- Working with Network Interface Cards
- Working with Network Connectivity Devices
- An operating system is used to configure and monitor a switch.
- Some Thoughts on PC Hardware
- Chapter Summary
An operating system is used to configure and monitor a switch.
Switch hardware can also take advantage of full-duplex access to the network media, which allows for the sending and receiving of data simultaneously on the network. This provides network access on an Ethernet network that would essentially be collision free (Ethernet networks experience data collisions pretty much as a rule; Ethernet is discussed in the next chapter). A computer on a Fast Ethernet network, which runs at 100Mbps, would actually realize a net total of 200Mbps throughput because sending and receiving can take place simultaneously on the full-duplex media.
Switches (because of the aforementioned reasons) are becoming very popular on large networks. They have all but replaced bridges as the internetworking devices for conserving network bandwidth and expanding LANs into larger corporate internetworks.
Routers
Routers are even smarter than bridges and switches (routers operate at the Network layer—a higher level in the OSI conceptual model than bridges and switches, which operate at the Data Link layer; we discuss all the layers of OSI in Chapter 5). A router uses a combination of hardware and software to actually "route" data from its source to its destination. (By software, I mean an operating system.) Routers actually have a very sophisticated OS that allows you to configure their various connection ports. You can set up a router to route data packets from a number of different network protocol stacks, including TCP/IP, IPX/SPX, and AppleTalk (protocols are discussed in Chapter 5).
Routers are used to segment LANs that have become very large and congested with data traffic. Routers are also used to connect remote LANs together using different WAN technologies.
Figure 3.7 shows a Cisco 2516 router. This router has a built-in hub and three different WAN connection points. Notice the BRI port marked in the figure. BRI stands for ISDN Basic Rate Interface, which allows this router to connect to a remote network using an ISDN connection (ISDN and other WAN technologies are discussed in Chapter 10, "Expanding a LAN with WAN Technology").
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Figure 3.7 Routers are used to segment networks into logical subsets.
Routers divide large networks into logical segments called subnets. This division of the network is based on the addressing scheme the network uses, such as IP addresses. Data traffic related to a particular subnet is kept local. The router only forwards data that is meant for other subnets on the extended network. This routing of network data helps conserve network bandwidth.
Routers decide how to forward data packets to their destinations based on a routing table. Routers use protocols built into their operating system to identify neighboring routers and their network addresses (such as IP addresses). This allows routers to build a routing table. Figure 3.8 shows the command-line interface used on a Cisco router. This figure also shows the IP routing table for a small network that consists of two connected Cisco routers. Each of the subnets shown at the bottom of the table (notice the list of IP addresses) represents a different router interface. 10.2.0.0 and 10.3.0.0 are on the router that supplied this screen. The subnets 10.1.0.0 and 132.1.0.0 were discovered by the router (using the RIP protocol) on a connect router.
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NOTE
No matter what operating system you use, computers use pretty much the same strategy to identify themselves on the network. This strategy involves broadcast messages, meaning that a message will go out to every other computer on the network, proclaiming a computer's identity or requesting information related to the identity of another computer on the network. Broadcast messages create what is called broadcast traffic, and broadcast traffic can suck up valuable network bandwidth that otherwise could be used to move LAN data. Routers keep broadcast traffic from spreading beyond a particular segment, thus conserving a lot of potential network bandwidth.
Figure 3.8 Routers build and use a routing table to determine where data packets should be forwarded.