How to recognize each format
An IPv4 address contains four decimal numbers separated by dots, such as 198.51.100.24. It contains 32 bits, which limits the total address space. An IPv6 address contains hexadecimal groups separated by colons, such as 2001:db8:42::24. It contains 128 bits and can shorten consecutive zero groups with ::.
| Characteristic | IPv4 | IPv6 |
|---|---|---|
| Address size | 32 bits | 128 bits |
| Common notation | Four decimal groups | Hexadecimal groups |
| Address sharing | NAT and CGNAT are common | Usually globally unique prefixes |
| Local-only example | 192.168.1.20 | fe80::1 link-local |
| Broadcast | Supported | Replaced by multicast mechanisms |
Why IPv4 commonly uses NAT
The public IPv4 pool is too small to give every modern device a unique public address. Home NAT allows devices with private addresses to share one public address. Providers may add CGNAT so multiple customer routers share another public layer. NAT conserves addresses, but inbound connections need explicit mappings and can fail when the user does not control every translation layer.
Does IPv6 remove the need for a firewall?
No. IPv6 can give a device a globally routable address, but routable does not mean that unsolicited traffic should be accepted. A properly configured router uses a stateful firewall to permit return traffic for connections initiated from inside while rejecting unexpected inbound attempts. Disabling the firewall is not an IPv6 troubleshooting shortcut.
What is dual stack?
A dual-stack network supports both protocols. A browser resolves a hostname and chooses a reachable address, often preferring IPv6 when it works. The same device can therefore present an IPv6 address to one service and an IPv4 address to another. This is normal and does not automatically indicate a leak.
Transition systems complicate the picture. Some mobile and broadband networks carry IPv4 traffic across an IPv6 core, synthesize addresses with NAT64, or use provider relays. The public address observed by a destination reflects the final protocol and exit used for that connection.
IPv6 privacy addresses
Modern operating systems can generate temporary IPv6 interface identifiers for outbound connections. This reduces the value of a stable device identifier within the assigned prefix. The network prefix can still remain recognizable, and websites still see the temporary public address used for the connection. Privacy addressing is not the same as anonymity.
Why only one protocol may appear
- The ISP may provide only IPv4 or may not delegate an IPv6 prefix correctly.
- The router may have IPv6 disabled or may block required control traffic.
- A VPN may tunnel IPv4 but disable IPv6 to prevent traffic escaping outside the tunnel.
- DNS may return only one address family for a destination.
- A broken IPv6 path may cause the browser to fall back to IPv4.
A safe troubleshooting sequence
- Run the IP checker and record which protocol appears.
- Check the router status for both an IPv4 WAN address and an IPv6 delegated prefix.
- Test without browser extensions that intentionally proxy traffic.
- If using a VPN, check the provider’s documented IPv6 behavior before changing settings.
- Do not expose devices by disabling the router firewall.
Interpretation tip: seeing IPv6 is not proof that IPv4 is unavailable, and seeing IPv4 does not prove that the access network lacks IPv6. The destination and browser choose one path for each connection.