--- old/src/java.base/share/classes/sun/nio/ch/DatagramChannelImpl.java	2020-01-06 11:04:29.000000000 +0000
+++ new/src/java.base/share/classes/sun/nio/ch/DatagramChannelImpl.java	2020-01-06 11:04:28.000000000 +0000
@@ -1,5 +1,5 @@
 /*
- * Copyright (c) 2001, 2019, Oracle and/or its affiliates. All rights reserved.
+ * Copyright (c) 2001, 2020, Oracle and/or its affiliates. All rights reserved.
  * DO NOT ALTER OR REMOVE COPYRIGHT NOTICES OR THIS FILE HEADER.
  *
  * This code is free software; you can redistribute it and/or modify it
@@ -1405,10 +1405,11 @@
             registry.forEach(k -> {
                 if (k instanceof MembershipKeyImpl.Type6) {
                     MembershipKeyImpl.Type6 key6 = (MembershipKeyImpl.Type6) k;
-                    Net.join6(fd, key6.groupAddress(), key6.index(), key6.source());
+                    Net.join6(fd, key6.groupAddress(), key6.interfaceIndex(), key6.source());
                 } else {
                     MembershipKeyImpl.Type4 key4 = (MembershipKeyImpl.Type4) k;
-                    Net.join4(fd, key4.groupAddress(), key4.interfaceAddress(), key4.source());
+                    Net.join4(fd, key4.groupAddress(), key4.interfaceIndex(),
+                              key4.interfaceAddress(), key4.source());
                 }
             });
         }
@@ -1466,6 +1467,10 @@
             throw new IllegalArgumentException("Address type not supported");
         }
 
+        // network interface, should always be >= 0
+        int index = interf.getIndex();
+        assert index >= 0;
+
         // check source address
         if (source != null) {
             if (source.isAnyLocalAddress())
@@ -1497,14 +1502,9 @@
             if ((family == StandardProtocolFamily.INET6) &&
                 ((group instanceof Inet6Address) || Net.canJoin6WithIPv4Group()))
             {
-                int index = interf.getIndex();
-                if (index == -1)
-                    throw new IOException("Network interface cannot be identified");
-
                 // need multicast and source address as byte arrays
                 byte[] groupAddress = Net.inet6AsByteArray(group);
-                byte[] sourceAddress = (source == null) ? null :
-                    Net.inet6AsByteArray(source);
+                byte[] sourceAddress = (source == null) ? null : Net.inet6AsByteArray(source);
 
                 // join the group
                 int n = Net.join6(fd, groupAddress, index, sourceAddress);
@@ -1512,8 +1512,7 @@
                     throw new UnsupportedOperationException();
 
                 key = new MembershipKeyImpl.Type6(this, group, interf, source,
-                                                  groupAddress, index, sourceAddress);
-
+                                                  groupAddress, sourceAddress);
             } else {
                 // need IPv4 address to identify interface
                 Inet4Address target = Net.anyInet4Address(interf);
@@ -1525,7 +1524,7 @@
                 int sourceAddress = (source == null) ? 0 : Net.inet4AsInt(source);
 
                 // join the group
-                int n = Net.join4(fd, groupAddress, targetAddress, sourceAddress);
+                int n = Net.join4(fd, groupAddress, index, targetAddress, sourceAddress);
                 if (n == IOStatus.UNAVAILABLE)
                     throw new UnsupportedOperationException();
 
@@ -1539,17 +1538,14 @@
     }
 
     @Override
-    public MembershipKey join(InetAddress group,
-                              NetworkInterface interf)
+    public MembershipKey join(InetAddress group, NetworkInterface interf)
         throws IOException
     {
         return innerJoin(group, interf, null);
     }
 
     @Override
-    public MembershipKey join(InetAddress group,
-                              NetworkInterface interf,
-                              InetAddress source)
+    public MembershipKey join(InetAddress group, NetworkInterface interf, InetAddress source)
         throws IOException
     {
         Objects.requireNonNull(source);
@@ -1566,13 +1562,12 @@
 
             try {
                 if (key instanceof MembershipKeyImpl.Type6) {
-                    MembershipKeyImpl.Type6 key6 =
-                        (MembershipKeyImpl.Type6)key;
-                    Net.drop6(fd, key6.groupAddress(), key6.index(), key6.source());
+                    MembershipKeyImpl.Type6 key6 = (MembershipKeyImpl.Type6)key;
+                    Net.drop6(fd, key6.groupAddress(), key6.interfaceIndex(), key6.source());
                 } else {
                     MembershipKeyImpl.Type4 key4 = (MembershipKeyImpl.Type4)key;
-                    Net.drop4(fd, key4.groupAddress(), key4.interfaceAddress(),
-                        key4.source());
+                    Net.drop4(fd, key4.groupAddress(), key4.interfaceIndex(),
+                              key4.interfaceAddress(), key4.source());
                 }
             } catch (IOException ioe) {
                 // should not happen
@@ -1623,13 +1618,13 @@
             if (key instanceof MembershipKeyImpl.Type6) {
                  MembershipKeyImpl.Type6 key6 =
                     (MembershipKeyImpl.Type6)key;
-                n = Net.block6(fd, key6.groupAddress(), key6.index(),
+                n = Net.block6(fd, key6.groupAddress(), key6.interfaceIndex(),
                                Net.inet6AsByteArray(source));
             } else {
                 MembershipKeyImpl.Type4 key4 =
                     (MembershipKeyImpl.Type4)key;
-                n = Net.block4(fd, key4.groupAddress(), key4.interfaceAddress(),
-                               Net.inet4AsInt(source));
+                n = Net.block4(fd, key4.groupAddress(), key4.interfaceIndex(),
+                               key4.interfaceAddress(), Net.inet4AsInt(source));
             }
             if (n == IOStatus.UNAVAILABLE) {
                 // ancient kernel
@@ -1651,15 +1646,13 @@
 
             try {
                 if (key instanceof MembershipKeyImpl.Type6) {
-                    MembershipKeyImpl.Type6 key6 =
-                        (MembershipKeyImpl.Type6)key;
-                    Net.unblock6(fd, key6.groupAddress(), key6.index(),
+                    MembershipKeyImpl.Type6 key6 = (MembershipKeyImpl.Type6)key;
+                    Net.unblock6(fd, key6.groupAddress(), key6.interfaceIndex(),
                                  Net.inet6AsByteArray(source));
                 } else {
-                    MembershipKeyImpl.Type4 key4 =
-                        (MembershipKeyImpl.Type4)key;
-                    Net.unblock4(fd, key4.groupAddress(), key4.interfaceAddress(),
-                                 Net.inet4AsInt(source));
+                    MembershipKeyImpl.Type4 key4 = (MembershipKeyImpl.Type4)key;
+                    Net.unblock4(fd, key4.groupAddress(), key4.interfaceIndex(),
+                                 key4.interfaceAddress(), Net.inet4AsInt(source));
                 }
             } catch (IOException ioe) {
                 // should not happen