Re: how to inject global handler that handles request to any OID?

On Tue, Dec 4, 2012 at 11:08 AM, STOTTS Timothy <
[email protected]> wrote:

> How can I do the following?
>
> 1. create a handler registration for the top OID of:
> const oid top_oid[] = { 1 };
> const size_t top_oid_len = OID_LENGTH(top_oid);
>
> 2. inject the handler such that any GET, SET, GETBULK (any USM
> authenticated access at all) of any node under the subtree of the top OID
> will call a function I specify
>
> 3. the handler function will have access to a value in memory that
> represents the IP address of the SNMP manager that is calling this SNMP
> agent as multiple managers/browsers will be accessing the device, and a
> decision must be made based on IP address
>

I seem to recall looking into getting the source IP address of the
originating manager
and concluding that the information is not currently available at this
level of messaging/API.
But,

... snip ...

I had to do this (sortof) in my (Perl based) SNMP network simulator.

NOTE, this is not an 'injector' as you are asking about,
but a complete replacement handler for any OIDs (which was what _I_ needed).

What I found was that I couldn't register the 'top OID' of '1'
but what I could do was register for each of the next levels down.
This isn't really a problem because your probably only interested in '1.3'.


My Perl snippet is below,
I hope it helps you, or gives you ideas.

Fulko



use NetSNMP::OID    (':all');
use NetSNMP::agent  (':all');
use NetSNMP::ASN    (':all');

my $oidId = '1.0';                                       # start at the top
of the ISO tree...
while (1) {
    $oid = getNextOidById($oidId) if (!defined($oid));   # look for the
'next known' OID/variable (it may be in another sub-tree)
    last unless defined($oid);                           # we're done
searching if nothing was found
    last unless (my ($suboid) = ($oid =~ /^1\.(\d*)/));  # also done if we
leave the '1.x' tree, else extract the 'x' part of the OID
    $oidId = "1.$suboid";                                # build a new base
OID based on the sub-tree ID we found something in
    my $regoid = new NetSNMP::OID(".$oidId");            # note that we
have to prepend a leading dot onto the OID
    $agent->register($0, $regoid, \&my_snmp_handler);    # in order to
register to receive transactions for that sub-tree
    print STDERR "Simulating OID sub-tree: $oidId\n";
    $suboid++;                                           # bump to the next
potential sub-tree after the one we found
    $oidId = "1.$suboid";                                # and make a new
top node
}

sub my_snmp_handler {
    my ($handler, $registration_info, $request_info, $requests) = @_;

    my $targetIp = inet_ntoa($request_info->getTargetIp());
    for (my $request = $requests; $request; $request = $request->next()) {
# loop over each component of the request
        simulate($targetIp, $request_info, $request);
# and pass it to the simulator
    }
}

    # the simulator is invoked with:
    #   the address of the simulated host,
    #   the SNMP operation (get, getnext, etc.)
    #   the request object

sub simulate {
    my ($targetIp, $request_info, $request) = @_;

    my $mode = $request_info->getMode();
    my $oid = $request->getOID();
    $oid =~ s/^ccitt\.//;               # 'iso' comes in as 'ccitt.1', so
we need to strip off the front part and leave the '.1' behind
    $oid =~ s/^iso/1/;                  # and then... replace the 'iso' at
the front of the OID with its numeric value

    if ($mode != MODE_GET && $mode != MODE_GETNEXT ) {
        print "Unsupported Operation - $mode\n";
        $request->setError($request_info, SNMP_ERR_GENERR);   # return the
'genErr' error
        return;
    }
    ...
    $request->setValue($type, $value);          # return the appropriate
value and type
    ...
    if ($mode == MODE_GETNEXT) {                # during getnext's only...
        $request->setOID(find_next_oid...());   # replace the pre-filled-in
response OID with
    }                                           # whatever we determine the
'next' one should be
}

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