a memo draft
>    http://www.potaroo.net/ietf/idref/draft-hardaker-snmp-session-sm/
> that attempts to address this.

That's something of a red herring here, I think.
Yes, it probably touches on some of the same ideas, but in
terms of Gemma's original question, it's not really relevant, 
The Net-SNMP use of sessions is purely concerned with bundling
assorted administrative information.

Dave



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