Novell Del Mar College
CIS 306 - Managing NOVELL® Networks
 Instructor: Michael P. Harris
Networking Primer

7. Real World Networking

In the real world, computer networks can combine a great number of physical and logical topologies. We've already seen a very simple network. Now let's take a look at more complex networks. We'll start with simple internetworks and work our way gradually through more complex situations. For the sake of simplicity and clarity, all of the subnetworks in our internetworks will be based on the NetWare client-server networking model.

One Server, Multiple Networks of the Same Type

The simplest form of an internetwork is two cabling (media) segments of the same media access control type sharing one network server (Internal Bridge/Router).

For example, one server could contain two Ethernet network adapters, each supporting a different cable segment. There could be several computers connected to each cable segment, in a star physical layout, with each cable segment using contention (CSMA/CD) for the media access control. Each of the cable segments would have a different network address—thus, each would be an independent subnetwork.

Together, the two separate networks would form an internetwork, connected by means of internal routing capabilities built into the server. (Remember, we have already said that in NetWare servers, internetworking is accomplished through routing at the network layer.)

Figure 23 illustrates the one-server internetwork described above.

Figure 23: Internetworking two networks using the same type of network adapter (MAC) in one NetWare server, by means of the server's internal routers

In the case of the above network, routing would be accomplished using the NetWare IPX™ protocol or the NetWare IP protocol, with support from the other NetWare routing protocols, as previously described.

Every NetWare server is capable of using internal routers to accomplish local network routing by means of the NetWare routing protocol set and AppleTalk. All NetWare internal routers operate at layer three of the OSI model and are for use with small workgroup or departmental networks. For larger or more complicated internetworks, or for departments with heavy server-processing requirements, the IntranetWare MultiProtocol Routers or dedicated routers from other vendors provide the necessary extra routing power and capabilities.

In a slightly more complex internetwork, a NetWare server could support multiple cable segments using the same physical layouts but different media access controls.

For example, a server could contain one Ethernet network adapter and one token-ring network adapter, with a cable segment attached to each. The Ethernet network might be connected in a physical star and use CSMA/CD for the media access control. The token-ring network might also be connected in a physical star, but it would use token passing for media access control. Like the simpler configuration explained in the previous section, each cable segment would have a different network address. Figure 24 illustrates this more complex one-server internetwork.

Figure 24: Internetworking two networks using different types of network adapters (MAC) in one NetWare server, by means of the server's internal routers

In the case of the internetwork shown above, routing would again be accomplished using the NetWare IPX or NetWare IP protocol, with support from the other NetWare routing protocols.

The two one-server networks we have seen each support only two separate subnetworks. As a matter of note, all NetWare servers are capable of supporting as many as four different network adapters (four separate subnetworks), in any combination of same or different types.

Please notice that even though the token-ring network above was described as a physical star, it is drawn as a ring to signify that it is a token-ring network (which uses token passing as the media access control). We will adhere to this convention throughout this primer because in virtually all illustrations, it will be more important to make the logical topology clear than to be concerned with the physical topology.

Multiple Servers With Multiple Networks of Different Types

In an even more complex internetwork, there may be multiple servers.

For example, a complex internetwork might consist of two one-server subnetworks connected by a standalone router, such as the IntranetWare MultiProtocol Router. Each server might contain multiple network interface adapters.

One server might contain two Ethernet network adapters and one token-ring network adapter, with a cable segment attached to each. One of the Ethernet adapters might support a PC network, and the other Ethernet adapter might connect to both PCs and Macintosh computers. The NetWare for Macintosh product running on the server would support the Macintosh computers.

The other server might contain one Ethernet adapter and one ARCnet adapter, with the Ethernet adapter again supporting both PCs and Macintoshes, and the ARCnet adapter supporting a cable segment with a number of PCs attached.

Each of the two servers would have a unique internal number (server address), and each cable segment in each server would have a unique physical network (cable segment) address.

In this case, there would be five subnetworks on the internetwork, three attached to one server and two attached to the other. The internal server routers would accomplish the routing between any two workstations on subnetworks attached directly to the same server. Both the internal server routers and the intermediate standalone router would be involved in the routing between any two workstations on subnetworks attached to different servers.

Figure 25 illustrates the two-server internetwork described above.

Figure 25: Internetworking multiple networks using different types of network adapters (MAC) in two NetWare servers, by means of internal and standalone routers

7.1  Host Access

An already complex multiserver internetwork becomes even more complex with the addition of connections to host computer systems, including mainframe computers such as IBM mainframes, to minicomputers such as IBM's AS/400 or a DEC VAX system, or to other hosts such as UNIX workstations.

Host systems can provide access to additional application software, additional resources such as data storage devices and printers, and additional processing power. For example, you might want to log in to an IBM AS/400 minicomputer to run an application available only on that computer or to use its processing power for one task while you were using the processing power of your own workstation for some other task. Or, you might want to print a large report on a high-speed printer connected to the AS/400.

The illustration in Figure 26 shows a multiserver NetWare network with an IBM mainframe, an IBM AS/400 minicomputer, and several UNIX workstations connected as host computers.

Figure 26: Host systems connected to a complex multiserver NetWare network

A number of leading networking companies have entered into original equipment manufacturer (OEM) partnerships with Novell. Many provide NetWare connectivity to host-based environments.

7.2  Wide Area Networking

So far, we have looked only at internetworks existing at one local site, with computers and other devices directly connected by some type of cabling. This type of network is commonly referred to as a "local area network" (LAN). Now let's add another level of complexity to the internetworking picture: Let's connect complex multiserver internetworks that exist at separate sites, which might be any number of miles apart. Connecting computer networks in these circumstances is called "wide area networking."

The traditional definition of wide area networking has been "connecting two or more networks existing at widely separate geographic sites." Some traditionalists also prescribe that the separate networks must be connected by means of common carrier telecommunication facilities (private companies that rent resources such as T1 lines and microwave transmission equipment). For the purposes of this primer, we'll use the first, general definition and let you decide how to apply it in specific internetworking cases. But, to give you some background to help you make such decisions, let's discuss a few specific internetworking cases and a few terms related to wide area networking.

Of course, like any general term used in connection with rapidly changing technology, not everyone will agree on an exact definition of wide area networking. What is "widely separate"? And, does the connection really have to be through a common carrier? Many major companies now own their own equipment linking networks many miles apart.

Let's look at some examples. Suppose you connect two networks in two different buildings 100 yards apart by means of asynchronous modems and common telephone lines. Is that wide area networking? Most knowledgeable computer networking people would say no—this would be "one-site" or "campus" networking. What if the networks were two miles apart and separated by a major interstate highway? Or, what if they were 15 miles apart, on opposite sides of a major city? There are many computer networking people who would still not call this wide area networking; they might use a recently coined term—"metropolitan area networking." Others consider metropolitan area networking a part of wide area networking. Of course, everyone would agree that two networks connected on opposite sides of a continent by means of a satellite microwave link rented from a common carrier is an example of a wide area network.

You can decide for yourself where you think wide area networking begins and ends. Now let's look at some general possibilities.

Figure 27 shows two separate branch office internetworks connected to a third internetwork at a main corporate office. Each of the three existing internetworks has multiple servers and existing host connections. One of the branch office networks is connected to the corporate network by means of asynchronous modems and regular voice-grade telephone lines. The other branch office network is connected by means of a common carrier-provided intermediate link—in this case an X.25 packet-switching network. Examples of such networks include Tymnet or Telnet.

However, either network could be connected by other means that we have discussed, such as frame relay or a dedicated leased line link, perhaps using PPP.

The following section describes important WAN and LAN technologies in greater detail.

Figure 27: Wide area networking: three networks at widely separated sites connected through asynchronous modems and an X.25 connection

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