Re: Query: SNMP Prococol

On 18 October 2010 12:57, Queenie de Melo <[email protected]> wrote:
> So the SNMP agent(Server) listens on port 161 for SNMP GET/SET requests
> from the SNMP Manager (Client)

Correct.

(Strictly speaking, the agent can listen on any available port,
 but port 161 is the standard port for SNMP information retrieval)



> What about in Case of traps?
>
> The SNMP Manager in this case listens on UDP port 162 for the Traps sent by
> the SNMP Agent. So in this case, is it that the SNMP Manager is .... the
> Server and SNMP Agent is the client??

That's right.

The SNMP agent (or some other application that generates traps) is the client
and the application that receives the trap is the server.
   The official terminology is "notification generator" and
"notification receiver".

The notification receiver may be the same SNMP manager application as the
one generating information retrieval requests.   Or it may be a dedicated
trap-receiving application (such as the Net-SNMP 'snmptrapd').
   But the most important thing here is that the client-server relationship is
reversed for traps, when compared to GET/SET requests.



> Another query i had is: what exactly are SNMP INFORMS?

A trap is sent from the agent to the trap receiver, but there's no
acknowledgement sent back.   So the agent doesn't know whether
the trap got there safely (let alone whether it was acted upon).

An INFORM is essentially the same as a trap, except that it *does*
trigger an acknowledgement.   So the agent (or other notification
generator application) knows that the inform was received.
   (Whether the receiver actually did anything with it is a different question!)

Think of this as the same as "read receipt messages" in the context of email.




>> SNMP inform is nothing it's an acknowledgment mechanisim in SNMP. which is
>> getting supported from snmpv2c and snmpv3 onwards
>
> Is it sent from the Manager to the Agent in response to a TRAP?

No

>                                                                            or is it
> sent from Agent to Manager just like a trap (but u want manager to ack the
> receiptof trap)

Yes.



>    or is it sent from NMS(SNMP Manager) to another SNMP Manager
> ????

"SNMP Manager" is something of a vague term.
Any SNMP application can act in various different roles - hence the
current specifications talk in terms of "notification receiver" or
"notification generator"  (and similarly for GET/SET requests)

It's perfectly possible for one SNMP manager application to signal
to another, using traps or informs.   But the most typical use of traps
or informs would be from an agent to an NMS.

Dave

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