What Is an IP Address? | NOC.org

What Is an IP Address?

An IP address (Internet Protocol address) is a unique numerical label assigned to every device connected to a network that uses the Internet Protocol for communication. It serves two fundamental purposes: identifying the host or network interface, and providing the location of the device in the network so traffic can be routed to it.

Every time you visit a website, your browser uses DNS to resolve the domain name into an IP address, then connects to that address to retrieve the page. Without IP addresses, there would be no way for data packets to find their destination across the internet.

IPv4 vs. IPv6

There are two versions of IP addresses in active use today:

• IPv4 uses 32-bit addresses written in dotted decimal notation — for example, 192.168.1.1. IPv4 provides approximately 4.3 billion unique addresses. This seemed like plenty in the 1980s, but address exhaustion became a real problem as the internet grew.
• IPv6 uses 128-bit addresses written in hexadecimal groups separated by colons — for example, 2001:0db8:85a3::8a2e:0370:7334. IPv6 provides 340 undecillion addresses (3.4 x 10³⁸), effectively eliminating the exhaustion problem for the foreseeable future.

Most of the internet currently runs on IPv4, with IPv6 adoption growing steadily. Modern servers and CDN infrastructure typically support both protocols through dual-stack configurations.

Public vs. Private IP Addresses

Not all IP addresses are routable on the public internet. The distinction between public and private addresses is critical for understanding how networks are structured:

• Public IP addresses are globally unique and routable on the internet. Your web server's IP address is public — anyone on the internet can send packets to it. Public IPv4 addresses are managed and allocated by regional internet registries (RIRs).
• Private IP addresses are reserved for use within local networks and are not routable on the public internet. The most common private ranges are 10.0.0.0/8, 172.16.0.0/12, and 192.168.0.0/16. Devices on a home or office network typically use private addresses and reach the internet through a router performing Network Address Translation (NAT).

In server environments, it is common for backend services (databases, caches, application servers) to communicate over private IP addresses while only the web-facing tier exposes a public IP.

Static vs. Dynamic IP Addresses

IP addresses can be assigned permanently or temporarily:

• Static IPs do not change. Servers, firewalls, and network infrastructure use static IP addresses so that DNS records, firewall rules, and access control lists remain valid over time.
• Dynamic IPs are assigned by a DHCP server and may change each time a device connects. Most home internet connections and employee workstations use dynamic addresses.

For web hosting and CDN configurations, static IP addresses are essential. DNS A records point a domain to a specific IPv4 address, so that address must remain stable. If the IP changes, DNS must be updated — and until the old TTL expires, some visitors may still be routed to the old address.

IP Addresses in DNS and CDN Context

Authoritative DNS servers are responsible for translating domain names into IP addresses. When you configure your domain to use a CDN, you typically point your DNS records to the CDN's IP addresses (or use a CNAME record) rather than directly to your origin server's IP. This allows the CDN to intercept traffic, serve cached content, and filter malicious requests before they reach your infrastructure.

Protecting your origin server's real IP address is a key security practice. If an attacker discovers the origin IP, they can bypass the CDN and attack the server directly. Best practices include restricting origin firewall rules to only allow traffic from the CDN's IP ranges and never exposing the origin IP in DNS history or email headers.