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Networking Basics
Packets and traffic
Information travels across a network in chunks called “packets.” Each packet has a header that tells where
the packet is from and where it’s going, similar to what you write on the envelope when you send a letter.
The flow of all these packets on the network is called “traffic.”
Hardware addresses
Your PC “listens” to all of the traffic on its local network and selects the packets that belong to it by check-
ing for its hardware address in the packet header or MAC (Media Access Control). Every hardware product
used for networking is required to have a unique hardware address permanently embedded in it.
IP addresses
Since the Internet is a network of networks (connecting millions of computers), hardware addresses alone
are not enough to deliver information on the Internet. It would be impossible for your computer to find its
packets in all the world’s network traffic, and impossible for the Internet to move all traffic to every net-
work, your PC also has an IP (Internet Protocol) address that defines exactly where and in what network
it’s located. IP addresses ensure that your local Ethernet network only
receives the traffic intended for it. Like the hierarchical system used to define zip codes, street names,
and street numbers, IP addresses are created according to a set of rules, and their assignment is carefully
administered.
Put another way, the hardware address is like your name; it uniquely and permanently identifies you. But it
doesn’t offer any clues about your location, so it’s only helpful in a local setting. An IP address is like your
street address, which contains the information that helps letters and packages find your house.
Rules for Sending Information (Protocols)
A protocol is a set of rules that define how communication takes place. For instance, a networking proto-
col may define how information is formatted and addressed, just as there’s a standard way to address an
envelope when you send a letter.
Networking Devices:
Bridges
A bridge joins two networks at the hardware level. This means that as far as other protocols are concerned,
the two networks are the same.
Routers
A router connects two IP networks. In contrast to a bridge, which joins networks at the hardware level, a
router directs network IP traffic based on information stored in its routing tables. A routing table matches
IP addresses with hardware addresses. The router stamps each incoming IP packet with the hardware
address that corresponds to that IP address. As a result, the packet can be picked up by the right computer
on the hardware network.
DNS (Domain Name Server)
Networks (domains) on the Internet have names that correspond to their IP addresses. A Domain Name
Server maintains a list of domain names and their corresponding addresses. This is why you can go to
Berkeley’s Web site by entering www.bvsystems.com, instead of the IP address.
Networking Terms:
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