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I'm currently looking into getting a static IP address at home. I believe that if we are given a static IP address by our ISP that will be assigned to the router, rather than a specific computer.

We have several computers that connect through the router (two desktops, a laptop, plus my iPhone and DS sometimes). Will all these computers have the same external IP address, or will it somehow be different for each one? And does it matter?

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Will all these computers have the same external IP address, or will it somehow be different for each one? And does it matter?

These computers, behind the router, will appear as just one computer from the outside (at least they will use the same IP address; websites are still able to distinguish them by using browser cookies and some information that the browser sends to the server).

Generally it doesn't matter, but all limitations which are IP-based apply. For example, if your IP is banned from editing some site, all of the computers behind the same router will be banned.

What is Static IP

Actually, you should distinguish between static vs dynamic IPs (it's a method of assignment), "real" IPs vs IPs from the private ranges, and internal vs external IP addresses.

Static means that you insert the IP address in the network settings directly, it is pre-assigned to this machine, and it is always the same. The machine doesn't need to ask anybody to know its own IP address.

Dynamic IP means that you do not assign any particular address in the network settings. Instead, it is assigned automatically (via DHCP). For this automatic configuration to work, there needs to be a device on the network, which gives IP addresses. This is called DHCP server. Usually, it's home router's task.

It doesn't matter in what way the address (and other network settings) were chosen, as long as they are correct. These are only two different ways to configure the network.

External and internal IPs

There are not enough possible IPv4 addresses available. To workaround this limitation, addresses from the private ranges (10.x.x.x, 172.16.x.x, 192.168.x.x) are used in the internal network, and the "real" public IP is used as a single gateway for the whole network. This is called Network Address Translation. Most home routers do this.

( Internet, outer network )
   \
    \
     1.2.3.4 (external IP)
      |
   [ NAT device ]
      |
     192.168.1.1 (internal private IP)
      |
      \_________________
       \                \
        \                \
        192.168.1.2     192.168.1.3
      [ PC of Alice ] [ Bob's laptop ]

It doesn't matter if your external IP is assigned statically or not (usually it is dynamic, given via DHCP, even if it appears to be the same most of the time), it doesn't matter if your internal addresses are assigned statically or dynamically. The network works as long as it is configured consistently, and all computers know that they should send everything to the router, and the router knows how to rewrite address for the outer network.

You will appear as using 1.2.3.4 IP address to most of the sites (you may go to ipchicken.com to check). And if you don't have Java installed, they will not be able to say what is your internal address (but Java plugin may report it; probably Flash and Silverlight can do it too).

It may happen, that the outer address of the router is from the private range too (e.g. 10.1.1.1). This means that there is at least yet another NAT before the internet.

When a static "real" IP is necessary?

There is a situation, when you want to have your external IP to be static and not from the private range ("real" IP). Usually, this is the case when you run servers at home.

You don't want them to change their IP addresses spontaneously (but you can use dyndns to deal with it). And you don't want your server to have an address from the private range, because then nobody from the outside can connect it. If it uses a private IP, you need to configure routers all the way to the outside to make server connectable from the outside. If your router's external address is not from a private range (is a "real" IP), you need to configure only your own router. But if router's external address is from a private range, you depend on your ISP to configure their routers for you (good luck with that).

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I am very curious why you think you might want a static IP instead of the more typical dynamic IP.

I'm not sure what advantage you think you might gain from this. Since almost every ISP client uses dynamic IPs, every site on the Internet has to deal with them properly.

If you just want to reliably access your home's IP address from another location then I suggest using one of the "free" dynamic DNS services, for example dyndns.com. You could also search superuser.com for more info on dynamic DNS services.

Perhaps you have a need for a static IP which dynamic DNS cannot address. But usually the best reason to get a static IP is it is an easy way to send more money to your ISP every month.

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If you get a static IP-Address for your connection, that specific address will usually get assigned to the router/modem.

All the connected devices on your network will get local IP-Addresses assigned by that router (DHCP leases). Everyone on the internet will see the static external IP-Address no matter which device you actually use, even when used at the same time.

So they will all have the same external IP-Address, and no this should not matter in day to day use.

P.S. Why exactly do you want/need a static IP-Address? Are you (planning to) hosting any servers?

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It's your router that has the outside IP address, since it's the one that's directly in your ISP's network. This address is shared by all the computers in your home, which are all contained in a separate internal network where internal IP addresses are granted by the router acting as DHCP master. The router acts as a gateway, since your internal home network is otherwise completely cut off from the rest of the world.

When connecting to the exterior, the router acts as your agent and establishes the connection for you, shuttling requests and data between your computer and the outside computer. That means that when connecting to the outside, ALL your internal computers seem to the Internet at large to have the same IP address, which is actually that of your router.

The site What is my IP address will tell you your IP address and explain all the involved concepts.

In conclusion: When the ISP assigns a static IP address, nothing will change for you. The only difference is that sites that your family members visit will be better able to use the static IP to track your visits.

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