fixed bug #38061 (wrong multicast routing in IPv4) by adding an optional default netif for multicast routing

CHANGELOG

@@ -202,6 +202,14 @@ HISTORY
 
   ++ Bugfixes:
 
+  2015-02-25: Simon Goldschmidt
+  * ip4.h/.c, udp.c: fixed bug #38061 (wrong multicast routing in IPv4) by
+    adding an optional default netif for multicast routing
+
+  2015-02-25: Simon Goldschmidt
+  * netconn API: fixed that netconn_connect still used message passing for
+    LWIP_TCPIP_CORE_LOCKING==1
+
   2015-02-22: patch by Jens Nielsen
   * icmp.c: fixed bug #38803 (Source address in broadcast ping reply)
 
@@ -239,17 +247,17 @@ HISTORY
   2015-02-11: patch by hichard
   * tcpip.c: fixed bug #43094 "The function tcpip_input() forget to handle IPv6"
 
-  2014-02-10: Simon Goldschmidt
+  2015-02-10: Simon Goldschmidt
   * netconn API: fixed that netconn_close/netconn_delete still used message passing
     for LWIP_TCPIP_CORE_LOCKING==1
 
-  2014-02-10: Simon Goldschmidt
+  2015-02-10: Simon Goldschmidt
   * netconn/socket api: fixed bug #44225 "closing TCP socket should time out
     eventually", implemented task #6930 "Implement SO_LINGER": closing TCP sockets
     times out after 20 seconds or after the configured SND_TIMEOUT or depending
     on the linger settings.
 
-  2014-01-27: Simon Goldschmidt
+  2015-01-27: Simon Goldschmidt
   * api_msg.c: fixed that SHUT_RD followed by SHUT_WR was different to SHUT_RDWR,
     fixed return value of lwip_netconn_do_close on unconnected netconns
 

src/core/ipv4/ip4.c

@@ -98,6 +98,18 @@ struct ip_globals ip_data;
 /** The IP header ID of the next outgoing IP packet */
 static u16_t ip_id;
 
+#if LWIP_IGMP
+/** The default netif used for multicast */
+static struct netif* ip_default_multicast_netif;
+
+/** Set a default netif for IPv4 multicast. */
+void
+ip_set_default_multicast_netif(struct netif* default_multicast_netif)
+{
+  ip_default_multicast_netif = default_multicast_netif;
+}
+#endif /* LWIP_IGMP */
+
 /**
  * Finds the appropriate network interface for a given IP address. It
  * searches the list of network interfaces linearly. A match is found
@@ -119,6 +131,13 @@ ip_route(const ip_addr_t *dest)
   }
 #endif
 
+#if LWIP_IGMP
+  /* Use administratively selected interface for multicast by default */
+  if (ip_addr_ismulticast(dest) && ip_default_multicast_netif) {
+    return ip_default_multicast_netif;
+  }
+#endif /* LWIP_IGMP */
+
   /* iterate through netifs */
   for (netif = netif_list; netif != NULL; netif = netif->next) {
     /* network mask matches? */

src/core/udp.c

@@ -559,15 +559,22 @@ udp_sendto_chksum(struct udp_pcb *pcb, struct pbuf *p, const ip_addr_t *dst_ip,
 
 #if LWIP_IPV6 || LWIP_IGMP
   if (ipX_addr_ismulticast(PCB_ISIPV6(pcb), dst_ip_route)) {
-    /* For multicast, find a netif based on source address. */
 #if LWIP_IPV6
     if (PCB_ISIPV6(pcb)) {
+      /* For multicast, find a netif based on source address. */
       dst_ip_route = &pcb->local_ip;
     } else
 #endif /* LWIP_IPV6 */
     {
 #if LWIP_IGMP
-      dst_ip_route = ip_2_ipX(&pcb->multicast_ip);
+      /* IPv4 does not use source-based routing by default, so we use an
+         administratively selected interface for multicast by default.
+         However, this can be overridden by setting an interface address
+         in pcb->multicast_ip that is used for routing. */
+      if (!ip_addr_isany(&pcb->multicast_ip) &&
+          !ip_addr_cmp(&pcb->multicast_ip, IP_ADDR_BROADCAST)) {
+        dst_ip_route = ip_2_ipX(&pcb->multicast_ip);
+      }
 #endif /* LWIP_IGMP */
     }
   }

src/include/lwip/ip4.h

@@ -133,6 +133,10 @@ err_t ip_output_if_opt_src(struct pbuf *p, const ip_addr_t *src, const ip_addr_t
        u16_t optlen);
 #endif /* IP_OPTIONS_SEND */
 
+#if LWIP_IGMP
+void  ip_set_default_multicast_netif(struct netif* default_multicast_netif);
+#endif /* LWIP_IGMP */
+
 #define ip_netif_get_local_ipX(netif) (((netif) != NULL) ? ip_2_ipX(&((netif)->ip_addr)) : NULL)
 
 #if IP_DEBUG