What is a Public IP Address & Do you need one?

In this article, let us see what is Public IP address, difference between static public IP address and dynamically assigned public IP address, the difference between public IP address and private IP address, applications of public IP address and how you can manage without a public IP address for those applications.

What is a Public IP address?

As you know, an IP address is a number in the format aaa.bbb.ccc.ddd. Devices trying to communicate with other devices over the Internet will use this IP address to reach / exchange messages with them. So, pubic IP addresses are those unique/ permanent IP addresses  assigned to Internet connected devices and they can be independently routed across the Internet. They are permanent addresses for devices connected to the Internet much like your permanent residential address.

When you type www.google.com (or) www.yahoo.com, the name gets converted in to an IP address (By a DNS Server) which is in turn used to locate the servers hosting those websites. These websites have a permanent IP address assigned to them, called as Public IP address. You can reach these websites using their public IP address or their domain name. Not all websites need to have their own public IP address.

If you are a large organization and are using Internet Leased Lines for connecting to the Internet, you could have been assigned with a public IP address by your ISP (Internet Service Provider). You can also buy more public IP addresses from your ISP. There is an organization called IANA – Internet Assigned Numbers Authority which oversees the allotment of public IP addresses.

Static Public IP address Vs Dynamically assigned IP address:

A Static IP address is the one that does not change. For example, if your organization has purchased an IP address from your ISP and you are using that to host your website, people can type that IP address in their browser to access the website from anywhere, anytime. Its sort of permanent and has been assigned to you. That is a Static Public IP address.

The ISP does not give a Static public IP address to most of the individual (home) subscribers. They give a Dynamic IP address (one that keeps changing every time you connect to the Internet (or) after a fixed point of time, as determined by the ISP).

In such situations, the ISP blocks a chunk of static IP addresses and it gives them to the subscribers (on lease for a short time), when they connect to the Internet. But the moment they log off their session, the IP address given to them is reclaimed by the ISP and the subscribers might most probably get a different IP address when they connect to the Internet the next time. So, you can’t use the Dynamic IP address to connect to your computer from a remote location, for example.

Within a LAN though, Static IP address refers to manually assigned IP address (to each computer) and Dynamic IP address refers to automatically assigned IP address by the DHCP Server. But this is different from the public IP address we are discussing in this article.

Public IP address Vs Private IP address:

The static IP address (that does not change with time, and assigned permanently by the ISP) is the Public IP address. Two devices with Public IP addresses can communicate with each other directly from anywhere as the public IP addresses are routable across the Internet. If your IP camera has been assigned a public IP address (for example), you can access it by just typing the public IP address in the URL box of your browser.

Private IP addresses are those that are assigned within a LAN (Local Area Network). If you have one Internet connection but 10 Computers sharing that Internet connection, you/ your ISP cannot assign a public IP address to each computer individually. So, you just assign a private IP address to each system (either manually or using a router/DHCP server) and they can share a single public IP address, when connecting to Internet.

In such cases the router uses something called as NAT – Network Address Translation where the request from each computer (with its own private IP address) is accepted but the IP address is swapped – the private IP address is discarded and a public IP address is attached to it and the request is sent to the Internet. When the response comes back, router remembers which computer made that request and swaps the public IP address with the private IP address of that computer and sends it back. So, multiple computers can share the same public IP address to connect to the Internet.

Range of Private IP addresses –

Class A – 10.0.0.0 to 10.255.255.255

Class B – 172.16.0.0 to 172.31.255.255

Class C – 192.168.0.0 to 192.168.255.255

It may not be a good idea to expose the range of private IP address you use within your organization to the outside world as it makes it easier for hackers to get access to your network (LAN). For this reason, it is recommended that you do not assign commonly assigned / easily guessable range of private IP addresses (like 192.168.0.1, 2, 3….) to the computers in your organization.

Applications of Public IP Address:

• A Web Server can be assigned with a public IP address so that people can reach the server from anywhere on the Internet.
• An IP Camera can be assigned with a public IP address so that the video from the IP Camera can be accessed from anywhere on the Internet.
• Remote Access to a Computer becomes easier if the computer has a public IP address.
• An Email Server can be hosted in your own premises using a public IP address.
• Public IP address can be used to obtain a unique SSL certificate for a website.
• Public IP address can be used to provide anonymous FTP access to few users.
• Large organizations / websites use their own public IP address to connect to the Internet.

What can you do if you don’t have a public IP address but still want the applications enabled by it?

Most of the applications mentioned above can be utilized without a public IP address as well – There are work around methods for the same.

For example, if you want to access your computer from a remote location (or) want to access your IP camera from a remote location, you can assign a Dynamic DNS (A domain name, instead of IP address) to those equipments. These (sub) domains are converted in to IP addresses by DDNS service providers (DynDNS, No-IP, etc).

Web Servers and Email Servers can be hosted with a shared hosting service provider. They may host multiple websites/ mail server accounts in a single server and share the same IP address for all the websites/ email accounts. Similarly, you can share your web-host’s SSL certificate as well if you don’t have a dedicated public IP address.

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