Find an unused expansion slot inside the computer.
⻬ A basic rule of Ethernet life is that a signal can’t pass through more than three repeaters on its way from one node to another. That doesn’t mean
you can’t have more than three repeaters or hubs, but if you do, you have to carefully plan the network cabling so that the three-repeater
rule isn’t violated.
⻬ A two-port 10Base2 repeater costs about 200. Sheesh I guess that’s one of the reasons few people use coaxial cable anymore.
⻬ Repeaters are legitimate components of a by-the-book Ethernet network. They don’t extend the maximum length of a single segment; they just
enable you to tie two segments together. Beware of the little black boxes that claim to extend the segment limit beyond the standard 185-meter
limit for Thinnet or the 100-meter limit for 10100BaseT cable. These products usually work, but playing by the rules is better.
Bridges
A bridge is a device that connects two networks. Bridges are used to partition one large network into two smaller networks for performance reasons. You
can think of a bridge as a kind of smart repeater. Repeaters listen to signals coming down one network cable, amplify them, and send them down the
other cable. They do this blindly, paying no attention to the content of the messages that they repeat.
In contrast, a bridge is a little smarter about the messages that come down the pike. For starters, most bridges have the capability to listen to the net-
work and automatically figure out the address of each computer on both sides of the bridge. Then the bridge can inspect each message that comes
from one side of the bridge and broadcast it on the other side of the bridge, but only if the message is intended for a computer that’s on the other side.
This key feature enables bridges to partition a large network into two smaller, more efficient networks. Bridges work best in networks that are highly segre-
gated. For example, suppose your network consists of two distinct groups of users: the Marketing Department and the Accounting Department, each with
their own servers.
A bridge would let you partition this network so that the Marketing side of the network isn’t bogged down by Accounting, and vice-versa. The bridge
automatically learns which computers are on each side of the bridge and forwards messages from the one side to the other only when necessary.
The overall performance of both networks improves, although the perfor- mance of any network operation that has to travel over the bridge slows
down a bit.
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Part II: Building Your Own Network
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.
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