I'm going to address your questions directly, and in order. I hope
that's acceptable to you.
1. How are IP Addresses assigned and used?
IP Addresses are assigned by the Internet Corporation for Assigned
Names and Numbers ( http://www.ICANN.org ). These 'blocks' of IP
addresses are leased to very large businesses and ISP's. Once an ISP
has a block of IP's, it split it up into manageable pieces and
(typically) assigns IP blocks based on some geographic map the ISP
decided on. Once that is completed, the ISP will offer service to the
public in that area, and assign the number of paid-for IP addresses to
the customers router and/or computers as needed.
2. Why do I see several different IP's when I type ipconfig /all?
Each device has a seperate IP address. Internally all your computers
have unique IP's that are unique per computer and per adapter. DHCP
(Dynamic Host Configuration Protocol) servers on your router typically
assign that unique IP address to the adapters when the adapter
requests a new lease of an IP address.
3. When I go to whatismyip.com, it shows all computers as having the same IP, why?
This is the most interesting question. The router replaces your
computers IP address (a private, non-routable address) with the public
IP of the router (which is routable). To keep track of WHICH computer
the packet was from (and the reply should be routed back to), it gives
the packet a serial number, and tags it with a unique computer number
(basically, the internal IP address). The server that you communicate
with on the internet, preserves the tag and unique serial numbers the
router places in the packet when it replies to the request. Your
router then finds the unique tag, substitutes the public IP for the
internal non-routable IP and delivers it to the final destination:
The reason that it does that is because, simply, that's the only way
to get multiple computers on the internet without paying for multiple
public IPs. The process is actually called NAT (Network Address
Translation) and can also be described as IP Maquerading. This process
allows you great freedom to add multiple computers and increases your
security as only packets that contain the secret serial number (which
changes per transaction) are able to actually reach any computer on
the internal network. Essentially, there is a physical barrier between
the internet and your internal home network.
Please understand, the questions you are asking are answered more
completely in rather large books that cover this in much more detail
than I can ever write on Google Answers. If you are seriously
interested in the complete inner workings of the internet, routing
tables, DNS, DHCP, IP MASQ, NAT, etc, etc, etc., I can recommend some
good (technical) books. But, I think the information I've give you
will answer your questions in a more meaningful way.
If any part of this question is unclear to you, or if you simply feel
that I didn't explain myself well enough on any of the points I've
raised, please, prior to rating this question, ask for clarification!
I will be happy to provide more information if needed.
I performed no searches in connection with this question. I am a
Microsoft Certified Systems Engineer, and am quite familiar with the