again MIBs-why?

[net.crops]

I am just confused after crawling through lot of SNMP baiscs in google.

All I understood is a network device( example router) having inbuilt agent,the agent which communicates with MIB databsase module of device inorder to get and set values as requested by NMS station.

My questions-

1.Why do I need to download MIBs once they are already preinstalled in device?.

2.OKay, after downloading MIBs from cisco or any vendor specific, where do I have to install them... and why?.Do I need to install in device or what?

3.Does the NMS station need to have all MIBS for that it monitors(routers,switches)...if so why?

4.What is Compling MIBs and whay do I need to do that.I have done this OID viewer recently...sorry I dont know whats story behind that.

I hope I wil get simple explanation.. thanks for time.

Regards,

netcrops

[Joe Clarke · Accepted solution]

Answers:

1. You don't. MIBs are there for humans to understand what the device is saying. The actual data on the wire is encoded object identifiers. Without MIBs, all you will see is numeric and character values for these OIDs, but they may not have any meaning for you. If you have the same MIBs that are supported by your device loaded into your SNMP manager, then the data returned via SNMP will be much more meaningful.

2. Depends on the SNMP management application. As for tips on how to install MIBs, see ftp://ftp.cisco.com/pub/mibs/app_notes/mib-compilers .

3. Having all the MIBs loaded will mean that you will have a better understanding of all of the information reported by your device(s). However, as I said before, SNMP is fully functional without MIBs. The data just won't be very meaningful.

4. Compiling, installing, registering, loading...they are all synonyms for the same thing. You are basically teaching your SNMP manager (your MIB viewer in this case) how to interpret the SNMP data from the device.

As a practical rule of thumb, you should attempt to load all the MIBs for your devices for at least the information you care about. For example, if you don't care about OSPF, then don't bother loading the OSPFs MIBs if you don't want.

There's also an Ask the Expert session on this list covering this exact topic right now. you may want to get in on that, and start reading through some of the posts.

[miheg]

1 No, you don't.

The mibs only describe what OID's are available and what they do. If you know what you want to poll then you don't need the mibs.

if you want your app to do an snmp get for .1.3.6.1.2.1.1.3 then you don't need anything but a program that can send an receive snmp packets.

if you want to tell it to get the sysUpTime then the program needs the mib2 mib to translate sysUpTime into .1.3.6.1.2.1.1.3

Basicly the mibs describe what the numbers mean.

2 you install them in the place that your applications use when they look for a name like sysUpTime. This place is different for each application. Sometimes you can tell the application where you placed the mibs.

3 if you or your NMS app knows the oid's then you don't, if it has to lookup the oid's for the name you provide then it does

4 compiling is usually importing the mib in a database so it can find the oid for a name or creating a sort of index.

the mib is a tree structure and the (vendor) mibs hang of a specific branch

Some apps parse the mibfiles in realtime other s "compile" the mibfiles in an internal database.

search google for netsnmp and getif to have some simple tools to try things and get a grip.

cheers,

Michel

[net.crops]

Thanks Joe and Michel,its great.

[dave.keith]

Good replys, but I'll add that some MIBs are dependant on other MIBs. Occasionally you may try to compile/import a MIB that is dependant on a MIB not in your system and it will fail because it references a missing MIB. If you want to install a particular MIB just have a look and see if there are any IMPORTS in the MIB, and if there are, make sure you have them loaded first.

As an example, the CISCO-QOS-POLICY-CONFIG-MIB has an IMPORT statement that imports a definition from CISCO-QOS-PIB-MIB.

Dave

[Joe Clarke]

Good point. As I mentioned in my response, one should definitely read the mib-compilers document before loading any Cisco MIBs as this covers things like load order and the IMPORTS clause.