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Are you just beginning to
learn the ropes as a network administrator ? Learn
how you can effectively use a MIB Browser to retrieve and set
configuration data in routers, switches, and servers.
- What is a MIB Browser ?
- Working with MIB Modules and enterprise MIBs
- How to select and read the MIB objects that are most
interesting to you ?
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What is a MIB Browser ?
A MIB Browser is a tool that allows you to pull out data
from SNMP enabled devices such as routers, switches, and
servers. In addition to pulling out data, a MIB Browser may
also perform the following functions.
- Retrieve and display MIB data in a human readable form
- Allow you to make it smarter by compiling in more MIB
definitions
- Set MIB variables, create, modify or delete conceptual
table rows
- Basic alarm ( trap ) management
- View the text file in a graphical manner usually featuring
a MIB tree
- Support all versions of SNMP including SNMPv3 security
What is a MIB
Walker ?
Nowadays, the term MIB
Walker and MIB Browser mean the same thing.
Originally, the term "MIB Walk" referred to the
ability to dump all or a section of the MIB tree via the snmpwalk
command.
Types of MIB Browsers
A MIB Browser can be as simple as a text based snmpwalk commandor as
sophisticated as Unbrowse
SNMP that uses a spreadsheet like
view. In some cases the command line may actually be a better
choice, such as when you are feeding the data to some other tool or
when you are running in a very resource constrained hardware.
Some alternate views of the same MIB data are shown in the
table below:
Text based
The simplest MIB Browser is the snmpwalk command. It talks to the agent
and dumps the MIB data in a easy to understand text console.
It is a must have tool, you never know when you might need
it. You can download the snmpwalk and other related utilities such as
(snmpset, snmpget, snmptable) from the Net-SNMP website.
http://www.net-snmp.org |
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Simple GUI
Many commercial products present the MIB data
to you in a nice list control. This allows you to see a more
structured form of the MIB data. |
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Spreadsheet
like
Some products like Unbrowse SNMP present MIB data in a spreadsheet like
interface. These products combine the raw MIB data along with the
knowledge of MIB definitions to present conceptual SNMP rows as real
spreadsheet rows. These tools also allow you to add rows, delete rows,
or modify cells. You can then commit all your changes in a single
button click. |
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MIB Modules and MIB Browsers
A MIB Module is just a file that contains definitions
of related MIB objects. The IF-MIB module for example defines
the
ifxTable, ifStack table and 50 other objects. These modules are defined
by experts in that area and are distributed in a plain text file in a
so-called SMI format. The file itself is quite hard to read and
comprehend.
The MIB Browser comes to the rescue here. It can understand the SMI
file either natively or by compiling it into an intermediate format. It
can then show the MIB in a graphical format that is easier to
comprehend and navigate. Some example are shown in the table
below.
Plain MIB
File
A plain MIB file looks like the image on the right. Some of
these plain MIB files run
into thousands of lines and are notoriously hard to read and
comprehend. These files are written in standard format
called the SMI format. The SMI format (officially called SMIv2 is
defined in RFC2578 |
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Graphical
format
Most MIB Browsers have the capability to transform the plain
text file into a graphical display. The goal is to employ elements
like bitmaps, lists, and fonts to present the MIB
definitions in the most intuitive way possible. See the screenshot on
the right for an example of Unbrowse
SNMP. |
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Dealing with MIB Modules
While working with SNMP, one of the key considerations is whether the
MIB Browser has sufficient knowledge of the MIBs. The unit of
definition of a MIB is a module. To effectively manage a particular
agent, you must tell the MIB browser about as many objects implemented
by the agent as possible. This means loading the MIB Browser with as
many enterprise (private) MIBs as you can lay your hands on.
Modules implemented by the router (agent)
A single MIB module defines a related group of SNMP
objects. An agent can choose not to implement a module at all or to
implement only a subset of objects from a module. An agent typically
implements objects from a large number of modules. Within
each module it may not support all objects.
For example the
Cisco Catalyst 4000 series switch implement MIB objects from
100+ different
MIB modules as shown here.
How to find out what modules are implemented by the agent ?
You may ask, "Well, how do I know what MIB modules I need to
manage my router model XXX ?".
There are several options.
- Just ask your router vendor for a list of modules
implemented by model XXX. Some vendors like Cisco and Juniper make it
easy by publishing this information on their websites. Most will tell
you the names of modules and may even provide you with MIB files you
can compile yourself.
- Use a discovery tool to check the sysORTable. The
sysORTable is basically a set of pointers to agent
capabilities (or) to modules implemented. Some tools
like Unbrowse SNMP allow you to check the sysORTable via a tool.
Note that this method may not work in many agents or may be
inaccurate due to faulty implementations. In those cases, you can use a
brute force method - which is the most accurate.
- Use a brute force discovery tool. The idea is to dump the
entire MIB database and then check each OID for a match against the MIB
browsers knowledge base of MIBs. Any unresolved OIDs can be dumped to
the screen. You can then hunt for these unknown OIDs in an online MIB
database such as mibdepot.
What does loading MIBs mean ?
The MIB browser is only as smart as the number of MIB definitions it
knows. If you have not "told" the MIB Browser about a particular group
of objects, the MIB browser is ignorant of that object. Loading MIBs
refers to the process of telling a MIB Browser to read in
some information from selected modules which are about to be used. It
is like saying, "Get ready, I am going to be using these modules X,Y,Z
anytime now".
Some MIB Browsers need you to explicitly load MIBs after you start,
even if you have already "told it" about the existance of those MIBs
via the act of compiling those modules. This form of loading means that
the loaded MIBs will be read in to memory. Unbrowse
SNMP does not
require you to take any explicit action of loading.
How to use a MIB Browser with real world agents
Routers, switches, storage networks, and servers implement thousands of
objects from several dozen modules. Some objects may not even be
publicly documented. What is the right way to effectively use a MIB
Browser in such a situation ?
- Get your hands on as many enterprise MIBs as you can for
that
particular vendor. If you are dealing with Cisco or Juniper, you are in
luck because all their MIBs are publicly available. If you are dealing
with other vendors you can visit a MIB database such as MIB Depot
(http://www.mibdepot.com)
- Compile those MIBs into your MIB Browser. It would help a
lot if
your MIB Browser has various leniency levels because not all enterprise
MIBs are clean nor do they follow the mib file naming conventions.
Unbrowse SNMP allows you to compile almost anything you throw at it and
does not expect any file name convention.
- You rarely want to pull the entire MIB database from the
router,
this is potentially huge amount of data. So, you must first figure out
what you are interested in and locate the MIB objects that can provide
you that information.
- Create a view of the MIB objects you are interested in.
Unbrowse
allows you to drag and drop all kinds of MIB objects into a "walk
view".
- If you are dealing with large tables such as accounting
tables, ATM
Virtual Circuit tables, or MPLS LSP related tables, you really do not
want all the rows back. Sometimes, the number of rows in those table
can exceed tens of thousands. So your MIB Browser must also allow you
to specify a subset of rows to retrieve. With Unbrowse you can select a
number of ranges of rows to retrieve.
- Your MIB Browser must allow you to save all the above
information
that you carefully put together, so that you do not have to go through
this process again. Unbrowse SNMP allows you to save this information,
the next time will be as easy as pressing a "Walk" button.
Get a MIB Browser and learning
If you want to learn more about MIB Browsers and SNMP, the best way it
to download a MIB Browser and start playing with it.
Try
Unbrowse SNMP now !
Happy browsing !
Glossary
| MIB |
Management
Information Base
You can consider it to be the "router database" for purposes of MIB
browsing. |
| SNMP |
Simple
Network Management Protocol |
| SMI |
Structure
of Management Information
Dictates the format of the MIB file (the plain text file) |
| Agent |
Typically
a router, switch, server or other network elements which are SNMP
capable. |
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