diff --git a/CHANGELOG b/CHANGELOG
index db65b0fd..d4bdd666 100644
--- a/CHANGELOG
+++ b/CHANGELOG
@@ -19,6 +19,12 @@ HISTORY
 
   ++ New features:
 
+  2007-11-16 Simon Goldschmidt
+  * new files: ipv4/inet.c, ipv4/inet_chksum.c, ipv6/inet6.c
+    removed files: core/inet.c, core/inet6.c
+    Moved inet files into ipv4/ipv6 directory; splitted inet.c/inet.h into
+    inet and chksum part; changed includes in all lwIP files as appropriate
+
   2007-11-16 Simon Goldschmidt
   * api.h, api_msg.h, api_lib.c, api_msg.c, socket.h, socket.c: Added sequential
     dns resolver function for netconn api (netconn_gethostbyname) and socket api
diff --git a/src/core/ipv4/icmp.c b/src/core/ipv4/icmp.c
index d5c7aa8c..b8f29f4a 100644
--- a/src/core/ipv4/icmp.c
+++ b/src/core/ipv4/icmp.c
@@ -45,6 +45,7 @@
 
 #include "lwip/icmp.h"
 #include "lwip/inet.h"
+#include "lwip/inet_chksum.h"
 #include "lwip/ip.h"
 #include "lwip/def.h"
 #include "lwip/stats.h"
diff --git a/src/core/ipv4/igmp.c b/src/core/ipv4/igmp.c
index 7040a3af..7a72b353 100644
--- a/src/core/ipv4/igmp.c
+++ b/src/core/ipv4/igmp.c
@@ -81,17 +81,18 @@ Steve Reynolds
 
 #if LWIP_IGMP /* don't build if not configured for use in lwipopts.h */
 
+#include "lwip/igmp.h"
 #include "lwip/debug.h"
 #include "lwip/def.h"
 #include "lwip/mem.h"
 #include "lwip/ip.h"
 #include "lwip/inet.h"
+#include "lwip/inet_chksum.h"
 #include "lwip/netif.h"
 #include "lwip/icmp.h"
 #include "lwip/udp.h"
 #include "lwip/tcp.h"
 #include "lwip/stats.h"
-#include "lwip/igmp.h"
 
 #include "string.h"
 
diff --git a/src/core/ipv4/inet.c b/src/core/ipv4/inet.c
new file mode 100644
index 00000000..24c7ff46
--- /dev/null
+++ b/src/core/ipv4/inet.c
@@ -0,0 +1,278 @@
+/**
+ * @file
+ * Functions common to all TCP/IPv4 modules, such as the byte order functions.
+ *
+ */
+
+/*
+ * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification,
+ * are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
+ * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
+ * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
+ * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
+ * OF SUCH DAMAGE.
+ *
+ * This file is part of the lwIP TCP/IP stack.
+ *
+ * Author: Adam Dunkels <adam@sics.se>
+ *
+ */
+
+#include "lwip/opt.h"
+
+#include "lwip/inet.h"
+
+/* Here for now until needed in other places in lwIP */
+#ifndef isprint
+#define in_range(c, lo, up)  ((u8_t)c >= lo && (u8_t)c <= up)
+#define isprint(c)           in_range(c, 0x20, 0x7f)
+#define isdigit(c)           in_range(c, '0', '9')
+#define isxdigit(c)          (isdigit(c) || in_range(c, 'a', 'f') || in_range(c, 'A', 'F'))
+#define islower(c)           in_range(c, 'a', 'z')
+#define isspace(c)           (c == ' ' || c == '\f' || c == '\n' || c == '\r' || c == '\t' || c == '\v')
+#endif    
+    
+/**
+ * Ascii internet address interpretation routine.
+ * The value returned is in network order.
+ *
+ * @param cp IP address in ascii represenation (e.g. "127.0.0.1")
+ * @return ip address in network order
+ */
+u32_t
+inet_addr(const char *cp)
+{
+  struct in_addr val;
+
+  if (inet_aton(cp, &val)) {
+    return (val.s_addr);
+  }
+  return (INADDR_NONE);
+}
+
+/**
+ * Check whether "cp" is a valid ascii representation
+ * of an Internet address and convert to a binary address.
+ * Returns 1 if the address is valid, 0 if not.
+ * This replaces inet_addr, the return value from which
+ * cannot distinguish between failure and a local broadcast address.
+ *
+ * @param cp IP address in ascii represenation (e.g. "127.0.0.1")
+ * @param addr pointer to which to save the ip address in network order
+ * @return 1 if cp could be converted to addr, 0 on failure
+ */
+int
+inet_aton(const char *cp, struct in_addr *addr)
+{
+  u32_t val;
+  int base, n, c;
+  u32_t parts[4];
+  u32_t *pp = parts;
+
+  c = *cp;
+  for (;;) {
+    /*
+     * Collect number up to ``.''.
+     * Values are specified as for C:
+     * 0x=hex, 0=octal, 1-9=decimal.
+     */
+    if (!isdigit(c))
+      return (0);
+    val = 0;
+    base = 10;
+    if (c == '0') {
+      c = *++cp;
+      if (c == 'x' || c == 'X') {
+        base = 16;
+        c = *++cp;
+      } else
+        base = 8;
+    }
+    for (;;) {
+      if (isdigit(c)) {
+        val = (val * base) + (int)(c - '0');
+        c = *++cp;
+      } else if (base == 16 && isxdigit(c)) {
+        val = (val << 4) | (int)(c + 10 - (islower(c) ? 'a' : 'A'));
+        c = *++cp;
+      } else
+        break;
+    }
+    if (c == '.') {
+      /*
+       * Internet format:
+       *  a.b.c.d
+       *  a.b.c   (with c treated as 16 bits)
+       *  a.b (with b treated as 24 bits)
+       */
+      if (pp >= parts + 3)
+        return (0);
+      *pp++ = val;
+      c = *++cp;
+    } else
+      break;
+  }
+  /*
+   * Check for trailing characters.
+   */
+  if (c != '\0' && (!isprint(c) || !isspace(c)))
+    return (0);
+  /*
+   * Concoct the address according to
+   * the number of parts specified.
+   */
+  n = pp - parts + 1;
+  switch (n) {
+
+  case 0:
+    return (0);       /* initial nondigit */
+
+  case 1:             /* a -- 32 bits */
+    break;
+
+  case 2:             /* a.b -- 8.24 bits */
+    if (val > 0xffffffUL)
+      return (0);
+    val |= parts[0] << 24;
+    break;
+
+  case 3:             /* a.b.c -- 8.8.16 bits */
+    if (val > 0xffff)
+      return (0);
+    val |= (parts[0] << 24) | (parts[1] << 16);
+    break;
+
+  case 4:             /* a.b.c.d -- 8.8.8.8 bits */
+    if (val > 0xff)
+      return (0);
+    val |= (parts[0] << 24) | (parts[1] << 16) | (parts[2] << 8);
+    break;
+  }
+  if (addr)
+    addr->s_addr = htonl(val);
+  return (1);
+}
+
+/**
+ * Convert numeric IP address into decimal dotted ASCII representation.
+ * returns ptr to static buffer; not reentrant!
+ *
+ * @param addr ip address in network order to convert
+ * @return pointer to a global static (!) buffer that holds the ASCII
+ *         represenation of addr
+ */
+char *
+inet_ntoa(struct in_addr addr)
+{
+  static char str[16];
+  u32_t s_addr = addr.s_addr;
+  char inv[3];
+  char *rp;
+  u8_t *ap;
+  u8_t rem;
+  u8_t n;
+  u8_t i;
+
+  rp = str;
+  ap = (u8_t *)&s_addr;
+  for(n = 0; n < 4; n++) {
+    i = 0;
+    do {
+      rem = *ap % (u8_t)10;
+      *ap /= (u8_t)10;
+      inv[i++] = '0' + rem;
+    } while(*ap);
+    while(i--)
+      *rp++ = inv[i];
+    *rp++ = '.';
+    ap++;
+  }
+  *--rp = 0;
+  return str;
+}
+
+/**
+ * These are reference implementations of the byte swapping functions.
+ * Again with the aim of being simple, correct and fully portable.
+ * Byte swapping is the second thing you would want to optimize. You will
+ * need to port it to your architecture and in your cc.h:
+ * 
+ * #define LWIP_PLATFORM_BYTESWAP 1
+ * #define LWIP_PLATFORM_HTONS(x) <your_htons>
+ * #define LWIP_PLATFORM_HTONL(x) <your_htonl>
+ *
+ * Note ntohs() and ntohl() are merely references to the htonx counterparts.
+ */
+
+#if (LWIP_PLATFORM_BYTESWAP == 0) && (BYTE_ORDER == LITTLE_ENDIAN)
+
+/**
+ * Convert an u16_t from host- to network byte order.
+ *
+ * @param n u16_t in host byte order
+ * @return n in network byte order
+ */
+u16_t
+htons(u16_t n)
+{
+  return ((n & 0xff) << 8) | ((n & 0xff00) >> 8);
+}
+
+/**
+ * Convert an u16_t from network- to host byte order.
+ *
+ * @param n u16_t in network byte order
+ * @return n in host byte order
+ */
+u16_t
+ntohs(u16_t n)
+{
+  return htons(n);
+}
+
+/**
+ * Convert an u32_t from host- to network byte order.
+ *
+ * @param n u32_t in host byte order
+ * @return n in network byte order
+ */
+u32_t
+htonl(u32_t n)
+{
+  return ((n & 0xff) << 24) |
+    ((n & 0xff00) << 8) |
+    ((n & 0xff0000UL) >> 8) |
+    ((n & 0xff000000UL) >> 24);
+}
+
+/**
+ * Convert an u32_t from network- to host byte order.
+ *
+ * @param n u32_t in network byte order
+ * @return n in host byte order
+ */
+u32_t
+ntohl(u32_t n)
+{
+  return htonl(n);
+}
+
+#endif /* (LWIP_PLATFORM_BYTESWAP == 0) && (BYTE_ORDER == LITTLE_ENDIAN) */
diff --git a/src/core/ipv4/inet_chksum.c b/src/core/ipv4/inet_chksum.c
new file mode 100644
index 00000000..0ba1a3e1
--- /dev/null
+++ b/src/core/ipv4/inet_chksum.c
@@ -0,0 +1,411 @@
+/**
+ * @file
+ * Incluse internet checksum functions.
+ *
+ */
+
+/*
+ * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
+ * All rights reserved.
+ *
+ * Redistribution and use in source and binary forms, with or without modification,
+ * are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission.
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT
+ * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL,
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT
+ * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING
+ * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY
+ * OF SUCH DAMAGE.
+ *
+ * This file is part of the lwIP TCP/IP stack.
+ *
+ * Author: Adam Dunkels <adam@sics.se>
+ *
+ */
+
+#include "lwip/opt.h"
+
+#include "lwip/inet_chksum.h"
+#include "lwip/inet.h"
+
+/* These are some reference implementations of the checksum algorithm, with the
+ * aim of being simple, correct and fully portable. Checksumming is the
+ * first thing you would want to optimize for your platform. If you create
+ * your own version, link it in and in your sys_arch.h put:
+ * 
+ * #define LWIP_CHKSUM <your_checksum_routine> 
+*/
+#ifndef LWIP_CHKSUM
+#define LWIP_CHKSUM lwip_standard_chksum
+
+#if 1 /* Version A */
+/**
+ * lwip checksum
+ *
+ * @param dataptr points to start of data to be summed at any boundary
+ * @param len length of data to be summed
+ * @return host order (!) lwip checksum (non-inverted Internet sum) 
+ *
+ * @note accumulator size limits summable length to 64k
+ * @note host endianess is irrelevant (p3 RFC1071)
+ */
+static u16_t
+lwip_standard_chksum(void *dataptr, u16_t len)
+{
+  u32_t acc;
+  u16_t src;
+  u8_t *octetptr;
+
+  acc = 0;
+  /* dataptr may be at odd or even addresses */
+  octetptr = (u8_t*)dataptr;
+  while (len > 1)
+  {
+    /* declare first octet as most significant
+       thus assume network order, ignoring host order */
+    src = (*octetptr) << 8;
+    octetptr++;
+    /* declare second octet as least significant */
+    src |= (*octetptr);
+    octetptr++;
+    acc += src;
+    len -= 2;
+  }
+  if (len > 0)
+  {
+    /* accumulate remaining octet */
+    src = (*octetptr) << 8;
+    acc += src;
+  }
+  /* add deferred carry bits */
+  acc = (acc >> 16) + (acc & 0x0000ffffUL);
+  if ((acc & 0xffff0000) != 0) {
+    acc = (acc >> 16) + (acc & 0x0000ffffUL);
+  }
+  /* This maybe a little confusing: reorder sum using htons()
+     instead of ntohs() since it has a little less call overhead.
+     The caller must invert bits for Internet sum ! */
+  return htons((u16_t)acc);
+}
+#endif
+
+#if 0 /* Version B */
+/*
+ * Curt McDowell
+ * Broadcom Corp.
+ * csm@broadcom.com
+ *
+ * IP checksum two bytes at a time with support for
+ * unaligned buffer.
+ * Works for len up to and including 0x20000.
+ * by Curt McDowell, Broadcom Corp. 12/08/2005
+ *
+ * @param dataptr points to start of data to be summed at any boundary
+ * @param len length of data to be summed
+ * @return host order (!) lwip checksum (non-inverted Internet sum) 
+ */
+
+static u16_t
+lwip_standard_chksum(void *dataptr, int len)
+{
+  u8_t *pb = dataptr;
+  u16_t *ps, t = 0;
+  u32_t sum = 0;
+  int odd = ((u32_t)pb & 1);
+
+  /* Get aligned to u16_t */
+  if (odd && len > 0) {
+    ((u8_t *)&t)[1] = *pb++;
+    len--;
+  }
+
+  /* Add the bulk of the data */
+  ps = (u16_t *)pb;
+  while (len > 1) {
+    sum += *ps++;
+    len -= 2;
+  }
+
+  /* Consume left-over byte, if any */
+  if (len > 0)
+    ((u8_t *)&t)[0] = *(u8_t *)ps;;
+
+  /* Add end bytes */
+  sum += t;
+
+  /*  Fold 32-bit sum to 16 bits */
+  while ((sum >> 16) != 0)
+    sum = (sum & 0xffff) + (sum >> 16);
+
+  /* Swap if alignment was odd */
+  if (odd)
+    sum = ((sum & 0xff) << 8) | ((sum & 0xff00) >> 8);
+
+  return sum;
+}
+#endif
+
+#if 0 /* Version C */
+/**
+ * An optimized checksum routine. Basically, it uses loop-unrolling on
+ * the checksum loop, treating the head and tail bytes specially, whereas
+ * the inner loop acts on 8 bytes at a time. 
+ *
+ * @arg start of buffer to be checksummed. May be an odd byte address.
+ * @len number of bytes in the buffer to be checksummed.
+ * @return host order (!) lwip checksum (non-inverted Internet sum) 
+ * 
+ * by Curt McDowell, Broadcom Corp. December 8th, 2005
+ */
+
+static u16_t
+lwip_standard_chksum(void *dataptr, int len)
+{
+  u8_t *pb = dataptr;
+  u16_t *ps, t = 0;
+  u32_t *pl;
+  u32_t sum = 0, tmp;
+  /* starts at odd byte address? */
+  int odd = ((u32_t)pb & 1);
+
+  if (odd && len > 0) {
+    ((u8_t *)&t)[1] = *pb++;
+    len--;
+  }
+
+  ps = (u16_t *)pb;
+
+  if (((u32_t)ps & 3) && len > 1) {
+    sum += *ps++;
+    len -= 2;
+  }
+
+  pl = (u32_t *)ps;
+
+  while (len > 7)  {
+    tmp = sum + *pl++;          /* ping */
+    if (tmp < sum)
+      tmp++;                    /* add back carry */
+
+    sum = tmp + *pl++;          /* pong */
+    if (sum < tmp)
+      sum++;                    /* add back carry */
+
+    len -= 8;
+  }
+
+  /* make room in upper bits */
+  sum = (sum >> 16) + (sum & 0xffff);
+
+  ps = (u16_t *)pl;
+
+  /* 16-bit aligned word remaining? */
+  while (len > 1) {
+    sum += *ps++;
+    len -= 2;
+  }
+
+  /* dangling tail byte remaining? */
+  if (len > 0)                  /* include odd byte */
+    ((u8_t *)&t)[0] = *(u8_t *)ps;
+
+  sum += t;                     /* add end bytes */
+
+  while ((sum >> 16) != 0)      /* combine halves */
+    sum = (sum >> 16) + (sum & 0xffff);
+
+  if (odd)
+    sum = ((sum & 0xff) << 8) | ((sum & 0xff00) >> 8);
+
+  return sum;
+}
+#endif
+
+#endif /* LWIP_CHKSUM */
+
+/* inet_chksum_pseudo:
+ *
+ * Calculates the pseudo Internet checksum used by TCP and UDP for a pbuf chain.
+ * IP addresses are expected to be in network byte order.
+ *
+ * @param p chain of pbufs over that a checksum should be calculated (ip data part)
+ * @param src source ip address (used for checksum of pseudo header)
+ * @param dst destination ip address (used for checksum of pseudo header)
+ * @param proto ip protocol (used for checksum of pseudo header)
+ * @param proto_len length of the ip data part (used for checksum of pseudo header)
+ * @return checksum (as u16_t) to be saved directly in the protocol header
+ */
+u16_t
+inet_chksum_pseudo(struct pbuf *p,
+       struct ip_addr *src, struct ip_addr *dest,
+       u8_t proto, u16_t proto_len)
+{
+  u32_t acc;
+  struct pbuf *q;
+  u8_t swapped;
+
+  acc = 0;
+  swapped = 0;
+  /* iterate through all pbuf in chain */
+  for(q = p; q != NULL; q = q->next) {
+    LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): checksumming pbuf %p (has next %p) \n",
+      (void *)q, (void *)q->next));
+    acc += LWIP_CHKSUM(q->payload, q->len);
+    /*LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): unwrapped lwip_chksum()=%"X32_F" \n", acc));*/
+    while ((acc >> 16) != 0) {
+      acc = (acc & 0xffffUL) + (acc >> 16);
+    }
+    if (q->len % 2 != 0) {
+      swapped = 1 - swapped;
+      acc = ((acc & 0xff) << 8) | ((acc & 0xff00UL) >> 8);
+    }
+    /*LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): wrapped lwip_chksum()=%"X32_F" \n", acc));*/
+  }
+
+  if (swapped) {
+    acc = ((acc & 0xff) << 8) | ((acc & 0xff00UL) >> 8);
+  }
+  acc += (src->addr & 0xffffUL);
+  acc += ((src->addr >> 16) & 0xffffUL);
+  acc += (dest->addr & 0xffffUL);
+  acc += ((dest->addr >> 16) & 0xffffUL);
+  acc += (u32_t)htons((u16_t)proto);
+  acc += (u32_t)htons(proto_len);
+
+  while ((acc >> 16) != 0) {
+    acc = (acc & 0xffffUL) + (acc >> 16);
+  }
+  LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): pbuf chain lwip_chksum()=%"X32_F"\n", acc));
+  return (u16_t)~(acc & 0xffffUL);
+}
+
+/* inet_chksum_pseudo:
+ *
+ * Calculates the pseudo Internet checksum used by TCP and UDP for a pbuf chain.
+ * IP addresses are expected to be in network byte order.
+ *
+ * @param p chain of pbufs over that a checksum should be calculated (ip data part)
+ * @param src source ip address (used for checksum of pseudo header)
+ * @param dst destination ip address (used for checksum of pseudo header)
+ * @param proto ip protocol (used for checksum of pseudo header)
+ * @param proto_len length of the ip data part (used for checksum of pseudo header)
+ * @return checksum (as u16_t) to be saved directly in the protocol header
+ */
+u16_t
+inet_chksum_pseudo_partial(struct pbuf *p,
+       struct ip_addr *src, struct ip_addr *dest,
+       u8_t proto, u16_t proto_len, u16_t chksum_len)
+{
+  u32_t acc;
+  struct pbuf *q;
+  u8_t swapped;
+  u16_t chklen;
+
+  acc = 0;
+  swapped = 0;
+  /* iterate through all pbuf in chain */
+  for(q = p; (q != NULL) && (chksum_len > 0); q = q->next) {
+    LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): checksumming pbuf %p (has next %p) \n",
+      (void *)q, (void *)q->next));
+    chklen = q->len;
+    if (chklen > chksum_len) {
+      chklen = chksum_len;
+    }
+    acc += LWIP_CHKSUM(q->payload, chklen);
+    chksum_len -= chklen;
+    LWIP_ASSERT("delete me", chksum_len < 0x7fff);
+    /*LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): unwrapped lwip_chksum()=%"X32_F" \n", acc));*/
+    while ((acc >> 16) != 0) {
+      acc = (acc & 0xffffUL) + (acc >> 16);
+    }
+    if (q->len % 2 != 0) {
+      swapped = 1 - swapped;
+      acc = ((acc & 0xff) << 8) | ((acc & 0xff00UL) >> 8);
+    }
+    /*LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): wrapped lwip_chksum()=%"X32_F" \n", acc));*/
+  }
+
+  if (swapped) {
+    acc = ((acc & 0xff) << 8) | ((acc & 0xff00UL) >> 8);
+  }
+  acc += (src->addr & 0xffffUL);
+  acc += ((src->addr >> 16) & 0xffffUL);
+  acc += (dest->addr & 0xffffUL);
+  acc += ((dest->addr >> 16) & 0xffffUL);
+  acc += (u32_t)htons((u16_t)proto);
+  acc += (u32_t)htons(proto_len);
+
+  while ((acc >> 16) != 0) {
+    acc = (acc & 0xffffUL) + (acc >> 16);
+  }
+  LWIP_DEBUGF(INET_DEBUG, ("inet_chksum_pseudo(): pbuf chain lwip_chksum()=%"X32_F"\n", acc));
+  return (u16_t)~(acc & 0xffffUL);
+}
+
+/* inet_chksum:
+ *
+ * Calculates the Internet checksum over a portion of memory. Used primarily for IP
+ * and ICMP.
+ *
+ * @param dataptr start of the buffer to calculate the checksum (no alignment needed)
+ * @param len length of the buffer to calculate the checksum
+ * @return checksum (as u16_t) to be saved directly in the protocol header
+ */
+
+u16_t
+inet_chksum(void *dataptr, u16_t len)
+{
+  u32_t acc;
+
+  acc = LWIP_CHKSUM(dataptr, len);
+  while ((acc >> 16) != 0) {
+    acc = (acc & 0xffff) + (acc >> 16);
+  }
+  return (u16_t)~(acc & 0xffff);
+}
+
+/**
+ * Calculate a checksum over a chain of pbufs (without pseudo-header, much like
+ * inet_chksum only pbufs are used).
+ *
+ * @param p pbuf chain over that the checksum should be calculated
+ * @return checksum (as u16_t) to be saved directly in the protocol header
+ */
+u16_t
+inet_chksum_pbuf(struct pbuf *p)
+{
+  u32_t acc;
+  struct pbuf *q;
+  u8_t swapped;
+
+  acc = 0;
+  swapped = 0;
+  for(q = p; q != NULL; q = q->next) {
+    acc += LWIP_CHKSUM(q->payload, q->len);
+    while ((acc >> 16) != 0) {
+      acc = (acc & 0xffffUL) + (acc >> 16);
+    }
+    if (q->len % 2 != 0) {
+      swapped = 1 - swapped;
+      acc = (acc & 0x00ffUL << 8) | (acc & 0xff00UL >> 8);
+    }
+  }
+
+  if (swapped) {
+    acc = ((acc & 0x00ffUL) << 8) | ((acc & 0xff00UL) >> 8);
+  }
+  return (u16_t)~(acc & 0xffffUL);
+}
diff --git a/src/core/ipv4/ip.c b/src/core/ipv4/ip.c
index 2b0ccdec..10534f1e 100644
--- a/src/core/ipv4/ip.c
+++ b/src/core/ipv4/ip.c
@@ -39,11 +39,12 @@
  */
 
 #include "lwip/opt.h"
+#include "lwip/ip.h"
 #include "lwip/def.h"
 #include "lwip/mem.h"
-#include "lwip/ip.h"
 #include "lwip/ip_frag.h"
 #include "lwip/inet.h"
+#include "lwip/inet_chksum.h"
 #include "lwip/netif.h"
 #include "lwip/icmp.h"
 #include "lwip/igmp.h"
diff --git a/src/core/ipv4/ip_frag.c b/src/core/ipv4/ip_frag.c
index 23e1de8f..bfea7ef6 100644
--- a/src/core/ipv4/ip_frag.c
+++ b/src/core/ipv4/ip_frag.c
@@ -39,8 +39,10 @@
  */
 
 #include "lwip/opt.h"
-#include "lwip/ip.h"
 #include "lwip/ip_frag.h"
+#include "lwip/ip.h"
+#include "lwip/inet.h"
+#include "lwip/inet_chksum.h"
 #include "lwip/netif.h"
 #include "lwip/snmp.h"
 #include "lwip/stats.h"
diff --git a/src/core/ipv6/inet6.c b/src/core/ipv6/inet6.c
new file mode 100644
index 00000000..c3de85c0
--- /dev/null
+++ b/src/core/ipv6/inet6.c
@@ -0,0 +1,163 @@
+/**
+ * @file
+ * Functions common to all TCP/IPv6 modules, such as the Internet checksum and the
+ * byte order functions.
+ *
+ */
+
+/*
+ * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
+ * All rights reserved. 
+ * 
+ * Redistribution and use in source and binary forms, with or without modification, 
+ * are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission. 
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED 
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT 
+ * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT 
+ * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING 
+ * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY 
+ * OF SUCH DAMAGE.
+ *
+ * This file is part of the lwIP TCP/IP stack.
+ * 
+ * Author: Adam Dunkels <adam@sics.se>
+ *
+ */
+
+#include "lwip/opt.h"
+
+#include "lwip/def.h"
+#include "lwip/inet.h"
+
+/* chksum:
+ *
+ * Sums up all 16 bit words in a memory portion. Also includes any odd byte.
+ * This function is used by the other checksum functions.
+ *
+ * For now, this is not optimized. Must be optimized for the particular processor
+ * arcitecture on which it is to run. Preferebly coded in assembler.
+ */
+
+static u32_t
+chksum(void *dataptr, u16_t len)
+{
+  u16_t *sdataptr = dataptr;
+  u32_t acc;
+  
+  
+  for(acc = 0; len > 1; len -= 2) {
+    acc += *sdataptr++;
+  }
+
+  /* add up any odd byte */
+  if (len == 1) {
+    acc += htons((u16_t)(*(u8_t *)dataptr) << 8);
+  }
+
+  return acc;
+
+}
+
+/* inet_chksum_pseudo:
+ *
+ * Calculates the pseudo Internet checksum used by TCP and UDP for a pbuf chain.
+ */
+
+u16_t
+inet_chksum_pseudo(struct pbuf *p,
+       struct ip_addr *src, struct ip_addr *dest,
+       u8_t proto, u32_t proto_len)
+{
+  u32_t acc;
+  struct pbuf *q;
+  u8_t swapped, i;
+
+  acc = 0;
+  swapped = 0;
+  for(q = p; q != NULL; q = q->next) {    
+    acc += chksum(q->payload, q->len);
+    while (acc >> 16) {
+      acc = (acc & 0xffff) + (acc >> 16);
+    }
+    if (q->len % 2 != 0) {
+      swapped = 1 - swapped;
+      acc = ((acc & 0xff) << 8) | ((acc & 0xff00) >> 8);
+    }
+  }
+
+  if (swapped) {
+    acc = ((acc & 0xff) << 8) | ((acc & 0xff00) >> 8);
+  }
+  
+  for(i = 0; i < 8; i++) {
+    acc += ((u16_t *)src->addr)[i] & 0xffff;
+    acc += ((u16_t *)dest->addr)[i] & 0xffff;
+    while (acc >> 16) {
+      acc = (acc & 0xffff) + (acc >> 16);
+    }
+  }
+  acc += (u16_t)htons((u16_t)proto);
+  acc += ((u16_t *)&proto_len)[0] & 0xffff;
+  acc += ((u16_t *)&proto_len)[1] & 0xffff;
+
+  while (acc >> 16) {
+    acc = (acc & 0xffff) + (acc >> 16);
+  }
+  return ~(acc & 0xffff);
+}
+
+/* inet_chksum:
+ *
+ * Calculates the Internet checksum over a portion of memory. Used primarely for IP
+ * and ICMP.
+ */
+
+u16_t
+inet_chksum(void *dataptr, u16_t len)
+{
+  u32_t acc, sum;
+
+  acc = chksum(dataptr, len);
+  sum = (acc & 0xffff) + (acc >> 16);
+  sum += (sum >> 16);
+  return ~(sum & 0xffff);
+}
+
+u16_t
+inet_chksum_pbuf(struct pbuf *p)
+{
+  u32_t acc;
+  struct pbuf *q;
+  u8_t swapped;
+  
+  acc = 0;
+  swapped = 0;
+  for(q = p; q != NULL; q = q->next) {
+    acc += chksum(q->payload, q->len);
+    while (acc >> 16) {
+      acc = (acc & 0xffff) + (acc >> 16);
+    }    
+    if (q->len % 2 != 0) {
+      swapped = 1 - swapped;
+      acc = (acc & 0xff << 8) | (acc & 0xff00 >> 8);
+    }
+  }
+ 
+  if (swapped) {
+    acc = ((acc & 0xff) << 8) | ((acc & 0xff00) >> 8);
+  }
+  return ~(acc & 0xffff);
+}
diff --git a/src/core/tcp_in.c b/src/core/tcp_in.c
index d8d813ce..7dbe1f93 100644
--- a/src/core/tcp_in.c
+++ b/src/core/tcp_in.c
@@ -45,13 +45,14 @@
 
 #if LWIP_TCP /* don't build if not configured for use in lwipopts.h */
 
+#include "lwip/tcp.h"
 #include "lwip/def.h"
 #include "lwip/ip_addr.h"
 #include "lwip/netif.h"
 #include "lwip/mem.h"
 #include "lwip/memp.h"
 #include "lwip/inet.h"
-#include "lwip/tcp.h"
+#include "lwip/inet_chksum.h"
 #include "lwip/stats.h"
 #include "lwip/snmp.h"
 #include "arch/perf.h"
diff --git a/src/core/tcp_out.c b/src/core/tcp_out.c
index a1434cd8..adb7cd80 100644
--- a/src/core/tcp_out.c
+++ b/src/core/tcp_out.c
@@ -42,6 +42,7 @@
 
 #if LWIP_TCP /* don't build if not configured for use in lwipopts.h */
 
+#include "lwip/tcp.h"
 #include "lwip/def.h"
 #include "lwip/mem.h"
 #include "lwip/memp.h"
@@ -49,7 +50,7 @@
 #include "lwip/ip_addr.h"
 #include "lwip/netif.h"
 #include "lwip/inet.h"
-#include "lwip/tcp.h"
+#include "lwip/inet_chksum.h"
 #include "lwip/stats.h"
 #include "lwip/snmp.h"
 
diff --git a/src/core/udp.c b/src/core/udp.c
index f78d55b0..454834fa 100644
--- a/src/core/udp.c
+++ b/src/core/udp.c
@@ -50,12 +50,13 @@
 
 #if LWIP_UDP /* don't build if not configured for use in lwipopts.h */
 
+#include "lwip/udp.h"
 #include "lwip/def.h"
 #include "lwip/memp.h"
 #include "lwip/inet.h"
+#include "lwip/inet_chksum.h"
 #include "lwip/ip_addr.h"
 #include "lwip/netif.h"
-#include "lwip/udp.h"
 #include "lwip/icmp.h"
 #include "lwip/stats.h"
 #include "lwip/snmp.h"
diff --git a/src/include/ipv4/lwip/igmp.h b/src/include/ipv4/lwip/igmp.h
index f0703e40..f27e99ff 100644
--- a/src/include/ipv4/lwip/igmp.h
+++ b/src/include/ipv4/lwip/igmp.h
@@ -36,7 +36,9 @@
 #define __LWIP_IGMP_H__
 
 #include "lwip/opt.h"
-#include "lwip/inet.h"
+#include "lwip/ip_addr.h"
+#include "lwip/netif.h"
+#include "lwip/pbuf.h"
 
 #if LWIP_IGMP /* don't build if not configured for use in lwipopts.h */
 
diff --git a/src/include/ipv4/lwip/inet.h b/src/include/ipv4/lwip/inet.h
index ccf69588..1ffcf707 100644
--- a/src/include/ipv4/lwip/inet.h
+++ b/src/include/ipv4/lwip/inet.h
@@ -34,25 +34,12 @@
 
 #include "lwip/opt.h"
 
-#include "lwip/pbuf.h"
 #include "lwip/ip_addr.h"
 
 #ifdef __cplusplus
 extern "C" {
 #endif
 
-u16_t inet_chksum(void *dataptr, u16_t len);
-#if 0 /* optimized routine */
-u16_t inet_chksum4(u8_t *dataptr, u16_t len);
-#endif
-u16_t inet_chksum_pbuf(struct pbuf *p);
-u16_t inet_chksum_pseudo(struct pbuf *p,
-       struct ip_addr *src, struct ip_addr *dest,
-       u8_t proto, u16_t proto_len);
-u16_t inet_chksum_pseudo_partial(struct pbuf *p,
-       struct ip_addr *src, struct ip_addr *dest,
-       u8_t proto, u16_t proto_len, u16_t chksum_len);
-
 u32_t inet_addr(const char *cp);
 int inet_aton(const char *cp, struct in_addr *addr);
 char *inet_ntoa(struct in_addr addr); /* returns ptr to static buffer; not reentrant! */
@@ -106,4 +93,3 @@ u32_t ntohl(u32_t x);
 #endif
 
 #endif /* __LWIP_INET_H__ */
-
diff --git a/src/include/ipv4/lwip/inet_chksum.h b/src/include/ipv4/lwip/inet_chksum.h
new file mode 100644
index 00000000..d7c74926
--- /dev/null
+++ b/src/include/ipv4/lwip/inet_chksum.h
@@ -0,0 +1,58 @@
+/*
+ * Copyright (c) 2001-2004 Swedish Institute of Computer Science.
+ * All rights reserved. 
+ * 
+ * Redistribution and use in source and binary forms, with or without modification, 
+ * are permitted provided that the following conditions are met:
+ *
+ * 1. Redistributions of source code must retain the above copyright notice,
+ *    this list of conditions and the following disclaimer.
+ * 2. Redistributions in binary form must reproduce the above copyright notice,
+ *    this list of conditions and the following disclaimer in the documentation
+ *    and/or other materials provided with the distribution.
+ * 3. The name of the author may not be used to endorse or promote products
+ *    derived from this software without specific prior written permission. 
+ *
+ * THIS SOFTWARE IS PROVIDED BY THE AUTHOR ``AS IS'' AND ANY EXPRESS OR IMPLIED 
+ * WARRANTIES, INCLUDING, BUT NOT LIMITED TO, THE IMPLIED WARRANTIES OF 
+ * MERCHANTABILITY AND FITNESS FOR A PARTICULAR PURPOSE ARE DISCLAIMED. IN NO EVENT 
+ * SHALL THE AUTHOR BE LIABLE FOR ANY DIRECT, INDIRECT, INCIDENTAL, SPECIAL, 
+ * EXEMPLARY, OR CONSEQUENTIAL DAMAGES (INCLUDING, BUT NOT LIMITED TO, PROCUREMENT 
+ * OF SUBSTITUTE GOODS OR SERVICES; LOSS OF USE, DATA, OR PROFITS; OR BUSINESS 
+ * INTERRUPTION) HOWEVER CAUSED AND ON ANY THEORY OF LIABILITY, WHETHER IN 
+ * CONTRACT, STRICT LIABILITY, OR TORT (INCLUDING NEGLIGENCE OR OTHERWISE) ARISING 
+ * IN ANY WAY OUT OF THE USE OF THIS SOFTWARE, EVEN IF ADVISED OF THE POSSIBILITY 
+ * OF SUCH DAMAGE.
+ *
+ * This file is part of the lwIP TCP/IP stack.
+ * 
+ * Author: Adam Dunkels <adam@sics.se>
+ *
+ */
+#ifndef __LWIP_INET_CHKSUM_H__
+#define __LWIP_INET_CHKSUM_H__
+
+#include "lwip/opt.h"
+
+#include "lwip/pbuf.h"
+#include "lwip/ip_addr.h"
+
+#ifdef __cplusplus
+extern "C" {
+#endif
+
+u16_t inet_chksum(void *dataptr, u16_t len);
+u16_t inet_chksum_pbuf(struct pbuf *p);
+u16_t inet_chksum_pseudo(struct pbuf *p,
+       struct ip_addr *src, struct ip_addr *dest,
+       u8_t proto, u16_t proto_len);
+u16_t inet_chksum_pseudo_partial(struct pbuf *p,
+       struct ip_addr *src, struct ip_addr *dest,
+       u8_t proto, u16_t proto_len, u16_t chksum_len);
+
+#ifdef __cplusplus
+}
+#endif
+
+#endif /* __LWIP_INET_H__ */
+
diff --git a/src/include/lwip/raw.h b/src/include/lwip/raw.h
index 5834fc95..20b0a11b 100644
--- a/src/include/lwip/raw.h
+++ b/src/include/lwip/raw.h
@@ -39,6 +39,7 @@
 #include "lwip/pbuf.h"
 #include "lwip/inet.h"
 #include "lwip/ip.h"
+#include "lwip/ip_addr.h"
 
 #ifdef __cplusplus
 extern "C" {
diff --git a/src/include/lwip/udp.h b/src/include/lwip/udp.h
index 89d1f5e7..9955638b 100644
--- a/src/include/lwip/udp.h
+++ b/src/include/lwip/udp.h
@@ -37,7 +37,8 @@
 #if LWIP_UDP /* don't build if not configured for use in lwipopts.h */
 
 #include "lwip/pbuf.h"
-#include "lwip/inet.h"
+#include "lwip/netif.h"
+#include "lwip/ip_addr.h"
 #include "lwip/ip.h"
 
 #ifdef __cplusplus