Turn the computer back on.

Here are a few additional things to consider about bridges: ⻬ As I mentioned, some bridges also have the capability to translate the messages from one format to another. For example, if the Marketing folks build their network with Ethernet and the accountants use Token Ring, a bridge can tie the two together. ⻬ You can get a basic bridge to partition two Ethernet networks for about 500 from mail-order suppliers. More sophisticated bridges can cost as much as 5,000 or more. Routers A router is like a bridge, but with a key difference. Bridges use actual hard- ware addresses known as MAC addresses to tell which network node each message is sent to so it can forward the message to the appropriate segment. However, a bridge doesn’t have the ability to actually look inside the message to see what type of information is being sent. A router can. As a result, routers work at a higher level than bridges. Thus, routers can perform additional tasks such as filtering packets based on their content. Note that many routers also have built-in bridging functions, so routers are often used as bridges. You can configure a network with several routers that can work cooperatively together. For example, some routers are able to monitor the network to deter- mine the most efficient path for sending a message to its ultimate destination. If a part of the network is extremely busy, a router can automatically route messages along a less-busy route. In this respect, the router is kind of like a traffic reporter up in a helicopter. The router knows that the 101 is bumper- to-bumper all the way through Sunnyvale, so it sends the message on the 280 instead. Here is some additional information about routers: ⻬ Routers used to be expensive and used only on large networks. However, the price of small routers has dropped substantially in recent years, so they’re now becoming common even on small networks. ⻬ The functional distinctions between bridges and routers — and switches and hubs, for that matter — get blurrier all the time. Multifunction routers, which combine the functions of routers, bridges, hubs, and switches are often used to handle some of the chores that used to require separate devices. ⻬ Some routers are nothing more than computers with delusions of grandeur — along with several network interface cards and special software to perform the router functions. 127

Chapter 9: Oh, What a Tangled Web We Weave