6in4 / IPv6 tunnel
Carrying IPv6 across an IPv4-only path.
How widely is it used?
Still around, but being replacedShrinking as native IPv6 rollout continues, still useful in labs.
How it works
IPv6 packets are encapsulated in IPv4 (protocol 41) and sent to a broker that routes them onto the IPv6 internet, giving a routed prefix to a network with no native IPv6.
Connects
Device/network → tunnel broker
Protocols
6in4, GRE, Tunnel brokers
Typical users
Home labs, Networks awaiting IPv6 rollout
Main use case
Getting IPv6 connectivity where the ISP provides none.
Advantages
- Routed IPv6 prefix without ISP support
- Simple to set up
Limitations
- No encryption whatsoever
- Protocol 41 is often blocked by NAT
- Extra latency via the broker
Not safe on its own
This technology isolates traffic but does not encrypt it. Run IPsec or WireGuard on top if confidentiality matters.
Related VPN types
GRE over IPsec
GRE carries what IPsec alone cannot; IPsec encrypts it.
Generate configVPLS / Layer-2 VPN
Remote sites share one broadcast domain as if on the same switch.
Generate configSite-to-Site VPN
Two gateways hold a permanent tunnel so whole networks can talk.
Generate config