IPv4 / IPv6 Checker
API & BackendTell IPv4 and IPv6 apart, expand or compress an IPv6 address, and check either one is valid.
Runs entirely in your browser — nothing is uploaded
Features
- Detects the version and validates the format of either.
- Expands IPv6 to all eight groups, or compresses it to RFC 5952 form.
- Spots IPv4-mapped addresses such as ::ffff:192.0.2.1.
- Classifies global unicast, unique local, link-local and multicast.
- Runs entirely in your browser.
How to use the IPv4 / IPv6 Checker
- 1Paste an address in either version.
- 2The version is detected automatically — no need to say which it is.
- 3Read the expanded and compressed forms, and what the address is used for.
Frequently asked questions
What is the difference between IPv4 and IPv6?
IPv4 uses 32 bits, written as four numbers like 192.168.1.1, which allows about 4.3 billion addresses — and the world ran out. IPv6 uses 128 bits, written as hexadecimal groups like 2001:db8::1, which is enough that exhaustion is not a concern. They are separate protocols: an IPv6-only host cannot talk to an IPv4-only host without a translator.
Why can the same IPv6 address be written several ways?
Because leading zeros in a group can be dropped and one run of zero groups can be replaced by "::". RFC 5952 sets the canonical form — lower case, no leading zeros, the longest zero run collapsed once — which is what the compressed output here gives you.
What is ::ffff:192.0.2.1?
An IPv4-mapped IPv6 address: an IPv4 address carried inside the IPv6 format so that dual-stack software can handle both with one code path. It is why server logs sometimes show ::ffff: in front of an otherwise ordinary IPv4 address.