IP addresses are identifiers used to transfer information across the Internet. If
you type www.microsoft.com into your browser, your computer resolves this
friendly name into the equivalent IP Address of Microsoft's web server, and
then retrieves their homepage using this IP address. While you are
connected to the Internet, you are assigned a unique IP address
which is shown at the top of this page. IP addresses are defined
in the TCP/IP protocol family, which is the basic technical foundation
of the Internet. In essence, you can consider your IP Address similar
to your home telephone number, it is a unique identifier assigned to you
while you are online and can be used to track your activities.
While browsing the Internet or sending an email your IP Address can be
used to locate your computer and disclose your identity. While this is
usually not a problem, there are cases where you would prefer not to be
identified. For example you may not be happy with the fact that your
employer has a complete record of all the websites you visited, or if
you live in China, Iran or other countries that do not respect freedom of
speech, protecting your privacy is of utmost importance. The IP Address
is also needed for other Internet services, such as Remote Control,
Voice over IP (VoIP), setting up firewalls, Geolocation, and most
importantly for testing and diagnostic purposes.
There are two ways to find out the owner of a IP
address.
The first and most common one is to send a ping or
make a traceroute, either manually or using a tool like PingPlotter, which
shows you the domain name. Then go to any registrar like
internic.net or networksolutions.com
and make a whois request.
Another, more direct but not that common way is to
go to the iana.org website
(Internet Assigned Numbers Authority) and search the IP address service
part for the "Internet Protocol v4 Address Space". Look in the
table for the first byte value of the IP address and read the organization
name which held these addresses. If it is the ARIN (American Registry for
Internet Numbers) for example, go to their web-site arin.net
- you find them on the home-page of iana.org
and make a whois request on the IP address. The result is the same.
A domain name is a word based representation of an IP Address.
There are distributed databases, containing all Internet domain names and hosts,
such as www.microsoft.com. The reason for using DNS names instead of IP
addresses is simple: meaningful names are much easier to deal with by
human beings than numbers, such 162.182.153.33.
This scenario is not the typical network design. Under normal conditions, VLANs are build to separate
broadcast domains which exists in a physical or switched LAN environment. Broadcasts are used to start
communication on layer 2 of the OSI model between two systems. An ARP request is a typical broadcast
sent out by an IP host to get the layer 2 (MAC-Media Access Control) address of another IP host.
But in some cases it is useful two allow separation into VLANs within one IP
subnet, e.g. for a test or a workaround. In that case, there is a possibility to do that: There must
be a router or layer 3 switch with proxy-ARP functionality. The only limitation is, that the IP
network must be subnetted and the router sits in between the both subnets. All other host do not
need to be configured for this subnets. This router will receive all ARP requests on a LAN, even
those which do not contain his IP address as destination. If the real destination is reachable in
the other subnet (VLAN, port), it will respond to that ARP request with its own MAC address as
destination. From that point, it will forward all traffic to the real destination (without the
knowledge of the source or the real destination).
This scenario is again not the typical design, since VLANs and subnets cover
typically the same topology. Two devices within two different IP networks (prefixes) need a router to
communicate between them. If there is a router in place on the same physical network, this router
need two IP addresses on its interface, one for each subnet. All traffic runs through that router,
even when this is not necessary by the physical network. If there is no router in the network, you
may use a trick. Set the default gateway of each device to its own IP address. Then, most operating
systems or IP stacks, will send the data direct to the destination (resolving the layer 2 address
with ARP).
