Can ISP give same public IP to multiple customers?

[Saji Thomas]

Hello Experts,

We had a friendly discussion at work about Public IP addressing. My friends says that ISP's like Verizon, Comcast etc assign same Public IP address to multiple customers and they all will work (same public IP to few thousand customers). I did not agree because if I host a web server in my location I wont be able to access it from the Internet if many people have the same IP address.

Any user who works with ISP or any of you experts will know better. Please help!!

Thanks! Saji

[Richard Burts]

Saji

An ISP can take traffic from multiple connected customers and by doing address translation can forward that traffic to the Internet. Theoretically the ISP could assign the same IP to multiple customers on the inside and still do address translation so that those customers could access the Internet. But I have never heard of an ISP that would assign the same public IP to multiple customers and then do address translation for them to reach the Internet.

HTH

Rick

[Saji Thomas]

Hi Rick,

Thanks for the reply. So does that mean that the customers will see the same IP as their Public IP? For Ex: If 50 customers with the same IP from the ISP check their Public IP on lets say "whatsmyip.com", would they all see the same Public IP?

Also, in that case, if few of them are running a web server at their sites with the Public IP's assigned to their websites, wont there be a conflict on that?

I know its too much to ask but if you can post a picture with explanation, that would help me a lot.

Thanks for your time kind Sir!

Saji

[Richard Burts]

Saji

In the scenario that I described the ISP would be doing address translation for the customer address. So if the customer went to whatsmyip.com they would not see the address that is configured on their device.

And you are correct that in this scenario there would be problems if the customer wanted to have a web server that is accessible from the Internet. To solve that issue the ISP would have to provide a static translation.

What I tried to convey in my first response may not have been clear so let me try it again with a slightly different approach. The answer that I gave to your original question describes something that is theoretically possible but is not a very realistic way to set up a network or to be an ISP.

HTH

Rick

[Joseph W. Doherty]

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Posting

I work for one of your named ISPs, although I support our internal Enterprise network, not our public side network.  That said, I don't believe we "reuse" customer public IPs.

We do, though, reuse large 10.x.x.x address blocks for customer device management.  This is a problem due to continued user growth.  So, we're very much into converting those to IPv6.