untangling_the_web

DOCID: 4046925
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Packets
At the (almost) simplest level of the Internet are things called packets. For our
purposes, a packet is the fundamental unit of data that is sent between an origin and
a destination on the Internet. How does a packet get from Point A to Point B? First, it
needs two addresses: one for its origin and one for its destination. The origin
address is known as the source IP address and the end address is known as the
destination IP address.
IP Addresses
Every device attached to the Internet must have an address. In IPv4,143 these
addresses are written as "dotted quads," i.e., four sets of numbers separated by
periods, as in 204.180.95.2. 144 Today, IP addresses are much more likely to identify
the public end point of a path than an individual computer. The last IP address you
see is likely the point at which the packet enters a private network, and you can't
normally see beyond that point.
IP addresses are similar to telephone numbers or house addresses, but that analogy
only goes so far because many IP addresses are temporary. Temporary IP
addresses are called dynamic IP addresses; the IP address your cable or DSL
provider assigns to you is probably dynamic. On the other hand, certain types of
devices on the Internet are usually assigned permanent or static IP addresses. One
of these types of devices is a router.
This brings us back to our traveling packet. Once we know that the packet has its
own address and a destination address, we then need to know how the packet gets
from one place to another. It gets there because of something called a router.
Routers
A router is a device that forwards packets from one network to another. Routers
used to be called gateways and you may still encounter that term. So, how does
routing work?
Routing
Think of routing as the process in which your computer (host) tries to find a
destination computer (host). Basically, your source IP address host with data to send
asks your ISP's router two very important questions:
143 IPv4 is Internet Protocol version 4, the current Internet Protocol or set of rules for exchanging data
across the Internet. It is in the process of being replaced by IP version 6. IPv4 uses 32-bit addresses
(allowing 4.3 billion addresses); IPv6 uses 128 bits (allowing 3.4x1038 addresses).
144 This type of IP address is an IPv4 address; the next generation Internet will use IPv6.
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