diff --git a/Cargo.lock b/Cargo.lock
index 8aa8f62..9287c76 100644
--- a/Cargo.lock
+++ b/Cargo.lock
@@ -1216,10 +1216,15 @@ name = "ptth_quic_client_gui"
 version = "0.1.0"
 dependencies = [
  "anyhow",
+ "blake3",
  "fltk",
  "quic_demo",
  "quinn",
+ "rand",
+ "rand_chacha",
  "reqwest",
+ "rmp-serde",
+ "serde",
  "structopt",
  "tokio",
  "tracing",
diff --git a/prototypes/ptth_quic_client_gui/Cargo.toml b/prototypes/ptth_quic_client_gui/Cargo.toml
index 27f81c1..23b6df2 100644
--- a/prototypes/ptth_quic_client_gui/Cargo.toml
+++ b/prototypes/ptth_quic_client_gui/Cargo.toml
@@ -9,10 +9,15 @@ license = "AGPL-3.0"
 
 [dependencies]
 anyhow = "1.0.38"
+blake3 = "1.0.0"
 fltk = "1.2.7"
 quic_demo = { path = "../quic_demo" }
 quinn = "0.7.2"
+rand = "0.8.4"
+rand_chacha = "0.3.1"
 reqwest = "0.11.4"
+rmp-serde = "0.15.5"
+serde = "1.0.130"
 structopt = "0.3.20"
 tokio = { version = "1.8.1", features = ["full"] }
 tracing-subscriber = "0.2.16"
diff --git a/prototypes/ptth_quic_client_gui/src/main.rs b/prototypes/ptth_quic_client_gui/src/main.rs
index b83adb5..6ee835b 100644
--- a/prototypes/ptth_quic_client_gui/src/main.rs
+++ b/prototypes/ptth_quic_client_gui/src/main.rs
@@ -12,6 +12,10 @@ use fltk::{
 	prelude::*, 
 	window::Window
 };
+use rand::{
+	Rng,
+	SeedableRng,
+};
 use structopt::StructOpt;
 use tokio::runtime::Runtime;
 
@@ -272,7 +276,8 @@ impl GuiPort {
 		row.set_size (&mut but_open, 80);
 		row.set_size (&mut but_close, 80);
 		
-		input_client_port.set_value ("0");
+		input_client_port.set_value ("");
+		input_client_port.set_readonly (true);
 		input_server_id.set_value ("bogus_server");
 		input_server_port.set_value ("5900");
 		
@@ -281,26 +286,32 @@ impl GuiPort {
 		but_close.set_trigger (CallbackTrigger::Release);
 		but_close.emit (fltk_tx, Message::ClosePort (port_idx));
 		
-		set_active (&mut but_open, true);
-		set_active (&mut but_close, false);
-		
 		row.end ();
 		
-		Self {
+		let mut output = Self {
 			row,
 			input_client_port,
 			input_server_id,
 			input_server_port,
 			but_open,
 			but_close,
-		}
+		};
+		
+		output.set_forwarding (false);
+		
+		output
 	}
 	
 	fn get_params (&self) -> anyhow::Result <ForwardingParams>
 	{
-		let client_tcp_port = u16::from_str (&self.input_client_port.value ())?;
-		let server_id = self.input_server_id.value ();
 		let server_tcp_port = u16::from_str (&self.input_server_port.value ())?;
+		let server_id = self.input_server_id.value ();
+		
+		let client_tcp_port = PortInfo {
+			relay_addr: "bogus_relay",
+			server_id: &server_id,
+			server_tcp_port,
+		}.random_eph_port ();
 		
 		Ok (ForwardingParams {
 			client_tcp_port,
@@ -310,7 +321,7 @@ impl GuiPort {
 	}
 	
 	fn set_forwarding (&mut self, x: bool) {
-		set_active (&mut self.input_client_port, !x);
+		set_active (&mut self.input_client_port, x);
 		set_active (&mut self.input_server_id, !x);
 		set_active (&mut self.input_server_port, !x);
 		set_active (&mut self.but_open, !x);
@@ -320,3 +331,63 @@ impl GuiPort {
 		self.but_close.set (!x);
 	}
 }
+
+// This can collide, but who cares
+// It's not secure or anything - It's just supposed to pick a port somewhat
+// deterministically based on the server and relay info.
+
+#[derive (serde::Serialize)]
+struct PortInfo <'a> {
+	relay_addr: &'a str,
+	server_id: &'a str,
+	server_tcp_port: u16
+}
+
+impl PortInfo <'_> {
+	// https://en.wikipedia.org/wiki/TCP_ports#Dynamic,_private_or_ephemeral_ports
+	
+	fn random_eph_port (&self) -> u16
+	{
+		let seed = blake3::hash (&rmp_serde::to_vec (self).expect ("Can't hash PortInfo - impossible error"));
+		
+		let mut rng = rand_chacha::ChaCha20Rng::from_seed (*seed.as_bytes ());
+		
+		let tcp_eph_range = 49152..=65535;
+		rng.gen_range (tcp_eph_range)
+	}
+}
+
+#[cfg (test)]
+mod test {
+	use blake3::Hasher;
+	
+	use super::*;
+	
+	#[test]
+	fn prng () {
+		let hasher = Hasher::default ();
+		let seed = hasher.finalize ();
+		
+		let mut rng = rand_chacha::ChaCha20Rng::from_seed (*seed.as_bytes ());
+		
+		let tcp_eph_range = 49152..=65535;
+		let port = rng.gen_range (tcp_eph_range);
+		assert_eq! (port, 49408);
+		
+		for (input, expected) in vec! [
+			(("bogus_relay", "bogus_server",   22), 62350),
+			(("real_relay",  "bogus_server",   22), 61081),
+			(("bogus_relay", "real_server",    22), 50513),
+			(("bogus_relay", "bogus_server", 5900), 60730),
+		] {
+			let (relay_addr, server_id, server_tcp_port) = input;
+			let input = PortInfo {
+				relay_addr,
+				server_id,
+				server_tcp_port,
+			};
+			let actual = input.random_eph_port ();
+			assert_eq! (expected, actual);
+		}
+	}
+}