I have a situation where I'm trying to do some MIB-processing on a pre-existing, non-translated SNMP walk in the cloud. I have a set of translated PySMI MIB json files, but I'm unsure how to match the correct MIB with OIDs within the walk.
I saw in this post that PySNMP was unable to automatically detect a MIB but that it was being worked on. I tried to create a simple implementation myself using regex, but I cannot find the correlation between a MIB's module identity and the OIDs that I am retrieving from the SNMP walk.
I've seen the MIB index that can be generated from PySMI, which seemed promising, but I'm not sure how I can use that to find the human-readable version of an OID from a collection of MIB files.
What am I missing? Thanks!
A way to deal with this would be to build the OID->MIB index by running PySMI-based script (or just vanilla mibdump tool) over your entire MIB collection. Actually, such index can be found here.
Once you have this OID->MIB mapping, you could run the OIDs your snmpwalk script receives, match them (or their prefixes) against the OID->MIB map and load up the required MIBs.
Unfortunately, this relatively simple process has not been built into pysnmp yet, but it should not be hard to implement within your script.
Related
We are implementing support for the Entity MIB module (RFC 6933) and related MIB modules as part of an SNMP agent (snmpd) using Net-SNMP.
Some of the data is shared between MIB tables and MIB modules, for example table indices and "contained in" objects between entPhysicalTable and entPhysicalContainsTable, and indices between entPhysicalTable and entPhySensorTable.
Note that MIB modules related to the Entity MIB module include the Entity Sensor and Entity Battery MIB modules (RFCs 3433 and 7577 respectively).
Are there any pointers or best practices on how to enable such sharing of data between tables using Net-SNMP?
Is there any built-in support provided by Net-SNMP to achieve this, e.g. any particular mib2c options to construct the relevant template source files for these MIB tables?
In particular, data such as indices needs to be dynamic, as entities such as Field-Replaceable Units (FRUs) may be added or removed whilst an SNMP agent is running.
I note that data (indices) is shared between tables such as ifTable and ifXtable, provided as part of the standard Net-SNMP implementation.
Thanks in advance for any help.
When you run mib2c and specify a table, and don't specify a configuration file, it will ask you questions about the style of code you want to generate. Generally speaking, the choices boil down to whether you want net-snmp to "own" the underlying data store (which you update as values change) or whether you will use your own data structures for the underlying data store (which you will implement hooks to that net-snmp calls to interact with your data). In the former case, net-snmp would handle this "shared data" because it owns it. In the latter case, how you handle it depends on how you organize your data structures.
Can anyone tell me why NMS implementations parse and save MIB items in a database?
I know one of the reasons is when they receive a trap and want to analyze it, then they use the parsed MIB. What else they do with parsed MIB?
For example, when the NMS sends a SNMP GET request to an agent, the programmer must specify which OIDs are being requested?
Does the the parsed MIB have a another purpose or do we parse MIBs only for analyzing SNMP traps?
You are on the right track - you parse the MIB at all in order to make it human-readable. That is for both traps (informs) and polled values. But if you parse it out to a text file, that's a huge amount of data to read/grep through to find out the description, message, possible values, related OIDs, etc.
Added to this is that there isn't just one MIB. There are dozens or hundreds that an NMS may be interested in. Since, on a host, you only add the MIBs that you want that host to respond to, the NMS has to have a copy of every MIB that ever device it is monitoring may have on IT so that it can understand the response the host returns.
So you parse each MIB and store it in a db to make it faster to search and to have everything all in one place. That could be so that you can find the messages associated with varbinds, or what all the possible enumerations are, etc.
Just to be clear, parsing the MIB isn't the same as doing an SNMPWalk on a host. SNMPWalk just gives you the current response to each OID in sequence.
I am using NET-SNMP (V5.6.1.1) on windows to read my MIB with snmpget & snmpwalk. When I try accessing the MIB I can only see some of the elements. I know the MIB is good since my colleague can extract the same revision of the MIB from the repository and can see all elements within the MIB. We are using the same SNMP command syntax to query the data. I have compared the MIB and snmp.conf files between his machine and mine and they are identical, so can only assume that it is due to a difference in the configuration of our respective PCs. I’ve also checked for any differences in the Environment Variables between our machines, but can see nothing obvious. Is there anything in the machine configuration that might explain why I can only see part of the MIB?
Edit: The MIB is implemented as a single bespoke executable, with the data held in a number of tables, for example:
mibTableA.parameter1
mibTableA.parameter2
mibTableA.parameter3
mibTableB.parameter4
mibTableB.parameter5
mibTableC.parameter6
mibTableC.parameter7
mibTableC.parameter8
None of these tables are dependant upon the availability of system hardware, etc. These tables can also be accesses via an RTA interface using PSQL queries, and using the RTA interface on both my machine and my colleague’s machines, I can see all the tables/parameters. Yet, for instance, accessing the MIB via SNMP I can only see the mibTableA on my machine.
First you need to identify which are the missing ones on your box. Show some examples in your question so that others can guess what can be the cause.
Second, SNMP query result is indeed machine dependent. For example, if your machine has less network adapters than your friend's, then it is reasonable some objects are missing.
I found the problem. There are some scalar fields in the MIB which define the table sizes and these had not been initialised correctly, but instead were picking up old values stored in tables in a C:\Documents and Settings\user\Application Data folder. Hence the difference in behaviour between my machine and my colleagues.
I'm still quite new to SNMP and I was wondering how I would go about getting an entire branch of a MIB with as few queries as possible.
My approach:
Use GETBULK messages to get pow(2,tries) entries at a time and then stop when I get an object that don't match as a child of the object specified by my OID
Why do I need it:
I'm trying to get a variant sized branch of the MIB, the ipRouteTable part to be specific.
Do you know SNMP has a WALK operation where you can visit all objects in turn? Net-SNMP has such a utility,
http://net-snmp.sourceforge.net/docs/man/snmpwalk.html
I'm querying a bunch of information from cisco switches using SNMP. For instance, I'm pulling information on neighbors detected using CDP by doing an snmpwalk on .1.3.6.1.4.1.9.9.23
Can I use this OID across different cisco models? What pitfalls should I be aware of? To me, I'm a little uneasy about using numeric OIDs - it seems like I should be using a MIB database or something and using the named OIDs, in order to gain cross-device compatibility, but perhaps I'm just imagining the need for that.
Once a MIB has been published it won't move to a new OID. Doing so would break network management tools and cause support calls, which nobody wants. To continue your example, the CDP MIB has been published at Cisco's SNMP Object Navigator.
For general code cleanliness it would be good to define the OIDs in a central place, especially since you don't want to duplicate the full OID for every single table you need to access.
The place you need to be most careful is a unique MIB in a product which Cisco recently acquired. The OID will change, if nothing else to move it into their own Enterprise OID space, but the MIB may also change to conform to Cisco's SNMP practices.
It is very consistent.
Monitoring tools depend on the consistency and the MIBs produced by Cicso rarely change old values and usually only implement new ones.
Check out the Cisco OID look up tool.
Notice how it doesn't ask you what product the look up is for.
-mw
The OIDs can vary with hardware but also with firmware version for the same hardware as, over time, the architecture of the management functions can change and require new MIBs. It is worth checking whether any of the OIDs you intend to use are in deprecated MIBs, or become so in the life of the application, as this indicates not only that the MIB could one day be unsupported but also that there is likely to be improved, richer data or access to data. It is also good practice to test management apps against a sample upgraded device as part of the routine testing of firmware updates before widespread deployment.
An example of a change of OID due to a MIB being deprecated is at
http://www.cisco.com/en/US/tech/tk648/tk362/technologies_configuration_example09186a0080094aa6.shtml
"This document shows how to copy a
configuration file to and from a Cisco
device with the CISCO-CONFIG-COPY-MIB.
If you start from Cisco IOS® software
release 12.0, or on some devices as
early as release 11.2P, Cisco has
implemented a new means of Simple
Network Management Protocol (SNMP)
configuration management with the new
CISCO-CONFIG-COPY-MIB. This MIB
replaces the deprecated configuration
section of the OLD-CISCO-SYSTEM-MIB. "
I would avoid putting in numeric OIDs and instead use 'OID names' and leave that hard work (of translating) to whatever SNMP API you are using.
If that is not possible, then it is okay to use OIDs as they should not change per the SNMP MIB guidelines. Unless the device itself changes but that requires a new MIB anyway which can't reuse old OIDs.
This is obvious, but be sure to look at the attributes of the SNMP MIB variable. Be sure not to query variables that have a status of 'obsolete'.
Jay..
In some cases, using the names instead of the numerical representations can be a serious performance hit due to the need to read and parse the MIB files to get the numerical representations of the OIDs that the lower level libraries need.
For instance, say your using a program to collect something every minute, then loading the MIBs over and over is very inefficient.
As stated by others, once published, the name to numerical mapping will never change, so the fact that you're hard-coding stuff into your programs is not really a problem.
If you have access to command line SNMP tools, check out 'snmptranslate' for a nice tool to get back and forth from text to numerical OIDs.
I think that is a common misconception (about MIB reload each time you resolve a name).
Most of the SNMP APIs (such as AdventNet, CMU) load the MIBS at startup and after that there is no 'overhead' of loading MIBs everytime you ask for a 'translation' from name to oid and vice versa. What's more, some of them cache the results and at that point, there is no difference between name lookups and directly coding the OID.
This is a bit similar to specifying an "IP Address" versus a 'hostname'.