6to4 Tunnel Address Calculator

Calculate 6to4 tunnel IPv6 addresses from your IPv4 address. Generate 2002: prefix addresses and understand 6to4 tunneling.

What Is 6to4 Tunneling?

6to4 (RFC 3056) is an IPv6 transition mechanism that encapsulates IPv6 packets within IPv4 packets using protocol 41. It automatically generates a /48 IPv6 prefix from your public IPv4 address by prepending 2002:. While largely deprecated in favor of native IPv6, understanding 6to4 helps when troubleshooting legacy tunnel configurations.

For modern IPv6 connectivity, check if your ISP provides native IPv6 using our Dual-Stack Checker. Native IPv6 is always preferred over any tunneling mechanism.

6to4 Address Structure

Bits	Field	Value
0-15	6to4 Prefix	2002 (fixed)
16-47	IPv4 Address (hex)	Your public IPv4 in hex
48-63	Subnet ID	0000-ffff (65,536 subnets)
64-127	Interface ID	Device identifier

Pro Tip: 6to4 is deprecated (RFC 7526) due to reliability issues with the relay infrastructure. If you need IPv6 and your ISP doesn't offer it natively, use a tunnel broker like Hurricane Electric (tunnelbroker.net) which provides a stable, managed tunnel. Check native IPv6 availability with What Is My IP first — most major ISPs now support it.

Note: 6to4 requires a public IPv4 address — it does not work behind NAT with private addresses like 192.168.1.x. If you're behind carrier-grade NAT (CGNAT), 6to4 won't work. Teredo (another tunnel mechanism) was designed for NAT traversal but is also deprecated. Native IPv6 from your ISP is the correct solution.

Why 6to4 Was Deprecated

Issue	Impact	Modern Solution
Unreliable relay routers	Intermittent connectivity	Native IPv6 from ISP
Doesn't work behind NAT	Most home users affected	ISP-provided IPv6
Higher latency	Extra encapsulation overhead	Direct IPv6 routing
Security concerns	Relay trust issues	End-to-end IPv6

Key Takeaways

6to4 generates a /48 IPv6 prefix from your public IPv4 by prepending 2002: to the hex IPv4.
6to4 is deprecated (RFC 7526) — use native IPv6 from your ISP whenever possible.
It does not work behind NAT — requires a public IPv4 address.
For IPv6 without ISP support, tunnel brokers (Hurricane Electric) are more reliable than 6to4.
Check native IPv6 with Dual-Stack Checker and What Is My IP.

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Frequently Asked Questions

What is a 6to4 tunnel?

6to4 encapsulates IPv6 packets within IPv4 using protocol 41. It generates a /48 IPv6 prefix from your public IPv4 address with the 2002: prefix.

Is 6to4 still used?

6to4 is deprecated per RFC 7526 due to reliability issues. Native IPv6 or managed tunnel brokers are preferred.

Does 6to4 work behind NAT?

No. 6to4 requires a public IPv4 address. It does not work behind NAT or carrier-grade NAT.

What replaced 6to4?

Native IPv6 from ISPs is the intended replacement. For users without ISP IPv6, tunnel brokers like Hurricane Electric provide reliable alternatives.

How is 6to4 different from 6in4?

6to4 uses automatic relay discovery (anycast 192.88.99.1) while 6in4 uses explicitly configured tunnel endpoints. 6in4 (tunnel brokers) is more reliable.

About Tommy N.

Tommy is the founder of RouterHax and a network engineer with 10+ years of experience in home and enterprise networking. He specializes in router configuration, WiFi optimization, and network security. When not writing guides, he's testing the latest mesh WiFi systems and helping readers troubleshoot their home networks.