Chapter 58. Upgrading from Bridges and Hubs to Routers and Switches

SOME OF THE MAIN TOPICS IN THIS CHAPTER ARE

Growing Beyond a Small LAN

From Bridges to Routers

From Bridges to Switches

You can use many kinds of network devices to expand a local area network (LAN) or to connect it to a wide area network (WAN). They range from simple repeaters to devices with more intelligence, such as bridges, routers, and switches. For the most part, traditional bridges have been replaced with switches. Both segregate network traffic to specific ports, but switches do so on a computer-by-computer basis, whereas traditional bridges do so based on LAN segments.

Note

Hubs, low-end repeaters, and simple bridges are generally not the best choice for networks today. Instead, switches have pretty much replaced them in the marketplace . Where hubs or multiport repeaters still exist, they're being replaced as applications and workstations require more and more bandwidth. For more information about these legacy devices, see "Bridges, Repeaters, and Hubs" on the upgradingandrepairingpcs.com Web site.

As a small LAN grew in the past, it was common to use bridges to segment a few small workgroups. Bridges were used to isolate local traffic among groups of users and thus cut down on the overall traffic on the LAN. However, depending on the kind of network (for example, ARCnet, Ethernet, or Token-Ring), there are limits to how many bridges (repeaters) could be used in a LAN. In addition to their usefulness in solving network traffic congestion problems, you can use routers or switches to solve several other problems: expanding the LAN beyond the size that bridges allow and connecting the LAN to other LANs to create a larger local network, or for a connection to a WAN, such as the Internet. In short, switches and routers offer the following benefits:

• Switches enable you to expand the LAN because they greatly limit the collision domain and switch traffic from one port to another, avoiding broadcasting packets unnecessarily on ports that don't have a route to the packet's destination.

• Routers enable you to connect to a much larger collection of networks, such as the Internet, and enable you to organize a large LAN into a hierarchical address space and many subnets.

You can find out more about how routers and switches function by reading Chapter 8, "Network Switches," and Chapter 10, "Routers."

A traditional bridge has just about outlived its usefulness in a modern network. Instead, switches (which are really glorified multiple bridges all in one box) and routers can be used to better segment a LAN and limit unnecessary network traffic on local LAN segments.

Note

The term bridge is used in this chapter to refer to a legacy device that connects several network segments and is used to limit network traffic to local segments.

Other types of bridges exist that are important in networking today. For example, there are translational bridges that can convert frames from one format to another, enabling you to connect different types of LANs. Another example is a SCSI-to “Fibre Channel bridge that enables you to connect legacy SCSI devices to a Fibre-Channel network, thus preserving your investment in older disks, tape drives , and so on.

In this chapter, the possibilities offered by upgrading to switches and routers are discussed, along with information you must consider when bringing such devices into your LAN.