Question Same Public IP Address

Tiago Arlan

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Feb 1, 2014
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Hi,

My neighbor just subscribed to a Local ISP yesterday, since the owner doesn't know how to configure his Router settings, he called me for help.
After setting up the router, i found out that his Public IP and my Public IP are the same. Probably we are on the same DSL Box, and no available port, tech just tap my neighbor's connection to mine?

Questions:
  1. Is it OK that 2 different subscribers are having the same Public IP?
  2. Will there be any effect on the Internet connectivity?
  3. What shall i do? Complain,report etc. to the local ISP or leave it that way?
Thanks,
Tiago
 
It actually won't work if you really have both been assigned the same IP.

Where are you finding the IP. Do you see it in the wan settings or on a site like whatsmyip.

It is actually very common to share public IP addresses. The carrier does not have enough so they run nat at the carrier level. BUT your router should still be assigned a unique IP address on its wan port. This is almost always some form of private IP but it can not be exactly the same as your neighbors. This would be like you trying to assign multiple PC in your house the same IP, it just does not really work.

Sharing a public IP via nat does not cause major issues. It is extremely common on cell phone type of network connections.

You can not run server type function which most people do not care. Some gamers who for whatever reason want to run a minecraft server seem to be the most common ones we see complaining on this forum. You also run the risk that someone does something bad on the IP and you get some form of ip ban. This is more a problem of stupid people not understanding how things work and think IP addresses restrictions accomplish something. Generally it is smaller sites that eventually learn attempting to ban ip will result in loss of customers who did nothing wrong and were just using the same ip.
 

Tiago Arlan

Honorable
Feb 1, 2014
64
0
10,640
3
I saw both IP at whatismyip.com..Thank you for the advice..

For curiosity reasons, what is the difference between whatismyip.com IP (Public IP) and Router WAN IP? I understand how Local IP works,just confused on the other 2.. thanks again
 
The router wan IP is what the ISP give your router.

The ISP has a nat router between you and the internet.

It works pretty much the same way as your router does. Your router gives all your devices unique IP addresses like 192.168.1.x. Your router then translates all these into the single IP address your ISP gives you.

For many people the IP the ISP gives you is a public IP. In your case it is just another level of private IP.

Kinda like if you resold internet to all your neighbors. Only your router would have a public IP (assuming your ISP actually gave you one to start with). Since you only have one IP address all the nieghbors would have to share that one IP address.

IP addresses have been very hard to get for many years. If you were a new ISP just starting out you would have to pay a larger ISP a large amount of money for a block large enough so each customer could have one. Since most people do not actually need a public IP of their own many ISP run with shared ones to save money
 
Hi,

My neighbor just subscribed to a Local ISP yesterday, since the owner doesn't know how to configure his Router settings, he called me for help.
After setting up the router, i found out that his Public IP and my Public IP are the same. Probably we are on the same DSL Box, and no available port, tech just tap my neighbor's connection to mine?

Questions:
  1. Is it OK that 2 different subscribers are having the same Public IP?
  2. Will there be any effect on the Internet connectivity?
  3. What shall i do? Complain,report etc. to the local ISP or leave it that way?
Thanks,
Tiago
Technically speaking that shouldn't be possible. The IP is assigned based on the MAC of the modem in question. That is the WAN IP. Are you sure you aren't looking as the local LAN IP? 192.168.1.1?

It is possible to wrap all the packets as a subnet between the two houses, or use IPv6. (Sort of like a guest network on a router) But I doubt this is what's happening.

That said your addresses are likely DHCP dynamic. Unless you purchase a static IP from the ISP (typically business class internet), your WAN address will be shared. Your WAN address will change as well. So your neighbor might have one of your old addresses, while you have a new one.
 
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