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RFC: Who wants to design a better SNMP API?

by Hercynium (Hermit)
on Nov 28, 2007 at 17:28 UTC ( [id://653590]=perlmeditation: print w/replies, xml ) Need Help??

I have what I hope is an interesting proposition for whomever's reading this node!

I am trying to design a distribution for working with SNMP, that I will eventually upload to CPAN. I've been disappointed in one way or another by the API of every SNMP module I've tried, but I haven't given up hope that there can be something better.

Smarter hackers than I have put their hands to this task before, but I still believe there's a better way and I need your help to find it!

Everything in this RFC is up for debate and constructive criticism, and if anyone wishes to collaborate further on this project, I welcome you!

To begin, I have laid out the following terminology: 
SNMP MIB Terminology:

  MIB - A Management Information Base. It's a database, essentially, j
+ust not
        a familiar RDBMS. Every device that supports SNMP has one, whi
+ch you can
        query and update, if you know it's schema. The schema of a MIB
+ is 
        defined in a set of MIB files where each file contains modular
+ portions
        of the schema. Since each device may implement a different ove
+rall 
        schema, a module-based approach allows for that sort of flexib
+ility
        
        
  MIB File - An ASCII text file written according to the SMI format, w
+hich is 
             based on and defined using ASN.1. The MIB file is used to
+ define 
             and describe the schema of an SNMP MIB, or a portion of o
+ne.
             
             
  MIB Object - A queriable entity from an SNMP MIB. In a MIB browser, 
+this is 
               often described as a leaf or column. Each MIB Object is
+ defined 
               in a MIB file using the OBJECT-TYPE syntax. A MIB Objec
+t would
               define the following properties:

    object_type:    The name of this object in the SMI OBJECT-TYPE def
+inition 
                    in the MIB File.
    type_oid:       The OID of the object_type, as defined in the MIB.
    index_name[n]:  The name of the n-th index of this object-type, as
+ defined in
                    the MIB. (only valid for tables, table entries, an
+d columns)

                    
  Object Instance - To borrow terminology from Object Oriented Program
+ming, if a
                    MIB Object is a class definition, an Object Instan
+ce is an 
                    instance of an object of a class. In addition to t
+he 
                    properties of a MIB Object, it has the following w
+hich 
                    establish it's identity and value:

    value:         The actual value, as returned from a query to a dev
+ice.
    instance_id:   The specific identity of this object instance in a 
+device in
                   relation to it's object_type. It is a portion of an
+ OID 
                   string that is composed by the concatenation of one
+ or more 
                   indices.
    index_val[n]:  The value of the n-th index of this object's instan
+ce
    full_oid:      The full identifier for this particular object inst
+ance in a
                   device's MIB. It's the same as concatenating the ty
+pe_oid and 
                   instance_id

[download]
Some additional notes:

An OID is a way of identifying objects in a MIB. an OID is composed of an array of Octets, represented by integers with a \. between each element. Each object in a MIB has a unique OID, and instances of objects have additional octets on the end that define their identity in relation to their object-type.

There are several types of objects, but only a few can be queried. The queriable object types are scalars and columns, but for the purposes of this we only will consider columns, because scalars are *much* simpler.

Column objects are assembled into groupings called Tables, and tables contain a Table Entry object which defines what indexes are used to construct the instance_id of available Object Instances of the column objects within the table.

These concepts are what SNMP is built on. SNMP is essentially object-oriented, but uses mechanisms and concepts that are (academically) supposed to be straight-forward to implement in C. (they usually aren't) It's both elegantly simple and frustratingly complex, depending on the implementation, much like some programming languages. ;)

With this terminology in mind, I have the following scenarios as 'use cases'for which I am trying to develop a clean, clear, flexible general API.

Objects that I am presenting in these use cases will be specified not using their Numeric OIDs (.1.3.6.1.4.1...) but rather their Symbolic OIDs (textual names defined in the MIB Files)

First, a simple one:
ifTable.ifEntry.ifType
  - value is an integer representing the type of interface
  - index_val[0] is an integer value known as an ifIndex

ifTable.ifEntry.ifAdminStatus
  - value is an integer that represents an interface's administrative 
+state 
   (1=up,2=down,3=testing)
  - index_val[0] is an integer value known as an ifIndex
  
ifTable.ifEntry.ifInOctets
  - value is the number of bytes that have passed through the interfac
+e since
    being turned up.
  - index_val[0] is an integer value known as an ifIndex

[download]
We want to retrieve the full_oid of any ifInOctets objects whose instance_id matches (the instance_ids of all ifType objects whose value is 18) and (the instance_ids of all ifAdminStatus objects whose value is 1)


Second, a more complex one:
adMX2820M13PrvSlotTable.adMX2820M13PrvSlotEntry.adMX2820M13PrvCardPair
+ID
  - value is the name of the protection pair
  - index_val[0] is the slot number of this card in the pair
  
  
adGenPortSlotMapTable.adGenPortSlotMapEntry.adGenSlotAddress 
  - value is the slot number an interface is provisioned on
    (many interfaces per slot)
  - index_val[0] is the ifIndex value that corresponds to an interface
+ 
  
  
adMX2820M13StatDS3Table.adMX2820M13StatDS3Entry.adMX2820M13NetFuncServ
+State
  - value is a bitmask with the status of a DS3 circuit
  - index_val[0] is the ifIndex value that corresponds to this interfa
+ce

[download]
We want to retrieve the values of the adMX2820M13NetFuncServState objects that are only provisioned in slots whose adMX2820M13PrvCardPairID value is not blank and does not match '/not in use/i'


If you could write code to implement any of these use cases any way you wished, what would it look like? Pseudo-code is just as welcome as Perl.

Replies are listed 'Best First'.
Re: RFC: Who wants to design a better SNMP API?
by Hercynium (Hermit) on Nov 29, 2007 at 16:54 UTC
    Here's a pseudo-SQL-style example for the second one:
    SELECT adMX2820M13PrvSlotTable.adMX2820M13NetFuncServState.value
  FROM adMX2820M13PrvSlotTable
  WHERE adMX2820M13PrvSlotTable.adMX2820M13NetFuncServState.index_val[
+0]
  IN ( 
    SELECT adGenPortSlotMapTable.adGenSlotAddress.index_val[0]
      FROM adGenPortSlotMapTable
      WHERE adGenPortSlotMapTable.adGenSlotAddress.value
      IN (
        SELECT adMX2820M13StatDS3Table.adMX2820M13PrvCardPairID.index_
+val[0]
          FROM adMX2820M13StatDS3Table
          WHERE adMX2820M13StatDS3Table.adMX2820M13PrvCardPairID.value
+ !~ /not in use/i 
          AND adMX2820M13StatDS3Table.adMX2820M13PrvCardPairID.value !
+= ''
      )
  )

    [download]
    This query string could be parsed and 'compiled' into a set of SNMP queries and then a set of lookup operations on the SNMP query results to return the specific data being requested.

    So, the SNMP queries generated by parsing this would probably be something like this:
    my $snmp1 = $sess->gettable(
        adMX2820M13StatDS3Table, 
        columns => ['adMX2820M13PrvCardPairID',],
);

my $snmp2 = $sess->gettable(
        adGenPortSlotMapTable,
        columns => ['adGenSlotAddress',],
);

my $snmp3 = $sess->gettable(
        adMX2820M13PrvSlotTable,
        columns => ['adMX2820M13NetFuncServState',],
);

# Code to correlate indices and values and such...
# I could do this in larger, combined steps, or in a more 
# functional fashion, but I want this code to be as clear 
# and linear as possible

# Inner-most sub-select:
my $res1 = match_by_value( $snmp1, sub { $_ !~ /not in use/i } );
my $res2 = match_by_value( $snmp1, sub { $_ != '' } );
my $res3 = and( $res1, $res2 );

my $res4 = extract_index_val( 0, $res3 );

# Next sub-select:
my $res5 = match_by_value( $snmp2, sub { $_ in( @$res4 ) } );

my $res6 = extract_index_val( 0, $res5 );

# Main select:
my $res7 = match_by_value( $snmp3, sub { $_ in( @$res6 ) } );

my $res8 = extract_value( $res7 );

my $result = $res8

    [download]
    Somehow, it didn't come out as clear as I had hoped.
[reply]
[d/l]
[select]
      Posting anonymously so people don't think I'm begging for XP

      Just for fun, Here's what the above code would look like if I eliminated all the temporary variables... 
      my $snmp1 = $sess->gettable(
        adMX2820M13StatDS3Table, 
        columns => ['adMX2820M13PrvCardPairID',],
);

my $snmp2 = $sess->gettable(
        adGenPortSlotMapTable,
        columns => ['adGenSlotAddress',],
);

my $snmp3 = $sess->gettable(
        adMX2820M13PrvSlotTable,
        columns => ['adMX2820M13NetFuncServState',],
);


# wheeeeee!

my $result = extract_value( 
  match_by_value( 
    $snmp3, 
    sub { 
      $_ in( 
        extract_index_val( 
          0, 
          match_by_value( 
            $snmp2, 
            sub { 
              $_ in( 
                extract_index_val( 
                  0, 
                  and( 
                    match_by_value( 
                      $snmp1, 
                      sub { 
                        $_ !~ /not in use/i 
                      } 
                    ), 
                    match_by_value( 
                      $snmp1, 
                      sub { 
                        $_ != '' 
                      } 
                    ) 
                  ) 
                ) 
              ) 
            } 
          ) 
        ) 
      ) 
    } 
  ) 
);

      [download]
[reply]
[d/l]

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