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IPv4 vs IPv6: Addresses, Public and Private Networks Explained

IPv4 uses 32-bit addresses while IPv6 uses 128-bit addresses; both route packets, can coexist on one device, and are separate from names, encryption and physical internet speed.

Timeline

  1. Name lookup: A device can use DNS to obtain one or more IPv4 or IPv6 addresses for a service.
  2. Address selection: A dual-stack device and network choose a reachable protocol path.
  3. Packet routing: Routers forward packets using the destination IP address while higher-layer protocols carry the application data.

An Internet Protocol address is a numerical label used to identify an interface and route packets across IP networks. It is not the same thing as a website name, an email address or a device's permanent identity. Domain Name System records can map a name to IPv4, IPv6 or both, and addresses can change as a device moves or a provider reassigns service. One phone can also hold several addresses at once for different interfaces and scopes. [1][2][6]

IPv4 uses 32-bit addresses, normally written as four decimal numbers separated by dots, such as 192.0.2.1. That design provides a finite address space whose freely available pools have been depleted in major registry regions. Networks extended IPv4 through conservation, address transfers and network address translation, which lets many devices use private addresses behind fewer public addresses. Those mechanisms keep IPv4 useful but add operational layers to a design created for a smaller internet. [2][3][4]

IPv6 is the successor protocol and expands the address field to 128 bits. Its usual notation uses hexadecimal groups separated by colons, with rules that can compress runs of zeroes. The much larger space supports extensive subnetting and simpler address configuration at scale. IPv6 also changes parts of the packet header and the handling of extensions; it is more than a longer spelling of the same IPv4 number, and the two versions are not wire-compatible. [1][2][6]

Public and private describe reachability and administrative use, not whether data is secret. IANA reserves three familiar IPv4 ranges—10.0.0.0/8, 172.16.0.0/12 and 192.168.0.0/16—for private networks, where the same numbers can be reused in many homes and organisations. Routers generally translate those addresses when users reach the public IPv4 internet. IPv6 has scoped and special-purpose addresses too, including link-local addresses and unique local addresses, but its design does not require copying every IPv4 NAT pattern. [3][4][5][6]

Migration is gradual because an IPv4-only system cannot directly exchange native IPv6 packets with an IPv6-only system. Many networks therefore use dual stack, assigning both versions and selecting a working path, while others use translation or tunnelling at boundaries. Seeing both an IPv4 and IPv6 address on a laptop is normal. It does not mean the device has two internet subscriptions, and disabling one version without understanding the network can make some services slower or unreachable. [1][2][7]

IPv6 is not automatically faster, private or encrypted. Performance depends on routing, access networks, servers and transition mechanisms. Both versions can carry protected or unprotected application traffic, so HTTPS, secure DNS choices, authentication and correctly configured firewalls still matter. A public address also does not by itself reveal a person's precise identity or location, although providers and services may combine address logs with other records. Protocol version should not be treated as a privacy verdict. [1][6][7]

For troubleshooting, first note whether an address contains dots or colon-separated hexadecimal, then identify its scope and the interface that owns it. A home router usually has provider-facing addresses plus internal ones, while each device has its own local configuration. Test DNS, IPv4 and IPv6 separately before blaming the application. For ordinary users, the practical goal is not to choose a winning protocol but to keep supported network software updated and let a correctly configured provider and device select the reachable path. [2][3][6][7]

Sources

  1. RFC 8200: Internet Protocol, Version 6 Specification
  2. IPv6 Information
  3. IANA Private-Use IP Addresses
  4. RFC 1918: Address Allocation for Private Internets
  5. RFC 4193: Unique Local IPv6 Unicast Addresses
  6. RFC 4291: IPv6 Addressing Architecture
  7. RFC 8305: Happy Eyeballs Version 2

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