IPv4 Service Continuity Prefix
updates
- rfc-6333 — Dual-Stack Lite Broadband Deployments Following IPv4 Exhaustion
Extracted elements (8)
Rather than reserving a separate prefix for every IPv6 transition solution (such as 464XLAT) that needs a non-routed IPv4 prefix, RFC 7335 generalizes the existing DS-Lite reservation (192.0.0.0/29) to cover all such cases, avoiding address space fragmentation.
The 192.0.0.0/29 prefix is suitable for reuse across transition solutions because, as established in RFC 6333 for DS-Lite, this subnet is only present internally (e.g., between B4 and AFTR) and never emits packets from this prefix on the wire.
464XLAT (RFC 6877) requires the CLAT element—when embedded in a host such as a smartphone or CPE—to have an IPv4 address configured for the host network stack and for applications to bind IPv4 sockets, driving the same need for a reserved non-routed IPv4 prefix as DS-Lite.
The generalization of 192.0.0.0/29 from DS-Lite-specific to the broader IPv4 Service Continuity Prefix does not impact existing DS-Lite deployments using this address block.
A host MUST NOT enable two active IPv4 continuity solutions simultaneously in a way that would cause a node to have overlapping 192.0.0.0/29 address space.
The 192.0.0.0/29 prefix is designated as the IPv4 Service Continuity Prefix, reserved for any system that requires IPv4 addresses for backward compatibility with IPv4 communications in an IPv6-only network but does not emit IPv4 packets 'on the wire'.
IANA updated the IPv4 Special-Purpose Address Registry entry for 192.0.0.0/29, renaming it from 'DS-Lite' (RFC 6333) to 'IPv4 Service Continuity Prefix' (RFC 7335), with attributes: Source=True, Destination=True, Forwardable=True, Global=False, Reserved-by-Protocol=False.
RFC 7335 introduces no new security considerations beyond those described in RFC 6333 (DS-Lite) and RFC 6877 (464XLAT).