A Short Trip from Your House (PC) to the Local Store
(Server)
I sometimes sit back and think about how big and populous the
world has gotten. Sometimes I'll drive down a large highway in rush hour, see
all the cars, and wonder how many cars drive on that road each day. Okay, maybe
I've got a little too much time on my hands if I have time to ponder such
things, but let's face it: The U.S. Department of Transportation (DOT) has to
worry about building roads that accommodate a lot of cars.
When the DOT builds highways in a major city, it typically has
to be ready to build lots of lanes, expecting possibly hundreds of thousands of
cars to drive over the road each day. Likewise, routers forward a lot of IP
packets on the average day. Some of the more expensive, faster routers claim to
be able to forward hundreds of millions of packets per second. Even the least
expensive routers from Cisco can forward tens of thousands of IP packets per
second. Like a busy intersection handles a lot of cars passing through it, a
router needs to handle a lot of individual packets passing through it.
Now, think like the people who made up IP and IP routing for a
moment. If you need to define protocols and standards about how to do something,
and that thing has to happen thousands or millions of times per second, you had
better follow the KISS (Keep it simple, stupid) principle! If you made routing
overly complicated, you would need really expensive router hardware to forward
all those packets. By keeping the amount of work per packet to a bare minimum,
the vendors could create routers that could meet the need to forward lots of
packets, while keeping the cost of the routers a little lower.
This part of the book takes a look at the life of a packet as
it goes from one computer (Hannah) to a web server ( http://www.example.com).
The process that each computer and router performs is indeed pretty simple,
which allows the router to move on to the next packet that's waiting to be
forwarded.
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