- can't decide on a port in the same message
- don't suffer from NAT port randomization
I'm not saying it will never happen, but the Venn diagram of this being the minimum complexity solution just doesn't seem very large?
I don’t think I’ve ever seen it done successfully and have often wondered if it’s for a lack of use cases or due to its bad success rate and complexity compared to UDP hole punching.
That said, I really wish there was a standardized way to do it. Some sort of explicit (or at least implicit but unambiguous) indicator to all firewalls that a connection from a given host/port pair is desired for the next few seconds. Basically a lightweight, in-band port mapping protocol.
It could have well been an official recommendation to facilitate TCP hole punching, but I guess it’s too late now, as firewall behaviors have had decades to evolve into different directions.
It is precisely this point that has flummoxed me when connecting my p2p wireguard config[1] with a friend that uses a pfsense router, no matter what we tried, pfsense always chooses a random source port.
But in the simple case this blog outlines, if both ends use the same source port, this method punches through 2 firewalls effortlessly:
The Solution (Static Port)
To fix this without a permanent port forward, you must enable Static Port in pfSense's Outbound NAT. This doesn't open a hole to the world; it simply tells pfSense: "When this internal IP sends UDP traffic, do not rewrite the source port."
Navigate to Firewall > NAT > Outbound.
Switch to Hybrid Outbound NAT (if not already).
Add a rule at the top:
Interface: WAN
Protocol: UDP
Source: [Friend's WireGuard Internal IP/Port]
Destination: [Your Public IP]
Translation: Check Static Port.
The most plausible output might be correct, or it might be utter bullshit hallucinations that only sound correct; the only way to tell is to actually try it or cross-reference primary sources. Unless you do, the AI answer is worthless.
The reason why they're getting so good at code now is that they can check their output by running and testing it; if you're just prompting questions into a chatbot and then copying their output verbatim to a comment, you're not adding any meaningful value.
In this era where AI is eating away at how deterministic computers are, I really appreciate reading about an elegant solution to a real problem using deterministic logic.
NAT is effectively your router doing DHCP with a 17-bit suffix (16-bit port + 1 bit for UDP vs TCP) to each of your applications and then not telling you the address it gave you or how long it is good for (which is what a regular DHCP lease does). This is in addition to it, most likely, already doing regular DHCP and allocating you a IP address that it does tell you about, but which is basically worthless since routing to just that prefix without the hidden suffix goes into a black hole.
If you could just ask your router for a lease on a chunk of IP+NAT addresses that you could allocate to your applications and rotate them as they expire, you would not need this horrifying mess.
The router would just need to maintain the last-leg routing table (what a concept, a router doing routing with routing tables) just like it already does DHCP.
The applications would have short-term stable addresses that they could just tell their peers and just directly tell the router/firewall to block anybody except the desired peer short-term address.
The “just” is doing a lot of lifting there. I’m glad the various port mapping protocols didn’t really take off and it looks like IPv6 is going to actually make it instead. Much less complexity in most parts of the stack and network.
I am pointing out how the problem NAT “solves” is just dynamic address configuration. They have implemented a N+K bit address where the N-bit prefix is routed and allocated using IP and the low K-bits are routed and allocated like a custom fever dream.
You can just do it all the same way instead of doing it differently and worse for the low bits.
To be clear, the router should rewrite zero bits in the packet under the scheme I am describing just like how routers have no need to rewrite any bits when routing to a specific globally-routable IP address.
You get a lease for a /N+K address. /N routes to your router which routes the last K bits just like normal as if it had a /N-M to a /N route. This is a generic description of homogenous hierarchical routing.
We could have a standard for doing that directly at the NAT box level instead of relying on a third party STUN server, it simply didn't happen (and in fairness, the benefits would be quite minimal).