A question about IP addresses

[emailer84]

Hello,

I have a question regarding IP addresses.

So, I understand that I have a home network where each device has its own IP address. Then, to connect to the outside world, my modem connects to my ISP’s server, where it is given an external IP address. This means that all my devices have the same external IP when connecting to the outside world. Also, I don’t have a static external IP, it’s dynamic (though seems to change pretty rarely).

Now my question is this:

Let’s say that someone in the same city uses the same ISP and connects to the same ISP server. Then, we both load the same website. In the analytics of that website, will these two independent connections display different IP addresses, or will they just see the server’s IP twice?

Essentially, what I’m asking is whether websites and their analytics receive the actual external IP address of each user, or only a common one per ISP server?

I’ve always been curious how this works and thought I’d ask.

[William9]

Your ISP assigns your modem/router a unique IP address, and in a similar way your router assigs every device on your home network its individual IP address.

[n5bb]

Because consumers now use multiple devices on one connection to their ISP, NAT (Network Address Translation) is used in addition to DHCP (Dynamic Host Configuration Protocol) to allow dynamically assigned local network devices to be connected through a dynamically assigned single public IP address. This allows efficient assignment of IP addresses, since you can have a couple of dozen local devices (each of which has a unique MAC address and private IP address) accessing the Internet through one public IP address (which to others just looks like one of the many assigned to your ISP from a huge block of IP addresses).

• For example, right now I'm at a restaurant using my iPad cellular modem to connect via LTE to the AT&T cellular network. The iPad requests a "temporary" public IP address from AT&T, and is assigned a public IP with a lease timeout. Before the lease times out, the iPad must request an extension or that IP will be released and might be reassigned to another device.
• This iPad includes a "personal hotspot" feature, which allows other devices to connect via WiFi (802.11 WLAN) to the iPad and get Internet access. So I'm actually using a Windows 8.1 laptop PC to post this message through the iPad to the LTE cellular network. The iPad includes it's own local DHCP feature, which assigns a local IP address to my PC (and other devices which might connect through the iPad personal hotspot).
• The iPad is currently assigned a public IP address by AT&T starting "166.147.xxx.xxx". That's a block assigned to AT&T Mobility.
• The laptop PC is currently assigned a local IP address by the iPad starting with "172.20.xxx.xxx". That is a range of IP addresses reserved for private use on local networks, and is not used for normal Internet connections.
• What ties all of this together is IP address translation by the NAT router in the iPad. This router feature allows many local private IP addresses to be translated into the one public Internet IP address. The NAT router tables keep track of multiple requests and translates the local and public IP addresses in both directions. Router firewalls prevent external attackers from getting access to my PC, but allow the PC to set up web, SMTP, IMAP, and other network connections to public servers.
• At home, my Verizon FIOS network connection works similarly, providing NAT and a WiFi hotspot with DHCP local private IP address assignments for my uses. Only one public IP address is dynamically leased from Verizon, but multiple devices in my house are assigned via DHCP lease private IP addresses by the WiFi access point router.

Bill

[emailer84]

Thanks.
So, on the internet, do websites see the unique IP address of each user, or the one of the ISP server to which the user is connected?

[janusz]

Not necessarily "unique IP address of each user". For example in a typical home setup there may be multiple users behind a router, all with the same external IP address.

[William9]

Originally Posted by emailer84

Thanks.
So, on the internet, do websites see the unique IP address of each user, or the one of the ISP server to which the user is connected?

Usually only the public IP address assigned to your router (Internet facing IP). The devices behind your router (local network) are typically hidden from the Internet, although any of them can be revealed by creating a NAT passthrough sometimes used for gaming or VOIP.

[kijinbear]

Originally Posted by emailer84

Thanks.
So, on the internet, do websites see the unique IP address of each user, or the one of the ISP server to which the user is connected?

Usually, websites see a unique IP address for each household or small office that has a cable, DSL, or fiber connection. Buying a router at home has no effect on the IP address that websites see.

Most homes have only one internet connection, so every device owned by every family member will show up as the same IP address.

Some small businesses have multiple internet connections, so there might be groups of employees who share an IP address.

Large corporations often have a lot of IP addresses and expensive equipment to handle them. In their case, the number of IP addresses they use is completely unrelated to how many wires run into their building.

Mobile devices on 3G or LTE connections are a bit more complicated. Most carriers will assign a single, dynamic IP address to each device, but since the world is running out of IPv4 addresses, more and more carriers might begin to put several subscribers on the same IP address. In that case, you might be sharing an IP address with a random stranger across the street.

[emailer84]

Originally Posted by kijinbear

Usually, websites see a unique IP address for each household or small office that has a cable, DSL, or fiber connection. Buying a router at home has no effect on the IP address that websites see.

Most homes have only one internet connection, so every device owned by every family member will show up as the same IP address.

Some small businesses have multiple internet connections, so there might be groups of employees who share an IP address.

Large corporations often have a lot of IP addresses and expensive equipment to handle them. In their case, the number of IP addresses they use is completely unrelated to how many wires run into their building.

Mobile devices on 3G or LTE connections are a bit more complicated. Most carriers will assign a single, dynamic IP address to each device, but since the world is running out of IPv4 addresses, more and more carriers might begin to put several subscribers on the same IP address. In that case, you might be sharing an IP address with a random stranger across the street.

Thanks, that's all very informative and answers my questions.