--- a/src/java.base/share/classes/sun/nio/ch/DatagramChannelImpl.java	Wed Oct 09 09:23:22 2019 -0700
+++ b/src/java.base/share/classes/sun/nio/ch/DatagramChannelImpl.java	Wed Oct 09 17:38:58 2019 +0100
@@ -875,6 +875,11 @@
                     if (state == ST_CONNECTED)
                         throw new AlreadyConnectedException();
 
+                    // ensure that the socket is bound
+                    if (localAddress == null) {
+                        bindInternal(null);
+                    }
+
                     int n = Net.connect(family,
                                         fd,
                                         isa.getAddress(),
@@ -932,8 +937,21 @@
                     remoteAddress = null;
                     state = ST_UNCONNECTED;
 
-                    // refresh local address
-                    localAddress = Net.localAddress(fd);
+                    // check whether rebind is needed
+                    InetSocketAddress isa = Net.localAddress(fd);
+                    if (isa.getPort() == 0) {
+                        // On Linux, if bound to ephemeral port,
+                        // disconnect does not preserve that port.
+                        // In this case, try to rebind to the previous port.
+                        int port = localAddress.getPort();
+                        localAddress = isa; // in case Net.bind fails
+                        Net.bind(family, fd, isa.getAddress(), port);
+                        isa = Net.localAddress(fd); // refresh address
+                        assert isa.getPort() == port;
+                    }
+
+                    // refresh localAddress
+                    localAddress = isa;
                 }
             } finally {
                 writeLock.unlock();