IP Address Converter

About the IP Address Converter

Type or paste an IP address in any notation and get every other form at once: for IPv4 the dotted, integer (unsigned and signed), hexadecimal, octal and binary forms, the IPv4-mapped and NAT64 IPv6 forms, the 6to4 prefix and the reverse-DNS name; for IPv6 the compressed form of RFC 5952, the fully expanded form, the 128-bit integer, binary and the ip6.arpa name.

Odd-looking hosts such as 0x7f.1, 2130706433 or 017700000001 are decoded exactly as browsers decode them — by the IPv4 parser of the WHATWG URL Standard — with each part explained, which makes this useful for checking suspicious links and server-side request filters. The address is then looked up in a snapshot of the IANA special-purpose, address-space and multicast registries, so you can see at a glance whether it is public, private, documentation, loopback, multicast or reserved. Everything runs in your browser.

Common uses

• Converting addresses stored as integers in databases and logs (MySQL INET_ATON, PostgreSQL, analytics exports) back to dotted form, and the other way round.
• Checking where a suspicious link with a numeric or hexadecimal host really points.
• Testing allow-lists and SSRF protections against every way a client may write the same address.
• Writing IPv6 addresses consistently for documentation, firewall rules and log searches.
• Finding the reverse-DNS (PTR) name to configure for a mail or web server.

Why browsers accept 0x7f.1 and 2130706433

When a URL’s host ends in a number, browsers parse it as IPv4 using rules inherited from the classic inet_aton() function, now specified in the WHATWG URL Standard:

• The host is split at dots into one to four parts.
• Each part is decimal, octal if it starts with 0, or hexadecimal if it starts with 0x.
• Every part except the last is one byte (0–255); the last part fills all remaining bytes — so 127.1 is 127.0.0.1 and 2130706433 alone is the whole 32-bit address.
• Anything else that ends in a number — 256.1.1.1, 1.2.3.4.5, 09 — makes the URL invalid.

The converter follows these steps exactly, and its tests compare thousands of random hosts with the WHATWG URL parser of Node.js. Security filters that compare host strings instead of parsed addresses can be bypassed with these forms, which is why server-side code should parse URLs the same way the client will.

IPv6 notation and addresses inside addresses

IPv6 addresses have one canonical text form (RFC 5952): lower-case hex, leading zeros dropped, and the longest run of two or more zero groups replaced by :: (the first one if two runs are equally long). The expanded form writes all 32 digits.

Some prefixes carry an IPv4 address inside the IPv6 one, and the converter extracts it:

• IPv4-mapped ::ffff:a.b.c.d — how dual-stack software represents IPv4 peers (RFC 4291).
• NAT64 64:ff9b::/96 — IPv6-only networks reaching IPv4 servers (RFC 6052). The well-known prefix must not be used with private IPv4 addresses.
• 6to4 2002::/16 — the site’s IPv4 address in bits 16–47 (RFC 3056).
• Teredo 2001::/32 — server and client addresses and the client’s port (RFC 4380).

For link-local and other addresses whose last 64 bits contain ff:fe, the MAC address of the network card is shown, because such identifiers are built from it (RFC 4291 Appendix A).

What the registry properties mean

The IANA special-purpose registries (RFC 6890, updated by RFC 8190) describe each block with five properties:

• Source / Destination: whether the address may appear as the sender or the receiver of a packet.
• Forwardable: whether routers may forward packets with it.
• Globally reachable: whether it works across the public internet — private (RFC 1918), shared CGNAT space (100.64.0.0/10), loopback, link-local and documentation blocks are not.
• Reserved by protocol: whether a protocol specification reserves it for special behaviour.

For ordinary addresses, the page shows which regional internet registry IANA allocated the block to (for example APNIC for 1.0.0.0/8). That is a block-level allocation: the organisation using an address today is found with an RDAP / WHOIS lookup.

Limitations

• Host names are not resolved — no DNS lookups are made.
• For non-ASCII input, only the conversions that matter for IP addresses are applied (full-width digits and letters, ideographic dots, percent-escapes); full IDNA processing of domain names is not.
• The registry information is a snapshot of the IANA registries; newer assignments may be missing.
• A zone index such as %eth0 is shown but not checked: it only exists on the computer that uses it.

Privacy

Everything happens in your browser. What you enter or open here is not uploaded or stored by MySmartCoPilot.