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Old 06-17-2011, 08:29 PM
 
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Quote:
Originally Posted by southseeker View Post
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.
a very little bit.

IP addresses are not "stored" in the modem, but the public IP assigned by your ISP is downloaded into either the internet side of your router if you have one, or assigned to the NIC card in the PC if no router exists.

Restarting or reconnecting the modem does NOT provide a new IP
If the lease on the current IP expires (IP addresses don't expire), the DHCP server will simply renew it, not change the IP

NO, office/business network workstations do not have static IP addresses assigned, but use DHCP. Printers, servers, and network devices will have static IP's.

ISP's will provide a static IP, for a fee, but it is primarily for businesses.
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Old 06-18-2011, 12:21 AM
 
Location: 10110001010110100
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What kazyn, macroy and asheville said.
If you do a Start > Run > (type) ncpa.cpl > OK, your network connection window should display, right-click on your Local Area Connection which is typically your default one, then click on "Properties" from the opening window click on Internet Protocol (TCP/IP) to highlight it then click on Properties button down below it to get the detail on the IP assignment.
At that opening window will you be able to tell if your IP assignment is dynamic or static:




You could have a DHCP on the network but a machine could have a static IP assignment for various reasons. For example almost any company I worked at, each network printer would typically have a static (reserved) IP address for obvious reasons.
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Old 06-18-2011, 09:55 AM
 
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Quote:
Originally Posted by dhyayi View Post
on some ISP servers, they set the DHCP for IP Address to expired in 24 hours or 7 days, even 1 year. So, it is up to your ISP. Some ISP's have set the static ip for your modem. you can check it by entering your modem menu, find the release ip button or kind of that. klik that button and see how is your new ipaddress
All that will do is "renew" the IP you currently have, even if your ISP is not providing a static IP to you.

When you say "modem" menu, are do you mean the "router" menu? If you have an ISR (integrated service router) that also has an inbuilt cable modem, your interface is to the "router" function of your device.
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Old 06-18-2011, 03:08 PM
 
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Quote:
Originally Posted by Asheville Native View Post
All that will do is "renew" the IP you currently have, even if your ISP is not providing a static IP to you.

When you say "modem" menu, are do you mean the "router" menu? If you have an ISR (integrated service router) that also has an inbuilt cable modem, your interface is to the "router" function of your device.
You can renew the connection from the modem menu/interface... but DHCP would not be used since the router would still have it's IP.
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Old 06-18-2011, 09:46 PM
 
Location: NC
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Everyone's answer of "it depends" is correct (as is in most computer-related questions).

If you were interested in the technicals of it, feel free to read rfc2131, its some pretty dry reading though

Most times you will find a lease time of 24 hours or 7 days. Whenever the time reaches half of the remaining time for the lease, it will try to renew (assiuming the dhcp implementation is rfc compliant). Thus, what is intended to happen is when you reboot the next time, morning, 2 days later, etc, your IP is generally not supposed to change as your lease time is never really supposed to run out. This is not to say that it can't or won't.
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Old 06-19-2011, 02:11 PM
 
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Quote:
Originally Posted by NJBest View Post
You can renew the connection from the modem menu/interface... but DHCP would not be used since the router would still have it's IP.
If you attempt to renew before the lease expires, nothing happens, lease expiration time remains unchanged.
If you 'release' then 'renew', DHCP is certainly used.

This applies to both the WAN side of the router, and the host connecting to the LAN side of the router.
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Old 06-19-2011, 05:22 PM
 
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Quote:
Originally Posted by Asheville Native View Post
If you attempt to renew before the lease expires, nothing happens, lease expiration time remains unchanged.
If you 'release' then 'renew', DHCP is certainly used.

This applies to both the WAN side of the router, and the host connecting to the LAN side of the router.
Yes...

My point was that the cable modem DOES have a menu/interface that is accessible by the user.
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Old 06-19-2011, 07:47 PM
 
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Quote:
Originally Posted by NJBest View Post
Yes...

My point was that the cable modem DOES have a menu/interface that is accessible by the user.
Yes, and it has an IP, and it also received additional information as part of its DHCP process, as that sets your download and upload speeds. That is why if your ISP increases everyone's speed (Charter did this a few months back) you either power cycle the modem so the new speeds can be installed, or wait until the lease expires on the current settings and the new speeds will be downloaded.

However the IP addresses assigned to the cable modem are not used for network traffic to/from your hosts.
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Old 06-19-2011, 07:52 PM
JL
 
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Quote:
Originally Posted by NJBest View Post
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.
Yes, you're correct. This is what happened to me.
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Old 06-19-2011, 08:05 PM
 
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Quote:
Originally Posted by Asheville Native View Post
Yes, and it has an IP, and it also received additional information as part of its DHCP process, as that sets your download and upload speeds. That is why if your ISP increases everyone's speed (Charter did this a few months back) you either power cycle the modem so the new speeds can be installed, or wait until the lease expires on the current settings and the new speeds will be downloaded.

However the IP addresses assigned to the cable modem are not used for network traffic to/from your hosts.
This isn't how it works for DOCSIS compliant cable modems. The cable modem has a static internal IP (192.168.100.1) which can access from your web browser.

AFTER DHCP, the cable modem downloads the configuration file via TFTP from the ISP's TFTP server. Folks trick their cable modem by downloading their configuration file from an alternate source (usually a local TFTP server) to remove speed limitations.
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