Internet Protocol Address.
This article will attempt to explain the basic understanding of how IP addresses
are used. The IP address can be compared to a unique street address
or identifier
assigned to a computer or device while connected to the internet
or private internal network. Please
see the related article
routers modems and switches.
IP addresses are used to communicate across public networks like the internet
and private internal business and home networks. Some are used by businesses and
organizations that host web servers, mail servers, DNS(Domain Name Service) servers
and a wider array of services. These same IP addresses are used to connect you to
the internet. Some IP addresses are used for specific roles to help computers and
devices communicate across networks.
The following five IP address settings are commonly used. The first three, IP
address, subnet mask, and gateway are internal private addresses on your network.
The last two DNS addresses are public addresses usually pointing to servers providing
(Domain Name Service) outside your network that help your computer find web sites by name for you. Click on each for a detailed description.
IP address - identifies computers or devices on a network.
Subnet Mask - determines the IP address range that can
be used on a particular network.
Gateway - identifies the device on the network connected to
the internet or other router.
DNS1 - server addresses which provide service for locating websites
by name.
DNS2 - alternate.
IP address:
There are two basic types of IP addresses, public and private.
The public IP address is the external web address your service provider
gives you also referred as your WAN(Wide Area Network)address. This is your public presence on the Internet and allows you
to host your own web servers and provide services or simply at its basic level use the internet.
This public address has four segments to it looking similar to 75.13.112.81 and
can be assigned to
you in two ways.
(1) Dynamic meaning that your Internet Service Provider may assign you a different
public IP address randomly and change it each time you log on to the web or unplugged
your modem. Sometimes this public
IP
address will change several times in the same day other times this address might not change for weeks. This doesn't effect the way an average user uses the internet, most users are assigned dynamic public IP
addresses.
(2) Fixed/Static meaning that your internet service provider has assigned you a
fixed public IP address that will not change, so
each time you turn on your devices and computer you have the same public IP address on the web. These Fixed/Static
public IP addresses are used by individuals and small to large sized companies with email or web servers on site
and actually want people to find them. Fixed/Static public IP addresses are much more
at risk from cyber attack, since the public IP address doesn't change, hackers can use automated systems 24/7 to keep pinging that IP address with tools that scan for any open ports.
So just like a street
address can be traced to the home owner, your public IP address is traced to your
ISP and to your DSL/Cable/T1 or dial up internet account. To find out what your current public IP address is, use a browser to a site
such as
http://whatismyipaddress.com
which will return to you the current public IP address assigned to your computer
or network by your ISP. There are many sites providing this service a search engine like Google
will also help display your public IP address.
It's important to realize that your public IP address is exposed to the internet by its very design, this is the
reason a well maintained
Firewall Service
of some kind is critical. In the past internet providers would commonly provide you with a simple DSL or Dial up modem and leave it up to the users computer
to provide the firewall
service.
However that trend has changed and many service
providers are now supplying firewall routers, or a combination of Modem/Firewall
routers to further protect their customers.
The private IP address is the private, non-routable internal IP
address used by the computers and devices on the inside of your network also has
4 segments looking similar to 192.168.1.2. This private address is also
handed out in the same two ways, it can be fixed/static for devices such as routers and printers or more commonly will be
dynamic and handed out by a
DHCP(Dynamic Host Configuration Protocol)
service running on a
DSL/Cable routerinside your network. In business
networks the
DHCP service may be running on a server. These private IP address ranges are called non-routable addresses and cannot
be seen or directly accessed from outside of your network or from the internet. There are several
ranges of non-routable addresses that are reserved for internal private
IP addressing, some include these common
examples.
192.168.1.x
192.168.0.x
10.0.x.x
172.16.x.x
To find out what private IP address DHCP assigned
to your computer or laptop go to Start/Run
Type in CMD and press enter. A black command line box with a blinking curser
will appear. Type in 'ipconfig' and press
enter. A listing similar to the following example
appears, of the information displayed here it’s the IP address we are interested
in, for this computer it was assigned 192.168.1.10.
Type Exit and press enter or close the window to exit.
Using the same command on a second computer
or laptop on the network might bring up the next address 192.168.1.11.
Your listing
may be different perhaps in the 192.168.0.x. range. Computers and devices on the same network will usually share the
first 3 sets of numbers for their IP address and be assigned a unique 4th number.
So each computer inside your private network actually has two IP addresses assigned to it, the public IP address
on the internet side of the firewall assigned by your Internet Service Provider
and the private IP address on the inside of your network assigned by your routers
DHCP
service. The private IP address is assigned to your computer or laptop network
connection also referred to as a LAN connection, or NIC. When you plug in your cable
or join a wireless network. The message Acquiring network address' is displayed
on your computer LAN or Wireless adapter as the DHCP service indentifies the new device and attempts to configure
its IP address to work on this network.
Once the DHCP service is successful in assigning the address the message 'Connected'
is displayed.
In the above example there are also two other necessary pieces of information in
order for your IP address to talk to other IP addresses.
Subnet mask: is a specialized private IP address setting that calculates
what set of IP address ranges can be used to communicate on the same network.
In the above example a subnet mask of 255.255.255.0 has been calculated to allow
the first usable address of 192.168.1.1 through the last usable address of 192.168.1.254
to be used on any private network allowing these computers and devices to talk to each
other. Most routers acting as gateways in private networks are normally assigned
the first or the last IP address in this range. Any computer or device wanting
to communicate with a computer belonging to the 192.168.1.x range on the same private
network must have the same subnet mask. The DHCP service takes care of this for
dynamic addresses, however if a fixed/static IP address is being used it must
be also be configured with the same subnet mask. The same subnet mask of 255.255.255.0
works for private networks using the 192.168.0.x
range as well and is commonly used
for internal private networks. Devices and computers will return an error when trying
to configure an IP address that doesn't match the calculated subnet mask.
Gateway: this is usually the address of the router or device
on your network that is connected in turn to another network like the internet.
It acts as the gateway telling all other devices where to find the doorway to the
next network which often is the internet.
In the ipconfig example above we can see that the gateway address of 192.168.1.1
is the same address as the router displayed in the network layout example below.
The router is using its
DHCP service and has handed out address ranges that
are above its own fixed/static IP address range. All the computers and devices on
this network share the same subnet mask of 255.255.255.0 and all know that 192.168.1.1
is the gateway to the internet based on the subnet mask and the gateway
settings above.
The the IP address Subnet mask, and Gateway allow your device or computer to talk to each other within
your private network and also use the gateway to the internet. You can use known public IP addresses of other networks to communicate
with them. However in order to use your internet browser to find websites by name another
setting must be used called DNS.
DNS: There are two additional settings that the
DHCP service provides automatically or must be set manually for static/fixed addresses in order for your browser and computers to find web sites by name. These settings are called DNS address
settings and provide the address to (Domain Name System) servers provided by your
ISP. DNS servers are basically used as databases that translate registered
internet names also called domain names into the actual public IP address they are
assigned. There are thousands of DNS servers around the world and they constantly
share the latest DNS registration changes. When a DNS change is made with a registered
website it takes less then 24 hours for most DNS servers to update with this information.
How do the DNS servers know the names of websites and their public IP addresses?
To be listed in DNS a unique website name needs to be registered with an official
internet Domain Name service company like Network Solutions
which takes care of registering your unique web site name and listing the name in DNS servers to be
propagated to DNS servers
around the world. During the registration the default public IP address listed in
DNS servers is usually the Domain Name service company. The Domain Name service
company will then allow you to point your DNS web name to any public IP address
where the actual web hosting is taking place.
Each web site on the internet has a public IP address and a registered web
site name. For example the registered web name of TechSupportFree.com is listed
in DNS servers as having a public IP address of 75.13.112.81. where the actual web
server is hosting the site.
When a browser is pointed to any site like http://TechSupportFree.com and the user clicks go, the request first goes to the
gateway device usually your router, the router then hands that request
off to the first DNS1 server address either assigned by DHCP or configured with
a fixed/static(usually provided by your ISP), the DNS server then looks
up the registered name of 'TechSupportFree.com' in its database finds the public IP address on file and sends
the web request to the public IP address of 75.13.112.81 this allows the TechSupportFree.com website
to be found and the default page to be displayed on your browser. If the name you
entered into your browser is not on file with DNS, the common error message such as 'internet
explorer cannot display the webpage' will be displayed. This message can also be displayed if the network is down, or
the DNS servers are down.
For your network to find these web sites by name your Internet Service Provider will
supply the correct list of DNS servers to use, usually they assign two or more
DNS addresses, one as
a primary the second as a backup in case of extreme traffic or if one DNS service
goes down the other will continue to function. The actual
DNS address information in most cases are set in the router's Internet/WAN
settings provided by the ISP along with the public IP address settings. The DHCP
service then uses the routers own private IP address as the DNS address to use for
computers inside your network.
In the example below we have used the ipconfig command again this time to include
the /all command which reveals more information about your internet LAN adapter
connection and what the DHCP service has assigned to it. You can see that both DNS addresses are pointing to the router gateway
address of 192.168.1.1 and since the router is the gateway to the internet and has been configured with the correct public
DNS server addresses, the computers and devices inside your network can simply use
the same gateway address as a DNS address and find web sites. The router will do
all the work.
It is possible however to assign the actual DNS server addresses if you configure
your LAN adapter to use a fixed/static address. In most cases this isn't
necessary. See (How to set a fixed static IP address).