TechRepublic Tutorial: SNMP 101

What it takes to set up SNMP on both NetWare and Windows NT Servers and what you need to look for in an SNMP console

As networks become more complex, you need a way to identify a problem before your users do. If that isn’t enough of a reason, think of it this way: Isn’t it better to take a proactive approach to fixing a problem than to have to react to a situation and take what could be a scattergun approach to fixing the problem? SNMP (Simple Network Management Protocol) can be a very deep subject to jump into. In this article, I’ll cover the basics of what it takes to set up SNMP on both NetWare and Windows NT Servers and what you need to look for in an SNMP console.

Intro to SNMP
They say that necessity is the mother of invention. The father of SNMP , Jeff Case, who is a network manager and computer instructor at the University of Tennessee, was trying to find a way of creating software tools to manage networks. SNMP has gone from being a tool that only very large networks used to being something from which even single-server networks can benefit.

There are quite a few acronyms and statements that you’ll hear when you delve into the world of SNMP. You’ll hear about GET, PUT, TRAP, MIB, Monitor community, and Control community. Don’t worry about trying to understand the intricacies of SNMP all at once; you’ll become familiar with them in time. GET refers to the retrieval of information from an SNMP-compliant device, and PUT infers that you are placing or writing information to an SNMP-compliant device. TRAP is a message that an SNMP-compliant device sends when certain conditions are met (for example, an error condition has occurred or a device has been reset). The TRAP message is sent to an SNMP manager or SNMP console. Both are terms for a workstation running a program that receives the message from the SNMP device, decodes the information in the message, and either acts on the information or displays it in such a way that you know which action to take. MIB (Management Information Base) is a text file that provides the SNMP console with a way of decoding what would appear to be a cryptic message into something that we can understand.

You can control access to and from SNMP devices. Using a Monitor community statement and setting it to a specified text string (the normal default is public), you can limit read-only access to a device to those SNMP consoles that use the same text variable as does the device being interrogated. The Control community is a write version of the Monitor community. As with the Monitor community, the text string must match exactly (including the case), or the requested change in the SNMP device won’t occur.

When selecting an SNMP console package, you may want to consider having more than one device capable of receiving the SNMP TRAPs. When an SNMP TRAP is sent, it’s literally thrown out on the wire with no checking done to see if the message was received at the desired target. Depending on how a TRAP message is displayed at the SNMP console, you may find that more information is available to you than if you use a single console. Having an additional console also can serve as a failsafe; if a message shows up on only one console, it’s clear that one of your consoles may not be functioning properly.

When SNMP first came onto the scene, you were pretty much limited to sending the TRAPs out over TCP/IP. Although it’s now possible to use IPX to perform this task, you may not find many SNMP consoles, other than Novell’s ManageWise package, that will offer this type of support. This article will address using SNMP over TCP/IP only.

Setting up NetWare for SNMP
You configure your NetWare Server with INETCFG.NLM. Once the NLM has been loaded, highlight the Protocols option from the main menu and press [Enter]. Select TCP/IP and press [Enter] again. Highlight the SNMP Manager Table option and press [Enter]. You’ll see a window that lists This number means that an SNMP TRAP message on a NetWare server will be sent to itself by default, regardless of whether the IP address is bound to the network card or the address is changed at a later date. You can add one or more additional addresses by pressing [Insert], entering the IP address of the device that will receive the TRAP message, and pressing [Enter]. Then, press [Esc], press [Y] to update the TCP/IP database, and press [Enter] to complete the process. You’ll need to exit INETCFG.NLM, type REINITIALIZE SYSTEM, and press [Enter] to update the server with new information.

By default, the Monitor and Control community strings are set to public. You can change these settings by selecting the Manage Configuration option, highlighting the Configure SNMP Parameters option, and pressing [Enter]. On a NetWare server, you have four options for controlling the actions:
  • ·        Allow any community to read for a Monitor community
  • ·        Restrict any community from reading information
  • ·        Designate which communities can read information
  • ·        Leave the default settings

Similar options are available for the Control community; however, the changes apply to changes that were written to the SNMP device. You also can have the server send no TRAPs, send TRAPs to a specific community, or use the default setting.

On NetWare 4 and 5 servers, you can see some of the information in a TRAP message without having to set up an SNMP console. The first step involves loading the SNMPLOG.NLM module on the server, which allows TCPCON.NLM to read the TRAP database on the server. You can get to this information by selecting the Display Local Traps option from the TCPCON.NLM main menu. You’ll see the Host Name (usually the IP address of the device that’s sending the message), the TRAP type, and the timestamp for when the message was received at the server. Don’t be alarmed when you see a TRAP type in the TCPCON.NLM module that displays Enterprise Specific and a series of numbers. It’s TCPCON.NLM’s way of telling you that it doesn’t have any further information on this event.

Setting up NT for SNMP
Setting up NT for SNMP involves using the Properties option in Network Neighborhood. Select the Services tab and click the Properties tab. Select the Traps tab, enter the community name, and click the Add button to insert the name into NT’s database. To enter the IP address of the SNMP console, click the Add button in the Trap Destination area, enter the IP address of the SNMP console, and click Add to add the address to the list that NT will use when it sends out the TRAP messages. Click OK to complete the process. A few limited tools in the NT Server Resource Kit will help you monitor the SNMP activity on the server, but don’t expect a whole lot of help from these tools.

Selecting an SNMP console
This is a journey that shouldn’t be taken lightly. You can try such sites as to examine SNMP consoles that may perform the tasks you require. On the NetworkShareware site, for example, you’ll see such packages as Trap Console 1.3, Visual SNMP 2.0, and Active SNMP. Novell’s ManageWise network management package has a built-in SNMP console. Look at the commercial packages as well, such as CAI’s Platinum offering and HP’s Openview. With these and other packages, you’ll see a certain amount of out–of-the-box support for devices created by companies other than the one that created the SNMP console that you’re using.

Using devices that are supported out of the box involves downloading an MIB from the OEM that made the equipment you want to monitor on the SNMP console and then compiling the MIB into a form that the SNMP console can use. You’ll want to take this process into account when you evaluate prospective SNMP consoles. There are slight differences in MIBs. You’ll see references to MIB-I and MIB-II. The differences involve how the information is formatted and what kind of detail is contained in the MIB. See which MIB versions the SNMP consoles support and if their tech support can help you resolve SNMP compiler problems and save you from having to learn how to construct and debug SNMP MIBs.

You should choose an SNMP console carefully. Examine as many of the options as you can. I suggest that you evaluate at least two or three consoles side-by-side. Keep a log of your likes and dislikes, the console installation steps, the steps involved in compiling the MIBs, and other factors that will help you make your decision. You may decide that a basic console will be the best way to start. Eventually, you’ll change to a more sophisticated console as you begin to understand your needs or as the number and complexity of SNMP-compliant devices grow on your network.

As you read more about SNMP, you’ll discover how sophisticated it can become. In this article, I’ve provided you with a starting point on your road to using SNMP. How you proceed is up to you.

Ronald Nutter is a senior systems engineer in Lexington, KY. He's an MCSE, Novell Master CNE, and Compaq ASE. Ron has worked with networks ranging in size from single servers to multiserver/multi-OS setups, including NetWare, Windows NT, AS/400, 3090, and UNIX. He's also the help desk editor for Network World. If you’d like to contact Ron, send him an e-mail . (Because of the large volume of e-mail that he receives, it's impossible for him to respond to every message. However, he does read them all.)

The authors and editors have taken care in preparation of the content contained herein, but make no expressed or implied warranty of any kind and assume no responsibility for errors or omissions. No liability is assumed for any damages. Always have a verified backup before making any changes.

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