http://www.rfc-editor.org/rfc/rfc7335.txt
RFC 7335: IPv4 Service Continuity Prefix, C. Byrne2014-08-01T23:00:00-00:00Dual-Stack Lite (DS-Lite), defined in RFC 6333, directs IANA to reserve 192.0.0.0/29 for the Basic Bridging BroadBand (B4) element. Per this memo, IANA has generalized that reservation to include other cases where a non-routed IPv4 interface must be numbered as part of an IPv6 transition solution.