Hubs, switches, and routers are all devices that let you connect one
or more computers to other computers, networked devices, or even other
networks. Each has two or more connectors called ports into which you
plug in the cables to make the connection. Varying degrees of magic
happen inside the device and therein lies the difference. I often see
the terms misused, so let's clarify what each one really means.
Hubs
A
hub is typically the least expensive, least intelligent,
and least complicated of the three. Its job is very simple - anything that comes
in one port is sent out to the others.
That's it.
If a message comes in for
computer "A", that message is sent out all the other ports, regardless of which
one computer "A" is on:
And when computer "A" responds, its response also goes out to every other
port on the hub:
Every computer connected to the hub "sees" everything that every other
computer on the hub sees. The computers themselves decide if they are the
targeted recipient of the message and when a message should be paid attention
to or not.
The hub itself is blissfully ignorant of the data being transmitted. For
years, simple hubs have been quick and easy ways to connect computers in small
networks.
Switches
A
switch does essentially what a hub does, but more
efficiently. By paying attention to the traffic that comes across it, it can
"learn" where particular addresses are.
Initially, a switch knows nothing and simply sends on incoming messages to
all ports:
Even accepting that first message, however, the switch has learned something
- it knows on which connection the sender of the message is located. Thus, when
machine "A" responds to the message, the switches only need to send that
message out to the one connection:
In addition to sending the response through to the originator, the switch
has now learned something else - it now knows on which connection machine "A" is
located.
That means that subsequent messages destined for machine "A" need only be
sent to that one port:
Switches learn the location of the devices that they are connected to almost
instantaneously. The net result is that most network traffic only goes where it
needs to rather than to every port. On busy networks, this can make the network
significantly faster.
Routers
A
router is the smartest and most complicated of the bunch.
Routers come in all shapes and sizes - from the small, four-port broadband routers
that are very popular right now to the large industrial strength devices that
drive the internet itself.
A simple way to think of a router is as a computer that can be programmed to
understand, possibly manipulate, and route the data that it's being asked to handle.
Many routers today are, in fact, little computers dedicated to the task of
routing network traffic.
As far as simple traffic routing is concerned, a router operates exactly as
a switch, learning the location of the computers on its connections and
routing traffic only to those computers.
Consumer grade routers perform at minimum two additional and important
tasks: DHCP and NAT.
DHCP - Dynamic Host Configuration Protocol - is the way dynamic IP addresses
are assigned. A device asks for an IP address to be assigned to it from
"upstream" and a DHCP server responds with an IP address assignment. A router
connected to your ISP-provided internet connection will typically ask your
ISP's server for an IP address; this will be your IP address on the
internet. Your local computers, on the other hand, will ask the router for an
IP address and these addresses are local to your network.
NAT - Network Address Translation - is the way that the router
translates the IP addresses of packets that cross the internet/local
network boundary. When computer "A" sends a packet out, the IP address that it's
"from" is that of computer "A" - 192.168.1.2 in the example above. When the
router passes that on to the internet, it replaces the local IP address with the
internet IP address assigned by the ISP. It also keeps track, so that if a
response comes back from somewhere on the internet, the router knows to do the
translation in reverse - replace the internet IP address with the local IP
address for machine "A" and then send that response packet on to machine
"A".
A side effect of NAT is that machines on the internet cannot initiate
communications to local machines - they can only respond to communications
initiated by those local machines.
The net effect is that the router then also acts as a firewall:
What that means is that malware that might spread by trying to independently
connect to your computer over the network cannot.
All routers include some kind of user interface for configuring how the
router will treat traffic. The really large routers include the equivalent of a
full-blown programming language to describe how they should operate as well as
the ability to communicate with other routers to describe or determine the best
way to get network traffic from point A to point B.
A note about speed
A quick note on one other thing that you'll often see mentioned with these
devices and that's network speed. Most devices now are capable of both 10mpps
(10 mega-bits, or million bits, per second) as well as 100mbps and will
automatically detect the speed.
More and more devices are now capable of handling 1000mbps or a billion bits
per second (1gpbs).
Similarly, many devices are now also wireless transmitters that simply act like
additional ports on the device.
Thanks
R.karthikeyan
Active
Directory Domain Services installation uses Server Manager and Windows
PowerShell, like all other server roles and features in Windows Server
2012. The Dcpromo.exe program no longer provides GUI configuration
options. 
Important 
You
can also use the Server Manager Dashboard on an existing domain
controller to select remote server AD DS installation with the role
already preselected by right clicking the AD DS dashboard tile and
selecting Add AD DS to Another Server. This is invoking Install-WindowsFeature AD-Domain-Services.
Additional Features can be added here as desired.
Warning 
When the Installation
page displays, the domain controller configuration begins and cannot be
halted or canceled. Detailed operations display on this page and are
written to logs:
The Results
page shows the success or failure of the promotion and any important
administrative information. The domain controller will automatically
reboot after 10 seconds.
