- Let's start by defining exactly what an internetwork is.
You create an internetwork
when you connect two or more networks via a router
and configure a logical networking addressing scheme
with a routed protocol, such as IP or IPv6.
Let's get started by taking a look at a basic network.
This graphic shows a basic local area network, or LAN,
that's connected using a hub,
which is just an antiquated device
that connects wires together.
A simple network like this would be considered
one collision domain and one broadcast domain.
So if Bob wants to send Sally a file,
in this kind of network,
he'll simply broadcast that he's looking for her.
Think of it like this.
Bob walks out of his house
and yells down the street in order to contact Sally.
This might work if Bob and Sally
were the only ones living there.
But if the street is crammed with homes,
there will always be someone
hollering up and down the street to their neighbors,
just like Bob.
Believe it or not,
our networks actually still work this way to a degree.
A hub is really a multi-port repeater.
A repeater receives a digital signal,
amplifies or regenerates that signal,
then forwards the signal out
all other ports without inspecting any data.
A hub receives a digital signal
and then forwards the signal out every other port.
This graphic shows a network
that's been segmented with a switch,
making each network segment that connects to the switch
its own separate collision domain.
Doing this results in a lot less yelling.
This is a great start, but you should know
that this network is still one single broadcast domain,
meaning that we've really only
decreased our screaming and yelling, not eliminated it.
If there's a vital announcment
that everyone needs to hear about,
it will definitely still get loud.
In this network, the hub extends the collision domain
of the switch port.
If Bob sends a message to John, Sally will not receive it.
If Bob had sent a broadcast instead,
everyone, including Sally, would have received it,
possibly causing unnecessary congestion.
Many of us experience congestion when commuting to work.
On a LAN, traffic can reach critical mass
and grind to a complete halt.
Again, the solution to this problem begins with breaking up
a massive network into a number of smaller ones,
something called network segmentation.
This concept is a lot like planning a new community
or modernizing an existing one.
More streets are added,
complete with new intersections and traffic signals.
Post offices are built with official maps
documenting all those street names and delivery directions.
New laws are enacted to keep order,
while police protect a neighborhood.
In a networking neighborhood environment,
all of this is carried out using devices
like routers, switches, and bridging technologies.