diff --git a/include/nuttx/net/netconfig.h b/include/nuttx/net/netconfig.h
index b589fc31df..d153a45d78 100644
--- a/include/nuttx/net/netconfig.h
+++ b/include/nuttx/net/netconfig.h
@@ -128,20 +128,10 @@
 #  endif
 #endif
 
-#ifndef CONFIG_NET_6LOWPAN_FRAG
-#  undef CONFIG_NET_6LOWPAN_MTU
-#  undef CONFIG_NET_6LOWPAN_TCP_RECVWNDO
-#endif
-
 #ifndef CONFIG_NET_6LOWPAN_MTU
-#  undef CONFIG_NET_6LOWPAN_TCP_RECVWNDO
-#  ifdef CONFIG_NET_6LOWPAN_FRAG
-#    define CONFIG_NET_6LOWPAN_MTU 1294
-#    define CONFIG_NET_6LOWPAN_TCP_RECVWNDO 1220
-#  else
-#    define CONFIG_NET_6LOWPAN_MTU CONFIG_NET_6LOWPAN_FRAMELEN
-#    define CONFIG_NET_6LOWPAN_TCP_RECVWNDO (CONFIG_NET_6LOWPAN_FRAMELEN - 25)
-#  endif
+#  define CONFIG_NET_6LOWPAN_MTU          1294
+#  undef  CONFIG_NET_6LOWPAN_TCP_RECVWNDO
+#  define CONFIG_NET_6LOWPAN_TCP_RECVWNDO 1220
 #endif
 
 /* We are supporting multiple network devices using different link layer
diff --git a/include/nuttx/net/sixlowpan.h b/include/nuttx/net/sixlowpan.h
index 02fb79f360..457044bca1 100644
--- a/include/nuttx/net/sixlowpan.h
+++ b/include/nuttx/net/sixlowpan.h
@@ -382,7 +382,6 @@ struct sixlowpan_reassbuf_s
 
   FAR struct sixlowpan_reassbuf_s *rb_flink;
 
-#if CONFIG_NET_6LOWPAN_FRAG
   /* Fragmentation is handled frame by frame and requires that certain
    * state information be retained from frame to frame.  That additional
    * information follows the externally visible packet buffer.
@@ -439,7 +438,6 @@ struct sixlowpan_reassbuf_s
    */
 
   systime_t rb_time;
-#endif /* CONFIG_NET_6LOWPAN_FRAG */
 };
 
 /****************************************************************************
diff --git a/net/sixlowpan/Kconfig b/net/sixlowpan/Kconfig
index a8b76568d1..8722f27a8c 100644
--- a/net/sixlowpan/Kconfig
+++ b/net/sixlowpan/Kconfig
@@ -5,17 +5,9 @@
 
 if NET_6LOWPAN
 
-config NET_6LOWPAN_FRAG
-	bool "6LoWPAN Fragmentation"
-	default y
-	---help---
-		CONFIG_NET_6LOWPAN_FRAG specifies if 6lowpan fragmentation should be
-		used or not. Fragmentation is on by default.
-
 config NET_6LOWPAN_NREASSBUF
 	int "Number of preallocated reassembly buffers"
 	default 2
-	depends on NET_6LOWPAN_FRAG
 	---help---
 		Large IPv6 packets will be fragmented by 6LoWPAN into multiple
 		frames and reconstitued into a reassembly buffer on the receiving
@@ -36,7 +28,6 @@ config NET_6LOWPAN_NREASSBUF
 config NET_6LOWPAN_REASS_STATIC
 	bool "Static reassembly buffers"
 	default n
-	depends on NET_6LOWPAN_FRAG
 	---help---
 		By default, reassembly buffers may be allocated dynamically from the
 		stack when all of the statically allocation reassembly buffers are
@@ -201,7 +192,6 @@ config NET_6LOWPAN_MTU
 	int "6LoWPAN packet buffer size"
 	default 1294
 	range 590 1518
-	depends on NET_6LOWPAN_FRAG
 	---help---
 		Packet buffer size.  This size includes the TCP/UDP payload plus the
 		size of TCP/UDP header, the IP header, and the Ethernet header.
@@ -215,8 +205,7 @@ config NET_6LOWPAN_MTU
 
 config NET_6LOWPAN_TCP_RECVWNDO
 	int "6LoWPAN TCP receive window size"
-	default 1220 if NET_6LOWPAN_FRAG
-	default 102 if !NET_6LOWPAN_FRAG
+	default 1220
 	depends on NET_TCP
 	---help---
 		The size of the advertised receiver's window.   Should be set low
diff --git a/net/sixlowpan/Make.defs b/net/sixlowpan/Make.defs
index 654a4e4bcc..ef49ab6e4d 100644
--- a/net/sixlowpan/Make.defs
+++ b/net/sixlowpan/Make.defs
@@ -41,6 +41,7 @@ ifeq ($(CONFIG_NET_6LOWPAN),y)
 
 NET_CSRCS += sixlowpan_initialize.c sixlowpan_globals.c sixlowpan_utils.c
 NET_CSRCS += sixlowpan_input.c sixlowpan_framer.c sixlowpan_framelist.c
+NET_CSRCS += sixlowpan_reassbuf.c
 
 ifeq ($(CONFIG_NET_TCP),y)
 NET_CSRCS += sixlowpan_tcpsend.c
@@ -68,10 +69,6 @@ ifeq ($(CONFIG_NET_6LOWPAN_COMPRESSION_HC06),y)
 NET_CSRCS += sixlowpan_hc06.c
 endif
 
-ifeq ($(CONFIG_NET_6LOWPAN_FRAG),y)
-NET_CSRCS += sixlowpan_reassbuf.c
-endif
-
 # Include the sixlowpan directory in the build
 
 DEPPATH += --dep-path sixlowpan
diff --git a/net/sixlowpan/sixlowpan_framelist.c b/net/sixlowpan/sixlowpan_framelist.c
index 3ce46dee4f..93edda8cca 100644
--- a/net/sixlowpan/sixlowpan_framelist.c
+++ b/net/sixlowpan/sixlowpan_framelist.c
@@ -385,11 +385,9 @@ int sixlowpan_queue_frames(FAR struct radio_driver_s *radio,
   FAR uint8_t *fptr;
   int framer_hdrlen;
   struct netdev_varaddr_s bcastmac;
-#ifdef CONFIG_NET_6LOWPAN_FRAG
   uint16_t pktlen;
   uint16_t paysize;
   uint16_t outlen = 0;
-#endif
   uint8_t protosize;
   int ret;
 
@@ -501,7 +499,6 @@ int sixlowpan_queue_frames(FAR struct radio_driver_s *radio,
 
   if (buflen > (SIXLOWPAN_FRAMELEN - g_frame_hdrlen - protosize))
     {
-#ifdef CONFIG_NET_6LOWPAN_FRAG
       /* qhead will hold the generated frame list; frames will be
        * added at qtail.
        */
@@ -705,13 +702,6 @@ int sixlowpan_queue_frames(FAR struct radio_driver_s *radio,
       /* Update the datagram TAG value */
 
       reass->rb_dgramtag++;
-#else
-      nerr("ERROR: Packet too large: %d\n", buflen);
-      nerr("       Cannot to be sent without fragmentation support\n");
-      nerr("       dropping packet\n");
-
-      return -E2BIG;
-#endif
     }
   else
     {
diff --git a/net/sixlowpan/sixlowpan_initialize.c b/net/sixlowpan/sixlowpan_initialize.c
index 8ad5bb9cd4..2f059cd049 100644
--- a/net/sixlowpan/sixlowpan_initialize.c
+++ b/net/sixlowpan/sixlowpan_initialize.c
@@ -69,11 +69,9 @@
 
 void sixlowpan_initialize(void)
 {
-#ifdef  CONFIG_NET_6LOWPAN_FRAG
   /* Initialize the reassembly buffer allocator */
 
   sixlowpan_reass_initialize();
-#endif
 
 #ifdef CONFIG_NET_6LOWPAN_COMPRESSION_HC06
   /* Initialize HC06 data data structures */
diff --git a/net/sixlowpan/sixlowpan_input.c b/net/sixlowpan/sixlowpan_input.c
index 2b9da05d59..66d53e1e12 100644
--- a/net/sixlowpan/sixlowpan_input.c
+++ b/net/sixlowpan/sixlowpan_input.c
@@ -115,11 +115,9 @@
  * Private Data
  ****************************************************************************/
 
-#ifdef CONFIG_NET_6LOWPAN_FRAG
 /* This big buffer could be avoided with a little more effort */
 
 static uint8_t g_bitbucket[UNCOMP_MAXHDR];
-#endif
 
 /****************************************************************************
  * Private Functions
@@ -252,25 +250,22 @@ static void sixlowpan_uncompress_ipv6hdr(FAR uint8_t *fptr, FAR uint8_t *bptr)
 static int sixlowpan_frame_process(FAR struct radio_driver_s *radio,
                                    FAR const void *metadata, FAR struct iob_s *iob)
 {
+  FAR struct sixlowpan_reassbuf_s *reass;
+  struct netdev_varaddr_s fragsrc;
   FAR uint8_t *fptr;          /* Convenience pointer to beginning of the frame */
   FAR uint8_t *bptr;          /* Used to redirect uncompressed header to the bitbucket */
   FAR uint8_t *hc1;           /* Convenience pointer to HC1 data */
+  FAR uint8_t *fragptr;       /* Pointer to the fragmentation header */
   uint16_t fragsize  = 0;     /* Size of the IP packet (read from fragment) */
   uint16_t paysize;           /* Size of the data payload */
+  uint16_t fragtag   = 0;     /* Tag of the fragment */
   uint8_t fragoffset = 0;     /* Offset of the fragment in the IP packet */
+  bool isfrag        = false; /* true: Frame is a fragment */
+  bool isfirstfrag   = false; /* true: Frame is the first fragement of the series */
   int reqsize;                /* Required buffer size */
   int hdrsize;                /* Size of the IEEE802.15.4 header */
   int ret;
 
-#ifdef CONFIG_NET_6LOWPAN_FRAG
-  FAR struct sixlowpan_reassbuf_s *reass;
-  struct netdev_varaddr_s fragsrc;
-  FAR uint8_t *fragptr;       /* Pointer to the fragmentation header */
-  bool isfrag        = false;
-  bool isfirstfrag   = false;
-  uint16_t fragtag   = 0;     /* Tag of the fragment */
-#endif /* CONFIG_NET_6LOWPAN_FRAG */
-
   /* Get a pointer to the payload following the IEEE802.15.4 frame header(s).
    * This size includes both fragmentation and FCF headers.
    */
@@ -287,7 +282,6 @@ static int sixlowpan_frame_process(FAR struct radio_driver_s *radio,
   g_uncomp_hdrlen = 0;
   g_frame_hdrlen  = hdrsize;
 
-#ifdef CONFIG_NET_6LOWPAN_FRAG
   /* Since we don't support the mesh and broadcast header, the first header
    * we look for is the fragmentation header.  NOTE that g_frame_hdrlen
    * already includes the fragementation header, if presetn.
@@ -420,9 +414,6 @@ static int sixlowpan_frame_process(FAR struct radio_driver_s *radio,
       bptr  = reass->rb_buf;
       break;
     }
-#else
-  bptr  = radio->r_dev.d_buf;
-#endif /* CONFIG_NET_6LOWPAN_FRAG */
 
   /* Process next dispatch and headers */
 
@@ -460,7 +451,6 @@ static int sixlowpan_frame_process(FAR struct radio_driver_s *radio,
       goto errout_with_reass;
     }
 
-#ifdef CONFIG_NET_6LOWPAN_FRAG
   /* Is this the first fragment is a sequence? */
 
   if (isfirstfrag)
@@ -482,7 +472,6 @@ static int sixlowpan_frame_process(FAR struct radio_driver_s *radio,
 
       g_uncomp_hdrlen = reass->rb_boffset;
     }
-#endif /* CONFIG_NET_6LOWPAN_FRAG */
 
   /* Copy "payload" from the frame buffer to the IEEE802.15.4 MAC driver's
    * packet buffer, d_buf.  If this frame is a first fragment or not part of
@@ -514,7 +503,6 @@ static int sixlowpan_frame_process(FAR struct radio_driver_s *radio,
   memcpy(radio->r_dev.d_buf + g_uncomp_hdrlen + (fragoffset << 3),
          fptr + g_frame_hdrlen, paysize);
 
-#ifdef CONFIG_NET_6LOWPAN_FRAG
   /* Update reass->rb_accumlen if the frame is a fragment, reass->rb_pktlen
    * otherwise.
    */
@@ -560,17 +548,6 @@ static int sixlowpan_frame_process(FAR struct radio_driver_s *radio,
 errout_with_reass:
   sixlowpan_reass_free(reass);
   return ret;
-
-#else
-  /* Deliver the packet to the IP stack */
-
-  radio->r_dev.d_len = paysize + g_uncomp_hdrlen;
-  return INPUT_COMPLETE;
-
-errout_with_reass:
-  return ret;
-
-#endif /* CONFIG_NET_6LOWPAN_FRAG */
 }
 
 /****************************************************************************
@@ -589,9 +566,7 @@ errout_with_reass:
 
 static int sixlowpan_dispatch(FAR struct radio_driver_s *radio)
 {
-#ifdef CONFIG_NET_6LOWPAN_FRAG
   FAR struct sixlowpan_reassbuf_s *reass;
-#endif
   int ret;
 
   sixlowpan_dumpbuffer("Incoming packet",
@@ -617,13 +592,11 @@ static int sixlowpan_dispatch(FAR struct radio_driver_s *radio)
 
   ret = ipv6_input(&radio->r_dev);
 
-#ifdef CONFIG_NET_6LOWPAN_FRAG
   /* Free the reassemby buffer */
 
   reass = (FAR struct sixlowpan_reassbuf_s *)radio->r_dev.d_buf;
   DEBUGASSERT(reass != NULL);
   sixlowpan_reass_free(reass);
-#endif
 
   return ret;
 }
diff --git a/net/sixlowpan/sixlowpan_internal.h b/net/sixlowpan/sixlowpan_internal.h
index bdd5b894d3..b8332b5c1a 100644
--- a/net/sixlowpan/sixlowpan_internal.h
+++ b/net/sixlowpan/sixlowpan_internal.h
@@ -704,9 +704,7 @@ int sixlowpan_extract_destaddr(FAR struct radio_driver_s *radio,
  *
  ****************************************************************************/
 
-#ifdef  CONFIG_NET_6LOWPAN_FRAG
 void sixlowpan_reass_initialize(void);
-#endif /* CONFIG_NET_6LOWPAN_FRAG */
 
 /****************************************************************************
  * Name: sixlowpan_reass_allocate
@@ -733,11 +731,9 @@ void sixlowpan_reass_initialize(void);
  *
  ****************************************************************************/
 
-#ifdef  CONFIG_NET_6LOWPAN_FRAG
 FAR struct sixlowpan_reassbuf_s *
   sixlowpan_reass_allocate(uint16_t reasstag,
                            FAR const struct netdev_varaddr_s *fragsrc);
-#endif /* CONFIG_NET_6LOWPAN_FRAG */
 
 /****************************************************************************
  * Name: sixlowpan_reass_find
@@ -758,11 +754,9 @@ FAR struct sixlowpan_reassbuf_s *
  *
  ****************************************************************************/
 
-#ifdef  CONFIG_NET_6LOWPAN_FRAG
 FAR struct sixlowpan_reassbuf_s *
   sixlowpan_reass_find(uint16_t reasstag,
                        FAR const struct netdev_varaddr_s *fragsrc);
-#endif /* CONFIG_NET_6LOWPAN_FRAG */
 
 /****************************************************************************
  * Name: sixlowpan_reass_free
@@ -784,9 +778,7 @@ FAR struct sixlowpan_reassbuf_s *
  *
  ****************************************************************************/
 
-#ifdef  CONFIG_NET_6LOWPAN_FRAG
 void sixlowpan_reass_free(FAR struct sixlowpan_reassbuf_s *reass);
-#endif /* CONFIG_NET_6LOWPAN_FRAG */
 
 #endif /* CONFIG_NET_6LOWPAN */
 #endif /* _NET_SIXLOWPAN_SIXLOWPAN_INTERNAL_H */
diff --git a/net/sixlowpan/sixlowpan_reassbuf.c b/net/sixlowpan/sixlowpan_reassbuf.c
index 4760488dd6..b308a04c8f 100644
--- a/net/sixlowpan/sixlowpan_reassbuf.c
+++ b/net/sixlowpan/sixlowpan_reassbuf.c
@@ -52,8 +52,6 @@
 
 #include "sixlowpan_internal.h"
 
-#ifdef CONFIG_NET_6LOWPAN_FRAG
-
 /****************************************************************************
  * Pre-processor Definitions
  ****************************************************************************/
@@ -454,5 +452,3 @@ void sixlowpan_reass_free(FAR struct sixlowpan_reassbuf_s *reass)
 #endif
     }
 }
-
-#endif /* CONFIG_NET_6LOWPAN_FRAG */