|Ethernet Delivers the Internet
IP addresses are better-organized for delivery across the world in a
world-wide collection of equipment and networks. It turns out that
Ethernet addresses cannot be used effectively for world-wide
distributions, because they are assigned more-or-less at random. Thereís
no rhyme or reason in the local distribution of Ethernet addresses on
your local network. The only requirement of Ethernet addresses is that
they be unique. Imagine how difficult it would be for a world-wide
postal service to address packages and envelopes if everybodyís address
were completely random. Although an individual letter-carrier could
probably memorize the few addresses on his local route, or carry a
simple little map to help him sort out the local addresses, it would be
completely unreasonable to expect world-wide postal delivery systems on
a continental or inter-continental scale to be able to handle completely
random address sorting. And thatís why Ethernet addresses cannot be used
effectively outside your local area network. They just wonít scale to
the world because they are distributed more-or-less at random.
IP addresses, on the other hand, are distributed in a more orderly
fashion by an authority in charge of the organization of the Internet.
And so the patterns in the numbers representing an Internet address help
to locate the networks and sub-networks in the world-wide Internet. This
notion of encapsulation is important to those of us with small networks,
because when we connect our small networks to the Internet, we're
actually merging two networks together. One Ethernet segment is actually
owned and managed by our Internet service provider, and our own Ethernet
is managed independently by our own policies and equipment.
And when an IP packet arrives from the Internet, we must remove it from
the Ethernet frame managed by our ISP network, and repackage it inside a
new Ethernet frame thatís understood by our local networking equipment
for delivery to a computer inside our home or small business.
On the other hand, when we want to send a message out to someone on the
world-wide Internet, our computers create an IP packet, which must be
wrapped in an Ethernet frame for delivery to the Internet. The
world-wide Internet is composed of millions of individual little
networks, and every time an IP packet traverses any of them, it is
encapsulated and then removed from framing such as that which we have
illustrated here with Ethernet.