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Every device on an TCP/IP network must have a unique IP address. IP addresses are assigned, either automatically by DHCP, or by manual configuration.

Given that IP address must be unique for every computer attached to the internet,how is it possible that we do not plug in IP addresses for the computer we want to connect?

Well, every device connected to the internet must have a unique IP, it's true. And they're assigned one of two ways: static or dynamic. But there's also a useful trick that lets multiple computers share a single IP address ... and that trick is called a router.

Static IP addresses are exactly that: static or unchanging. They are assigned by your network administrator or ISP, and yes, you do have to configure the computer or other internet device manually to respond to that specific address.

But, as you point out, most folks don't need to do that. So how do they get their IP addresses?

Enter the dynamic IP address and "DHCP" or Dynamic Host Configuration Protocol.

Using DHCP (which is the default for Windows TCP/IP connections) the computer broadcasts a special request for an IP address to the network. An upstream device, commonly belonging to your ISP, responds with an IP address that the computer then configures itself to use. Especially when many computers aren't connected continuously, this allows the ISP to reuse the IP addresses of computers that have disconnected from the internet.

If you need your computer to be identifiable on the internet ... for example if you're running a web server or want people to be able to connect to your machine, you'll probably need or use a static IP address. On the other hand, if all you do is connect out to surf or read email, as most users do, then a dynamic IP address is the easiest to configure.

Routers are devices that allow multiple computers to "share" a single IP address. The device that's connected to the internet is the router, and it has a unique IP address. The router can then act as the DHCP server to the local network handing out local IP addresses to the computers connected to it. As traffic flows across the router, it does the job of translating the IP addresses from the local addresses it has assigned, to the external IP address it was assigned, and routing the right bits of data to the right computer ... hence the name.

One of the many side effects of using a router is that it can be assigned a static address on the internet, and hand out dynamic IP addresses locally, vice versa, or any combination.

Article C2328 - April 10, 2005 « »

Leo Leo A. Notenboom has been playing with computers since he was required to take a programming class in 1976. An 18 year career as a programmer at Microsoft soon followed. After "retiring" in 2001, Leo started Ask Leo! in 2003 as a place for answers to common computer and technical questions. More about Leo.

Not what you needed?

July 6, 2005 5:03 AM

Hello Sir

I tried to give static ip address but thats not working at all.when i give command ipconfig no ip address was found


August 10, 2005 11:10 PM

how to set static isp ip address used in my pc

Robert Pence
September 15, 2005 7:38 AM

When I click run and type in ipconfig, my black window comes only for a split second, and then disaapears. I can't check my ip address or anything else. What is wrong with it?

September 15, 2005 8:20 AM

Run a command prompt (usually in Programs->Accessories) and type your ipconfig in that.

October 12, 2005 2:10 PM

How to get an external ip address of my computer connected to a router?

October 12, 2005 8:51 PM

There are several sites that'll tell you. If you visit it'll show you that.

October 13, 2005 11:19 PM

Some One Says They Have Got My I.p Address An Can Hack Into My Computor , Is This Possible?

October 14, 2005 10:52 AM

It depends on how well protected you are, but it's possible, yes. This article is worth reading:

November 2, 2005 9:34 AM

Is there any way to fool IP reading websites into thinking you have a different IP from the same computer? For example some websites limit the amount of downloads one IP address can make. Is there any way to make it think I have a different IP address even though I'm on the same computer?

November 23, 2005 9:58 AM

when will you post your answer to the question posted by Mark on Nov.2, 2005 asking if you can fool IP reading websites into thinking you have a different IP from the same computer.

Leo A. Notenboom
November 23, 2005 11:45 AM

There's no way that I know of. Your IP address is fundamental to locating your computer on the network. Trying to "fooling" it would only break the communication.

November 29, 2005 9:37 AM

you can use a anonymous proxy to trick the servers into thinking your someone else.

December 29, 2005 10:54 PM

My Pc is connected to a router.
Say my ip address is and the router assigns the ip address to my PC... what Ip address must i use when setting up an ftp server on my PC. (Submask -

March 11, 2006 4:24 PM

Hey, I need your help !

I was a tourist in Rome and tricked by a group of Dominican priests. They stole my valuable belongings and used dirty tricks to get me to drink and into bed with them.

I want to send those sick Dominican priests into jail. But those group of sick priests , they protect each others.

I know two keys priests email address and I tried to track them and asked them to tell me the whole truth - who was involved for the dirty plans and actions.

I tracked one of the priests. His email address is

Below is my tracking details:
I want to hack into email account , please help me.

Tracking Details
Opened 12-Mar-06 at 03:55:15am (UTC +07:00) - 2mins22secs after sending
Opened on (8815393229:22438)
Language of recipient's PC: en-us (English/United States), fr;q=0.5 (French)
Browser used by recipient: Moz/4.0 (MSIE 6.0; WinNT 5.1; SV1; .NET CLR 1.1.4322; .NET CLR 2.0.50727)
Referrer http://e1. f316. mail. yahoo. com/ym/ShowLetter?MsgId=4549_1521412_34553_2780_1573_0_12283_6223_3986143784& Idx=0& YY=90958& inc=25& o

May 21, 2006 4:07 PM

how can i manually set my IP address?

March 21, 2007 11:52 AM

A group of IP addresses are assigned to your ISP, it will give you one of it, or they will do something to get one ip address from that group each time you connect to the internet.

If you do some investigations and some look-ups using , you will see that IP's assigned to each country are someway grouped.

July 10, 2007 5:28 PM

Say I have a business out of Canada that I'm running from the United States.
Is there anyway I can get my IP address in the united states to match my business location in Canada? Any help greatly appreciated.

August 22, 2007 3:45 PM

I was trying to connect to my internet with a Compaq laptop that was given to me. I have Charter High Speed Internet. It will not connect and after the Charter IT person came out to my house, he said that the Compaq laptop that was given to me has a bad IP address. How do I correct a bad IP address in the laptop?

November 28, 2007 2:58 AM

My ISP has given me what they say is a fixed IP address but when I switch off my PC my IP address gets assigned to another PC somewhere else. I don't use a router so can't leave it switched on with the fixed ip address stored in it.
My ISP says "it happens" and I'm "unlucky" to loose my IP address, is this heard of or is there a way around this?

Leo A. Notenboom
November 28, 2007 4:48 PM

Hash: SHA1

If it can change, you have a dynamic IP address, no matter what your ISP says.
What you want, it seems, is a "static" address.



Version: GnuPG v1.4.7 (MingW32)


November 30, 2007 9:10 AM

My roommate has my ip address, can they get acccess into my computer through theirs? Like can they see what I do and see my email?
I gave it to them so they could try to get online with their computer, but now I'm not so sure I should of gave it to them.
By the way I have a cable connection if that matters and no router.
Please help!
Thank you

danny curtean
April 1, 2008 12:34 AM

I have a sonicwall TZ 180 and I want to make 3 servers static. For some reason I cannot get the sonicwall to work with static ip addresses that I set in windows (TCP/IP settings). It works just fine with DHCP on router, but I cannot get the servers to work statically. Am I missing something?

June 4, 2008 11:01 PM

WRONG! A router connects two (or more) networks together. Look up what a gateway and proxy are. And read a book. It's always funny to see n00bs writting articles for other n00bs trying to sound like they know what they are doing.

June 20, 2008 9:15 PM

HI this article was really very simple to understand and was very helpful


mack nicks
September 12, 2008 4:58 AM

Can we assign an IP address to an ARM microcontroller?

September 16, 2008 9:52 PM

I have a hp pavilion desk top,I'm try to set up my quest qiuckconnect,The phone company told me I need to set my IP address to default,How do I do this?

September 18, 2008 2:51 PM

if only the last two number is not the same and im getting email from 2 different person from same ip for eg

does this mean they using one pc ??

December 10, 2008 1:13 AM

setting up a security system with internet connection with a router on the network. however when trying to connect from net no response. when ping the ip message destination port unknown comes up

February 12, 2009 11:33 PM

how my dhcp scope will create to my local lan while there is no scope creation for ipv6.

G Mylonas
March 20, 2009 4:12 AM

good day Leo

I have a static IP at home but i cannot get througth to my pc from the my office.

can you tell me if i have to do some adjustments to my home pc.

thanks regards

April 26, 2009 7:54 PM


June 20, 2009 5:17 AM

Thanks for your information.And i know my ip address by using ip-details

September 25, 2009 8:06 PM

Here Only i know what's the purpose of router and i want more basic network concepts like this........

March 10, 2010 12:41 AM

I have a static IP configured in my server. How can I connect througth server from home

With Regards

Hitesh Joshi
March 30, 2010 10:26 PM

Dear Sir,

I have a static IP configured but I have not connected my home and office computer. my router is connected with my static ip but my both computer not connected... please give me some guide...

With Regards,
Hitesh Joshi

July 26, 2010 8:00 AM

hey you gave the clear info of router

February 2, 2011 9:54 PM

i want to know whether my ip address changes if i change my service provider

Almost certainly, yes.

mike butler
March 8, 2011 8:54 PM

What causes multiple computers set for DHCP to fail to the internet. If a static address is assigned it will connect, but it will not connect via DHCP. Or if it does, it drops out eventually. This happens with both ethernet and wireless clients.

I'd suspect a problem with the router or gateway device. If you have a consumer router, try just rebooting it.

July 28, 2011 10:07 AM

can every computer with a external ip address able to ping every other computer to its external ip address.
I am unable to ping my computer connected using one ISP with my friends ip connected using another ISP provider.

Sometimes ping is blocked. Usually it works, but not all the time.

September 22, 2011 2:10 PM

1/ Do I need to pay for a static IP address from the ISP? Ex.
2/ If I get this static IP address - I would use it for my router. Can I then create a range for all devices connected to this router? Example -

1) typically, yes, but it depends on your ISP. 2) typically NO. You would have to get those IP addresses from your ISP as well. Usually you would get local IP addresses (192.168.x.x) behind your router.

Scott Logan
January 30, 2012 5:13 PM

I have satellite Internet service providing a single IP address. I can only connect with one PC on my network. I've been told to install a router ahead of our Netgear 16-port switch which is what you've described here and it makes perfect sense but will any router work for this application or do I need something very specific?

Nope, pretty much any consumer-level router should do the trick. It's perhaps the single most common reason people get, need and use a router at home.
April 19, 2012 12:59 PM

What does ip planning mean?

May 30, 2012 11:29 AM

Hi Leo,

Running home office notebook PC computer #1 (Windows XP Home addition Service Pack 3) connected by Ethernet cable to an all in one Motorola Surfboard SBG 6580 modem/router. System working correctly with this configuration; can access the internet through Ethernet connection.

Problem (error message see below) when disconnecting notebook from Ethernet cable and turning on notebook wireless connection. Wireless device is an Athero AR5005G Wireless Network Adapter with current driver. System properties indicate that network adapter is working properly.

Error Message – Windows System Error

There is an IP address conflict with another system on the network.

I’ve reconnected the Ethernet cable and turned off the notebook wireless adapter, then login to the Motorola all in one modem/router online using IP address Then proceeded to select wireless section then access control section.

Screen shows Connected Clients:
IP Address Host Name 2nd Notebook with wireless connection LG Home Entertainment Center Wireless Printer

If I leave the Ethernet cable plugged into #1 Notebook then turn on the wireless network adapter the Desktop Tray shows that the Motorola wireless adapter is now connected and signal excellent.

Shortly afterwards an error message appears on the 1st notebook screen reading:

Windows System Error

There is an IP address conflict with another system on the network.

Also, internet connection is lost. Must turn off the wireless adapter and select refresh the internet browser to reconnect to the internet through the ethernet cable connection.

Is there a way I can try and resolve this IP address conflict and be able to use #1 notebook using the wireless adapter?

Thank you. Gary

July 31, 2012 11:56 AM

I have a two part question. Perhaps I lack the understanding to ask the right question or perhaps the answer is too long and interwoven and I am not putting the pieces together. I ran across your page, and wonder if you might help.

a) how does one IP address become blocked on a "gateway" inhibiting entire populations of customers from one ISP to become blocked from visiting 1 site? (Gateway being the term used by those who "fixed the problem)

b) How does an IP address get listed by spam sites leading to blacklists, etc. Could this be caused by behavior of the IP provider, the previous assigned user of the IP?

c) suggested remedy for the above?

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