diff --git a/internal/client/connection.go b/internal/client/connection.go
index ffc3c77..fc16f38 100644
--- a/internal/client/connection.go
+++ b/internal/client/connection.go
@@ -9,6 +9,14 @@
  * Beschreibung:
  * Aufbau einer Verbindung zwischen einem lokalen virtuellen seriellen Port
  * und dem zugehörigen entfernten Gerät.
+ *
+ * Die konfigurierte lokale virtuelle Schnittstelle wird dabei exakt
+ * übernommen. Eine Konfiguration wie
+ *
+ *     /dev/ttyUSB100 -> radio
+ *
+ * führt somit technisch auch zur Erzeugung beziehungsweise Verwendung von
+ * /dev/ttyUSB100 und nicht einfach zum nächsten freien Port.
  * ============================================================================
  */
 package client
@@ -16,19 +24,65 @@ package client
 import (
 	"fmt"
 	"net"
+	"strconv"
+	"strings"
 
 	"git.lang-dieter.de/rs2322tcp/internal/config"
 	"git.lang-dieter.de/rs2322tcp/internal/transport"
 )
 
+///////////////////////////////////////////////////////////////////////////////
+// Virtual port configuration
+///////////////////////////////////////////////////////////////////////////////
+
+// virtualPortNumber converts a configured /dev/ttyUSBxxx path into its
+// numeric virtual port number.
+//
+// The client configuration stores the complete Linux device path, while
+// VirtualPortManager works with the numeric port number. Only the exact
+// /dev/ttyUSB<number> format is accepted here.
+func virtualPortNumber(path string) (int, error) {
+	const prefix = "/dev/ttyUSB"
+
+	if !strings.HasPrefix(path, prefix) {
+		return 0, fmt.Errorf(
+			"invalid virtual port %q: expected /dev/ttyUSB<number>",
+			path,
+		)
+	}
+
+	value := strings.TrimPrefix(path, prefix)
+
+	if value == "" {
+		return 0, fmt.Errorf(
+			"invalid virtual port %q: port number is missing",
+			path,
+		)
+	}
+
+	number, err := strconv.Atoi(value)
+	if err != nil {
+		return 0, fmt.Errorf(
+			"invalid virtual port %q: invalid port number",
+			path,
+		)
+	}
+
+	return number, nil
+}
+
 ///////////////////////////////////////////////////////////////////////////////
 // Virtual port connection
 ///////////////////////////////////////////////////////////////////////////////
 
-// connectVirtualPort opens the local virtual port and the corresponding
-// remote TCP data connection and returns both endpoints.
+// connectVirtualPort opens the configured local virtual port and the
+// corresponding remote TCP data connection and returns both endpoints.
 //
 // The caller owns the returned virtual port and TCP connection.
+//
+// The local virtual port is opened using exactly the port number specified
+// in virtualPortConfig.Port. This preserves the user's configured mapping
+// between local virtual interfaces and remote devices.
 func connectVirtualPort(
 	c *Client,
 	manager *VirtualPortManager,
@@ -48,10 +102,16 @@ func connectVirtualPort(
 		return nil, nil, err
 	}
 
-	virtualPort, err := manager.Open()
+	portNumber, err := virtualPortNumber(virtualPortConfig.Port)
+	if err != nil {
+		return nil, nil, err
+	}
+
+	virtualPort, err := manager.OpenSpecific(portNumber)
 	if err != nil {
 		return nil, nil, fmt.Errorf(
-			"open virtual port for %q: %w",
+			"open virtual port %q for %q: %w",
+			virtualPortConfig.Port,
 			virtualPortConfig.RemoteDevice,
 			err,
 		)
diff --git a/internal/client/connection_test.go b/internal/client/connection_test.go
index 46d0d65..74f9192 100644
--- a/internal/client/connection_test.go
+++ b/internal/client/connection_test.go
@@ -367,6 +367,83 @@ func TestConnectVirtualPortSuccess(t *testing.T) {
 	}
 }
 
+func TestConnectVirtualPortUsesConfiguredPort(t *testing.T) {
+	dataAddress, accepted := startTestDataServer(t)
+
+	device := remoteDeviceFromAddress(
+		t,
+		"radio",
+		dataAddress,
+	)
+
+	client := newTestClient(t)
+
+	manager := NewVirtualPortManager(
+		config.VirtualPortRangeConfig{
+			First: 100,
+			Last:  199,
+		},
+	)
+
+	cfg := config.VirtualPortConfig{
+		Port:         "/dev/ttyUSB150",
+		RemoteDevice: "radio",
+	}
+
+	virtualPort, dataConn, err := connectVirtualPort(
+		client,
+		manager,
+		cfg,
+		[]transport.RemoteDeviceInfo{device},
+	)
+	if err != nil {
+		t.Fatalf("connectVirtualPort: %v", err)
+	}
+
+	if virtualPort == nil {
+		t.Fatal("virtual port is nil")
+	}
+
+	if dataConn == nil {
+		t.Fatal("data connection is nil")
+	}
+
+	defer virtualPort.Close()
+	defer dataConn.Close()
+
+	if virtualPort.Path() != "/dev/ttyUSB150" {
+		t.Fatalf(
+			"virtual port path = %q, want %q",
+			virtualPort.Path(),
+			"/dev/ttyUSB150",
+		)
+	}
+
+	// Port 100 must still be available. This proves that the connection
+	// did not simply take the first free port from the configured range.
+	number, err := manager.Reserve()
+	if err != nil {
+		t.Fatalf("Reserve() after connection: %v", err)
+	}
+
+	if number != 100 {
+		t.Fatalf(
+			"first free port after connection = %d, want 100",
+			number,
+		)
+	}
+
+	manager.Release(number)
+
+	select {
+	case conn := <-accepted:
+		_ = conn.Close()
+
+	case <-t.Context().Done():
+		t.Fatal("test context cancelled while waiting for data connection")
+	}
+}
+
 func TestConnectBridgeSuccess(t *testing.T) {
 	dataAddress, accepted := startTestDataServer(t)
 
diff --git a/internal/client/virtual_port_manager.go b/internal/client/virtual_port_manager.go
index 8998617..a365f90 100644
--- a/internal/client/virtual_port_manager.go
+++ b/internal/client/virtual_port_manager.go
@@ -9,6 +9,19 @@
  * Beschreibung:
  * Verwaltung und Auswahl der für rs2322tcp reservierten virtuellen
  * seriellen Ports.
+ *
+ * Der VirtualPortManager verwaltet den für rs2322tcp vorgesehenen Bereich
+ * von /dev/ttyUSBxxx-Schnittstellen.
+ *
+ * Ports können entweder automatisch über den nächsten freien Port oder
+ * gezielt über eine vorgegebene Portnummer reserviert werden.
+ *
+ * Die gezielte Reservierung ist insbesondere für die aus client.json
+ * geladene Konfiguration erforderlich. Dadurch bleibt eine Zuordnung wie
+ *
+ *     /dev/ttyUSB100 -> radio
+ *
+ * auch technisch exakt erhalten.
  * ============================================================================
  */
 package client
@@ -64,6 +77,9 @@ func (m *VirtualPortManager) PortPath(number int) string {
 //
 // Es wird immer mit dem kleinsten freien Port im konfigurierten Bereich
 // begonnen.
+//
+// Diese Methode bleibt für Fälle erhalten, in denen keine bestimmte
+// Portnummer vorgegeben ist.
 func (m *VirtualPortManager) Reserve() (int, error) {
 	if m == nil {
 		return 0, fmt.Errorf("virtual port manager is nil")
@@ -89,6 +105,42 @@ func (m *VirtualPortManager) Reserve() (int, error) {
 	)
 }
 
+// ReserveSpecific reserviert exakt den angegebenen virtuellen Port.
+//
+// Der Port muss innerhalb des konfigurierten Bereichs liegen und darf
+// momentan nicht bereits reserviert sein.
+//
+// Diese Methode wird für konfigurierte Zuordnungen verwendet, bei denen
+// die Portnummer aus client.json verbindlich ist.
+func (m *VirtualPortManager) ReserveSpecific(number int) error {
+	if m == nil {
+		return fmt.Errorf("virtual port manager is nil")
+	}
+
+	m.mu.Lock()
+	defer m.mu.Unlock()
+
+	if number < m.first || number > m.last {
+		return fmt.Errorf(
+			"virtual port %d is outside configured range %d-%d",
+			number,
+			m.first,
+			m.last,
+		)
+	}
+
+	if m.used[number] {
+		return fmt.Errorf(
+			"virtual port %d is already reserved",
+			number,
+		)
+	}
+
+	m.used[number] = true
+
+	return nil
+}
+
 // Release gibt einen zuvor reservierten Port wieder frei.
 func (m *VirtualPortManager) Release(number int) {
 	if m == nil {
diff --git a/internal/client/virtual_port_manager_linux.go b/internal/client/virtual_port_manager_linux.go
index 34812f0..d190ca1 100644
--- a/internal/client/virtual_port_manager_linux.go
+++ b/internal/client/virtual_port_manager_linux.go
@@ -14,6 +14,9 @@
  * Der öffentliche /dev/ttyUSBxxx-Eintrag wird bei der Installation
  * bereitgestellt. Der Client verwaltet ausschließlich den internen Link
  * unter ~/.rs2322tcp/virtual/.
+ *
+ * Virtuelle Ports können entweder automatisch über den nächsten freien Port
+ * oder gezielt über eine vorgegebene Portnummer geöffnet werden.
  * ============================================================================
  */
 package client
@@ -140,6 +143,9 @@ func (p *ManagedVirtualPort) Close() error {
 //
 // The internal PTY is created by newVirtualSerial(). The internal
 // ~/.rs2322tcp/virtual/ttyUSBxxx link is then pointed at the PTY.
+//
+// Open retains the automatic allocation behavior used by the existing
+// client code.
 func (m *VirtualPortManager) Open() (*ManagedVirtualPort, error) {
 	if m == nil {
 		return nil, fmt.Errorf("virtual port manager is nil")
@@ -150,6 +156,39 @@ func (m *VirtualPortManager) Open() (*ManagedVirtualPort, error) {
 		return nil, err
 	}
 
+	return m.openReserved(number)
+}
+
+// OpenSpecific creates a new virtual serial port using exactly the specified
+// port number.
+//
+// Unlike Open, this method does not select the next free port. The requested
+// number is reserved explicitly and is therefore suitable for the
+// VirtualPortConfig.Port value loaded from client.json.
+//
+// If creation of the PTY or the internal link fails, the reservation is
+// released again.
+func (m *VirtualPortManager) OpenSpecific(number int) (*ManagedVirtualPort, error) {
+	if m == nil {
+		return nil, fmt.Errorf("virtual port manager is nil")
+	}
+
+	if err := m.ReserveSpecific(number); err != nil {
+		return nil, err
+	}
+
+	return m.openReserved(number)
+}
+
+///////////////////////////////////////////////////////////////////////////////
+// Internal open helper
+///////////////////////////////////////////////////////////////////////////////
+
+// openReserved creates the actual virtual serial port for an already
+// reserved port number.
+//
+// The caller must reserve the port before calling this method.
+func (m *VirtualPortManager) openReserved(number int) (*ManagedVirtualPort, error) {
 	portPath := m.PortPath(number)
 
 	serial, err := newVirtualSerial()
diff --git a/internal/client/virtual_port_manager_linux_test.go b/internal/client/virtual_port_manager_linux_test.go
index ad02ca3..810ea9a 100644
--- a/internal/client/virtual_port_manager_linux_test.go
+++ b/internal/client/virtual_port_manager_linux_test.go
@@ -79,6 +79,59 @@ func TestVirtualPortManagerOpen(t *testing.T) {
 	}
 }
 
+func TestVirtualPortManagerOpenSpecific(t *testing.T) {
+	tempHome := t.TempDir()
+	t.Setenv("HOME", tempHome)
+
+	manager := NewVirtualPortManager(
+		config.VirtualPortRangeConfig{
+			First: 100,
+			Last:  199,
+		},
+	)
+
+	port, err := manager.OpenSpecific(150)
+	if err != nil {
+		t.Fatalf("OpenSpecific(150) failed: %v", err)
+	}
+
+	if port == nil {
+		t.Fatal("OpenSpecific(150) returned nil")
+	}
+
+	if port.Path() != "/dev/ttyUSB150" {
+		t.Errorf(
+			"Path() = %q, want %q",
+			port.Path(),
+			"/dev/ttyUSB150",
+		)
+	}
+
+	linkPath, err := virtualPortLinkPath(port.Path())
+	if err != nil {
+		t.Fatalf("virtualPortLinkPath() failed: %v", err)
+	}
+
+	target, err := os.Readlink(linkPath)
+	if err != nil {
+		t.Fatalf("Readlink() failed: %v", err)
+	}
+
+	if target == "" {
+		t.Fatal("internal virtual port link has empty target")
+	}
+
+	if err := port.Close(); err != nil {
+		t.Fatalf("Close() failed: %v", err)
+	}
+
+	if _, err := os.Lstat(linkPath); !os.IsNotExist(err) {
+		t.Fatalf(
+			"internal link still exists after Close(): %q",
+			linkPath,
+		)
+	}
+}
 func TestVirtualPortManagerOpenUsesNextPort(t *testing.T) {
 	tempHome := t.TempDir()
 	t.Setenv("HOME", tempHome)
diff --git a/internal/client/virtual_port_manager_test.go b/internal/client/virtual_port_manager_test.go
index 9a2da9c..7d59fc3 100644
--- a/internal/client/virtual_port_manager_test.go
+++ b/internal/client/virtual_port_manager_test.go
@@ -8,6 +8,10 @@
  *
  * Beschreibung:
  * Tests für die Auswahl und Verwaltung virtueller serieller Ports.
+ *
+ * Die Tests decken sowohl die automatische Reservierung über Reserve()
+ * als auch die gezielte Reservierung eines bestimmten Ports über
+ * ReserveSpecific() ab.
  * ============================================================================
  */
 package client
@@ -201,6 +205,84 @@ func TestVirtualPortManagerPortPath(t *testing.T) {
 	}
 }
 
+func TestVirtualPortManagerReserveSpecific(t *testing.T) {
+	manager := NewVirtualPortManager(config.VirtualPortRangeConfig{
+		First: 100,
+		Last:  199,
+	})
+
+	if err := manager.ReserveSpecific(150); err != nil {
+		t.Fatalf("ReserveSpecific(150) failed: %v", err)
+	}
+
+	if !manager.used[150] {
+		t.Fatal("ReserveSpecific(150) did not reserve port 150")
+	}
+}
+
+func TestVirtualPortManagerReserveSpecificOutsideRange(t *testing.T) {
+	manager := NewVirtualPortManager(config.VirtualPortRangeConfig{
+		First: 100,
+		Last:  199,
+	})
+
+	tests := []int{
+		99,
+		200,
+	}
+
+	for _, number := range tests {
+		if err := manager.ReserveSpecific(number); err == nil {
+			t.Errorf(
+				"ReserveSpecific(%d) succeeded, want range error",
+				number,
+			)
+		}
+
+		if manager.used[number] {
+			t.Errorf(
+				"ReserveSpecific(%d) marked out-of-range port as used",
+				number,
+			)
+		}
+	}
+}
+
+func TestVirtualPortManagerReserveSpecificAlreadyReserved(t *testing.T) {
+	manager := NewVirtualPortManager(config.VirtualPortRangeConfig{
+		First: 100,
+		Last:  199,
+	})
+
+	if err := manager.ReserveSpecific(100); err != nil {
+		t.Fatalf("first ReserveSpecific(100) failed: %v", err)
+	}
+
+	if err := manager.ReserveSpecific(100); err == nil {
+		t.Fatal("second ReserveSpecific(100) succeeded, want already-reserved error")
+	}
+}
+
+func TestVirtualPortManagerReserveSpecificAfterRelease(t *testing.T) {
+	manager := NewVirtualPortManager(config.VirtualPortRangeConfig{
+		First: 100,
+		Last:  199,
+	})
+
+	if err := manager.ReserveSpecific(150); err != nil {
+		t.Fatalf("first ReserveSpecific(150) failed: %v", err)
+	}
+
+	manager.Release(150)
+
+	if err := manager.ReserveSpecific(150); err != nil {
+		t.Fatalf(
+			"ReserveSpecific(150) after Release() failed: %v",
+			err,
+		)
+	}
+}
+
 func TestVirtualPortManagerNil(t *testing.T) {
 	var manager *VirtualPortManager
 
@@ -212,5 +294,9 @@ func TestVirtualPortManagerNil(t *testing.T) {
 		t.Fatal("nil Reserve() succeeded, want error")
 	}
 
+	if err := manager.ReserveSpecific(100); err == nil {
+		t.Fatal("nil ReserveSpecific() succeeded, want error")
+	}
+
 	manager.Release(100)
 }