Have you ever wondered how your smartphone, computer, or other devices access the internet? How they connect to both local networks and global sites and services? A key enabling technology is IP addressing – the networking "phone numbers" enabling these connections.
In this post, we‘ll explore the core concepts around IP addressing, specifically diving into the crucial differences between public and private IP addresses. I‘ll explain in depth how they function, key benefits and tradeoffs, address ranges, use cases, and more – speaking as both a technology expert and a friend.
My goal is to help demystify these foundational networking building blocks, so you can better understand how devices communicate on both local networks and the global public internet.
Let‘s get started!
Public and Private IP Addresses: A Quick Overview
At the highest level, IP addresses serve as unique identifiers allowing computers and other devices to communicate directly. Just like houses have physical mailing addresses to route postal mail, devices have IP addresses routing digital communications.
There are two primary types of IP addresses:
Public IP Addresses: Globally-unique addresses identifying networked devices on the public internet. Public IPs facilitate communication across the broader internet.
Private IP Addresses: Addressing used locally to identify devices on private, isolated local area networks (LANs). Private IPs enable internal communications between devices on these closed subnets.
Key Differences:
| Public IP Addresses | Private IP Addresses | |
|---|---|---|
| Accessibility | Global – Allow public internet access | Local – Only allow access within private networks |
| Uniqueness | Globally unique addresses | Duplicate use allowed on private LANs |
| Management | Assigned by ISPs | Assigned locally by network admins |
| Security | More exposed on public internet | More secure on isolated local networks |
With this quick overview of public versus private IP addresses, let‘s now dive deeper comparing the two.
Private IP Addresses and Address Ranges
First, a closer look at private IP addresses often used within homes and organizations.
As the name suggests, private IP addresses uniquely identify devices locally on private, closed networks. These ensure devices can communicate with each other on local area networks (LANs) within an organization, without being publicly addressable across the broader public internet.
Some common private IP address ranges include:
- Class A –
10.0.0.0to10.255.255.255 - Class B –
172.16.0.0to172.31.255.255 - Class C –
192.168.0.0to192.168.255.255
For example, your home WiFi router likely assigns private addresses to devices starting with 192.168.1.xxx. This places devices into a private Class C subnet.
Similarly, within a corporate network, devices may be assigned to private IP address subnets like 10.183.64.xxx.
These private IP ranges are defined in RFC 1918 as being reserved for local communications. Public internet traffic cannot be directly routed to these private address spaces.
Being isolated locally, private IP addresses may be assigned dynamically as devices connect to the network. The tradeoff of this local reuse is that no two devices can have the same private IP address within the same logical subnet at the same time. Conflicts would prevent unique local addressing enabling communication.
But in general, extensive private IP reuse across entirely separate private networks is not an issue – since those layers stay self-contained to begin with.
Network Address Translation (NAT)
You may be wondering – if devices utilize private IP addresses on local networks, how do they access the public internet?
This is thanks to Network Address Translation (NAT).
NAT technology provides IP address translation between public and private networks. It allows devices on private subnets with unrouteable IP addresses to communicate out to the public internet by mapping those private IPs to the public IP address of a NAT gateway device.
Concretely, home and organization networks sit behind router devices that serve as NAT gateways to translate outbound connection requests from private IP addresses on the LAN to the singular public IP address on the gateway.
When responses come back destined to the public IP of the gateway, it maps those packets back to the correct internal private IP address that made the initial request. This enables internet connectivity from the local network.
By allowing extensive private IP address reuse behind public IP gateway aggregation points, NAT slows public IP address exhaustion allowing the still ongoing expansion of devices connecting to the internet. Today over 464 million NAT gateways exist allowing private networks access.
And NAT will continue playing a crucial role in the transition from IPv4 to IPv6 networking (more later).
Now, let‘s shift our focus to public IP addresses that serve a very different purpose – uniquely identifying devices globally across the open internet.
Public IP Addresses
In contrast to private addresses used locally on LANs, public IP addresses serve a distinct role: publicly identifying networked devices across the global public internet. They facilitate open communication between sources and destinations across the broader networked world.
Public IP addresses get assigned in blocks to Internet Service Providers (ISPs) by regional internet registries like ARIN and RIPE NCC. ISPs then allocate public IP addresses to home internet connections and organizations.
These public IP addresses cannot be arbitrarily chosen – they must be assigned from designated public address blocks in order to avoid conflicts. Public IP addresses uniquely pinpoint specific endpoints across the global internet routing fabric.
For example, a web server hosting a public website requires a public IP address reachable by anyone across internet backbone networks. Client requests can arrive at the static public IP, with responses routed back to visitor devices.
Similarly, internet-connected smart home devices, gaming consoles, and streaming video players typically use public IPs to facilitate access to external public-facing services and content.
However, clients typically connect from transient private IP addresses behind NAT gateways as described earlier. This aligns with a typical pattern on today‘s internet of clients with private IPs initiating connections to public IP servers providing services.
Public IP addresses help power public cloud services, websites, APIs, media delivery – much of the vibrant, interconnected applications powering today‘s digital world.
Security: Public vs Private IP Tradeoffs
Public and private IP approaches carry distinct security profiles:
Private IP Security: Private networks provide increased security through isolation from the public internet. Without external routability, discovery and access from public threats is very limited. Communications stay local.
Public IP Exposure: Public IPs aid global interconnectivity but sacrifice obscurity. Services reachable from public IP addresses may be discovered and vulnerable to attacks like DDoS. Additional threat monitoring and protection is key for public assets.
Hybrid environments leverage both – private IPs protecting assets locally, with public IPs carefully exposing only what‘s necessary for broader external access. Strict firewall policies can help restrict traffic between network zones.
The principle of "defense in depth" applies – using both close control of public access and robust inner defenses even for private networks, avoiding a false sense of security.
Public Internet Address Changes
The global internet still predominantly relies on the IPv4 protocol standardized in 1981, which provides approximately 4 billion unique addresses – now fully allocated as more devices come online!
This hampers growth of the public internet without some changes. The successor IPv6 fortunately massively expands available address space – but adoption is still gradually ramping up.
Multiple techniques have evolved to cope with IPv4 address exhaustion like NAT described earlier, along with dynamic allocation and tighter policies to conserve allocation. But legacy IPv4 remains common today.
Longer term, adoption of IPv6 will provide effectively unlimited global address capacity using its 128-bit addresses. Support for IPv6 has grown substantially, now reaching over 30% of Google users. But legacy DHCPv4 and NAT traversal will still be required during this transition phase.
For now, organizations use IPv4 space conservatively. But longer term, IPv6 plus private networking will offer effectively unlimited global and local addressing capacity to connect people and devices.
Finding Your Public and Private IP Address
To wrap up our comparison, let‘s discuss how to find your own public versus private IP address…
Finding Your Public IP:
Discovering your public IP address is straightforward from any internet-connected device:
- Google Search for "What is my IP address"
- Visit sites like WhatIsMyIPAddress.com
- Query command-line utilities like
curl ifconfig.me
Finding Your Private IP:
Uncovering your private IP address assigned on a LAN requires checking your internal network adapters‘ configurations:
- Windows: Open Control Panel -> Network & Internet -> Network Connections
- MacOS: Click the Apple Icon -> System Preferences -> Network -> View status next to connected network
- Linux: Check
ifconfigorip addr showcommand output for the active non-loopback interface - Smartphones: Consult wireless/network settings showing currently assigned private IP
So in summary – public IPs can be externally queried online, while private IPs require inspecting internal network status from the specific device.
Common Usage Scenarios
Let‘s discuss some common use cases taking advantage of public and private IP addresses:
Public IP Address Use Cases:
- Hosting websites and web applications accessible on the public internet
- Cloud services offered to global end users like IaaS, PaaS, SaaS
- Internet-facing databases, API servers, communications platforms
- Media servers streaming audio, video content publicly
- Online gaming servers allowing players to connect across the internet
- General outbound access to public internet sites and services
Private IP Address Use Cases:
- Connecting devices like laptops, printers, phones on a local home or office network
- Accessing locally-hosted intranet sites internal to an organization
- Communicating with servers hosting private databases, apps, resources
- Streaming media, gaming, IoT within a local wired/wireless network bubble
- Segmenting device access across departments/zones using VLAN subnetworks
So in summary:
- Public IP addresses facilitate publicly-reachable services and global connectivity
- Private IP addresses help enable local device communications and access to internal resources
Public vs Private IP Addresses: Pros and Cons
To recap, what are some of the tradeoffs of using public vs private IP addresses?
| Public IP Address Pros | Public IP Address Cons | |
|---|---|---|
| Accessibility | Enables globally reaching services across the open internet | More exposed – Increased vulnerability to discovery & attacks |
| Convenience | Allows easy direct access publicly | Requires ISP assignment and ongoing management |
| Utility | Uniquely identifies devices across global internet | IPv4 exhaustion requires migrations to IPv6 over time |
| Private IP Address Pros | Private IP Address Cons | |
|---|---|---|
| Security | Local isolation limits external threats | Lack of routed access sacrifices public connectivity |
| Simplicity | Allows locally reuseable "Free" private IPs | Requires NAT gateways to reach internet |
| Scale | Facilitates massive device density via subnetting | Cannot directly participate publicly on the open internet |
Depending on accessibility, security and functional requirements – leveraging public and/or private IP approaches provides distinct benefits.
Wrapping Up: Public vs Private IP Address Differences
I hope this post has helped explain some key concepts around public and private IP addressing many of our home consumer devices and workplace enterprise networks rely on everyday without us even realizing it!
We covered quite a bit:
- Definitions – Public IPs identify devices globally on the internet, private IPs do so locally on private LANs
- Key differences in management, security, accessibility, and functionality
- How Network Address Translation (NAT) gateways connect private networks to the public internet
- IP address ranges from standards like RFC 1918 used in private networks
- Public IPv4 address exhaustion motivates transitions to IPv6 addressing long-term
- How to discover your own public vs private IP address
- When to leverage public vs private IP addresses depending on use case needs
With strong foundations around public and private IP addressing, concepts like subnets, VLANs, and CIDR notation become much easier to pick up. But those more intermediate topics may be future blog post ideas!
I aimed for a conversational, easy-to-digest yet information-rich tone explaining these crucial networking foundations. Please let me know in the comments if any areas need clarification or expansion! I‘m passionate about demystifying technical topics so they become more accessible to broader audiences.
On behalf of my inner geek, thanks for learning with me!