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Old 06-16-2011, 12:54 PM
 
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If you have a DSL modem that is on all the time, and your computer is set to get IP addresses automatically -

do you get a new IP address each time you turn the computer on - or do you just get a new IP address whenever the DSL modem is restarted?

Another question: if you work in an office with a LAN (and the computers are set to get IP addresses automatically) - do you get a new IP address each time you turn the computer on?
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Old 06-16-2011, 01:14 PM
 
Location: Land of Free Johnson-Weld-2016
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I don't do anything professionally with networking, but I did study it in school. Based on my own network and general knowledge:

Outside IP Address - There's normally ONE per DSL account. It can be something like 95.54.1.18 (may be invalid, but you get the picture). I believe your ISP can legally and technically reset the IP anytime they desire...unless you PAY for a "dedicated" IP address. Otherwise it MAY be reset when your modem is restarted. The external IP address is UNIQUE in the WORLD.

Inside IP Address - These usually start with the number 10 or 198 and may be like 198.1.1.1. There can be billions of these repeated in the WORLD, and are only for the computers inside the house or "local area network" to talk to one another. Your Modem gives internal addresses to your laptop, PC and any other IP-addressable computers or smart hardware that is in your house. These MAY be reset for a specific computer every time you turn it off. If you know how to set up the networking, I believe you can assign a Dedicated Internal IP address to your internal computers as well.

Hope that helps.

Stuff at Work - Recently at companies I work for, the network gives a DEDICATED IP address to each computer. So I always have the same IP address when I turn my computer on or off. If you want to check your IP address on windows...Click Start > Run ...Then type "cmd" to open a command prompt.

Type "ipconfig /all" and press enter. You will see your IP address and a bunch of other stuff. You can restart your computer and then see if you have the same one.
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Old 06-16-2011, 01:21 PM
 
2,182 posts, read 4,705,982 times
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Quote:
Originally Posted by robertpasa View Post
If you have a DSL modem that is on all the time, and your computer is set to get IP addresses automatically -

do you get a new IP address each time you turn the computer on - or do you just get a new IP address whenever the DSL modem is restarted?
Short answer is it depends. It is based on whatever settings your ISP chooses to use.

Most of the time, there is a timeout on a particular IP before it is dropped back in the pool and another one is hooked out for you. Sometimes you may turn your router off and back on, and get the same IP you had before. It all depends on your ISP.


What are your motives behind the question? That may help us to help you a bit better.

Quote:
Originally Posted by robertpasa View Post
Another question: if you work in an office with a LAN (and the computers are set to get IP addresses automatically) - do you get a new IP address each time you turn the computer on?
Sometimes yes, sometimes no. If you have 2 people in the office, there's a high likelyhood that you'll have the same IP address all the time.

You can attempt to get a new address by going into CMD and typing these two commands, one after the other:

ipconfig /release
ipconfig /renew

This won't work very efficiently if you always turn off/on your PC every day. If your DHCP server says your PC still has X amount of time on your IP lease, you will receive the same IP. But, if your lease has expired, when you shut down and restart, you may receive a new one.
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Old 06-16-2011, 03:42 PM
 
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Typically no. DHCP servers recognize the MAC of the requesting device and assign the IP address they had previously if it is not assigned to another device. Since broadband ISPs provide service to customers with "always on" devices, they have sufficient addresses in their pool to not have to reassign to other devices.

In a business it is almost certainly a private address (192.168.xxx.xxx) and each host will receive the same IP each time it boots.

I have also seen AT&T DSL customers that receive a private address from their ISP. The NAT to a public done somewhere in the AT&T realm.
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Old 06-16-2011, 10:40 PM
 
Location: Louisiana
494 posts, read 1,467,158 times
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Quote:
Originally Posted by robertpasa View Post
If you have a DSL modem that is on all the time, and your computer is set to get IP addresses automatically -

do you get a new IP address each time you turn the computer on - or do you just get a new IP address whenever the DSL modem is restarted?

Another question: if you work in an office with a LAN (and the computers are set to get IP addresses automatically) - do you get a new IP address each time you turn the computer on?
I don't know a lot about network, but I know a bit.

First of all, the IP info for your connection is stored in the modem and not your computer. So with that said, you get a new IP three ways: If the modem is restarted, reconnected, or if the current IP expires and it needs to fetch a new one. This is assuming that you were assigned a dynamic IP by your ISP and not static. A static IP simply means your IP never changes.

As far as the office, no. For office LANs, they are usually using static IPs. It would be headache to us IT people if the IPs were dynamic because we would have to reconnect computers to the network constantly. Having said that, in most cases, the incoming connection from the ISP is usually using a static IP too. This is perfect solution for web-hosting and other things that need it.
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Old 06-17-2011, 02:23 AM
 
40,169 posts, read 41,782,366 times
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My experience with Comcast which is cable is they always assign you the same IP when the modem is rebooted. I had same IP for years until I moved. I'll note it was never off for maybe more than 24 hours at the most.
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Old 06-17-2011, 02:32 AM
 
24,503 posts, read 35,958,754 times
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Quote:
Originally Posted by thecoalman View Post
My experience with Comcast which is cable is they always assign you the same IP when the modem is rebooted. I had same IP for years until I moved. I'll note it was never off for maybe more than 24 hours at the most.
The external IP is not assigned to the cable modem, but to the computer attached to it. With Comcast specifically, the lease lasts for several days and is automatically renewed if the computer is on while the lease expires. If the computer is off, then the lease will expire and not be renewed until the computer is turned back on (at which point it will be assigned a new IP).

If you use a router (like most people), the router acts as the computer. So if you leave your router off for over the lease period your IP will change.

I just checked my lease time and it says:

Remaining Lease Time 2 days 21:29:29

So if I were to turn off my router for more than 2 days and 22 hours, I would get another IP. Alternately one could easily force themselves to get a new IP on Comcast very easily.
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Old 06-17-2011, 06:44 AM
 
Location: HoCo, MD
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The answer depends on how the ISP/organization sets it up.

IP's are attached to network devices and they must be unique to the subnet they sit on. As NJBest indicated - cable modems are not layer 3 devices, so they technically do not have an IP. That IP is usually attached to a layer 3 device (be it a computer or gateway/router). Today, most people will have a gateway/router behind the cable modem, and the external interface (WAN) will be assigned the address from the ISP - whether or not this is static, dynamic, or dynamically reserved will depend on how the ISP sets it up.

Just as on the internal side, you can have all of your computers's IP's configured statically, dynamically, or reserved. Reserved is simply having your computer configured to received a dynamic address from the DHCP server, but configuring the DHCP server to reserve addresses for specific hosts.

Internal addresses that are mentioned above are non-routable on the internet. They were reserved for private use purposes (google RFC1918 for more info). Back in the day when they classified IP addresses, one set from each class of A, B and C was designated. So private addresses can be 10.x.x.x., 192.168.x.x., or 172.16.x.x - 172.31.x.x.

As for corporations - you'll find a mixture of configurations. But just about all of them are using RFC1918 addresses internally. I know back in the day, larger corporations like Compaq/DEC still assigned class A's to their printers and even workstations. But not sure if that is still the case today.

Corporate LAN will usually assign DHCP addresses for workstations while their servers will still be static or reserved. But again - it all depends on how their IT folks structured them.
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Old 06-17-2011, 08:51 AM
 
Location: WV and Eastport, ME
11,707 posts, read 11,301,056 times
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Quote:
Originally Posted by southseeker View Post
<snip> As far as the office, no. For office LANs, they are usually using static IPs. It would be headache to us IT people if the IPs were dynamic because we would have to reconnect computers to the network constantly. Having said that, in most cases, the incoming connection from the ISP is usually using a static IP too. This is perfect solution for web-hosting and other things that need it.
I'm sitting here using a computer connected to a network with over 20,000 users, all of whom get there IP addresses via DHCP.
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Old 06-17-2011, 11:20 AM
 
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Quote:
Originally Posted by mensaguy View Post
I'm sitting here using a computer connected to a network with over 20,000 users, all of whom get there IP addresses via DHCP.
As it should be
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