Mid Level Manager MIB and SNMP Script Language

David Levi
SNMP Research
levi@snmp.com

History

Language designed for XNETMON
~late 1992
Customers requested language without GUI
~mid 1993
Created Mid-Level Manager
Customers requested a GUI to help configure MLM
~early 1994
Created Mid-Level Manager config tool

Goals

Ease burden of management stations
Reduce/localize network traffic
Expand domain of manageable devices
Automatic corrective behaviors

Architecture

          _________________________________________
         |                ________          Other  |
         |  ____  ____   |  MLM   |   ____  Mgmt   |
         | |    ||    |  | config |  |    | Apps   |
         | |    ||    |  |  tool  |  |    | -----  |        
  NMS    | |____||____|  |________|  |____|        |
         |     \    \        |         /           |
         |      \    \ ______|______  /            |
         |       \____|    Brass    |/             |
         |            |    Server   |              |
         |            |_____________|              |
         |___________________|_____________________|
                             | 
          ___________________|_____________________
         |           ________________              |
         |          |     Emanate    |             |
         |          |     Master     |             |
         |          |     Agent      |             |
         | Other    |________________|             |
         | Subagents  /      |     \               |
         |   ____    /       |      \     ____     |
  MLM    |  |    |__/   _____|____   \___|    |    |
         |  |    |     |          |      |    |    |
         |  |____|     |          |      |____|    |
         |             |---MLM----|                | 
         |   ____      |          |       ____     | 
         |  |    |     |__________|      |    |    | 
         |  |    |           |           |    |    |
         |  |____|      _____|____       |____|    |
         |       \     |   Brass  |     /   Other  |
         |        \____|  Server  |____/    Mgmt   |
         |             |__________|         Apps   |
         |___________________|_____________________|
                         / / | \ \
                        / /  |  \ \
                       /  |  |  |  \
                      __ __ __ __ __
                      || || || || ||
                      -- -- -- -- --
                           Agents

Architecture

                     _____________
                    |    Master   |
                    |    Agent    |
                    |_____________|
                           |
                           |
         __________________|____________________
        |         Emanate SADK Library          |
        |_______________________________________|
        |               MLM MIB                 |
   _ _ _|_ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _ _|_ _ _
        |         Script Engine Library         |
        |_______________________________________|
        |          Brass MADK Library           |
        |_______________________________________|
                           |
                           |
                     ______|______
                    |    Brass    |
                    |    Server   | 
                    |_____________|

MLM MIB

3 Tables:

mlmScriptTable
mlmCompileTable
mlmResultTable

mlmScriptTable used to upload/download Scripts between the MLM and manager, e.g., the MLM config tool

Scripts are stored as Octet Strings

mlmCompileTable used for configuring and running scripts

can contain filename of script or pointer to mlmScriptTable
can specify arguments to pass to a script
can specify frequency to run script periodically
can command script to be run once

mlmResultTable used to make result of running script available in MIB variables

Scripts return varbind lists
Result Table contains encoding of varbind lists:

mlmResultOID
mlmResultType
mlmIntegerValue
mlmOctetStringValue
etc.
.
.
.
[blech]

Script Language

All variables are varbind lists
Basic control structures (if, while)
Various logical/mathematical operators
Language can be extended by registering C functions with script library
Scripts run asynchronously

Basic Script Capabilities

SNMP operations (get, set, etc.) result assigned to script variable
Send trap or M2M inform request
Log data to a file
Fork, call, or jump to another script
Launch another application

Experience

Have written many MLM applications, for example:

Intruder detection script
- uses RMON to capture source addr of packet
- script checks if packets are from a "trusted" device
- if not, script issues a warning (should be a set request, send e-mail, etc.)
Audio counter-attack script
- monitors audio MIB for noise level
- if level is above threshold, turn on UPS with set
- if level stays above threshold, do set to play back the noise
M2M-like scripts
- retrieves several MIB variables, possibly from several agents
- combines the variables using a mathematical expression
- if a threshold is crossed, send an inform request

Future Directions

MLM MIB Separate mlmCompileTable into an "available scripts" table and a "script execution" table
Explore alternative means for NMS applications to get results from MLM
Define useful extensions to script language
Harmonization between script language and SNMP-TCL