Use Tunnel to make IPV4 to IPV6 port translation

Il hoped to find a “socat” on Saas (for personnal use) to test a behaviour of a SMTP relay. But my relay is IPV6 only and the client to test it is IPV4 only). In searched any way to make a public IPV4 intermediate service to tunnel all tcp communications to my IPV6 server while the client only configurated to communicate with the IPV4 service.
I can not change the client (no warp possible). I found cloudflare tunnel, but i’m not sure he is able to do that.
Any help to solve this ?


If I understand you correctly, your goal is to expose your IPv6 SMTP Relay via a tunnel (cloudflared), without requiring any software on the client. This is not possible.

Cloudflare Tunnels use Cloudflare’s proxy, which only supports proxying HTTP Traffic. If you want to use non-http applications over your tunnel, like SMTP/Arbitrary TCP, you need the client to either run cloudflared (tcp only) or WARP Private Networking (tcp/udp/icmp supported)…

Cloudflare does have Cloudflare Spectrum, a reverse proxy for generic tcp/udp applications, but you would need Enterprise to use it with for SMTP (Arbitrary TCP/UDP).

Your best options are probably either to use a simple VPS with IPV4 & a gre/wireguard tunnel back to your IPv6 Server, or something like ngrok, which are both outside the scope of this forum.

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