View Full Version : IP address question

12-13-2006, 07:55 AM
What exactly has an IP address, the pc or the connection? Meaning, let's say I have one pc connected to the modem and the IP address ends with 205, if I were to switch that pc with another, will the replacement pc have a different IP address?

12-13-2006, 09:02 AM


Don't take this personal but some of these questions you ask take a matter of seconds to google / yahoo / MS search to get answers on.

The concern I have is that without your searching the internet for some reliable locations (wikipedia has always been a good start for most questions) you might be missing points that you have not thought to ask or we have not thought to expand on.

But anyways an IP address is assigned either by dynamic or static assignment. To use your example the computer COULD get the same address depending on how long the lease was by the DHCP server / service or it could be assigned a new ip address if the lease is a longer period of time.

12-13-2006, 09:12 AM
I have Mike Meyer's Network+ book Dan and I had searched the net and posted on other forums for this but could not get a clear proven answer. The wikipedia link doesn't do it for me either. "Your" answer suggests to me that it is NOT the pc itself that has the IP address but the connection, am I correct?

12-13-2006, 09:44 AM
Before going any further Dan and everyone else, I should have mentioned this in the beginning [sorry]. My reason for asking this question is I am planning to start installing OTSDJ and setting up music for people in my area after having a lot of requests for this whenever people see my music setup on my pc so I will work out a deal with the company, what I am concerned about is "piracy". I don't want a person to install the software multiple times each on different pc's and sell the pc's. What led me to this is my situation right now, last night I tried a "few" times to install the software each time getting a license for the install, I was doing this while on the phone with the software company in Australia.

The above led me to thinking that anyone can say they are having problems and install the software multiple times on different machines, how will the software company know if they are doing this or not? If an IP address was within a pc itself then they would be able to track each download but if it's only on the connection then one can simply switch pc's and the company will be none the wiser. I don't wish to purchase licenses for strangers and they do stuff like this so I have to know what's what before going into this, your thoughts anyone?

12-13-2006, 10:00 AM
Every device on a network must have an IP address. Devices include, but are not limited to computers, routers, printers, etc. Everything that is connected via an RJ-45 jack has an IP address. Devices connected wirelessly also have
IP addresses. That's how devices know where to direct the TCP packets.

IP addresses are in the form of three sets of decimal numbers separated by periods. e.g.

In most home applications, devices get their IP address assigned dynamically via software by the router. This is know as DHCP. No two devices should have the same address.

The other method of assigning addresses is to to manually assign specific addresses to each device.

Now to confuse matters a bit more, each device also has a physical address that is unique to each machine. This address, known as the MAC address, is hardcoded at the factory. These addresses are in the form of 6 pairs of hexidecimal digits. e.g. 00-12-35-A4-9D-F2.


12-13-2006, 10:20 AM
Very well explained, so then a software company should issue a license for a specific MAC address and not an IP address, wouldn't this make more sense?

12-13-2006, 10:42 AM
Alright,now we're getting to the bottom of this, I am being told this

A "logical" address such as an IP address "binds" itself to the "physical" MAC address of the NIC. So it belongs to the NIC and only that NIC, and not the port coming out of the router. This binding is done by the protocol (TCP/IP or other protocol) on the machine itself and has nothing to with the router, other than getting the address from DHCP if the router has DHCP enabled, and DHCP is enabled on the machine.

I will contact the software company to verify all of this or to tell me how piracy can be prevented in this situation and get back here when they give me an answer.

12-13-2006, 10:57 AM
It gets a little more complicated than that...

Whatever connection type you use, be it cable, DSL, or dialup, your "gateway" gets assigned and IP by the server that handles the network.
There are "static" or fixed IPs (for which you generally pay a higher price) and dynamic IPs where the server assigns open numbers in random order to open slots.
Your public IP can change at any given time and you have no control over it. While a cable IP may remain the same for months, even years, if your modem is offline more than X hours, or there is a power outage that shuts down the server for any time, once it comes back on it will re-assign all the IPs in the network it serves. The ISP may re-configure their own network and alter the root suffix of a particular node thus changing your IP.

From their end of the network, your IP is your modem and the number assigned by their server and your MAC address is that of your modem. The MAC on your modem won't change unless you change modems. For cable, the modem MAC is what ties it to billing and your account.

If you use a router, all web connection comes in and out of your modem at xxx.xxx.xxx. The router translates that to your local network machines on yyy.yyy.yyy.
NAT =Network Address Translation
Your local machines 192.168.02 and 192.168.03 mean nothing to the ISP network as your Modem at sends traffic to the router at 192.168.01 and then the router sends it to machine etc.

You can set up static routes on your network to any IP range and subnet mask you want so long as they all match.

Add to that port forwarding and firewalls.
In order for you to connect to my FTP server, your request has to come to my modem at 68.37.107.xxx. The modem sends it to the router at The "Listening Port" for inbound FTP connections, 21 must be set in port forwarding in my router to direct that request to machine and the firewall on that machine must be set to accept inbound port connections on port 21 and allow outbound response.
To make that even more confusing, I can change the default port 21 to any of the thousands of other numbers I want.
Without having the correct setup, the inbound request hits a dead end and is discarded.