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 checking for its hardware
address in the packet header or MAC (Media Access Control). This address is a number unique to your computer. 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 traf-
fic, and impossible for the Internet to move all traffic to every network, 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 protocol 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:
TCP/IP (Transport Control Protocol/Internet Protocol)
TCP/IP is a collection of protocols that underlies almost every form of communication on the
Internet.
DHCP (Dynamic Host Control Protocol)
DHCP is a method of automatically assigning IP addresses. Instead of assigning addresses to individual users, addresses are
assigned by the DHCP server when clients need them. This means that instead of entering several fields of long addresses,
users need only to select DHCP as their configuration method for IP networking.
PPP (Point-to-Point Protocol)
PPP is the most common protocol for providing IP services over a modem.
NAT (Network Address Translation)
NAT is used to share one IP address among several computers. A device set up as a NAT router uses a collection of “private”
IP addresses (in the range 10.0.1.2 to 10.0.1.254) to allow several computers to access the Internet using one “public” IP
address. When a computer using a private IP address requests information from the Internet, the NAT router keeps a record of
the computer making the request, and sends the information to the Internet using its own IP address. When the response comes
back from the Internet, the NAT router forwards the packet to the appropriate computer.
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