Getting More Speed from an NT Network

In "Techniques to Speed Up Your NT Network" (April 1997), Joel Sloss describes how to create a network to connect clients to Windows NT servers. In this article, I'll show you another network design that can increase network speeds even more. I always try to design networks that install easily, work fast, reduce costs, and increase reliability. To create such networks, you need to avoid subnets and reduce the number of routers.

To Subnet or Not to Subnet: That's the Real Question
One major difference between Joel's design and mine is the use of IP subnets. Joel's design features four subnets. I prefer to configure a network without subnets because their use increases complexity and usually decreases performance.

Ethernet switching provides an easy way to segment a network without subnets. The difference between Ethernet switching and IP routing is how deep the device must look into the packet to determine where to send it. In IP routing, the device must look deep into the packet. In Ethernet switching, the device has to look at only the first few bytes, enabling much faster traversal of the network. Ethernet switches are protocol independent and require minimal, if any, configuration. In other words, they're almost Plug and Play.

You can also use IP switches (new devices that offer the speeds of switches and the ability to route packets simultaneously), but their cost is high. As the price of IP switches drops, they will become viable for networks. But at this time, you can justify them for only extremely high-speed TCP/IP networks.

In addition to speed and simplicity, switches offer versatility. With Ethernet switches, you can mix 10Base-T and 100Base-T adapters on the same network, decreasing costs. Many Ethernet adapters feature either 10 Megabits per second (Mbps) or 100Mbps operation. The only difference is the port they plug into. Because the network automatically detects the adapter's speed, you don't need any protocol or setup modifications.

With Ethernet adapters, you can connect 10Base-T hubs to 10/100 network cards in your workstations and servers. Then as the need develops, you simply plug the 10/100 network card into a 100Base-T hub, increasing throughput without touching the workstation.

Routers: A Path Not Taken?
Another difference between Joel's design and mine is how the network connects to other corporate networks or the Internet. Joel suggests that you create a router-to-router connection to link networks. Routers, however, have too many configuration parameters that you can inadvertently misconfigure. As a result, I suggest that you use a port on the existing corporate router to link to other corporate networks. To connect to the Internet, you probably need another router to link to your Internet Service Provider (ISP). You might also need a firewall to provide protection.

Table 1: Cost Per Port
Port Type	Cost
10Base-T Hub	$10
100Base-T Hub	$60
10Base-T Switched	$100
100Base-T Switched	$600
10Base-T to 100Base-T Converter	$500

To minimize costs while keeping network throughput high, I use 10Base-T ports for standard workstations, 100Base-T ports for advanced workstations, and 100Base-T switched ports for servers. As Table 1 shows, ports for 10Base-T are inexpensive. But, if you have the money, you can connect everyone to 100Base-T, which will increase throughput for network intensive applications.

Although I try to avoid using routers and subnets, they do have their place. I can't always design a network without subnets. Subnets work effectively for linking locations with low-speed connections, connecting large numbers of computers, and setting up networks that have many protocols.

Similarly, you might need to use routers. But router configuration isn't for the beginner. With a few hundred parameters to configure, you need to know what you are doing.

Putting Thoughts to Paper: The Network Design
With these considerations in mind, you can start putting the network design on paper. To begin, you must determine the configuration of the hubs, switches, and routers. An average small office needs to provide for about 50 low-speed hub connections, 12 high-speed connections, and 6 high-speed switched connections for the servers.

You can use low-speed connections for a majority of the devices on the network, such as standard workstations, printers, routers, and other instruments. You need to use high-speed connections for engineering workstations and other devices that need high-speed access but usually talk to only one or two other devices. You must use high-speed switched connections to servers or to any device that needs high-speed access and connects to many different devices on your network.

You can configure the network in many different ways. I like to use a 10/100 switch as the central point and connect the 10Base-T hubs, 100Base-T hubs, and servers to it. Figure 1 shows this configuration.

The amount of available bandwidth can help you determine whether to use a hub, switch, or router as the central point in your network. As Figure 2 shows, using a hub is like using one garden hose to connect all the devices. All information flows through the same line.

Using a switch or router is like using several garden hoses to connect each device on the switch or router. Because information flows through several lines, throughput increases significantly.

Routers and switches differ in their total speed capability. Routing imparts a significant penalty: Many smaller routers have problems keeping up with 10Base-T. Some smaller routers can't even handle a T-1 line at 1.544Mbps. Most switches provide full throughput between ports, providing a total of 400Mbps for an 8-port 100Base-T switch.

To provide the fastest connections to the application servers, I give the servers a dedicated 100Mbps port on the switch. If the switch and the network adapter support full duplex, you can run both devices at 200Mbps with no collisions. This configuration provides an extremely fast connection from the clients to the server. Collisions are isolated to the user segments, and each server can obtain full 200Mbps throughput.

Designing the Network Services
After designing the network, you need to create the network services design. Because you don't have multiple subnets to worry about, you might be tempted to put all the network services--such as Primary Domain Controller (PDC), Domain Name System (DNS), Windows Internet Name Service (WINS), and Dynamic Host Configuration Protocol (DHCP)--on one server. But you don't want to build in a single point of failure.

Instead, you can use two servers, each capable of performing all the necessary services. Neither server needs to be very large or fast, just reliable. Two 486 or small Pentium systems, for example, can easily fill the needs of up to 100 users.

When designing the services, you first need to determine the domain controller architecture. An NT domain controller provides security for a network. It lets you centralize user administration to provide a fairly secure network. The NT domain system consists of a PDC and any number of Backup Domain Controllers (BDCs).

Although BDCs are optional, I strongly suggest having at least one. If your PDC fails and you don't have a BDC, you will lose all security information and the ability to access most of the network. Thus, you need to configure both a PDC and BDC. (For more information about how to configure PDCs and BDCs, see Ed Tittel and Mary Madden, "PDCs, BDCs, and Availability," August 1996.)

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