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Can anyone tell me how the IP ban system works. I have Dynamic IP, every time i start my PC I have a different IP. I want to know how a site (like a chat system) knows my IP and it keeps me banned...

  • I know what dynamic IP is
  • I know how to get my IP
  • I know the difference between local IP and external IP
  • I just want to know how a server can keep me banned based on my IP (not by user name)


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up vote 3 down vote accepted

Probably your IP address really isn't changing. Most times a "dynamic ip" is simply not static. For example, I have a "dynamic" IP address but it only changes every couple of days. The only way to have a true "dynamic" IP address is with dial up.

They could also have blocked an IP range from your ISP.

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Maybe. or can help to find this out. – kolypto Apr 16 '10 at 19:21
ok, that is what i'm thinking, but then how can i find my ISP's IP range – Remus Rigo Apr 16 '10 at 19:29
No idea. Why were you blocked? Give your ISP a call. – Josh K Apr 16 '10 at 19:37
Just fyi, dynamic IP addresses are provided on ADSL providers too, not just dialup. My broadband connection's IP address changes everytime I connect, although the first two octets are always the same. – Om Nom Nom Apr 17 '10 at 4:29
I also have a "dynamic" IP, and mine only changes every few months, if that often. – Joel Coehoorn Jan 17 '11 at 16:49

They don't ban your numerical address, they (often) use the other form of address, which is more like a domain. As shown in the link below, the ip can be turned into an address, this is similar to what IRC does. IRC is the best example, a type 2 ban will include some * in it, but will generally only affect one person. Another type of ban will ban the whole isp.

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There isn't one central program or system for IP based banning. Some sites will ban a single ip, or if there is an especially annoying trouble maker they will ban an entire IP range. Most likely though if you have a truly dynamic IP and are still getting re-banned the moment you log in, it isn't your IP which is giving away your identity it's a cookie stored on your browser saying you are banned, or a flash cookie, or maybe something which was cached.

Your best bet is to just clear all your browser history, cookies, etc.

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If you haven't already verified that your external/public IP address is changing, then I'd tend to assume that it isn't. Although there are exceptions (such as Om Nom Nom's ISP) where cable/DSL providers will assign a new/different IP address every time you connect, my experience has been that the public IP for any broadband connection will always receive the same IP address except in unusual circumstances (e.g., the ISP reconfigures their infrastructure) or after spending a long enough time disconnected that the address gets assigned to someone else.

The reason for this, even when you have a dynamic IP address, is that DHCP (the mechanism used to request a dynamic address) clients and servers both remember the last IP address each client has been assigned. When reconnecting, clients (such as your router) will typically request that they be given the same address again; servers will generally comply with this request if the address is available. If the client does not request a specific address and the server recognizes it, the server will frequently offer the same address again anyhow.

If you've confirmed that your external IP actually is changing, then I'm going to have to agree with Daisetsu: Assuming web-based chat, you're probably being blocked based on a cookie that the site has set.

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Unless you're connecting your computer directly to your internet, your home IP is different from your computer IP address. Your house will usually have an IP address dictated by your ISP while the IP addresses inside of your house are dictated by your router or switch. When someone bans you by IP they are banning your home IP address (which only changes when your IP wants it to, or when you re-lease your home's IP) not your computer IP address.

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You're mixing up "home" and "internal" IP address. Your "internal" IP address shouldn't change either, unless you have a weird lease on your router. Either way the "external" IP address is set by the ISP and yes changes when they want it but normally on some sort of event. – Josh K Apr 16 '10 at 19:16
@Josh K:Right. he's asking how a Chat Program (Like IRC) would block him. He's most likely blocked by External IP. Not internal IP because them being able to see what his specific computer's IP is would be odd. So, if you're being blocked by a website you're internal ip won't matter. It's your house's IP address which can only change when you get them to give you a new ip, or if they "for some reason" give you a different IP (mine changes every month or so) – Kravlin Apr 16 '10 at 19:18
Now you're confusing even me. Your cable / dsl modem has an IP address. This is the external IP address. It isn't "static" so it can change randomly at intervals. Normally every few days depending on the ISP. This is what the web site / service sees. Nothing else. Of course the internal IP doesn't matter. – Josh K Apr 16 '10 at 19:25
We're arguing the same point. that it's not his computer's IP address that matters, it's the external IP, the house's IP or whatever you want to call it that's assigned to the router. However, he wants to know how they know what IP he's using because every time that he starts his computer he has a different IP address but it's very possible that he doesn't realize the house has it's own IP address that is unaffected by his computer's address and that they're banning him by his router's IP instead of his individual computer's IP. – Kravlin Apr 16 '10 at 19:31
Yet it's also highly probably that he has visited WhatIsMyIp and realized that his 192. / 10. address isn't what the server is reading it as. – Josh K Apr 16 '10 at 19:41

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