RFC 6052 / START HERE
IPv4 inside IPv6, before the details
RFC 6052 explains IPv4 addresses embedded inside IPv6 translator addresses. IPv4 and IPv6 are two versions of the Internet Protocol.
It gives a predictable way to place the 32 bits of an IPv4 address within a 128-bit IPv6 address, using a configured leading prefix.
The idea in one picture
Choose prefix
Place IPv4 bits
Recover address
A simplified picture of the idea; the chapters explain the actual mechanisms.
Why it exists
A device or gateway may need to represent an IPv4 peer while working with IPv6 addresses. This publication defines address mapping; routing, packet translation and DNS answers require additional mechanisms.
A familiar example
In a documentation-only example, prefix 2001:db8:122::/48 and IPv4 address 192.0.2.33 produce 2001:db8:122:c000:2:2100::. The reserved zero byte explains the unusual split. Correct bits alone do not make a service safe or reachable.
Helpful background
You can start here without reading another RFC. If these ideas are unfamiliar, these short introductions may help.
What you’ll learn next
Begin with chapter one, or choose a topic.
- Distinguish the address rolesAn IPv4-embedded IPv6 address carries 32 IPv4 bits. Its role depends on whether it represents an IPv4 node or is assigned to an IPv6 node for stateless translation.→
- Place the bits for six prefix lengthsA prefix is the leading fixed part of an address. Its bit length determines where the four IPv4 octets go, including the reserved u octet.→
- Compose and extract an addressUse the configured prefix length in both directions. The /48 worked example makes the reserved-byte boundary visible.→
- Choose a prefix within its deployment limitsThe Well-Known Prefix and an organization’s Network-Specific Prefix have different operational constraints. A correct bit layout alone does not authorize translation.→
- Route and filter the translated identityRouting advertisements and security checks must respect what the embedded address means. IPv6 spelling must not let a blocked IPv4 identity slip through.→
This introduction explains RFC 6052 (2010). Read the original RFC ↗