The Internet is basically made up of
Internet service providers known as ISPs
who connect each other's networks. How
does an ISP in Kenya talk to an ISP in
Japan? How does that ISP talk to
customers of the ISP in Japan and get
responses back? How is this any different
from communication between two devices
on local Ethernet? Remember that two-way
packet flow is needed for communication
between any two devices. The ISP in Kenya
could buy a direct connection to the ISP
in Japan; however, this would not scale.
For it would mean that thousands of ISPs
would have to buy connections to all
other ISPs they need to talk to, thereby
making the operational costs
astronomical. Instead the ISP in Kenya
tells his neighboring ISP what customers
he has and the neighboring ISPs pass
this information on to their neighbors
and so on. This process repeats until the
information reaches the ISP in Japan. This
process is called routing. The mechanisms
used are called routing protocols.
Routing and routing protocols ensures
that the Internet can scale and
thousands of ISPs can provide
connectivity to each other,
thereby creating the Internet as we see
it today. The ISP in Kenya does not
actually tell his neighboring ISPs the
names of the customers because the
network equipment does not understand
names. Instead he receives an IP
address block as a member of the
regional internet registry serving Kenya.
His customers have received address space
from this address block as part of their
internet service and he announces this
address block on his router to his
neighboring ISPs.
This is called "announcing a route".
© Produced by Philip Smith and the Network Startup Resource Center, through the University of Oregon.
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