diff --git a/CHANGELOG b/CHANGELOG
index ea72631d..28a4f309 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -6,6 +6,10 @@ HISTORY
 
   ++ New features:
 
+  2015-10-09: Simon Goldschmidt
+  * started to move "private" header files containing implementation details to
+    "lwip/priv/" include directory to seperate the API from the implementation.
+
   2015-10-07: Simon Goldschmidt
   * added sntp client as first "supported" application layer protocol implementation
     added 'apps' folder
diff --git a/src/api/api_lib.c b/src/api/api_lib.c
index 3ad26f8e..68a2e129 100644
--- a/src/api/api_lib.c
+++ b/src/api/api_lib.c
@@ -44,14 +44,13 @@
 #if LWIP_NETCONN /* don't build if not configured for use in lwipopts.h */
 
 #include "lwip/api.h"
-#include "lwip/tcpip.h"
 #include "lwip/memp.h"
 
 #include "lwip/ip.h"
 #include "lwip/raw.h"
 #include "lwip/udp.h"
-#include "lwip/tcp.h"
-#include "lwip/tcp_impl.h"
+#include "lwip/priv/tcp_priv.h"
+#include "lwip/priv/tcpip_priv.h"
 
 #include <string.h>
 
diff --git a/src/api/api_msg.c b/src/api/api_msg.c
index 466e4888..96dcde42 100644
--- a/src/api/api_msg.c
+++ b/src/api/api_msg.c
@@ -40,7 +40,7 @@
 
 #if LWIP_NETCONN /* don't build if not configured for use in lwipopts.h */
 
-#include "lwip/api_msg.h"
+#include "lwip/priv/api_msg.h"
 
 #include "lwip/ip.h"
 #include "lwip/udp.h"
@@ -48,10 +48,10 @@
 #include "lwip/raw.h"
 
 #include "lwip/memp.h"
-#include "lwip/tcpip.h"
 #include "lwip/igmp.h"
 #include "lwip/dns.h"
 #include "lwip/mld6.h"
+#include "lwip/priv/tcpip_priv.h"
 
 #include <string.h>
 
diff --git a/src/api/netifapi.c b/src/api/netifapi.c
index 4985f80c..7fd92591 100644
--- a/src/api/netifapi.c
+++ b/src/api/netifapi.c
@@ -36,8 +36,8 @@
 #if LWIP_NETIF_API /* don't build if not configured for use in lwipopts.h */
 
 #include "lwip/netifapi.h"
-#include "lwip/tcpip.h"
 #include "lwip/memp.h"
+#include "lwip/priv/tcpip_priv.h"
 
 #define NETIFAPI_VAR_REF(name)      API_VAR_REF(name)
 #define NETIFAPI_VAR_DECLARE(name)  API_VAR_DECLARE(struct netifapi_msg, name)
diff --git a/src/api/sockets.c b/src/api/sockets.c
index 6dab6e05..4f34bd04 100644
--- a/src/api/sockets.c
+++ b/src/api/sockets.c
@@ -50,9 +50,9 @@
 #include "lwip/tcp.h"
 #include "lwip/raw.h"
 #include "lwip/udp.h"
-#include "lwip/tcpip.h"
 #include "lwip/memp.h"
 #include "lwip/pbuf.h"
+#include "lwip/priv/tcpip_priv.h"
 #if LWIP_CHECKSUM_ON_COPY
 #include "lwip/inet_chksum.h"
 #endif
diff --git a/src/api/tcpip.c b/src/api/tcpip.c
index 7c53e144..74b8fd44 100644
--- a/src/api/tcpip.c
+++ b/src/api/tcpip.c
@@ -40,11 +40,12 @@
 
 #if !NO_SYS /* don't build if not configured for use in lwipopts.h */
 
+#include "lwip/tcpip.h"
+#include "lwip/priv/tcpip_priv.h"
 #include "lwip/sys.h"
 #include "lwip/memp.h"
 #include "lwip/mem.h"
 #include "lwip/pbuf.h"
-#include "lwip/tcpip.h"
 #include "lwip/init.h"
 #include "lwip/ip.h"
 #include "netif/etharp.h"
@@ -506,7 +507,8 @@ tcpip_pppapi_lock(struct pppapi_msg* pppapimsg)
  * @param ctx parameter passed to function
  * @return a struct pointer to pass to tcpip_trycallback().
  */
-struct tcpip_callback_msg* tcpip_callbackmsg_new(tcpip_callback_fn function, void *ctx)
+struct tcpip_callback_msg*
+tcpip_callbackmsg_new(tcpip_callback_fn function, void *ctx)
 {
   struct tcpip_msg *msg = (struct tcpip_msg *)memp_malloc(MEMP_TCPIP_MSG_API);
   if (msg == NULL) {
@@ -523,7 +525,8 @@ struct tcpip_callback_msg* tcpip_callbackmsg_new(tcpip_callback_fn function, voi
  *
  * @param msg the message to free
  */
-void tcpip_callbackmsg_delete(struct tcpip_callback_msg* msg)
+void
+tcpip_callbackmsg_delete(struct tcpip_callback_msg* msg)
 {
   memp_free(MEMP_TCPIP_MSG_API, msg);
 }
diff --git a/src/core/init.c b/src/core/init.c
index 4fdc581f..009baf8d 100644
--- a/src/core/init.c
+++ b/src/core/init.c
@@ -49,7 +49,7 @@
 #include "lwip/ip.h"
 #include "lwip/raw.h"
 #include "lwip/udp.h"
-#include "lwip/tcp_impl.h"
+#include "lwip/priv/tcp_priv.h"
 #include "lwip/snmp.h"
 #include "lwip/autoip.h"
 #include "lwip/igmp.h"
diff --git a/src/core/ipv4/ip4.c b/src/core/ipv4/ip4.c
index cbe003ee..e968436a 100644
--- a/src/core/ipv4/ip4.c
+++ b/src/core/ipv4/ip4.c
@@ -52,7 +52,7 @@
 #include "lwip/igmp.h"
 #include "lwip/raw.h"
 #include "lwip/udp.h"
-#include "lwip/tcp_impl.h"
+#include "lwip/priv/tcp_priv.h"
 #include "lwip/dhcp.h"
 #include "lwip/autoip.h"
 #include "lwip/stats.h"
diff --git a/src/core/ipv6/ip6.c b/src/core/ipv6/ip6.c
index 1be9944e..aa2f5969 100644
--- a/src/core/ipv6/ip6.c
+++ b/src/core/ipv6/ip6.c
@@ -52,7 +52,7 @@
 #include "lwip/icmp6.h"
 #include "lwip/raw.h"
 #include "lwip/udp.h"
-#include "lwip/tcp_impl.h"
+#include "lwip/priv/tcp_priv.h"
 #include "lwip/dhcp6.h"
 #include "lwip/nd6.h"
 #include "lwip/mld6.h"
diff --git a/src/core/memp.c b/src/core/memp.c
index 6ecfc49f..8ebde2d8 100644
--- a/src/core/memp.c
+++ b/src/core/memp.c
@@ -44,12 +44,10 @@
 #include "lwip/pbuf.h"
 #include "lwip/udp.h"
 #include "lwip/raw.h"
-#include "lwip/tcp_impl.h"
 #include "lwip/igmp.h"
 #include "lwip/api.h"
-#include "lwip/api_msg.h"
+#include "lwip/priv/api_msg.h"
 #include "lwip/sockets.h"
-#include "lwip/tcpip.h"
 #include "lwip/sys.h"
 #include "lwip/timers.h"
 #include "lwip/stats.h"
@@ -66,6 +64,8 @@
 #include "lwip/nd6.h"
 #include "lwip/ip6_frag.h"
 #include "lwip/mld6.h"
+#include "lwip/priv/tcp_priv.h"
+#include "lwip/priv/tcpip_priv.h"
 
 #include <string.h>
 
@@ -136,7 +136,7 @@ static
 #endif
 const u16_t memp_sizes[MEMP_MAX] = {
 #define LWIP_MEMPOOL(name,num,size,desc)  LWIP_MEM_ALIGN_SIZE(size),
-#include "lwip/memp_std.h"
+#include "lwip/priv/memp_std.h"
 };
 
 #if !MEMP_MEM_MALLOC /* don't build if not configured for use in lwipopts.h */
@@ -144,14 +144,14 @@ const u16_t memp_sizes[MEMP_MAX] = {
 /** This array holds the number of elements in each pool. */
 static const u16_t memp_num[MEMP_MAX] = {
 #define LWIP_MEMPOOL(name,num,size,desc)  (num),
-#include "lwip/memp_std.h"
+#include "lwip/priv/memp_std.h"
 };
 
 /** This array holds a textual description of each pool. */
 #ifdef LWIP_DEBUG
 static const char *memp_desc[MEMP_MAX] = {
 #define LWIP_MEMPOOL(name,num,size,desc)  (desc),
-#include "lwip/memp_std.h"
+#include "lwip/priv/memp_std.h"
 };
 #endif /* LWIP_DEBUG */
 
@@ -164,12 +164,12 @@ static const char *memp_desc[MEMP_MAX] = {
  */
 #define LWIP_MEMPOOL(name,num,size,desc) u8_t memp_memory_ ## name ## _base \
   [((num) * (MEMP_SIZE + MEMP_ALIGN_SIZE(size)))];
-#include "lwip/memp_std.h"
+#include "lwip/priv/memp_std.h"
 
 /** This array holds the base of each memory pool. */
 static u8_t *const memp_bases[] = {
 #define LWIP_MEMPOOL(name,num,size,desc) memp_memory_ ## name ## _base,
-#include "lwip/memp_std.h"
+#include "lwip/priv/memp_std.h"
 };
 
 #else /* MEMP_SEPARATE_POOLS */
@@ -177,7 +177,7 @@ static u8_t *const memp_bases[] = {
 /** This is the actual memory used by the pools (all pools in one big block). */
 static u8_t memp_memory[MEM_ALIGNMENT - 1
 #define LWIP_MEMPOOL(name,num,size,desc) + ( (num) * (MEMP_SIZE + MEMP_ALIGN_SIZE(size) ) )
-#include "lwip/memp_std.h"
+#include "lwip/priv/memp_std.h"
 ];
 
 #endif /* MEMP_SEPARATE_POOLS */
@@ -210,7 +210,7 @@ memp_sanity(void)
 #if defined(LWIP_DEBUG) && MEMP_STATS
 static const char * memp_overflow_names[] = {
 #define LWIP_MEMPOOL(name,num,size,desc) "/"desc,
-#include "lwip/memp_std.h"
+#include "lwip/priv/memp_std.h"
   };
 #endif
 
diff --git a/src/core/netif.c b/src/core/netif.c
index 4e28fb29..66b212b2 100644
--- a/src/core/netif.c
+++ b/src/core/netif.c
@@ -42,7 +42,7 @@
 #include "lwip/ip_addr.h"
 #include "lwip/ip6_addr.h"
 #include "lwip/netif.h"
-#include "lwip/tcp_impl.h"
+#include "lwip/priv/tcp_priv.h"
 #include "lwip/udp.h"
 #include "lwip/snmp_mib2.h"
 #include "lwip/igmp.h"
diff --git a/src/core/pbuf.c b/src/core/pbuf.c
index ba747c76..a6d08382 100644
--- a/src/core/pbuf.c
+++ b/src/core/pbuf.c
@@ -70,7 +70,7 @@
 #include "lwip/pbuf.h"
 #include "lwip/sys.h"
 #if LWIP_TCP && TCP_QUEUE_OOSEQ
-#include "lwip/tcp_impl.h"
+#include "lwip/priv/tcp_priv.h"
 #endif
 #if LWIP_CHECKSUM_ON_COPY
 #include "lwip/inet_chksum.h"
diff --git a/src/core/snmp/mib2.c b/src/core/snmp/mib2.c
index 515517ca..0d0bb0ca 100644
--- a/src/core/snmp/mib2.c
+++ b/src/core/snmp/mib2.c
@@ -56,7 +56,7 @@
 #include "lwip/ip.h"
 #include "lwip/ip_frag.h"
 #include "lwip/mem.h"
-#include "lwip/tcp_impl.h"
+#include "lwip/priv/tcp_priv.h"
 #include "lwip/udp.h"
 #include "lwip/snmp_asn1.h"
 #include "lwip/snmp_structs.h"
diff --git a/src/core/stats.c b/src/core/stats.c
index 7452f4e3..43734cee 100644
--- a/src/core/stats.c
+++ b/src/core/stats.c
@@ -56,7 +56,7 @@ stats_init(void)
 #if MEMP_STATS
   const char * memp_names[] = {
 #define LWIP_MEMPOOL(name,num,size,desc) desc,
-#include "lwip/memp_std.h"
+#include "lwip/priv/memp_std.h"
   };
   int i;
   for (i = 0; i < MEMP_MAX; i++) {
@@ -127,7 +127,7 @@ stats_display_memp(struct stats_mem *mem, int index)
 {
   const char * memp_names[] = {
 #define LWIP_MEMPOOL(name,num,size,desc) desc,
-#include "lwip/memp_std.h"
+#include "lwip/priv/memp_std.h"
   };
   if (index < MEMP_MAX) {
     stats_display_mem(mem, memp_names[index]);
diff --git a/src/core/tcp.c b/src/core/tcp.c
index eee80fdd..a477ef7d 100644
--- a/src/core/tcp.c
+++ b/src/core/tcp.c
@@ -48,7 +48,7 @@
 #include "lwip/mem.h"
 #include "lwip/memp.h"
 #include "lwip/tcp.h"
-#include "lwip/tcp_impl.h"
+#include "lwip/priv/tcp_priv.h"
 #include "lwip/debug.h"
 #include "lwip/stats.h"
 #include "lwip/ip6.h"
diff --git a/src/core/tcp_in.c b/src/core/tcp_in.c
index aedb2462..14a59b2f 100644
--- a/src/core/tcp_in.c
+++ b/src/core/tcp_in.c
@@ -45,7 +45,7 @@
 
 #if LWIP_TCP /* don't build if not configured for use in lwipopts.h */
 
-#include "lwip/tcp_impl.h"
+#include "lwip/priv/tcp_priv.h"
 #include "lwip/def.h"
 #include "lwip/ip_addr.h"
 #include "lwip/netif.h"
diff --git a/src/core/tcp_out.c b/src/core/tcp_out.c
index a205e8a1..11380f33 100644
--- a/src/core/tcp_out.c
+++ b/src/core/tcp_out.c
@@ -42,7 +42,7 @@
 
 #if LWIP_TCP /* don't build if not configured for use in lwipopts.h */
 
-#include "lwip/tcp_impl.h"
+#include "lwip/priv/tcp_priv.h"
 #include "lwip/def.h"
 #include "lwip/mem.h"
 #include "lwip/memp.h"
diff --git a/src/core/timers.c b/src/core/timers.c
index ebaae508..c361f4f8 100644
--- a/src/core/timers.c
+++ b/src/core/timers.c
@@ -42,13 +42,13 @@
 #include "lwip/opt.h"
 
 #include "lwip/timers.h"
-#include "lwip/tcp_impl.h"
+#include "lwip/priv/tcp_priv.h"
 
 #if LWIP_TIMERS
 
 #include "lwip/def.h"
 #include "lwip/memp.h"
-#include "lwip/tcpip.h"
+#include "lwip/priv/tcpip_priv.h"
 
 #include "lwip/ip_frag.h"
 #include "netif/etharp.h"
diff --git a/src/include/lwip/memp.h b/src/include/lwip/memp.h
index 8b5228b5..9e3808e8 100644
--- a/src/include/lwip/memp.h
+++ b/src/include/lwip/memp.h
@@ -41,12 +41,12 @@ extern "C" {
 
 /* run once with empty definition to handle all custom includes in lwippools.h */
 #define LWIP_MEMPOOL(name,num,size,desc)
-#include "lwip/memp_std.h"
+#include "lwip/priv/memp_std.h"
 
 /* Create the list of all memory pools managed by memp. MEMP_MAX represents a NULL pool at the end */
 typedef enum {
 #define LWIP_MEMPOOL(name,num,size,desc)  MEMP_##name,
-#include "lwip/memp_std.h"
+#include "lwip/priv/memp_std.h"
   MEMP_MAX
 } memp_t;
 
@@ -60,7 +60,7 @@ typedef enum {
 #define LWIP_MALLOC_MEMPOOL_START 1
 #define LWIP_MALLOC_MEMPOOL(num, size) * MEMP_POOL_##size + 0
 #define LWIP_MALLOC_MEMPOOL_END
-#include "lwip/memp_std.h"
+#include "lwip/priv/memp_std.h"
     ) ,
     /* Get the last (via:
        MEMP_POOL_HELPER_END = ((u8_t) 0 + MEMP_POOL_A*0 + MEMP_POOL_B*0 + MEMP_POOL_C*1) */
@@ -69,7 +69,7 @@ typedef enum {
 #define LWIP_MALLOC_MEMPOOL_START
 #define LWIP_MALLOC_MEMPOOL(num, size) 0 + MEMP_POOL_##size *
 #define LWIP_MALLOC_MEMPOOL_END 1
-#include "lwip/memp_std.h"
+#include "lwip/priv/memp_std.h"
     )
 } memp_pool_helper_t;
 
diff --git a/src/include/lwip/api_msg.h b/src/include/lwip/priv/api_msg.h
similarity index 100%
rename from src/include/lwip/api_msg.h
rename to src/include/lwip/priv/api_msg.h
diff --git a/src/include/lwip/memp_std.h b/src/include/lwip/priv/memp_std.h
similarity index 100%
rename from src/include/lwip/memp_std.h
rename to src/include/lwip/priv/memp_std.h
diff --git a/src/include/lwip/tcp_impl.h b/src/include/lwip/priv/tcp_priv.h
similarity index 100%
rename from src/include/lwip/tcp_impl.h
rename to src/include/lwip/priv/tcp_priv.h
diff --git a/src/include/lwip/tcpip.h b/src/include/lwip/priv/tcpip_priv.h
similarity index 85%
rename from src/include/lwip/tcpip.h
rename to src/include/lwip/priv/tcpip_priv.h
index ec5480c6..91cdc2ca 100644
--- a/src/include/lwip/tcpip.h
+++ b/src/include/lwip/priv/tcpip_priv.h
@@ -29,14 +29,15 @@
  * Author: Adam Dunkels <adam@sics.se>
  *
  */
-#ifndef LWIP_HDR_TCPIP_H
-#define LWIP_HDR_TCPIP_H
+#ifndef LWIP_HDR_TCPIP_PRIV_H
+#define LWIP_HDR_TCPIP_PRIV_H
 
 #include "lwip/opt.h"
 
 #if !NO_SYS /* don't build if not configured for use in lwipopts.h */
 
-#include "lwip/api_msg.h"
+#include "lwip/tcpip.h"
+#include "lwip/priv/api_msg.h"
 #include "lwip/netifapi.h"
 #include "lwip/pppapi.h"
 #include "lwip/pbuf.h"
@@ -132,23 +133,10 @@ extern sys_mutex_t lock_tcpip_core;
 #endif /* LWIP_MPU_COMPATIBLE */
 
 
-
-/** Function prototype for the init_done function passed to tcpip_init */
-typedef void (*tcpip_init_done_fn)(void *arg);
-/** Function prototype for functions passed to tcpip_callback() */
-typedef void (*tcpip_callback_fn)(void *ctx);
-
-/* Forward declarations */
-struct tcpip_callback_msg;
-
-void tcpip_init(tcpip_init_done_fn tcpip_init_done, void *arg);
-
 #if LWIP_NETCONN || LWIP_SOCKET
 err_t tcpip_apimsg(struct api_msg *apimsg);
 #endif /* LWIP_NETCONN || LWIP_SOCKET */
 
-err_t tcpip_input(struct pbuf *p, struct netif *inp);
-
 #if PPPOS_SUPPORT && !PPP_INPROC_IRQ_SAFE
 err_t tcpip_pppos_input(struct pbuf *p, struct netif *inp);
 #endif /* PPPOS_SUPPORT && !PPP_INPROC_IRQ_SAFE */
@@ -167,21 +155,6 @@ err_t tcpip_pppapi_lock(struct pppapi_msg *pppapimsg);
 #endif /* LWIP_TCPIP_CORE_LOCKING */
 #endif /* LWIP_PPP_API */
 
-err_t tcpip_callback_with_block(tcpip_callback_fn function, void *ctx, u8_t block);
-#define tcpip_callback(f, ctx)              tcpip_callback_with_block(f, ctx, 1)
-
-struct tcpip_callback_msg* tcpip_callbackmsg_new(tcpip_callback_fn function, void *ctx);
-void   tcpip_callbackmsg_delete(struct tcpip_callback_msg* msg);
-err_t  tcpip_trycallback(struct tcpip_callback_msg* msg);
-
-/* free pbufs or heap memory from another context without blocking */
-err_t pbuf_free_callback(struct pbuf *p);
-err_t mem_free_callback(void *m);
-
-#if LWIP_TCPIP_TIMEOUT
-err_t tcpip_timeout(u32_t msecs, sys_timeout_handler h, void *arg);
-err_t tcpip_untimeout(sys_timeout_handler h, void *arg);
-#endif /* LWIP_TCPIP_TIMEOUT */
 
 enum tcpip_msg_type {
 #if LWIP_NETCONN || LWIP_SOCKET
@@ -242,4 +215,4 @@ struct tcpip_msg {
 
 #endif /* !NO_SYS */
 
-#endif /* LWIP_HDR_TCPIP_H */
+#endif /* LWIP_HDR_TCPIP_PRIV_H */
diff --git a/src/include/netif/ppp/vj.h b/src/include/netif/ppp/vj.h
index 3780667b..b8e46697 100644
--- a/src/include/netif/ppp/vj.h
+++ b/src/include/netif/ppp/vj.h
@@ -29,7 +29,7 @@
 #define VJ_H
 
 #include "lwip/ip.h"
-#include "lwip/tcp_impl.h"
+#include "lwip/priv/tcp_priv.h"
 
 #define MAX_SLOTS 16 /* must be > 2 and < 256 */
 #define MAX_HDR   128