diff --git a/README.txt b/README.txt
index 59648d01f4c..5d3721f4c50 100644
--- a/README.txt
+++ b/README.txt
@@ -464,9 +464,9 @@ Notes about Header Files
 
     Certain header files, such as setjmp.h, stdarg.h, and math.h, may still
     be needed from your toolchain and your compiler may not, however, be able
-    to find these if you compile NuttX without using standard header file.
-    If that is the case, one solution is to copy those header file from
-    your toolchain into the NuttX include directory.
+    to find these if you compile NuttX without using standard header files
+    (ie., with -nostdinc).  If that is the case, one solution is to copy
+    those header file from your toolchain into the NuttX include directory.
 
   Duplicated Header Files.
 
diff --git a/include/nuttx/net/netconfig.h b/include/nuttx/net/netconfig.h
index 1e79580ee35..77689ae32c5 100644
--- a/include/nuttx/net/netconfig.h
+++ b/include/nuttx/net/netconfig.h
@@ -226,6 +226,12 @@
 #  define MIN_NET_DEV_MTU   CONFIG_NET_6LOWPAN_MTU
 #  define MAX_NET_DEV_MTU   CONFIG_NET_6LOWPAN_MTU
 
+/* For the IEEE802.15.4 MAC device, we will use the packet MTU
+ * (which is probably much larger than the IEEE802.15.4 fram size)
+ */
+
+#  define NET_LO_MTU        MAX_NET_DEV_MTU
+
 #else
   /* Perhaps only Unix domain sockets or the loopback device */
 
@@ -418,24 +424,105 @@
  * the minimum MSS for that case.
  */
 
-#define TCP_MSS(d,h)        (NET_DEV_MTU(d) - NET_LL_HDRLEN(d) - TCP_HDRLEN - (h))
-#define LO_TCP_MSS(h)       (NET_LO_MTU - (h))
+#define TCP_MSS(d,h)            (NET_DEV_MTU(d) - NET_LL_HDRLEN(d) - TCP_HDRLEN - (h))
+#define LO_TCP_MSS(h)           (NET_LO_MTU - (h))
 
-/* If Ethernet is supported, then it will have the smaller MSS */
-
-#if defined(CONFIG_NET_SLIP)
-#  define SLIP_TCP_MSS(h)   (CONFIG_NET_SLIP_MTU - (h))
-#  define __MIN_TCP_MSS(h)  SLIP_TCP_MSS(h)
-#elif defined(CONFIG_NET_LOOPBACK)
-#  define LO_TCP_MSS(h)      (NET_LO_MTU - (h))
-#  define __MIN_TCP_MSS(h)   LO_TCP_MSS(h)
-#endif
+/* Get the smallest and largest  */
 
 #ifdef CONFIG_NET_ETHERNET
-#  define ETH_TCP_MSS(h)    (CONFIG_NET_ETH_MTU - ETH_HDRLEN - (h))
-#  undef __MIN_TCP_MSS
-#  define __MIN_TCP_MSS(h)  ETH_TCP_MSS(h)
-#  define __MAX_TCP_MSS(h)  ETH_TCP_MSS(h)
+#  define ETH_TCP_MSS(h)        (CONFIG_NET_ETH_MTU - ETH_HDRLEN - (h))
+#  ifndef CONFIG_NET_MULTILINK
+#    define __MIN_TCP_MSS(h)    ETH_TCP_MSS(h)
+#    define __MAX_TCP_MSS(h)    ETH_TCP_MSS(h)
+#  endif
+#endif
+
+#ifdef CONFIG_NET_6LOWPAN
+#  define IEEE802154_TCP_MSS(h) CONFIG_NET_6LOWPAN_MAXPAYLOAD
+#  ifndef CONFIG_NET_MULTILINK
+#    define __MIN_TCP_MSS(h)    IEEE802154_TCP_MSS(h)
+#    define __MAX_TCP_MSS(h)    IEEE802154_TCP_MSS(h)
+#  endif
+#endif
+
+#ifdef CONFIG_NET_LOOPBACK
+#  define LO_TCP_MSS(h)         (NET_LO_MTU - (h))
+#  ifndef CONFIG_NET_MULTILINK
+#    define __MIN_TCP_MSS(h)    LO_TCP_MSS(h)
+#    define __MAX_TCP_MSS(h)    LO_TCP_MSS(h)
+#  endif
+#endif
+
+#ifdef CONFIG_NET_SLIP
+#  define SLIP_TCP_MSS(h)       (CONFIG_NET_SLIP_MTU - (h))
+#  ifndef CONFIG_NET_MULTILINK
+#    define __MIN_TCP_MSS(h)    SLIP_TCP_MSS(h)
+#    define __MAX_TCP_MSS(h)    SLIP_TCP_MSS(h)
+#  endif
+#endif
+
+#ifdef CONFIG_NET_MULTILINK
+#  undef __LAST_MIN_TCP_MSS
+#  undef __LAST_MAX_TCP_MSS
+
+#  ifdef CONFIG_NET_ETHERNET
+#    ifdef __LAST_MIN_TCP_MSS
+#      define __MIN_TCP_MSS(h)  MIN(ETH_TCP_MSS(h),__LAST_MIN_TCP_MSS(h))
+#      define __MAX_TCP_MSS(h)  MAX(ETH_TCP_MSS(h),__LAST_MAX_TCP_MSS(h))
+#    else
+#      define __MIN_TCP_MSS(h)  ETH_TCP_MSS(h)
+#      define __MAX_TCP_MSS(h)  ETH_TCP_MSS(h)
+#    endif
+#    undef __LAST_MIN_TCP_MSS
+#    undef __LAST_MAX_TCP_MSS
+#    define __LAST_MIN_TCP_MSS(h) __MIN_TCP_MSS(h)
+#    define __LAST_MAX_TCP_MSS(h) __MAX_TCP_MSS(h)
+#  endif
+
+#  ifdef CONFIG_NET_6LOWPAN
+#    ifdef __LAST_MIN_TCP_MSS
+#      define __MIN_TCP_MSS(h)  MIN(IEEE802154_TCP_MSS(h),__LAST_MIN_TCP_MSS(h))
+#      define __MAX_TCP_MSS(h)  MAX(IEEE802154_TCP_MSS(h),__LAST_MAX_TCP_MSS(h))
+#    else
+#      define __MIN_TCP_MSS(h)  IEEE802154_TCP_MSS(h)
+#      define __MAX_TCP_MSS(h)  IEEE802154_TCP_MSS(h)
+#    endif
+#    undef __LAST_MIN_TCP_MSS
+#    undef __LAST_MAX_TCP_MSS
+#    define __LAST_MIN_TCP_MSS(h) __MIN_TCP_MSS(h)
+#    define __LAST_MAX_TCP_MSS(h) __MAX_TCP_MSS(h)
+#  endif
+
+#  ifdef CONFIG_NET_LOOPBACK
+#    ifdef __LAST_MIN_TCP_MSS
+#      define __MIN_TCP_MSS(h)  MIN(LO_TCP_MSS(h),__LAST_MIN_TCP_MSS(h))
+#      define __MAX_TCP_MSS(h)  MAX(LO_TCP_MSS(h),__LAST_MAX_TCP_MSS(h))
+#    else
+#      define __MIN_TCP_MSS(h)  LO_TCP_MSS(h)
+#      define __MAX_TCP_MSS(h)  LO_TCP_MSS(h)
+#    endif
+#    undef __LAST_MIN_TCP_MSS
+#    undef __LAST_MAX_TCP_MSS
+#    define __LAST_MIN_TCP_MSS(h) __MIN_TCP_MSS(h)
+#    define __LAST_MAX_TCP_MSS(h) __MAX_TCP_MSS(h)
+#  endif
+
+#  ifdef CONFIG_NET_SLIP
+#    ifdef __LAST_MIN_TCP_MSS
+#      define __MIN_TCP_MSS(h)  MIN(SLIP_TCP_MSS(h),__LAST_MIN_TCP_MSS(h))
+#      define __MAX_TCP_MSS(h)  MAX(SLIP_TCP_MSS(h),__LAST_MAX_TCP_MSS(h))
+#    else
+#      define __MIN_TCP_MSS(h)  SLIP_TCP_MSS(h)
+#      define __MAX_TCP_MSS(h)  SLIP_TCP_MSS(h)
+#    endif
+#    undef __LAST_MIN_TCP_MSS
+#    undef __LAST_MAX_TCP_MSS
+#    define __LAST_MIN_TCP_MSS(h) __MIN_TCP_MSS(h)
+#    define __LAST_MAX_TCP_MSS(h) __MAX_TCP_MSS(h)
+#  endif
+
+#  undef __LAST_MIN_TCP_MSS
+#  undef __LAST_MAX_TCP_MSS
 #endif
 
 /* If SLIP is supported, then it will have the larger MSS */
diff --git a/net/sixlowpan/sixlowpan_tcpsend.c b/net/sixlowpan/sixlowpan_tcpsend.c
index b515933053f..4e9f01d2378 100644
--- a/net/sixlowpan/sixlowpan_tcpsend.c
+++ b/net/sixlowpan/sixlowpan_tcpsend.c
@@ -126,14 +126,22 @@ ssize_t psock_6lowpan_tcp_send(FAR struct socket *psock, FAR const void *buf,
 
 #ifdef CONFIG_NETDEV_MULTINIC
   dev = netdev_findby_ipv6addr(conn->u.ipv6.laddr, conn->u.ipv6.raddr);
+#ifdef CONFIG_NETDEV_MULTILINK
   if (dev == NULL || dev->d_lltype != NET_LL_IEEE802154)
+#else
+  if (dev == NULL)
+#endif
     {
       nwarn("WARNING: Not routable or not IEEE802.15.4 MAC\n");
       return (ssize_t)-ENETUNREACH;
     }
 #else
   dev = netdev_findby_ipv6addr(conn->u.ipv6.raddr);
+#ifdef CONFIG_NETDEV_MULTILINK
+  if (dev == NULL || dev->d_lltype != NET_LL_IEEE802154)
+#else
   if (dev == NULL)
+#endif
     {
       nwarn("WARNING: Not routable\n");
       return (ssize_t)-ENETUNREACH;
diff --git a/net/sixlowpan/sixlowpan_udpsend.c b/net/sixlowpan/sixlowpan_udpsend.c
index be128918caf..7f558101805 100644
--- a/net/sixlowpan/sixlowpan_udpsend.c
+++ b/net/sixlowpan/sixlowpan_udpsend.c
@@ -127,14 +127,22 @@ ssize_t psock_6lowpan_udp_send(FAR struct socket *psock, FAR const void *buf,
 
 #ifdef CONFIG_NETDEV_MULTINIC
   dev = netdev_findby_ipv6addr(conn->u.ipv6.laddr, conn->u.ipv6.raddr);
+#ifdef CONFIG_NETDEV_MULTILINK
   if (dev == NULL || dev->d_lltype != NET_LL_IEEE802154)
+#else
+  if (dev == NULL)
+#endif
     {
       nwarn("WARNING: Not routable or not IEEE802.15.4 MAC\n");
       return (ssize_t)-ENETUNREACH;
     }
 #else
   dev = netdev_findby_ipv6addr(conn->u.ipv6.raddr);
+#ifdef CONFIG_NETDEV_MULTILINK
+  if (dev == NULL || dev->d_lltype != NET_LL_IEEE802154)
+#else
   if (dev == NULL)
+#endif
     {
       nwarn("WARNING: Not routable\n");
       return (ssize_t)-ENETUNREACH;