Comment by orangeboats
21 hours ago
You can't selectively use IPv6 in the WAN and IPv4 in the LAN.
How would an IPv4 client send a packet to an IPv6 server? The IPv4 packet has only 4 bytes to spare for the destination address.
You can't.
Anything longer, even if it's just 1 bit, would require a new IP version.
You can run a 4to6 NAT, where specific v6 addresses (the ones you’re talking to) are aliased to reserved v4 addresses out of the PUA.
I have seen people suggesting this before, but it's problematic for a few reasons:
- If you are managing the 4to6 mappings manually, it's obviously not going to be scalable. Just to give people an idea, websites nowadays can connect to 10+ IPs in a single page due to CDN load balancing and stuff.
- If you are handling the mappings automatically, such as by monitoring DNS queries and creating dynamic mappings based on that, the issues become more insidious: applications with hardcoded IP literals would fail without an obvious reason.
The "solution" is that IPv6-only servers do not exist and will never exist.
I have encountered multiple IPv6-only domains - certain random domains were accessible through Chrome, but unreachable from any command line tools. Turns out they were IPv6-only, and Chrome was doing its own DNS resolution, while anything that was using the platform DNS stack was hitting a black hole between OPNsense and my ONT.