Expand 6to4 Transition Address 2002:c000:0204::1
Expand a 6to4 transition address and understand how IPv4 addresses are encoded in the 2002::/16 prefix. Learn about 6to4 tunneling mechanisms.
Transition
Detailed Explanation
6to4 Transition Addresses
The address 2002:c000:0204::1 expands to:
2002:c000:0204:0000:0000:0000:0000:0001
6to4 Address Structure
6to4 addresses use the 2002::/16 prefix and encode an IPv4 address in groups 2 and 3:
| Group | Value | Meaning |
|---|---|---|
| 1 | 2002 | 6to4 prefix |
| 2 | c000 | First 2 bytes of IPv4 |
| 3 | 0204 | Last 2 bytes of IPv4 |
| 4 | 0000 | Subnet ID (optional) |
| 5-8 | ... | Interface ID |
Extracting the IPv4 Address
c000:0204
c0 = 192, 00 = 0, 02 = 2, 04 = 4
IPv4 = 192.0.2.4
So 2002:c000:0204::1 is a 6to4 address derived from IPv4 address 192.0.2.4.
How 6to4 Works
- A host with public IPv4 address
A.B.C.Dcreates the prefix2002:AABB:CCDD::/48 - IPv6 packets are encapsulated in IPv4 for transit across IPv4 networks
- A 6to4 relay router at the destination decapsulates and forwards the IPv6 packet
Current Status
6to4 is deprecated (RFC 7526) due to reliability and security issues. Modern alternatives include:
- NAT64/DNS64: For IPv6-only networks accessing IPv4 services
- 464XLAT: For IPv4 applications on IPv6-only networks
- Native dual-stack: Running both IPv4 and IPv6 simultaneously
Use Case
Primarily encountered in legacy network configurations and transition planning. Understanding 6to4 addresses helps when migrating from IPv4 to IPv6 and when troubleshooting historical tunnel configurations that may still be present in older infrastructure.