Monitoring RAS Performance

By Brien M. Posey | Oct 31, 2000 | Print this Page
http://www.enterprisenetworkingplanet.com/netsysm/article.php/624781/Monitoring-RAS-Performance.htm

If you look at any book written about remote access, its primary focus will probably be security, and for good reason. Remote access servers (RAS) open your network to the rest of the world, and you must protect your critical resources. Such books usually do a good job of discussing the ins and outs of RAS security. However, I've noticed that they almost always omit one aspect of RAS: performance.

Often, administrators are so obsessed with RAS security that they forget to monitor how RAS services affect the overall performance of the network, and of the server that's hosting the RAS services. In this article, I'll discuss how to monitor RAS performance in a Windows 2000 environment.

Monitoring Communications Ports

When monitoring the impact of RAS services from a performance perspective, it's nice to be able to monitor specific communications ports. For example, suppose you have four phone lines connected to a remote access server. Now suppose that these four lines are all accessible through a single access phone number that leads to four different modems, all of which are connected to different COM ports. In such an arrangement, all remote users will be dialing the same phone number and could end up being connected to any one of the four modems, depending on which modem the phone switch rolls them to.

Now, suppose your help desk started getting calls from remote users who were being dropped or were experiencing very slow communications. If all these remote users were using different computers and all those computers previously worked with no problems, then it would be reasonable to suspect that the problem is related to your remote access server. I've seen countless situations in which a single modem in a bank of modems went bad and caused such problems. Other times, one of the modems in the modem bank may simply need to be reset. You need a way to determine which modem is causing the problem.

In the past, this was usually accomplished through the process of elimination. For example, you might disconnect all remote users and then watch the modem bank as designated users dial in, to see who is connected to which modem and who is having problems. Although this method works, it can be very time consuming. Troubleshooting four modems through this process is a little slow, but troubleshooting a bank of 256 modems is practically impossible.

Fortunately, Windows 2000 offers a method for monitoring the individual RAS ports. To check the status of a RAS port, follow these steps:

  1. Open the Routing and Remote Access console by clicking Start|Programs|Administrative Tools|Routing and Remote Access. In the console, navigate through the left pane until you locate the Ports section.

  2. Select Ports, and a list of all the available communications ports will appear in the list on the right. To begin the troubleshooting process, select the communications port you want to monitor.

  3. Right-click on the port, and select Status from the resulting context menu. When you do, you'll see a window that displays the port's status, as shown in Figure 1.

Figure 1
Figure 1: You can monitor the performance of any individual communications port.

As you can see, you can gather some very impressive information about the port. For starters, you can see which (if any) user is authenticated through the port. You can also see how long the session has been active and the IP address assigned to the session. Having this information can be very handy if a user calls with a problem--you can use this screen to see exactly which port the user is connected through.

Once you've looked at the basic connection information, you can begin the troubleshooting process. As Figure 1 shows, the port's information window also displays such information as the connection speed, buffer overruns, hardware overruns, time-outs, CRC errors, and more. You can use the buttons at the bottom of the screen to terminate or reset the connection, or to refresh the statistics that Windows has gathered.

Measuring the Impact of RAS Services

In the case of a typical RAS server, the impact that RAS services have on overall network performance is insignificant. To see why this is the case, imagine that you have a 56Kbps modem attached to each of a machine's four COM ports. In such a situation, the most bandwidth that all four modems could simultaneously consume would be 224Kbps, or roughly one quarter of one megabit. When you consider that even a slow Ethernet connection runs at 10 megabits, you can see just how insignificant that a RAS server's impact on the overall system really is.
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Of course, that's just one example. Many factors can contribute to an RAS server's impact on a network. For example, if an RAS server uses more ports or a faster type of connection than I used in my example, the overall impact will be significantly higher. At any rate, it's important to know just how much of an impact your RAS services have on the rest of your network. I'll discuss this and other aspects that you need to measure in Part 2 of this series. //

Brien M. Posey is an MCSE who works as a freelance writer. His past experience includes working as the director of information systems for a national chain of health care facilities and as a network engineer for the Department of Defense. Because of the extremely high volume of e-mail that Brien receives, it's impossible for him to respond to every message, although he does read them all.