Wi-SUN MTU size update and IPv6 minium MTU routing skip

Wi-SUN interface MTU config to 1576.

Minium link MTU usage skipped for IPv6 routing.

Tunneled IPv6 Packet will follow MTU size 1280. Bigger Ones will be fragmented.

Author: Juha Heiskanen

source/6LoWPAN/ws/ws_bootstrap.c

@@ -2337,6 +2337,8 @@ int ws_bootstrap_init(int8_t interface_id, net_6lowpan_mode_e bootstrap_mode)
         goto init_fail;
     }
 
+    cur->ipv6_neighbour_cache.link_mtu = cur->max_link_mtu = WS_MPX_MAX_MTU;
+
     cur->if_up = ws_bootstrap_up;
     cur->if_down = ws_bootstrap_down;
     cur->ws_info->neighbor_storage = neigh_info;

source/6LoWPAN/ws/ws_common_defines.h

@@ -239,6 +239,13 @@ typedef struct ws_bs_ie {
 #define MPX_KEY_MANAGEMENT_ENC_USER_ID 0x0001   /**< MPX Key management user ID */
 #define MPX_LOWPAN_ENC_USER_ID 0xA0ED           /**< MPX Lowpan User Id */
 
+/*
+ * Wi-SUN MPX MTU size
+ *
+ */
+
+#define WS_MPX_MAX_MTU 1576
+
 #define WS_FAN_VERSION_1_0 1
 
 #define WS_NEIGHBOR_LINK_TIMEOUT 2200
@@ -373,4 +380,5 @@ typedef struct ws_bs_ie {
 #define BR_EAPOL_RELAY_SOCKET_PORT            10255
 #define PAE_AUTH_SOCKET_PORT                  10254
 
+
 #endif /* WS_COMMON_DEFINES_H_ */

source/Common_Protocols/ipv6.c

@@ -613,6 +613,16 @@ buffer_t *ipv6_forwarding_down(buffer_t *buf)
 
     /* Routing code may say it needs to tunnel to add headers - loop back to IP layer if requested */
     if (exthdr_result == IPV6_EXTHDR_MODIFY_TUNNEL) {
+
+        if (buffer_data_length(buf) > IPV6_MIN_LINK_MTU) {
+            /* recover IP addresses that icmpv6_error needs, which routing code will have overwritten */
+            buf->src_sa.addr_type = ADDR_IPV6;
+            memcpy(buf->src_sa.address, buffer_data_pointer(buf) + IPV6_HDROFF_SRC_ADDR, 16);
+            buf->dst_sa.addr_type = ADDR_IPV6;
+            memcpy(buf->dst_sa.address, buffer_data_pointer(buf) + IPV6_HDROFF_DST_ADDR, 16);
+            return icmpv6_error(buf, NULL, ICMPV6_TYPE_ERROR_PACKET_TOO_BIG, 0, IPV6_MIN_LINK_MTU);
+        }
+
         /* Avoid an infinite loop in the event of routing code failure - never
          * let them ask for tunnelling more than once.
          */
@@ -623,6 +633,7 @@ buffer_t *ipv6_forwarding_down(buffer_t *buf)
         buf->options.tunnelled = true;
 
         buf->options.ip_extflags = 0;
+        buf->options.ipv6_use_min_mtu = -1;
 
         /* Provide tunnel source, unless already set */
         if (buf->src_sa.addr_type == ADDR_NONE) {
@@ -1003,7 +1014,7 @@ static buffer_t *ipv6_consider_forwarding_unicast_packet(buffer_t *buf, protocol
 
     /* route_info.pmtu will cover limits from both the interface and the
      * route. As a bonus, it will also cover any PMTUD we happen to have done
-     * to that destination ourselves, as well as mop up any tunnelling issues.
+     * to that destination ourselves. Extra limits due to tunnelling are checked on tunnel entry in ipv6_down.
      */
     if (routing->route_info.pmtu < buffer_data_length(buf)) {
         buf->interface = cur;

source/Common_Protocols/ipv6.h

@@ -57,7 +57,7 @@ typedef enum ipv6_exthdr_stage {
  * If it needs to insert headers that are not present, it can force insertion
  * into a tunnel, by:
  *    setting dst_sa and src_sa appropriate for the tunnel endpoints
- *      XXX does this work out okay with dest cache and PMTU?
+ *    src_sa.addr_type can be set to ADDR_NONE to auto-select tunnel source address
  *    updating route info like next hop if necessary (probably not)
  *    returning IPV6_EXTHDR_MODIFY_TUNNEL
  * During new header formation for the tunnel, IPV6_EXTHDR_INSERT will be

source/MPL/mpl.c

@@ -1065,6 +1065,7 @@ static buffer_t *mpl_exthdr_provider(buffer_t *buf, ipv6_exthdr_stage_t stage, i
     if (!domain) {
         // We will need to tunnel - do nothing on the inner packet
         *result = 0;
+        buf->options.ipv6_use_min_mtu = 1;
         return buf;
     }
 

source/RPL/rpl_data.c

@@ -374,6 +374,7 @@ static buffer_t *rpl_data_exthdr_provider_hbh_2(buffer_t *buf, rpl_instance_t *i
         case IPV6_EXTHDR_INSERT: {
             if (!destination_in_instance) {
                 /* We don't add a header - we'll do it on the tunnel */
+                buf->options.ipv6_use_min_mtu = 1;
                 *result = 0;
                 return buf;
             }
@@ -965,6 +966,7 @@ static buffer_t *rpl_data_exthdr_provider_srh(buffer_t *buf, ipv6_exthdr_stage_t
         if (!buf->options.tunnelled) {
             if (stage == IPV6_EXTHDR_SIZE || stage == IPV6_EXTHDR_INSERT) {
                 *result = 0;
+                buf->options.ipv6_use_min_mtu = 1;
                 return buf;
             }
         }

source/ipv6_stack/ipv6_routing_table.c

@@ -1195,17 +1195,6 @@ static const bool ipv6_route_probing[ROUTE_MAX] = {
     [ROUTE_RPL_INSTANCE] = true,
 };
 
-/* Which route types get minimum link MTU by default */
-/* Makes life easier for tunnel-based systems like RPL */
-static const bool ipv6_route_min_mtu[ROUTE_MAX] = {
-    [ROUTE_RPL_DAO] = true,
-    [ROUTE_RPL_DAO_SR] = true,
-    [ROUTE_RPL_DIO] = true,
-    [ROUTE_RPL_ROOT] = true,
-    [ROUTE_RPL_INSTANCE] = true,
-    [ROUTE_MPL] = true,
-};
-
 // Remember when a route source has deleted an entry - allows buffers still in
 // event queue to have their route info invalidated.
 static bool ipv6_route_source_invalidated[ROUTE_MAX];
@@ -1647,7 +1636,7 @@ ipv6_route_t *ipv6_route_add_metric(const uint8_t *prefix, uint8_t prefix_len, i
         route->info.info = info;
         route->info.source_id = source_id;
         route->info.interface_id = interface_id;
-        route->info.pmtu = ipv6_route_min_mtu[source] ? IPV6_MIN_LINK_MTU : 0xFFFF;
+        route->info.pmtu = 0xFFFF;
         if (next_hop) {
             route->on_link = false;
             memcpy(route->info.next_hop_addr, next_hop, 16);