Most of your understandings about IP Addresses are correct but at the same time, many of them are contingent on your setup (modem only, router or switch attached to modem then to various devices, router hardwired only or WiFi, who or which hardware controls DHCP, static IPs assigned or not, etc.
I'm not sure where you are located or which ISP you use and that could make a difference. Most of the major ISP's in the US assign the modem a "semi-static" IP that stays assigned to your modem for some fixed period of time (called a "lease") as long as the modem stays plugged in and connected. For some it might be a month and for most when the lease expires it is automatically renewed - sometimes renewed with the same number, sometimes not (hence the "semi-static"). Some folks want (or need) an actual "static" IP which never changes but most could care less. Depending on the modem, it may or may not assign the device connected to it a "discreet" IP or just "pass through" the modem's IP.
If you go to this site, look at the very top of the page and it will say "This is your IP".
That number is the IP address of your MODEM (the "gateway" to your LAN), it's the one assigned by your ISP and probably won't change day to day, nor can you change it without requesting a change from your ISP and having them do it (usually). It is NOT the IP of any one of your devices that are connected - those are assigned by the router.www.whatsmyip.org/
If your setup includes a router/switch (to allow simultaneous connection of multiple devices) then it's the job of the router to assign each device its' own, unique IP address, keep track of those already assigned, and never assign the same one twice. In the router setup you define a bunch of parameters that tell the router how to do this. For example you can tell it "assign numbers within this range 192.168.001.xxx" where the xxx might be 001-010. While this will work, it will also restrict your network to a max of 10 simultaneous connections, regardless of the capabilities of your hardware. If 10 devices (or whatever the limit defined is) are connected there are no IP #'s available to assign to another and you'll get an error message.
I doubt this is what is causing your problem but it's worth taking a look around in the router settings for other settings that might be causing the conflict. Most router setup aps also include a table listing the numbers currently in use and/or assigned.
One of settings tables allows you to set static IP's (within the subnet) for specific devices. There are good reasons why you may want to do this, other reasons why it's preferable to just let the router assign them all. Remember though if you do assign a static IP it uses up one of the available "slots" (in the IP range) whether it's connected or not and that number isn't ever available to any other device.
Another possibility is that the router is not "releasing" the IP # (and returning it to the pool of available #'s) when you disconnect the device from the network. So, even if there are 100 numbers in the IP range from which it can assign a newly connected device, if every time you connect it gets a new # and then doesn't release it when you disconnect and assigns another when you reconnect, it won't be long before all 100 are "used up". If this is the case, and a "hard" reboot of the router doesn't fix it, it's time for a new router. If however, just resetting (booting) the device, as you say, "fixes" it - that's probably not the case.
This isn't the type of problem that, even if "anyone else" here is having, the reasons why are common to your problem. There are simply too many variables (ISP, modem, router, etc) and they would all have to be exactly the same for their problem and yours to have the same cause in common.
In most cases the internal IP isn't assigned "by the net" except for the modem itself and even then only if the modem is rebooted.
With the number of devices you speak of I have to believe that you are using a router and most likely one with WiFi and that's the likely culprit. You might try posting on the owners forum for your particular router asking if anyone else with your model is experiencing the same problem. While you are there, check to see if there are firmware updates for your model since if this was a "known" issue with your model (and it's from a reputable manufacturer) they might well have fixed it with a firmware update that you don't have yet. If you've never done a firmware update it isn't something to fear. Generally it involves downloading a binary file, saving it someplace on your box, and following the step by step install procedure (which probably is someplace in the router set up screen.)
That's probably where I would start.
You already know that rebooting the affected device will solve it but that get's old if it's happening frequently.
Another method, if you are comfortable working in DOS (on windows boxes) is to open a command prompt and type in:
Forgot to add, anytime you are messing around with the modem (rebooting or disconnecting/reconnecting a router e.g.) ALWAYS unplug the router power plug, do whatever you are going to do to the modem, reboot the modem and then repower the router (the order matters) - gives the router a "fresh start" and clears out any "garbage" that might be lingering. Some routers (newer ones) do this automagically, most don't.
Also, if you have a home server on your LAN - all bets are off!
If you do, and the home server is set to assign IP's to network devices (either static or via DHCP) that's the FIRST place to look. (and be sure if it is, that DHCP is set to "off" on the router).
This also applies if you have more than one router "strung together" (maybe to add hardwire ports, or maybe to locate the WiFi router in a better physical location for coverage).
Generally, the first router (closest connection to the modem) should be set to assign IP's and the "downstream" ones set to off but it varies by models and if the WiFi is set to be an "access point"....check the set up guides for your specific models.
Edited by: DEANSDAD at: 4/29/2014 (22:07)
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