Re: Configuring a new vacmContextName

On 09/04/2008, Joan Landry <Joan.Landry@overturenetworks.com> wrote:
> >>If you are using "com2sec", then this relates to SNMPv1/2.
>
> What should I use for SNMPv3?

Take a step back.
Think about what the "com2sec" directive is doing.

It's taking the only administrative information that is available
in SNMPv1/2c (the community string), and mapping it into a
security name and an (optional) context.

Now think about the admin information that is available
with SNMPv3. There's a username (which isn't strictly the
same as a security name, but is close enough), and an
(optional) context. So the same information is there
already, as part of the SNMPv3 protocol.

The basic purpose of "com2sec" is precisely to bring
SNMPv1/2c up into line with SNMPv3. From there on,
the rest of the configuration (group/view/access) works
in the same way for all three versions.



> >>Also, what MIB information have you registered in "context1", and how
> have you done this?
>
> I do not know what this means, so can you tell me what I have to do to
> register mibs into context1?

Contexts are essentially a way of having multiple copies of the same
MIB structure, supported in parallel. So the agent can report different
collections of values, depending on the context of the request.

But in order to do this, the agent needs to know what information is
available for each context. This doesn't happen by magic - it needs
to be told.

Whenever you implement a MIB module, you register various OIDs
with the agent (so that the agent knows to call this routine when it
gets an appropriate request). If you don't register the OID(s), then
the agent won't answer requests for them.

But you don't register the OIDs in isolation - you register them in a
particular context. (Typically the default context - ""). So the previous
paragraph should actually read something like
"The agent receives a request for certain OIDs *in a given context*",
and "you register OIDs with the agent *in a particular context*", etc


If you only register MIB modules in the default context, then even if
you set up the access control correctly, the agent won't know about
any information to report in other contexts. So queries in a non-default
context will always return nothing - 'cos there's nothing to return!


See the Wiki page
http://www.net-snmp.org/wiki/index.p...SNMPv3_context
and the FAQ entry
How can I register a MIB module in a different (SNMPv3) context?
http://www.net-snmp.org/wiki/index.php/FAQ:Coding_22

for more details.

Dave

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