Public vs Private IP Addresses: What’s the Difference?

Every network, whether it’s the entire internet or your home Wi-Fi, needs a way to tell devices apart. That’s where IP addresses come in. An IP address is basically a unique ID made up of numbers separated by dots.

IP addresses can be public (or “white”), which are used to connect to the wider internet, or private (internal), which are used within local networks like your home or office.

Also, IPs can be static (they stay the same) or dynamic (they change over time), and they follow one of two standards: IPv4 or the newer IPv6.

In this article, we’ll break down what IP addresses are, how they work, and why understanding the difference between public and private IPs actually matters.

What Is an IP Address and Why Is It Needed?

An IP address (Internet Protocol Address) is a unique identifier assigned to every computing device on a network. It consists of numbers separated by dots.

When a user visits a website, a request is sent from their IP to a remote server, which then responds with the web page. Without IP addresses, computers and smartphones wouldn’t be able to locate each other online. They wouldn’t know where to send or receive data.

An IP address is comparable to a postal code, which tells the postman where to deliver a letter and tells the recipient where it came from.

What Does an IP Address Look Like?

All IP addresses are unique, since they identify individual devices in a network. However, they follow the same structural format.

Examples of IPv4 addresses, which consist of four integers:

• 78.129.229.78
• 172.16.254.1
• 203.0.113.5
• 192.162.74.34
• 184.12.203.67

Examples of IPv6 addresses, made up of eight hexadecimal blocks:

• 2606:4700:4700:0db8:2001:1111
• 2001:4860:4860::8888
• fe80::1a2b:3c4d:5e6f:7g8h
• 1050:0:0:0:5:600:300c:326b
• 2001:0db8:aa10:0001:7g8h::00fb

Some IPv6 addresses may contain two colons in a row (::), which represent a sequence of zeroes. For example:

• Full: 2001:0db8:0000:0000:0000:0000:0000:1
• Shortened: 2001:db8::1

However, the double colon (::) can only appear once in an IPv6 address, or else it would be unclear how many zeroes are omitted.

For instance, the address 2001::5e6f::4860 could ambiguously mean:

• 2001:0000:0000:5e6f:0000:4860
• or 2001:0000:5e6f:0000:0000:4860

If no double colon is used, then either the address is complete or contains full zeroes.

Most operating systems allow local communication via a reserved domain name — localhost.

Types and Categories of IP Addresses

It’s important to distinguish between the types and categories of IP addresses.

Categories of IP addresses:

• Public IP (Public): Identifies a device on the global internet.
• Private IP (Private): Identifies a device within a local network.

Types of IP addresses:

• Static: The IP address remains the same each time the device connects to the network. Used by corporate servers.
• Dynamic: A new IP address is assigned each time the device connects. Used by home devices.

Classification by protocol:

• IPv4: Four integers (0–255) separated by dots, 32 bits in size, up to 4.3 billion addresses. E.g., 192.168.1.1
• IPv6: Eight hexadecimal blocks, 128 bits in size, nearly unlimited addresses. E.g., fe80::1a2b:3c4d:5e6f:7g8h

In summary, categories define whether an IP is public or private, while types define whether it's permanent or temporary.

What Is a Public IP and How Does It Work?

A public IP address is a public (external) IP that identifies a computing device on the internet.

Regular internet users connect to websites and game servers using public IPs.

Domain names (like hostman.com), resolved through DNS (Domain Name System), are simply a user-friendly wrapper around public IP addresses.

Thus, having a public IP is a prerequisite for any computing device to interact directly with the internet.

What Is a Private IP and Why Is It Used?

A private IP address is a private (internal) IP used to identify a device within a local network.

The main purpose of private IPs is to conserve public IPs, which are limited in number.

IPv4 uses 32 bits to encode IPs, yielding a range from 0.0.0.0 to 255.255.255.255, totaling 4,294,967,296 possible addresses (256^4, not 255^4, because counting starts from 0).

With over 8 billion people on Earth, and each using multiple devices (laptops, smartphones, TVs, smart speakers, etc.), there's clearly not enough public IPs for everyone.

This limitation is addressed with private IPs. These are used within local networks to identify multiple devices, all of which connect to the internet through a single public IP that represents the whole network globally.

Private IPs solve several problems:

• Communication: Devices like computers, printers, servers, and storage systems can exchange data within a local network without each requiring its own public IP. Thousands of private IPs can coexist under a single public IP.
• Architecture: Enable dividing networks into subnets, like one for employees and another for guests.
• Security: Since private IPs are not accessible from the internet, they are shielded from direct attacks like DDoS or port scanning, reducing the risk of hacking.

In short, private IP addresses:

• Enable local communication.
• Conserve public IP addresses.
• Reduce internet traffic load.
• Structure local networks.
• Increase device security.

A practical example:

A home Wi-Fi router connects multiple devices (PC, phone, TV, smart speaker). All these are part of the local network and have private IPs.

However, the Wi-Fi router itself is part of the global Internet and has a public IP address.

Converting a Public IP to a Private IP

For an internal device to access the external internet, its private IP address is converted into a public IP using NAT (Network Address Translation) technology.

The conversion occurs in several steps:

1. Request: A device with a private IP sends a request to the Internet.
2. Translation: A router with NAT receives the request and replaces the private IP with its own public IP.
3. Response: The remote server receives the request from the router’s public IP and sends back a response.
4. Reverse Translation: The NAT router receives the response and, using a matching table (a list of private IPs of internal devices), forwards it to the correct internal device.

In essence, NAT rewrites IPs in data packets, enabling private IP devices to interact with the internet. There are several types of IP substitution:

• SNAT (Source NAT): Replaces IP in outgoing packets. Outbound requests from a private IP are forwarded through a public IP.
• DNAT (Destination NAT): Replaces IP in incoming packets. Inbound requests to a public IP are forwarded to an internal device’s private IP.
• PAT (Port Address Translation): Replaces IP in outgoing packets while retaining the original port. A variation of SNAT.
• Full Cone NAT: Replaces IPs in both directions. Connections can be initiated by internal or external devices. Combines SNAT and DNAT.
• Restricted NAT: Replaces IPs in both directions. Only internal devices can initiate connections. A limited version of SNAT + DNAT.
• Symmetric NAT: Replaces IPs for each unique connection, creating a new mapping every time. Only internal devices can initiate connections. A modified SNAT + DNAT combination.

Until the world fully transitions to IPv6, which removes the limitations of IPv4, NAT will continue to be used in Wi-Fi routers, modems, and local networks.

Of course, sharing a single public IP among multiple devices isn’t always ideal.

For example, if three players are gaming on a remote server using the same Wi-Fi router, and one gets IP-banned for cheating, all three could be banned, which seems unfair.

However, in such cases, rebooting the router may assign a new dynamic public IP address.

Also, the router's bandwidth is shared among all connected users. So, the more devices are connected to a router, the slower the connection speed for each.

Where Do public and Private IP Addresses Come From?

Regardless of the IP type, a common question is: Who assigns these identifiers to devices? The answer is: DHCP.

DHCP (Dynamic Host Configuration Protocol) is a technology that automatically assigns IP addresses to all new devices in a network.

Whether it's a local or global network, IP assignment follows these steps:

1. Discovery: A device connects to the network and sends a DHCPDISCOVER request for an IP.
2. Offer: The DHCP server processes the request, finds a free IP, and replies with a DHCPOFFER, including IP, subnet mask, gateway, lease time, and DNS servers.
3. Request: The device accepts the IP and sends a DHCPREQUEST.
4. Acknowledge: The DHCP server confirms with a DHCPACK. The device is now authorized for the lease duration.

In some cases, a private IP can be manually set on a device, which it then proposes to the DHCP server.

A public IP can only be manually set if it is static and pre-assigned by an ISP.

If an IP conflict arises (two devices use the same IP), the DHCP server reassigns IPs to both.

Public vs Private IP: Key Differences

Although public and private IPs are structurally identical, they differ in usage context:

• Public IPs are assigned by an ISP via a DHCP server and are required for global internet access.
• Private IPs are assigned by a local administrator (via DHCP or manually) and are for local network identification.

A public IP can connect to the Internet directly. A private IP can only connect to the Internet through NAT using a public IP.

Public IPs can be static or dynamic, while private IPs are typically static.

When Do You Need a Public IP and When a Private IP?

It’s incorrect to view public and private IPs as alternatives. For Internet access, a public IP is essential — without it, the global network is inaccessible.

• A public IP is needed when a device must be accessible from the Internet — typically web servers or game servers.
• A private IP is needed for identifying devices in a local network — such as computers, smartphones, routers, or printers.

In reality, local and global networks are interconnected.

Multiple devices in a local network may have unique private IPs, but all access the Internet through a single public IP.

Conclusion

• Public IPs face outward to the global network; private IPs face inward to local networks.
• A public IP is essential for Internet access.
• A private IP is vital for internal network organization — separating devices and conserving limited public IPs.
• Public IPs are assigned by ISPs, while private IPs are managed by local admins. Both use DHCP to automate the process.
• Typically, public IPs are dynamic, and private IPs are static.
• A full shift from IPv4 to IPv6 will eventually eliminate the need for private IPs — but this will take time, resources, and infrastructure upgrades.