Oh, no! More MIBs!?
Variety of MIBs
Yeah, it really gets kind of boring. Don't worry, I will not take you through any detailed examination of these MIBs - you now know how to explore any MIB you want or need using a MIB browser or even the Simpleweb website. Rather, I'll just give you an overview of the variety of standard MIBs that are out there. Let's first be certain it is clear how to find where each MIB is situated in the management information tree.
We saw that there are nodes defined under the mib-2 node in the original MIB-2, and we also saw an example in the previous chapter of how a MIB module - it happed to be the Appletalk MIB - is defined to be under a particular node. At the beginning of every MIB document, there is a statement that defines its location in the management tree. Recall that the location is defined by the OID (Object Identifier). In our BlackOwl MIB browser, in the Available MIBs frame, we see at the top a MIB called Host Resources MIB. (This is RFC 2790.) If you select it and scroll down a bit in the text, you'll find the OID for this mib. The statement is host OBJECT IDENTIFIER ::= { mib-2 25 }, as we see in Figure 38.
Figure 38: Host Resources MIB OID Definition
That means that the host MIB is placed under the 25th node under the mib-2. What is the OID of the host MIB? OK, load the MIB, switch to the tree view, and check yourself! (See Figure 39.)
Figure 39: Host Resources MIB OID
Transmission Group MIBs
While looking at the MIB tree all these times you might have noticed something interesting in the mib-2 groups. One of the original MIB-2 groups has no expansion, i.e., it has no objects under it. That is the transmission node. You can look at your tree (or Figure 39, again) to see it. For those who wish, you can go back to the Available MIBs frame and select RFC1213-MIB, or look at the RFC on the web and find the definition of the Transmission Group. You will find that the Transmission Group was defined to be a placeholder for MIB modules that were yet to be defined, such that each module would be for a particular transmission type, such as Ethernet, ATM, etc. However, for reasons unclear to me, not all MIBs that were defined for transmission technologies ended up being placed under the transmission node.
Take a look at the Simpeweb's list of Transmission MIBs. There's a lot of them! Some of the latest ones, such as the EPON MIB (you can also select from the list itself instead of opening another window from my link) are defined as nodes directly under mib-2. The EPON MIB is defined as ::= { mib-2 155 }. On the other hand, the ADSL2 MIB is placed at ::= { transmission 238 } (you have to scroll through a lot of stuff to find the OID). In any event, the OID for a MIB module is assigned by IANA.
A really cool website called the OID Repository allows you to find out information about any OID (that has been registered with the site) and its child OIDs. So, for example, enter the OID of the transmission group, 1.3.6.1.2.1.10, in the query field, and you'll get information about the transmission node under mib-2. There is a drop-down menu from which you can select any of the MIB modules that are defined under the transmission node, the last one being the ADSL2 MIB mentioned in the previous paragraph. If you have the time, navigate around that site, take a look at their tree display, and you'll get an idea of how the SNMP Management Tree is just a subset of a much more extensive tree!
Remote Monitoring and Measuring
Another interesting category of MIBs are those that are intended for remote monitoring. You might ask - "Isn't managing any device with SNMP remote management? Can't I also monitor my devices? What is the difference?" So, let's clarify what we mean by "remote monitoring". Many of you (maybe all of you) are familiar with devices (or software) that capture packets on a network for analysis. In fact, in the chapters on SNMP messages, we'll be using open source (and free) software to do just that. Network managers might wish to leave network "probes" in place and to be able to query them to find out the statistics and other information they've collected. Using SNMP and appropriately defined MIBs permits this.
We saw in the previous chapter that the ifTable has statistics (such as ifInOctets) and, in fact, the IP, ICMP, TCP, and UDP groups all collect statistics. The difference between such statistics collection and what is considered a remote management device is that routers, switches, hosts, etc. all have another purpose in life. But a network probe's only purpose is to collect data from the network. Therefore, it can collect much more detailed data than we can expect of other devices, which should be expending its resources on doing its real job (though nothing prevents a manufacturer from including a probe module in its Ethernet switch).
The primary MIB defined for remote monitoring is the RMON MIB defined in RFC 4502. If you are interested in further description and detail of what this MIB contains, you can look at the the text in your MIB browswer (it happened to be included in the original packate) or at its structure with your Tree view (after loading it). Or, you can use the tree shown on the Simpleweb. The RMON MIB (this is version 2) is the 16th node under the mib-2 node in the management information tree, and you can see this in either tree view.
The categorization of MIBs on the the Simpleweb makes it easy for you to see other MIBs associated with Remote Monitoring. If you scroll on that page, you'll see a related categorization of MIBs, for Distributed Management. For example, the Remote Ping, Traceroute, and Lookup MIB allows managers to use these tools remotely on a device. Of course, many managers just use telnet to do that, but using SNMP with the appropriate MIB permits collection of information (and requires more resources and more complex setup).
Applications and Others
If you've explored any of the links that I've provided on the Simpleweb website - whether the categorization of MIBs or the page where you can load a mib to a tree view (and they have other ways of organizing the MIBs - explore!), you certainly would have noticed a wide variety of other types of MIBs - for applications, for hardware such as printers, etc., etc. If you've really been alert, you would have noticed the Coffee Pot MIB. (No, the devices listed on the bottom right of that page do not support the Coffee Pot MIB.) Remember the SNMP-managed toaster (described in an earlier chapter)? Well, you need coffee to go with that toast, don't you?
With that, I leave you to explore all the MIBs you want, but we will take a few minutes in the next chapter to see what private enterprise MIBs are and how they fit into the management structure.
