IPv4 ↔︎ IPv6 (mapped)
Convert between IPv4 and IPv4-mapped IPv6 (::ffff:x.x.x.x).
About This Tool
The IPv4-Mapped IPv6 Converter translates between standard IPv4 addresses and their IPv4-mapped IPv6 equivalents (::ffff:x.x.x.x format). IPv4-mapped IPv6 addresses are used in dual-stack systems to represent IPv4 addresses within the IPv6 address space, enabling IPv6-only applications to communicate with IPv4 hosts. This mechanism is essential for IPv6 transition scenarios, socket programming with AF_INET6, and understanding how modern operating systems handle both IP versions simultaneously. The tool provides both compressed and expanded formats along with the dotted-quad notation variant.
How to Use
- To convert IPv4 to IPv6: Enter an IPv4 address (e.g., 192.0.2.1) and click the arrow button
- View the mapped IPv6 address in compressed format (::ffff:192.0.2.1)
- See the expanded format (0000:0000:0000:0000:0000:ffff:c000:0201)
- View the dotted format (::ffff:192.0.2.1) which uses IPv4 notation in the last 32 bits
- To convert back: Enter an IPv4-mapped IPv6 address in any format and click the arrow
- The tool accepts both ::ffff:192.0.2.1 and ::ffff:c000:0201 notations
- Error messages will appear if the IPv6 address is not a valid IPv4-mapped address
Features
- Bidirectional conversion between IPv4 and IPv4-mapped IPv6
- Shows compressed, expanded, and dotted-quad formats
- Accepts multiple IPv6 input notations
- Validates that IPv6 addresses are proper IPv4-mapped addresses
- Displays all representation variants for learning
- Real-time conversion with instant results
- Clear error messages for invalid inputs
- RFC 4291 compliant conversion
Common Use Cases
- Understanding dual-stack networking and IPv6 transition mechanisms
- Socket programming with AF_INET6 that accepts both IPv4 and IPv6
- Configuring applications that use IPv6 sockets for IPv4 connections
- Debugging network issues in dual-stack environments
- Learning how operating systems represent IPv4 in IPv6 contexts
- Working with libraries that use IPv4-mapped addresses internally
- Analyzing packet captures from dual-stack systems
- Configuring firewalls and access control lists in mixed environments
- Understanding ::ffff:0:0/96 prefix behavior
- Educational purposes for IPv6 transition learning
Technical Details
IPv4-mapped IPv6 addresses represent IPv4 addresses within the IPv6 address space using the special ::ffff:0:0/96 prefix. The last 32 bits contain the IPv4 address.
Format Structure:
- Prefix: 80 bits of zeros (0000:0000:0000:0000:0000)
- Mapping: 16 bits of ones (ffff)
- IPv4 Address: Last 32 bits (the IPv4 address)
Example: 192.0.2.1 (0xC0.0x00.0x02.0x01)
- Compressed: ::ffff:192.0.2.1 or ::ffff:c000:0201
- Expanded: 0000:0000:0000:0000:0000:ffff:c000:0201
- Binary: 96 zero bits + 16 one bits + 11000000 00000000 00000010 00000001
RFC 4291 Specification:
IPv4-mapped IPv6 addresses are defined in RFC 4291 section 2.5.5.2. They allow IPv6 applications to communicate with IPv4 hosts using IPv6 APIs:
- Format: ::ffff:a.b.c.d where a.b.c.d is the IPv4 address
- Prefix: ::ffff:0:0/96
- Not routable on the Internet (used internally by systems)
Dual-Stack Socket Behavior:
When an application creates an IPv6 socket (AF_INET6) on a dual-stack system:
- It can accept connections from both IPv4 and IPv6 clients
- IPv4 connections appear as IPv4-mapped IPv6 addresses
- Example: IPv4 client 192.0.2.1 appears as ::ffff:192.0.2.1 to the IPv6 socket
- This allows a single socket to handle both protocols
Common Notations:
- ::ffff:192.0.2.1 (dotted-quad notation, most readable)
- ::ffff:c000:0201 (hexadecimal notation)
- 0:0:0:0:0:ffff:192.0.2.1 (uncompressed with dotted-quad)
Important Notes:
- IPv4-mapped addresses are different from IPv4-compatible addresses (::a.b.c.d, now deprecated)
- They are not routable on the IPv6 Internet
- Used for internal system representation only
- Some systems can disable IPv4-mapped address support for security