net/: There are many different checks for IPv6 multicast addresses. M…

…ost of the checks are different. RFC 3513 clearly specifies how to detect an IPv6 multilcast address: they should begin with 0xffxx. I did not change some of the checks in ipv6_input.c, however. In that file, the comments indicate that the code should only pick of certain mulicast address that begin withi 0xff02.

include/nuttx/net/ip.h

@@ -587,7 +587,19 @@ bool net_ipv6addr_maskcmp(const net_ipv6addr_t addr1,
  * Name: net_is_addr_mcast
  *
  * Description:
- *   Is address a multicast address? see RFC 3513.
+ *   Is address a multicast address?  See RFC 3513:
+ *
+ *   An IPv6 multicast address is an identifier for a group of interfaces
+ *   (typically on different nodes).  An interface may belong to any number
+ *   of multicast groups.  Multicast addresses have the following format:
+ *
+ *     |   8    |  4 |  4 |                  112 bits                   |
+ *     +------ -+----+----+---------------------------------------------+
+ *     |11111111|flgs|scop|                  group ID                   |
+ *     +--------+----+----+---------------------------------------------+
+ *
+ *   binary 11111111 at the start of the address identifies the address as
+ *   being a multicast address.
  *
  ****************************************************************************/
 

net/icmpv6/icmpv6_solicit.c

@@ -67,7 +67,8 @@
 /****************************************************************************
  * Private Data
  ****************************************************************************/
-/* First 6 swords of the multi-cast address in network byte order */
+
+/* First 6 hwords of the multi-cast address in network byte order */
 
 static const uint16_t g_icmpv_mcastaddr[6] =
 {

net/netdev/netdev_findbyaddr.c

@@ -300,13 +300,9 @@ FAR struct net_driver_s *netdev_findby_ipv6addr(const net_ipv6addr_t lipaddr,
   int ret;
 #endif
 
-  /* First, check if this is the multicast IP address  We should actually
-   * pick off certain multicast address (all hosts multicast address, and
-   * the solicited-node multicast address).  We will cheat here and accept
-   * all multicast packets that are destined for the ff02::/16 addresses.
-   */
+  /* First, check if this is the multicast IP address */
 
-  if (ripaddr[0] == HTONS(0xff02))
+  if (net_is_addr_mcast(ripaddr))
     {
       /* Yes.. Check the local, bound address.  Is it INADDR_ANY? */
 

net/sixlowpan/sixlowpan_utils.c

@@ -235,7 +235,7 @@ int sixlowpan_nexthopaddr(FAR struct radio_driver_s *radio,
  *
  *    128  112  96   80    64   48   32   16
  *    ---- ---- ---- ----  ---- ---- ---- ----
- *    ff02 xxxx xxxx xxxx  xxxx xxxx xxxx xxxx Multicast
+ *    ffxx xxxx xxxx xxxx  xxxx xxxx xxxx xxxx Multicast address (RFC 3513)
  *    ff02 0000 0000 0000  0000 0000 0000 0001 All nodes multicast group
  *    xxxx 0000 0000 0000  0000 00ff fe00 xx00 1-byte short address IEEE 48-bit MAC
  *    xxxx 0000 0000 0000  0000 00ff fe00 xxxx 2-byte short address IEEE 48-bit MAC
@@ -274,7 +274,7 @@ int sixlowpan_destaddrfromip(FAR struct radio_driver_s *radio,
 
    /* Check for a multicast address */
 
-   if (ipaddr[0] == HTONS(0xff02))
+   if (net_is_addr_mcast(ipaddr[0]))
      {
         DEBUGASSERT(radio->r_properties != NULL);
         ret = radio->r_properties(radio, &properties);
@@ -299,6 +299,9 @@ int sixlowpan_destaddrfromip(FAR struct radio_driver_s *radio,
             memcpy(destaddr, &properties.sp_bcast,
                    sizeof(struct netdev_varaddr_s));
           }
+
+        /* Some other RFC 3513 multicast address */
+
         else
           {
             memcpy(destaddr, &properties.sp_mcast,

net/udp/udp_finddev.c

@@ -193,16 +193,9 @@ FAR struct net_driver_s *udp_find_raddr_device(FAR struct udp_conn_s *conn)
           /* Check if the remote, destination address is a multicast
            * address.  If this is the case, select the device
            * using the locally bound address (assuming that there is one).
-           *
-           * The general form of all well-known, reserved IPv6 multicast
-           * addresses is:  ff0x::xx/16 (which includes most, but not all
-           * possible multicast addresses).
            */
 
-          if ((conn->u.ipv6.raddr[0] & HTONS(0xfff0)) == HTONS(0xff00) &&
-              conn->u.ipv6.raddr[1] == 0 && conn->u.ipv6.raddr[2] == 0 &&
-              conn->u.ipv6.raddr[3] == 0 && conn->u.ipv6.raddr[4] == 0 &&
-              conn->u.ipv6.raddr[5] == 0 && conn->u.ipv6.raddr[6] == 0)
+          if (net_is_addr_mcast(conn->u.ipv6.raddr))
             {
               /* Make sure that the socket is bound to some non-zero, local
                * address.  Zero is used as an indication that the laddr is