Add #define for minimum IPv6 MTU length

src/core/ipv6/nd6.c

@@ -693,7 +693,7 @@ nd6_input(struct pbuf *p, struct netif *inp)
         }
         mtu_opt = (struct mtu_option *)buffer;
         mtu32 = lwip_htonl(mtu_opt->mtu);
-        if ((mtu32 >= 1280) && (mtu32 <= 0xffff)) {
+        if ((mtu32 >= IP6_MIN_MTU_LENGTH) && (mtu32 <= 0xffff)) {
 #if LWIP_ND6_ALLOW_RA_UPDATES
           if (inp->mtu) {
             /* don't set the mtu for IPv6 higher than the netif driver supports */
@@ -2340,7 +2340,7 @@ nd6_get_destination_mtu(const ip6_addr_t *ip6addr, struct netif *netif)
     return netif_mtu6(netif);
   }
 
-  return 1280; /* Minimum MTU */
+  return IP6_MIN_MTU_LENGTH; /* Minimum MTU */
 }
 
 

src/include/lwip/prot/ip6.h

@@ -44,6 +44,8 @@
 extern "C" {
 #endif
 
+#define IP6_MIN_MTU_LENGTH 1280
+
 /** This is the packed version of ip6_addr_t,
     used in network headers that are itself packed */
 #ifdef PACK_STRUCT_USE_INCLUDES

src/netif/lowpan6.c

@@ -881,7 +881,7 @@ lowpan6_if_init(struct netif *netif)
   MIB2_INIT_NETIF(netif, snmp_ifType_other, 0);
 
   /* maximum transfer unit */
-  netif->mtu = 1280;
+  netif->mtu = IP6_MIN_MTU_LENGTH;
 
   /* broadcast capability */
   netif->flags = NETIF_FLAG_BROADCAST /* | NETIF_FLAG_LOWPAN6 */;

src/netif/lowpan6_ble.c

@@ -417,7 +417,7 @@ rfc7668_if_init(struct netif *netif)
   MIB2_INIT_NETIF(netif, snmp_ifType_other, 0);
 
   /* maximum transfer unit, set according to RFC7668 ch2.4 */
-  netif->mtu = 1280;
+  netif->mtu = IP6_MIN_MTU_LENGTH;
 
   /* no flags set (no broadcast, ethernet,...)*/
   netif->flags = 0;