NAT64: Move IPv6-IPv4 virtual reassembly code from MAP-T to common library (VPP-708)

Change-Id: I9ad636f80bf109ffac9ca1b6d80d5f2c31f2076a
Signed-off-by: Matus Fabian <matfabia@cisco.com>

1 files changed, 577 insertions, 0 deletions

diff --git a/src/vnet/ip/ip4_to_ip6.h b/src/vnet/ip/ip4_to_ip6.h
new file mode 100644
index 00000000000..96b8bf1e676
--- /dev/null
+++ b/src/vnet/ip/ip4_to_ip6.h
@@ -0,0 +1,577 @@
+/*
+ * Copyright (c) 2017 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ *     http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/**
+ * @file
+ * @brief IPv4 to IPv6 translation
+ */
+#ifndef __included_ip4_to_ip6_h__
+#define __included_ip4_to_ip6_h__
+
+#include <vnet/ip/ip.h>
+
+
+/**
+ * IPv4 to IPv6 set call back function type
+ */
+typedef int (*ip4_to_ip6_set_fn_t) (ip4_header_t * ip4, ip6_header_t * ip6,
+				    void *ctx);
+
+/* *INDENT-OFF* */
+static u8 icmp_to_icmp6_updater_pointer_table[] =
+  { 0, 1, 4, 4, ~0,
+    ~0, ~0, ~0, 7, 6,
+    ~0, ~0, 8, 8, 8,
+    8, 24, 24, 24, 24
+  };
+/* *INDENT-ON* */
+
+#define frag_id_4to6(id) (id)
+
+/**
+ * @brief Get TCP/UDP port number or ICMP id from IPv4 packet.
+ *
+ * @param ip4        IPv4 header.
+ * @param sender     1 get sender port, 0 get receiver port.
+ *
+ * @returns Port number on success, 0 otherwise.
+ */
+always_inline u16
+ip4_get_port (ip4_header_t * ip, u8 sender)
+{
+  if (ip->ip_version_and_header_length != 0x45 ||
+      ip4_get_fragment_offset (ip))
+    return 0;
+
+  if (PREDICT_TRUE ((ip->protocol == IP_PROTOCOL_TCP) ||
+		    (ip->protocol == IP_PROTOCOL_UDP)))
+    {
+      udp_header_t *udp = (void *) (ip + 1);
+      return (sender) ? udp->src_port : udp->dst_port;
+    }
+  else if (ip->protocol == IP_PROTOCOL_ICMP)
+    {
+      icmp46_header_t *icmp = (void *) (ip + 1);
+      if (icmp->type == ICMP4_echo_request || icmp->type == ICMP4_echo_reply)
+	{
+	  return *((u16 *) (icmp + 1));
+	}
+      else if (clib_net_to_host_u16 (ip->length) >= 64)
+	{
+	  ip = (ip4_header_t *) (icmp + 2);
+	  if (PREDICT_TRUE ((ip->protocol == IP_PROTOCOL_TCP) ||
+			    (ip->protocol == IP_PROTOCOL_UDP)))
+	    {
+	      udp_header_t *udp = (void *) (ip + 1);
+	      return (sender) ? udp->dst_port : udp->src_port;
+	    }
+	  else if (ip->protocol == IP_PROTOCOL_ICMP)
+	    {
+	      icmp46_header_t *icmp = (void *) (ip + 1);
+	      if (icmp->type == ICMP4_echo_request ||
+		  icmp->type == ICMP4_echo_reply)
+		{
+		  return *((u16 *) (icmp + 1));
+		}
+	    }
+	}
+    }
+  return 0;
+}
+
+/**
+ * @brief Convert type and code value from ICMP4 to ICMP6.
+ *
+ * @param icmp      ICMP header.
+ * @param inner_ip4 Inner IPv4 header if present, 0 otherwise.
+ *
+ * @returns 0 on success, non-zero value otherwise.
+ */
+always_inline int
+icmp_to_icmp6_header (icmp46_header_t * icmp, ip4_header_t ** inner_ip4)
+{
+  *inner_ip4 = NULL;
+  switch (icmp->type)
+    {
+    case ICMP4_echo_reply:
+      icmp->type = ICMP6_echo_reply;
+      break;
+    case ICMP4_echo_request:
+      icmp->type = ICMP6_echo_request;
+      break;
+    case ICMP4_destination_unreachable:
+      *inner_ip4 = (ip4_header_t *) (((u8 *) icmp) + 8);
+
+      switch (icmp->code)
+	{
+	case ICMP4_destination_unreachable_destination_unreachable_net:	//0
+	case ICMP4_destination_unreachable_destination_unreachable_host:	//1
+	  icmp->type = ICMP6_destination_unreachable;
+	  icmp->code = ICMP6_destination_unreachable_no_route_to_destination;
+	  break;
+	case ICMP4_destination_unreachable_protocol_unreachable:	//2
+	  icmp->type = ICMP6_parameter_problem;
+	  icmp->code = ICMP6_parameter_problem_unrecognized_next_header;
+	  break;
+	case ICMP4_destination_unreachable_port_unreachable:	//3
+	  icmp->type = ICMP6_destination_unreachable;
+	  icmp->code = ICMP6_destination_unreachable_port_unreachable;
+	  break;
+	case ICMP4_destination_unreachable_fragmentation_needed_and_dont_fragment_set:	//4
+	  icmp->type =
+	    ICMP6_packet_too_big;
+	  icmp->code = 0;
+	  {
+	    u32 advertised_mtu = clib_net_to_host_u32 (*((u32 *) (icmp + 1)));
+	    if (advertised_mtu)
+	      advertised_mtu += 20;
+	    else
+	      advertised_mtu = 1000;	//FIXME ! (RFC 1191 - plateau value)
+
+	    //FIXME: = minimum(advertised MTU+20, MTU_of_IPv6_nexthop, (MTU_of_IPv4_nexthop)+20)
+	    *((u32 *) (icmp + 1)) = clib_host_to_net_u32 (advertised_mtu);
+	  }
+	  break;
+
+	case ICMP4_destination_unreachable_source_route_failed:	//5
+	case ICMP4_destination_unreachable_destination_network_unknown:	//6
+	case ICMP4_destination_unreachable_destination_host_unknown:	//7
+	case ICMP4_destination_unreachable_source_host_isolated:	//8
+	case ICMP4_destination_unreachable_network_unreachable_for_type_of_service:	//11
+	case ICMP4_destination_unreachable_host_unreachable_for_type_of_service:	//12
+	  icmp->type =
+	    ICMP6_destination_unreachable;
+	  icmp->code = ICMP6_destination_unreachable_no_route_to_destination;
+	  break;
+	case ICMP4_destination_unreachable_network_administratively_prohibited:	//9
+	case ICMP4_destination_unreachable_host_administratively_prohibited:	//10
+	case ICMP4_destination_unreachable_communication_administratively_prohibited:	//13
+	case ICMP4_destination_unreachable_precedence_cutoff_in_effect:	//15
+	  icmp->type = ICMP6_destination_unreachable;
+	  icmp->code =
+	    ICMP6_destination_unreachable_destination_administratively_prohibited;
+	  break;
+	case ICMP4_destination_unreachable_host_precedence_violation:	//14
+	default:
+	  return -1;
+	}
+      break;
+
+    case ICMP4_time_exceeded:	//11
+      *inner_ip4 = (ip4_header_t *) (((u8 *) icmp) + 8);
+      icmp->type = ICMP6_time_exceeded;
+      break;
+
+    case ICMP4_parameter_problem:
+      *inner_ip4 = (ip4_header_t *) (((u8 *) icmp) + 8);
+
+      switch (icmp->code)
+	{
+	case ICMP4_parameter_problem_pointer_indicates_error:
+	case ICMP4_parameter_problem_bad_length:
+	  icmp->type = ICMP6_parameter_problem;
+	  icmp->code = ICMP6_parameter_problem_erroneous_header_field;
+	  {
+	    u8 ptr =
+	      icmp_to_icmp6_updater_pointer_table[*((u8 *) (icmp + 1))];
+	    if (ptr == 0xff)
+	      return -1;
+
+	    *((u32 *) (icmp + 1)) = clib_host_to_net_u32 (ptr);
+	  }
+	  break;
+	default:
+	  //All other codes cause error
+	  return -1;
+	}
+      break;
+
+    default:
+      //All other types cause error
+      return -1;
+      break;
+    }
+  return 0;
+}
+
+/**
+ * @brief Translate ICMP4 packet to ICMP6.
+ *
+ * @param p         Buffer to translate.
+ * @param fn        The function to translate outer header.
+ * @param ctx       A context passed in the outer header translate function.
+ * @param inner_fn  The function to translate inner header.
+ * @param inner_ctx A context passed in the inner header translate function.
+ *
+ * @returns 0 on success, non-zero value otherwise.
+ */
+always_inline int
+icmp_to_icmp6 (vlib_buffer_t * p, ip4_to_ip6_set_fn_t fn, void *ctx,
+	       ip4_to_ip6_set_fn_t inner_fn, void *inner_ctx)
+{
+  ip4_header_t *ip4, *inner_ip4;
+  ip6_header_t *ip6, *inner_ip6;
+  u32 ip_len;
+  icmp46_header_t *icmp;
+  ip_csum_t csum;
+  ip6_frag_hdr_t *inner_frag;
+  u32 inner_frag_id;
+  u32 inner_frag_offset;
+  u8 inner_frag_more;
+  u16 *inner_L4_checksum = 0;
+  int rv;
+
+  ip4 = vlib_buffer_get_current (p);
+  ip_len = clib_net_to_host_u16 (ip4->length);
+  ASSERT (ip_len <= p->current_length);
+
+  icmp = (icmp46_header_t *) (ip4 + 1);
+  if (icmp_to_icmp6_header (icmp, &inner_ip4))
+    return -1;
+
+  if (inner_ip4)
+    {
+      //We have 2 headers to translate.
+      //We need to make some room in the middle of the packet
+      if (PREDICT_FALSE (ip4_is_fragment (inner_ip4)))
+	{
+	  //Here it starts getting really tricky
+	  //We will add a fragmentation header in the inner packet
+
+	  if (!ip4_is_first_fragment (inner_ip4))
+	    {
+	      //For now we do not handle unless it is the first fragment
+	      //Ideally we should handle the case as we are in slow path already
+	      return -1;
+	    }
+
+	  vlib_buffer_advance (p,
+			       -2 * (sizeof (*ip6) - sizeof (*ip4)) -
+			       sizeof (*inner_frag));
+	  ip6 = vlib_buffer_get_current (p);
+	  clib_memcpy (u8_ptr_add (ip6, sizeof (*ip6) - sizeof (*ip4)), ip4,
+		       20 + 8);
+	  ip4 =
+	    (ip4_header_t *) u8_ptr_add (ip6, sizeof (*ip6) - sizeof (*ip4));
+	  icmp = (icmp46_header_t *) (ip4 + 1);
+
+	  inner_ip6 =
+	    (ip6_header_t *) u8_ptr_add (inner_ip4,
+					 sizeof (*ip4) - sizeof (*ip6) -
+					 sizeof (*inner_frag));
+	  inner_frag =
+	    (ip6_frag_hdr_t *) u8_ptr_add (inner_ip6, sizeof (*inner_ip6));
+	  ip6->payload_length =
+	    u16_net_add (ip4->length,
+			 sizeof (*ip6) - 2 * sizeof (*ip4) +
+			 sizeof (*inner_frag));
+	  inner_frag_id = frag_id_4to6 (inner_ip4->fragment_id);
+	  inner_frag_offset = ip4_get_fragment_offset (inner_ip4);
+	  inner_frag_more =
+	    ! !(inner_ip4->flags_and_fragment_offset &
+		clib_net_to_host_u16 (IP4_HEADER_FLAG_MORE_FRAGMENTS));
+	}
+      else
+	{
+	  vlib_buffer_advance (p, -2 * (sizeof (*ip6) - sizeof (*ip4)));
+	  ip6 = vlib_buffer_get_current (p);
+	  clib_memcpy (u8_ptr_add (ip6, sizeof (*ip6) - sizeof (*ip4)), ip4,
+		       20 + 8);
+	  ip4 =
+	    (ip4_header_t *) u8_ptr_add (ip6, sizeof (*ip6) - sizeof (*ip4));
+	  icmp = (icmp46_header_t *) u8_ptr_add (ip4, sizeof (*ip4));
+	  inner_ip6 =
+	    (ip6_header_t *) u8_ptr_add (inner_ip4,
+					 sizeof (*ip4) - sizeof (*ip6));
+	  ip6->payload_length =
+	    u16_net_add (ip4->length, sizeof (*ip6) - 2 * sizeof (*ip4));
+	  inner_frag = NULL;
+	}
+
+      if (PREDICT_TRUE (inner_ip4->protocol == IP_PROTOCOL_TCP))
+	{
+	  inner_L4_checksum = &((tcp_header_t *) (inner_ip4 + 1))->checksum;
+	  *inner_L4_checksum =
+	    ip_csum_fold (ip_csum_sub_even
+			  (*inner_L4_checksum,
+			   *((u64 *) (&inner_ip4->src_address))));
+	}
+      else if (PREDICT_TRUE (inner_ip4->protocol == IP_PROTOCOL_UDP))
+	{
+	  inner_L4_checksum = &((udp_header_t *) (inner_ip4 + 1))->checksum;
+	  if (!*inner_L4_checksum)
+	    {
+	      return -1;
+	    }
+	  *inner_L4_checksum =
+	    ip_csum_fold (ip_csum_sub_even
+			  (*inner_L4_checksum,
+			   *((u64 *) (&inner_ip4->src_address))));
+	}
+      else if (inner_ip4->protocol == IP_PROTOCOL_ICMP)
+	{
+	  //We have an ICMP inside an ICMP
+	  //It needs to be translated, but not for error ICMP messages
+	  icmp46_header_t *inner_icmp = (icmp46_header_t *) (inner_ip4 + 1);
+	  csum = inner_icmp->checksum;
+	  //Only types ICMP4_echo_request and ICMP4_echo_reply are handled by icmp_to_icmp6_header
+	  csum = ip_csum_sub_even (csum, *((u16 *) inner_icmp));
+	  inner_icmp->type = (inner_icmp->type == ICMP4_echo_request) ?
+	    ICMP6_echo_request : ICMP6_echo_reply;
+	  csum = ip_csum_add_even (csum, *((u16 *) inner_icmp));
+	  csum =
+	    ip_csum_add_even (csum, clib_host_to_net_u16 (IP_PROTOCOL_ICMP6));
+	  csum =
+	    ip_csum_add_even (csum, inner_ip4->length - sizeof (*inner_ip4));
+	  inner_icmp->checksum = ip_csum_fold (csum);
+	  inner_L4_checksum = &inner_icmp->checksum;
+	  inner_ip4->protocol = IP_PROTOCOL_ICMP6;
+	}
+      else
+	{
+	  /* To shut up Coverity */
+	  os_panic ();
+	}
+
+      csum = *inner_L4_checksum;	//Initial checksum of the inner L4 header
+
+      inner_ip6->ip_version_traffic_class_and_flow_label =
+	clib_host_to_net_u32 ((6 << 28) + (inner_ip4->tos << 20));
+      inner_ip6->payload_length =
+	u16_net_add (inner_ip4->length, -sizeof (*inner_ip4));
+      inner_ip6->hop_limit = inner_ip4->ttl;
+      inner_ip6->protocol = inner_ip4->protocol;
+
+      if ((rv = inner_fn (inner_ip4, inner_ip6, inner_ctx)) != 0)
+	return rv;
+
+      if (PREDICT_FALSE (inner_frag != NULL))
+	{
+	  inner_frag->next_hdr = inner_ip6->protocol;
+	  inner_frag->identification = inner_frag_id;
+	  inner_frag->rsv = 0;
+	  inner_frag->fragment_offset_and_more =
+	    ip6_frag_hdr_offset_and_more (inner_frag_offset, inner_frag_more);
+	  inner_ip6->protocol = IP_PROTOCOL_IPV6_FRAGMENTATION;
+	  inner_ip6->payload_length =
+	    clib_host_to_net_u16 (clib_net_to_host_u16
+				  (inner_ip6->payload_length) +
+				  sizeof (*inner_frag));
+	}
+
+      csum = ip_csum_add_even (csum, inner_ip6->src_address.as_u64[0]);
+      csum = ip_csum_add_even (csum, inner_ip6->src_address.as_u64[1]);
+      csum = ip_csum_add_even (csum, inner_ip6->dst_address.as_u64[0]);
+      csum = ip_csum_add_even (csum, inner_ip6->dst_address.as_u64[1]);
+      *inner_L4_checksum = ip_csum_fold (csum);
+    }
+  else
+    {
+      vlib_buffer_advance (p, sizeof (*ip4) - sizeof (*ip6));
+      ip6 = vlib_buffer_get_current (p);
+      ip6->payload_length =
+	clib_host_to_net_u16 (clib_net_to_host_u16 (ip4->length) -
+			      sizeof (*ip4));
+    }
+
+  //Translate outer IPv6
+  ip6->ip_version_traffic_class_and_flow_label =
+    clib_host_to_net_u32 ((6 << 28) + (ip4->tos << 20));
+
+  ip6->hop_limit = ip4->ttl;
+  ip6->protocol = IP_PROTOCOL_ICMP6;
+
+  if ((rv = fn (ip4, ip6, ctx)) != 0)
+    return rv;
+
+  //Truncate when the packet exceeds the minimal IPv6 MTU
+  if (p->current_length > 1280)
+    {
+      ip6->payload_length = clib_host_to_net_u16 (1280 - sizeof (*ip6));
+      p->current_length = 1280;	//Looks too simple to be correct...
+    }
+
+  //Recompute ICMP checksum
+  icmp->checksum = 0;
+  csum = ip_csum_with_carry (0, ip6->payload_length);
+  csum = ip_csum_with_carry (csum, clib_host_to_net_u16 (ip6->protocol));
+  csum = ip_csum_with_carry (csum, ip6->src_address.as_u64[0]);
+  csum = ip_csum_with_carry (csum, ip6->src_address.as_u64[1]);
+  csum = ip_csum_with_carry (csum, ip6->dst_address.as_u64[0]);
+  csum = ip_csum_with_carry (csum, ip6->dst_address.as_u64[1]);
+  csum =
+    ip_incremental_checksum (csum, icmp,
+			     clib_net_to_host_u16 (ip6->payload_length));
+  icmp->checksum = ~ip_csum_fold (csum);
+
+  return 0;
+}
+
+/**
+ * @brief Translate IPv4 fragmented packet to IPv6.
+ *
+ * @param p   Buffer to translate.
+ * @param fn  The function to translate header.
+ * @param ctx A context passed in the header translate function.
+ *
+ * @returns 0 on success, non-zero value otherwise.
+ */
+always_inline int
+ip4_to_ip6_fragmented (vlib_buffer_t * p, ip4_to_ip6_set_fn_t fn, void *ctx)
+{
+  ip4_header_t *ip4;
+  ip6_header_t *ip6;
+  ip6_frag_hdr_t *frag;
+  int rv;
+
+  ip4 = vlib_buffer_get_current (p);
+  frag = (ip6_frag_hdr_t *) u8_ptr_add (ip4, sizeof (*ip4) - sizeof (*frag));
+  ip6 =
+    (ip6_header_t *) u8_ptr_add (ip4,
+				 sizeof (*ip4) - sizeof (*frag) -
+				 sizeof (*ip6));
+  vlib_buffer_advance (p, sizeof (*ip4) - sizeof (*ip6) - sizeof (*frag));
+
+  //We know that the protocol was one of ICMP, TCP or UDP
+  //because the first fragment was found and cached
+  frag->next_hdr =
+    (ip4->protocol == IP_PROTOCOL_ICMP) ? IP_PROTOCOL_ICMP6 : ip4->protocol;
+  frag->identification = frag_id_4to6 (ip4->fragment_id);
+  frag->rsv = 0;
+  frag->fragment_offset_and_more =
+    ip6_frag_hdr_offset_and_more (ip4_get_fragment_offset (ip4),
+				  clib_net_to_host_u16
+				  (ip4->flags_and_fragment_offset) &
+				  IP4_HEADER_FLAG_MORE_FRAGMENTS);
+
+  ip6->ip_version_traffic_class_and_flow_label =
+    clib_host_to_net_u32 ((6 << 28) + (ip4->tos << 20));
+  ip6->payload_length =
+    clib_host_to_net_u16 (clib_net_to_host_u16 (ip4->length) -
+			  sizeof (*ip4) + sizeof (*frag));
+  ip6->hop_limit = ip4->ttl;
+  ip6->protocol = IP_PROTOCOL_IPV6_FRAGMENTATION;
+
+  if ((rv = fn (ip4, ip6, ctx)) != 0)
+    return rv;
+
+  return 0;
+}
+
+/**
+ * @brief Translate IPv4 UDP/TCP packet to IPv6.
+ *
+ * @param p   Buffer to translate.
+ * @param fn  The function to translate header.
+ * @param ctx A context passed in the header translate function.
+ *
+ * @returns 0 on success, non-zero value otherwise.
+ */
+always_inline int
+ip4_to_ip6_tcp_udp (vlib_buffer_t * p, ip4_to_ip6_set_fn_t fn, void *ctx)
+{
+  ip4_header_t *ip4;
+  ip6_header_t *ip6;
+  ip_csum_t csum;
+  u16 *checksum;
+  ip6_frag_hdr_t *frag;
+  u32 frag_id;
+  int rv;
+
+  ip4 = vlib_buffer_get_current (p);
+
+  if (ip4->protocol == IP_PROTOCOL_UDP)
+    {
+      udp_header_t *udp = ip4_next_header (ip4);
+      checksum = &udp->checksum;
+
+      //UDP checksum is optional over IPv4 but mandatory for IPv6
+      //We do not check udp->length sanity but use our safe computed value instead
+      if (PREDICT_FALSE (!checksum))
+	{
+	  u16 udp_len = clib_host_to_net_u16 (ip4->length) - sizeof (*ip4);
+	  csum = ip_incremental_checksum (0, udp, udp_len);
+	  csum = ip_csum_with_carry (csum, clib_host_to_net_u16 (udp_len));
+	  csum =
+	    ip_csum_with_carry (csum, clib_host_to_net_u16 (IP_PROTOCOL_UDP));
+	  csum = ip_csum_with_carry (csum, *((u64 *) (&ip4->src_address)));
+	  *checksum = ~ip_csum_fold (csum);
+	}
+    }
+  else
+    {
+      tcp_header_t *tcp = ip4_next_header (ip4);
+      checksum = &tcp->checksum;
+    }
+
+  csum = ip_csum_sub_even (*checksum, ip4->src_address.as_u32);
+  csum = ip_csum_sub_even (csum, ip4->dst_address.as_u32);
+
+  // Deal with fragmented packets
+  if (PREDICT_FALSE (ip4->flags_and_fragment_offset &
+		     clib_host_to_net_u16 (IP4_HEADER_FLAG_MORE_FRAGMENTS)))
+    {
+      ip6 =
+	(ip6_header_t *) u8_ptr_add (ip4,
+				     sizeof (*ip4) - sizeof (*ip6) -
+				     sizeof (*frag));
+      frag =
+	(ip6_frag_hdr_t *) u8_ptr_add (ip4, sizeof (*ip4) - sizeof (*frag));
+      frag_id = frag_id_4to6 (ip4->fragment_id);
+      vlib_buffer_advance (p, sizeof (*ip4) - sizeof (*ip6) - sizeof (*frag));
+    }
+  else
+    {
+      ip6 = (ip6_header_t *) (((u8 *) ip4) + sizeof (*ip4) - sizeof (*ip6));
+      vlib_buffer_advance (p, sizeof (*ip4) - sizeof (*ip6));
+      frag = NULL;
+    }
+
+  ip6->ip_version_traffic_class_and_flow_label =
+    clib_host_to_net_u32 ((6 << 28) + (ip4->tos << 20));
+  ip6->payload_length = u16_net_add (ip4->length, -sizeof (*ip4));
+  ip6->hop_limit = ip4->ttl;
+  ip6->protocol = ip4->protocol;
+
+  if (PREDICT_FALSE (frag != NULL))
+    {
+      frag->next_hdr = ip6->protocol;
+      frag->identification = frag_id;
+      frag->rsv = 0;
+      frag->fragment_offset_and_more = ip6_frag_hdr_offset_and_more (0, 1);
+      ip6->protocol = IP_PROTOCOL_IPV6_FRAGMENTATION;
+      ip6->payload_length = u16_net_add (ip6->payload_length, sizeof (*frag));
+    }
+
+  if ((rv = fn (ip4, ip6, ctx)) != 0)
+    return rv;
+
+  csum = ip_csum_add_even (csum, ip6->src_address.as_u64[0]);
+  csum = ip_csum_add_even (csum, ip6->src_address.as_u64[1]);
+  csum = ip_csum_add_even (csum, ip6->dst_address.as_u64[0]);
+  csum = ip_csum_add_even (csum, ip6->dst_address.as_u64[1]);
+  *checksum = ip_csum_fold (csum);
+
+  return 0;
+}
+
+#endif /* __included_ip4_to_ip6_h__ */
+
+/*
+ * fd.io coding-style-patch-verification: ON
+ *
+ * Local Variables:
+ * eval: (c-set-style "gnu")
+ * End:
+ */