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Q: IP Addresses ( Answered 5 out of 5 stars,   1 Comment )
Subject: IP Addresses
Category: Computers > Internet
Asked by: aflaton-ga
List Price: $25.00
Posted: 14 Aug 2005 08:18 PDT
Expires: 13 Sep 2005 08:18 PDT
Question ID: 555614
How are IP addresses assigned and used? I have home network and I see
that the DHCP server assigns an IP address. But when I type
ipconfig/all I see several different IP addresses. I have also used and it shows the same IP address for all six
computers on our home network. How does a webserver know which
computer it is sending stuff to when all our computers show the same
IP address?

Request for Question Clarification by palitoy-ga on 14 Aug 2005 08:58 PDT
Hello aflaton-ga

Thank-you for your question.

IP addresses are analogous to a telephone number and are used by
computers to refer to each other when sending and receiving data on
the internet.  The assignment of the IP address and how your network
can be difficult to explain without the use of diagrams and I am
unsure how much information you require to answer this question and to
what level of expertise.

The tutorials below are especially interesting and
informative, these also include images and diagrams which are
difficult for the Google Answers to reproduce here.

What is an IP Address?

How Network Address Translation Works

How Home Networking Works

How Routers Work

Network address translation

Dynamic Host Configuration Protocol

Please review these tutorials and let me know if this is sufficient
for an answer.  Please also let me know if you have any further
questions on this subject and I will do my best to respond swiftly.
Subject: Re: IP Addresses
Answered By: legolas-ga on 15 Aug 2005 22:13 PDT
Rated:5 out of 5 stars
Hi aflaton-ga,

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 ( ). 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, 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:
your computer.

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
topic covered.
aflaton-ga rated this answer:5 out of 5 stars and gave an additional tip of: $10.00
Great answer. Thanks very much. I would love to have your book
recommendations, if there is a book that explains these issues well.

Subject: Re: IP Addresses
From: legolas-ga on 16 Aug 2005 22:46 PDT
Thanks so much for the tip and the 5-star rating! For the record, this
was my 100th answer, and you've helped me keep my 4.5 star rating :-)

As far as book suggestions, probably the best books on the topic are
published by O'Reilly press. There are quite a few books on
Networking. You can see the list here:

However, probably a good place to start is TCP/IP Network
Administration which can be found here:

The TCP/IP book covers the basics, and explains a lot about the
fundamentals of the TCP/IP protocol. I actually read the book
cover-to-cover, and it's actually a fairly good read.

Thanks again!


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