School of Information Technology and Engineering (SITE) CEG 4395: Computer Network Management Lab 3: Simple Network Management Protocol (SNMP) Operations Objective To become familiar with basic SNMP operations by configuring and managing a desktop computer and a CICSO router. Background SNMP Service Management Windows XP Windows XP can be configured to be managed using SNMP commands. The workstations in the lab have the SNMP service installed to allow SNMP management. To start it, go to the Services Control Panel of Windows XP by choosing the Start -> Settings -> Control Panel -> Administrative Tools -> Services. Start the SNMP and SNMP Trap Service. Once the SNMP Service is started it is possible to configure it to allow an SNMP agent to get access to the system. This is done by opening the properties window of the SNMP Service and setting the Agent, Trap, and Security Settings. Below you see a screen dump of the Agent window of the SNMP Service properties task. You need to set these values to any name and location you want. Services types are listed at the bottom of the panel. They provide information
that can be stored in the MIB-2 variables in the System Group of MIB-2. End-to-End refers to TCP MIB variables, Internet to IP MIB and Datalink to Ethernet Hardware addresses. The Security tab specifies what the accepted community names and their appropriate access rights to the MIB variables are. The figure below and to the left shows the community name public having READ ONLY access. The public community is a default. You should add the tei_admin community for READ WRITE access. The Traps tab specifies where the traps captured by SNMP are to be sent. This community will be the name used by the OS in trap messages. The name must be the same as that configured by the receiving Management Station for receiving trap messages. The trap destinations box will reflect the IP address where the NMS is hosted. Add to this the mon_admin community name by choosing Add to list button and set the destination to the IP address of your machine or 127.0.0.1. WinSNMP WinSNMP is a set of APIs for SNMP management for the Windows OS. It is installed when the SNMP service is installed. It can be used to develop an SNMP agent or client. The SNMPUtil and SNMPUtilg executables use it. SNMPUtilg The SNMPUtilg is a windows based SNMP interface for getting and setting SNMP parameters. Procedure
Execute the SNMPUtilg program that should be located on the C:\Program Files\SNMP folder. If not, you can download it from the lab s website. Run it and you will see something like this: Configure the window just like you see above and proceed to answer the following questions. 1. Which object identifier is displayed as the default? Hint: execute the command once, then execute the command again and you should see the next value in the MIB. This should be the Object Identifier. Go to the web site http://www.iana.org/assignments/enterprise-numbers and determine which enterprise does this object belong to. 2. Switch the SNMP Function to execute to the value Get the value of the current OID. Type in the system.sysdescr OID 1.3.6.1.2.1 and execute this command. What occurs when the OID is 1.3.6.1.2.1? Why does this error occur 3. What OID value would you enter to get the system.syscontact? Hint: You can determine this by looking at the system group layout in the MIT. Enter this value and execute the command. What is the result? 4. If you walk the tree down from this level how many objects do you get in the system group? What is the object(s) name and value? What will be the next object after the last value of the system object is displayed?
5. What OID entry value would you enter to try to get the workstations IP address mask? There are 2 possible answers here depending on whether you use the local IP address 127.0.0.1 or the IP address of your workstation. What is the OID value you used? SNMP Traps SNMP Traps can also be captured with the proper client software. Download snmputil.exe from the lab s website and place it in the SNMP folder. Open a DOS window and execute the command snmputil trap. This will run snmputil in a mode where it is capturing traps that are sent to it. Recall that the SNMP service was set for sending traps if a NMS tries to access it with the wrong password. 6. From the SNMPUtilg program change the community name to a value other than public. Try to access the sysdescr object values 1.3.6.1.2.1.0 What is the output in the snmputil window? Where in the process did you specify where the traps were going to be sent? Change the community name to tei_admin and try the query again. You should not get an error this time. Using an NMS As you can tell SNMPUtilg analyzer is not a powerful tool since it only supports the reading of SNMP values and it is necessary to know the object IDs. A better tool is the Meterware NMS tool. Launch this application from the desktop and add your workstation as a device. This can be done by choosing in the Edit menu of Meterware the New Device option. This will pop up a window like below where it is necessary to fill in the device name, IP addresse, SNMP Level, etc. Fill the values in this window as shown and press the resolve button to commence polling.
7. When the HiFn analyzer shows a green up arrow the workstation is being polled. Meterware uses a graphical MIB browser that simplifies the viewing and setting of MIB parameters. Determine the MAC address of your interface card by opening the MIB browser window from the Tools menu and browsing to the interfaces object. What is the name of the object that you would choose to get the interfaces MAC address? What is your MAC address? You get the values of the objects by pressing on the icon button that looks like a traffic light. Why is there more than 1 interface? Look at the contents of the system.syscontact object. Set this value to Your Name by double clicking on the value of the MIB Variable Instance and typing in the string that corresponds to your name. At this point you are ready to explore connecting to a router on your own private network. We will perform some simple connections and later explore some more detailed Network Monitoring. Configure the following simple network shown below: Router 192.168.0.2/24 F0/0: 192.168.0.1/24 Make certain that the PC can PING the router and vice-versa. Configuring SNMP in the CISCO 2600 Router The router needs to be configured to allow the PC to access the Network Management Information. The first step is to create an access list for the router using the following command. Router(config)# access-list 1 permit 192.168.0.2 0.0.0.0 8. This command creates an access list that permits host 192.168.0.2 to access the router. Why is the mask is 0.0.0.0? The SNMP configuration begins by specifying the SNMP host access rights and community name: Router(config)# snmp-server community tei_admin RW 1 This command specifies the community name and the MIB access as well as added security level using the host access list. In order to enable trap messages to be sent the following command has to be entered: Router(config)# snmp-server host 192.168.0.2 rmon_admin snmp
This states that host 192.168.0.2 will be the recipient of traps generated by the router and the trap community name will be rmon_admin. You can now start up the HiFn Analyzer and add to the list of devices the routers F0/0 IP address. Use the tei_admin community name as follows: When you press the resolve button the Analyzer should resolve the MAC address and IP address and then press OK. The status of the router should come up to a green arrow. 9. Open the MIB Browser and take a look at the interface status by viewing the ifadminstatus object as shown in the screenshot on the next page. How many interfaces do you see? How can you determine which interfaces these are? List them. 10. The integer values of the status correspond to the following 1=UP 2=DOWN. What is the status of if3? Now set the value of the ifadmin3 to 1. What happened? Look at the Hyperterminal connection you have. What occurred to the state of f0/0? 11. In order to appreciate the composition of the SNMP messages, run Ethereal and capture an SNMP GET request. Show the screen dump of this message. What transport protocol is used by SNMP? What port is the GET request sent to? 12. Use the Hifn MIB browser to capture a query for the values of the ipaddrtable of the router. Show a screen dump of the values and explain the name of the MIB Variable Instance. Which object is the index? Explain how the variable instance values are lexicographically ordered.