What is an IP Address?

An IP address (Internet Protocol address) is a unique numeric identifier assigned to every device connected to a network. It serves two purposes: identifying the device and providing a location for routing traffic to it.

IPv4 Addresses

The most familiar form is the IPv4 address — four numbers separated by dots, each ranging from 0 to 255. For example, 8.8.8.8 is Google's public DNS server. IPv4 addresses are 32 bits long, giving a theoretical maximum of about 4.3 billion unique addresses.

In the early days of the internet, this seemed like more than enough. Today, with billions of connected devices, the IPv4 address space is fully exhausted — all addresses have been allocated.

IPv6 Addresses

To solve the exhaustion problem, IPv6 was developed. IPv6 addresses are 128 bits long, written as eight groups of four hexadecimal digits separated by colons. For example, 2606:4700::1111 is Cloudflare's DNS server in IPv6.

IPv6 provides approximately 340 undecillion addresses — enough to assign a unique address to every atom on the surface of the earth and still have addresses left over.

Public vs. Private Addresses

Not all IP addresses are reachable from the internet:

• Public addresses are globally unique and routable on the internet. When you look up an IP in a BGP looking glass, you are querying public addresses.
• Private addresses are reserved for internal networks and are not routable on the public internet. The private ranges are:
  • 10.0.0.0/8 — 16 million addresses
  • 172.16.0.0/12 — 1 million addresses
  • 192.168.0.0/16 — 65,536 addresses

Your home router typically assigns private addresses to your devices internally and uses Network Address Translation (NAT) to share a single public address with the internet.

How IP Addresses Relate to BGP

Public IP addresses are organized into prefixes — contiguous blocks that are announced via BGP. Each prefix is originated by an autonomous system. When you look up an IP address, the looking glass finds the most specific BGP prefix covering that address and shows you the origin AS, the AS path, and other routing details.

Look Up an IP

Try looking up these well-known IP addresses:

• 8.8.8.8 — Google DNS
• 1.1.1.1 — Cloudflare DNS
• 208.67.222.222 — OpenDNS