Helping people with computers... one answer at a time.
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.
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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.
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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 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.
September 22, 2011 2:10 PM
1/ Do I need to pay for a static IP address from the ISP? Ex. 125.25.5.1
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 125.25.5.2 - 125.25.5.30...
Thanks
Provi
23-Sep-2011
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?
31-Jan-2012
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 192.168.0.1. Then proceeded to select wireless section then access control section.
Screen shows Connected Clients:
IP Address Host Name
192.168.0.2 2nd Notebook with wireless connection
192.168.0.4 LG Home Entertainment Center
192.168.0.7 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?