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Re: Net::SNMP get_bulk_request Not Working

by Corion (Pope)
on Jul 30, 2010 at 20:31 UTC ( #852165=note: print w/replies, xml ) Need Help??


in reply to Net::SNMP get_bulk_request Not Working

I presume this is somewhat related to Net::SNMP Query Returns Error: No response from remote host, as it seems you posted the same code.

Have you tried a network sniffer to find out what the difference is between the requests that both programs send over the wire?

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Re^2: Net::SNMP get_bulk_request Not Working
by spickles (Scribe) on Jul 31, 2010 at 01:04 UTC

    It's the same code, but different issues. Khen suggested I turn on debugging for the no response issue, which appears to be host specific. For that, I'll put a sniffer on the wire as you suggest, but I'm not good at reading those. I think my current problem with why Net::SNMP doesn't do what I want is the following:

    SolarWinds will do a MIB walk, starting on the branch OID that I specified and I'm assuming that's how it 'discovers' the other device specific OIDs. What I'm trying to do with Net::SNMP is essentially the same thing, but I now understand that the get_request and get_bulk_request methods are for known OIDs rather than a MIB walk. So it may turn out that Net::SNMP can't do a MIB walk? At this point I don't understand enough of the module to know for sure. I'll keep working on it and hopefully people will post back with other useful pointers for me.

    Regards,
    Scott
      Actually, it does mibwalk. There's an example script in the examples directory. See: snmpwalk.pl.
        my $punishment = new punisher(); while (idiot) { $punishment->slap ( -forehead => hard ); }

        Thanks Khen. I thought that the examples were all included on the main page. I turns out that I also figured out that the function get_table returned what I wanted. The example you provided has lots of arguments and some decent checks.

        Thanks,
        Scott
        Can anybody write how to extract measure units (Kb, Mb, e.t.c.) from get_bulk_request unless it's impossible.

      The general idea: SNMP v1 has set, get, get_next. set($oid,$value); ($oid, $value) = get($oid); ($oid, $value) = get_next($root). For the set, get you a full OID leaf value, for the get_next you can use either any OID value because get_next returns the next available OID in the MIB after the one you gave it. So if you have a tree like:

      1.2.1.1.0 = 42
      1.2.1.1.1 = 43
      1.2.1.1.3 = 44
      1.2.1.2.0 = 'a'
      1.2.1.2.1 = 'b'
      1.2.1.2.3 = 'c'
      
      get(1.2.1.1) -> error
      get_next(1.2.1.1) -> (1.2.1.1.0, 42)
      get_next(1.2.1.1.0) -> (1.2.1.1.1, 43)
      ...
      get_next(1.2.1.1.3) -> 1.2.1.2.0, 'a)
      ...
      get_next(1.2.1.2.3) -> 1.2.1.3.something, something)
      

      A walk just does a get_next over and over until the returned OID is outside of the tree root you gave it to start with. In this case if you started with 1.2.1.1 it would stop at 1.2.1.1.3 and not give you 1.2.1.2 and later.

      A get_table is just a wrapper that walks multiple tree roots at the same time, e.g. get_table(1.2.1.1, 1.2.1.2) would return all six of the above values.

      SNMP v2c and v3 have the bulk versions of these, they can just request/get multiple OIDs in the same data packet rather than doing a get_next for each OID in turn.

      IIRC, the Net::SNMP module returns everything in a hash reference. The SNMP module for the net-snmp library returns VarBind objects (array references) and will return a get_table in columns like:

      [
       [ 1.2.1.1.0, 42,  1.2.1.2.0, 'a' ],
       [ 1.2.1.1.1, 43,  1.2.1.2.1, 'b' ],
      ]
      

      This is by no means a detailed description, method names, signatures, returns, details differ depending on which SNMP module you're using, and which version of SNMP you're using to communicate with the device. But it all pretty much breaks down to set, get, get_next.

        HI guys i think when u r using snmp version 2. Net::SNMP uses one optional variable -maxrepetitions for get_bulk_request() function. default it was set to 0. you need to set it to 1.then it will work

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