As IPv6 has matured and people have gained operational experience, various co-existence and transition techniques have either been shown to be unsatisfactory or have simply been overtaken by events. This section simply lists such techniques, with minimal explanation. Readers are advised to ignore these techniques for new deployments, and to consider removing them from existing deployments.
Tunneling IPv6 over IPv4, or the converse, remains fundamental to co-existence, although various specific tunnel mechanisms are listed below as obsolete.
Note that three such mechanisms (6to4, Teredo and ISATAP) have left behind them some operational security risks related to IPv4 protocol type 41, as described in Plight at the End of the Tunnel - Legacy IPv6 Transition Mechanisms in the Wild, preprint here.
-
Transmission of IPv6 over IPv4 Domains without Explicit Tunnels [RFC2529]. As far as is known, this was never deployed in practice.
-
IPv6 Tunnel Broker [RFC3053].
-
Connection of IPv6 Domains via IPv4 Clouds ("6to4") [RFC3056] [RFC3068]. The problems with this are documented in RFC 6343 and it was largely deprecated by RFC 7526.
-
Teredo: Tunneling IPv6 over UDP through Network Address Translations (NATs) [RFC4380].
-
SOCKS-based IPv6/IPv4 Gateway [RFC3089].
-
ISATAP [RFC5214].
-
6rd [RFC5569].
-
An Incremental Carrier-Grade NAT (CGN) for IPv6 Transition [RFC6264].
-
6a44 [RFC6751].
-
In the context of NAT64, RFC 7050 should no longer be used.