IP Address Assignment: How are IP Addresses Assigned?

[WWGD]

Hi All,
I am just curious. I am in a coffee shop using the internet. My (external) IP address in this coffee shop ( given by whatismyip.com) is the same as the IP address assigned to me at home by my ISP. I thought IP addresses are assigned dynamically when one logs into a network and the network used by the coffee shop is not the same as that of my ISP. How is that so? Doesn't a DHCP server assign an address dynamically when I log in and then remove it from circulation when I log of ?
Thanks.

 

[jedishrfu]

I think it can either be static or dynamic and is dependent on your service provider. You might find a better explanation in this article:

https://en.m.wikipedia.org/wiki/IP_address

The whatismyip.com website had disclaimer about not necessarily returning the correct address when asked due to many reasons outlined

https://www.whatismyip.com/ip-address-lookup/?iref=cta

 

[StevieTNZ]

Perhaps try again, but before doing so clear your cache.

 

[Fervent Freyja]

This could happen if you are using a proxy browser.

 

[StevieTNZ]

Or even try a DNS flush. Instructions can be found doing a quick google.

 

[rkolter]

Hi All,
I am just curious. I am in a coffee shop using the internet. My (external) IP address in this coffee shop ( given by whatismyip.com) is the same as the IP address assigned to me at home by my ISP. I thought IP addresses are assigned dynamically when one logs into a network and the network used by the coffee shop is not the same as that of my ISP. How is that so? Doesn't a DHCP server assign an address dynamically when I log in and then remove it from circulation when I log of ?
Thanks.

Specific answer to your questions:
IP addresses can be set static, but if you had set your IP address static, you'd probably know. And, if you'd set it static, you wouldn't be able to connect at the coffee shop. Your IP address is most likely assigned via DHCP. Those are assigned when requested by your device, and made available again when your device is no longer connected. As a general rule, no two networks should hand out the same IP address. There is however, an exception.

Most small private networks use a non-routable subnet starting with 192.168.x.x for connected devices. You didn't mention what your IP address was, but I would be willing to bet its 192.168.x.x - if that is the case, then it's entirely possible that you got the same address at home and at the coffee shop - but because the address is non-routable, only the network you are communicating with can route to you. In that case, it is perfectly reasonable (although maybe lucky) that you got the same address at home and at the coffee shop.

If the IP address you have isn't 192.168.x.x then you most likely have a Proxy configured (Fervent Freyja's answer) or a VPN configured. In both these cases, the IP address you are seeing was handed out by a different source than your home or coffee shop, and the lease might persist longer.

 

[WWGD]

Perhaps try again, but before doing so clear your cache.

Thank you, this has worked a few times. In case anyone else using Windows has trouble accessing the web, go to the
CMD line and type :
ipconfig/flushdns

 

[pbuk]

Wow, you had to clear your DNS cache after more than 3 years?!

 

[WWGD]

Wow, you had to clear your DNS cache after more than 3 years?!

No, just did a search and ended up in this post.

 

[Svein]

A lot of IP addresses are reserved (see https://en.wikipedia.org/wiki/Reserved_IP_addresses ) mostly for historical reasons. Several of those are not allowed on the Internet and must be translated to a valid address by the router.

 

[Tom.G]

Thank you, this has worked a few times. In case anyone else using Windows has trouble accessing the web, go to the
CMD line and type :
ipconfig/flushdns

Don't forget to put a space before the '/', else it won't work!