src/vnet/ip/ip6_to_ip4.h - fdio/vpp - Gitiles

 /*
  * 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 IPv6 to IPv4 translation
  */
 #ifndef __included_ip6_to_ip4_h__
 #define __included_ip6_to_ip4_h__

 #include <vnet/ip/ip.h>

 /**
  * IPv6 to IPv4 set call back function type
  */
 typedef int (*ip6_to_ip4_set_fn_t) (ip6_header_t * ip6, ip4_header_t * ip4,
 				    void *ctx);

 /* *INDENT-OFF* */
 static u8 icmp6_to_icmp_updater_pointer_table[] =
   { 0, 1, ~0, ~0,
     2, 2, 9, 8,
     12, 12, 12, 12,
     12, 12, 12, 12,
     12, 12, 12, 12,
     12, 12, 12, 12,
     24, 24, 24, 24,
     24, 24, 24, 24,
     24, 24, 24, 24,
     24, 24, 24, 24
   };
 /* *INDENT-ON* */

 #define frag_id_6to4(id) ((id) ^ ((id) >> 16))

 /**
  * @brief Parse some useful information from IPv6 header.
  *
  * @param ip6             IPv6 header.
  * @param buff_len        Buffer length.
  * @param l4_protocol     L4 protocol number.
  * @param l4_offset       L4 header offset.
  * @param frag_hdr_offset Fragment header offset if present, 0 otherwise.
  *
  * @returns 0 on success, non-zero value otherwise.
  */
 static_always_inline int
 ip6_parse (const ip6_header_t * ip6, u32 buff_len,
 	   u8 * l4_protocol, u16 * l4_offset, u16 * frag_hdr_offset)
 {
   if (ip6->protocol == IP_PROTOCOL_IPV6_FRAGMENTATION)
     {
       *l4_protocol = ((ip6_frag_hdr_t *) (ip6 + 1))->next_hdr;
       *frag_hdr_offset = sizeof (*ip6);
       *l4_offset = sizeof (*ip6) + sizeof (ip6_frag_hdr_t);
     }
   else
     {
       *l4_protocol = ip6->protocol;
       *frag_hdr_offset = 0;
       *l4_offset = sizeof (*ip6);
     }

   return (buff_len < (*l4_offset + 4)) ||
     (clib_net_to_host_u16 (ip6->payload_length) <
      (*l4_offset + 4 - sizeof (*ip6)));
 }

 /**
  * @brief Get TCP/UDP port number or ICMP id from IPv6 packet.
  *
  * @param ip6        IPv6 header.
  * @param sender     1 get sender port, 0 get receiver port.
  * @param buffer_len Buffer length.
  *
  * @returns Port number on success, 0 otherwise.
  */
 always_inline u16
 ip6_get_port (ip6_header_t * ip6, u8 sender, u16 buffer_len)
 {
   u8 l4_protocol;
   u16 l4_offset;
   u16 frag_offset;
   u8 *l4;

   if (ip6_parse (ip6, buffer_len, &l4_protocol, &l4_offset, &frag_offset))
     return 0;

   if (frag_offset &&
       ip6_frag_hdr_offset (((ip6_frag_hdr_t *)
 			    u8_ptr_add (ip6, frag_offset))))
     return 0;			//Can't deal with non-first fragment for now

   l4 = u8_ptr_add (ip6, l4_offset);
   if (l4_protocol == IP_PROTOCOL_TCP || l4_protocol == IP_PROTOCOL_UDP)
     {
       return (sender) ? ((udp_header_t *) (l4))->src_port : ((udp_header_t
 							      *)
 							     (l4))->dst_port;
     }
   else if (l4_protocol == IP_PROTOCOL_ICMP6)
     {
       icmp46_header_t *icmp = (icmp46_header_t *) (l4);
       if (icmp->type == ICMP6_echo_request)
 	{
 	  return (sender) ? ((u16 *) (icmp))[2] : -1;
 	}
       else if (icmp->type == ICMP6_echo_reply)
 	{
 	  return (sender) ? -1 : ((u16 *) (icmp))[2];
 	}
     }
   return 0;
 }

 /**
  * @brief Convert type and code value from ICMP6 to ICMP4.
  *
  * @param icmp      ICMP header.
  * @param inner_ip6 Inner IPv6 header if present, 0 otherwise.
  *
  * @returns 0 on success, non-zero value otherwise.
  */
 static_always_inline int
 icmp6_to_icmp_header (icmp46_header_t * icmp, ip6_header_t ** inner_ip6)
 {
   *inner_ip6 = NULL;
   switch (icmp->type)
     {
     case ICMP6_echo_request:
       icmp->type = ICMP4_echo_request;
       break;
     case ICMP6_echo_reply:
       icmp->type = ICMP4_echo_reply;
       break;
     case ICMP6_destination_unreachable:
       *inner_ip6 = (ip6_header_t *) u8_ptr_add (icmp, 8);

       switch (icmp->code)
 	{
 	case ICMP6_destination_unreachable_no_route_to_destination:	//0
 	case ICMP6_destination_unreachable_beyond_scope_of_source_address:	//2
 	case ICMP6_destination_unreachable_address_unreachable:	//3
 	  icmp->type = ICMP4_destination_unreachable;
 	  icmp->code =
 	    ICMP4_destination_unreachable_destination_unreachable_host;
 	  break;
 	case ICMP6_destination_unreachable_destination_administratively_prohibited:	//1
 	  icmp->type =
 	    ICMP4_destination_unreachable;
 	  icmp->code =
 	    ICMP4_destination_unreachable_communication_administratively_prohibited;
 	  break;
 	case ICMP6_destination_unreachable_port_unreachable:
 	  icmp->type = ICMP4_destination_unreachable;
 	  icmp->code = ICMP4_destination_unreachable_port_unreachable;
 	  break;
 	default:
 	  return -1;
 	}
       break;
     case ICMP6_packet_too_big:
       *inner_ip6 = (ip6_header_t *) u8_ptr_add (icmp, 8);

       icmp->type = ICMP4_destination_unreachable;
       icmp->code = 4;
       {
 	u32 advertised_mtu = clib_net_to_host_u32 (*((u32 *) (icmp + 1)));
 	advertised_mtu -= 20;
 	//FIXME: = minimum(advertised MTU-20, MTU_of_IPv4_nexthop, (MTU_of_IPv6_nexthop)-20)
 	((u16 *) (icmp))[3] = clib_host_to_net_u16 (advertised_mtu);
       }
       break;

     case ICMP6_time_exceeded:
       *inner_ip6 = (ip6_header_t *) u8_ptr_add (icmp, 8);

       icmp->type = ICMP4_time_exceeded;
       break;

     case ICMP6_parameter_problem:
       *inner_ip6 = (ip6_header_t *) u8_ptr_add (icmp, 8);

       switch (icmp->code)
 	{
 	case ICMP6_parameter_problem_erroneous_header_field:
 	  icmp->type = ICMP4_parameter_problem;
 	  icmp->code = ICMP4_parameter_problem_pointer_indicates_error;
 	  u32 pointer = clib_net_to_host_u32 (*((u32 *) (icmp + 1)));
 	  if (pointer >= 40)
 	    return -1;

 	  ((u8 *) (icmp + 1))[0] =
 	    icmp6_to_icmp_updater_pointer_table[pointer];
 	  break;
 	case ICMP6_parameter_problem_unrecognized_next_header:
 	  icmp->type = ICMP4_destination_unreachable;
 	  icmp->code = ICMP4_destination_unreachable_port_unreachable;
 	  break;
 	case ICMP6_parameter_problem_unrecognized_option:
 	default:
 	  return -1;
 	}
       break;
     default:
       return -1;
       break;
     }
   return 0;
 }

 /**
  * @brief Translate TOS value from IPv6 to IPv4.
  *
  * @param ip6 IPv6 header.
  *
  * @returns IPv4 TOS value.
  */
 static_always_inline u8
 ip6_translate_tos (const ip6_header_t * ip6)
 {
   return (clib_net_to_host_u32 (ip6->ip_version_traffic_class_and_flow_label)
 	  & 0x0ff00000) >> 20;
 }

 /**
  * @brief Translate ICMP6 packet to ICMP4.
  *
  * @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
 icmp6_to_icmp (vlib_buffer_t * p, ip6_to_ip4_set_fn_t fn, void *ctx,
 	       ip6_to_ip4_set_fn_t inner_fn, void *inner_ctx)
 {
   ip6_header_t *ip6, *inner_ip6;
   ip4_header_t *ip4, *inner_ip4;
   u32 ip6_pay_len;
   icmp46_header_t *icmp;
   ip_csum_t csum;
   int rv;

   ip6 = vlib_buffer_get_current (p);
   ip6_pay_len = clib_net_to_host_u16 (ip6->payload_length);
   icmp = (icmp46_header_t *) (ip6 + 1);
   ASSERT (ip6_pay_len + sizeof (*ip6) <= p->current_length);

   //No extensions headers allowed here
   if (ip6->protocol != IP_PROTOCOL_ICMP6)
     return -1;

   //There are no fragmented ICMP messages, so no extension header for now
   if (icmp6_to_icmp_header (icmp, &inner_ip6))
     return -1;

   if (inner_ip6)
     {
       u16 *inner_L4_checksum, inner_l4_offset, inner_frag_offset,
 	inner_frag_id;
       u8 *inner_l4, inner_protocol;

       //We have two headers to translate
       //   FROM
       //   [   IPv6   ]<- ext ->[IC][   IPv6   ]<- ext ->[L4 header ...
       // Handled cases:
       //                     [   IPv6   ][IC][   IPv6   ][L4 header ...
       //                 [   IPv6   ][IC][   IPv6   ][Fr][L4 header ...
       //    TO
       //                               [ IPv4][IC][ IPv4][L4 header ...

       if (ip6_parse (inner_ip6, ip6_pay_len - 8,
 		     &inner_protocol, &inner_l4_offset, &inner_frag_offset))
 	return -1;

       inner_l4 = u8_ptr_add (inner_ip6, inner_l4_offset);
       inner_ip4 =
 	(ip4_header_t *) u8_ptr_add (inner_l4, -sizeof (*inner_ip4));
       if (inner_frag_offset)
 	{
 	  ip6_frag_hdr_t *inner_frag =
 	    (ip6_frag_hdr_t *) u8_ptr_add (inner_ip6, inner_frag_offset);
 	  inner_frag_id = frag_id_6to4 (inner_frag->identification);
 	}
       else
 	{
 	  inner_frag_id = 0;
 	}

       //Do the translation of the inner packet
       if (inner_protocol == IP_PROTOCOL_TCP)
 	{
 	  inner_L4_checksum = (u16 *) u8_ptr_add (inner_l4, 16);
 	}
       else if (inner_protocol == IP_PROTOCOL_UDP)
 	{
 	  inner_L4_checksum = (u16 *) u8_ptr_add (inner_l4, 6);
 	}
       else if (inner_protocol == IP_PROTOCOL_ICMP6)
 	{
 	  icmp46_header_t *inner_icmp = (icmp46_header_t *) inner_l4;
 	  //It cannot be of a different type as ip6_icmp_to_icmp6_in_place succeeded
 	  inner_icmp->type = (inner_icmp->type == ICMP6_echo_request) ?
 	    ICMP4_echo_request : ICMP4_echo_reply;
 	  inner_protocol = IP_PROTOCOL_ICMP;	//Will be copied to ip6 later
 	  inner_L4_checksum = &inner_icmp->checksum;
 	}
       else
 	{
 	  return -1;
 	}

       csum = *inner_L4_checksum;
       csum = ip_csum_sub_even (csum, inner_ip6->src_address.as_u64[0]);
       csum = ip_csum_sub_even (csum, inner_ip6->src_address.as_u64[1]);
       csum = ip_csum_sub_even (csum, inner_ip6->dst_address.as_u64[0]);
       csum = ip_csum_sub_even (csum, inner_ip6->dst_address.as_u64[1]);
       *inner_L4_checksum = ip_csum_fold (csum);

       if ((rv = inner_fn (inner_ip6, inner_ip4, inner_ctx)) != 0)
 	return rv;

       inner_ip4->ip_version_and_header_length =
 	IP4_VERSION_AND_HEADER_LENGTH_NO_OPTIONS;
       inner_ip4->tos = ip6_translate_tos (inner_ip6);
       inner_ip4->length =
 	u16_net_add (inner_ip6->payload_length,
 		     sizeof (*ip4) + sizeof (*ip6) - inner_l4_offset);
       inner_ip4->fragment_id = inner_frag_id;
       inner_ip4->flags_and_fragment_offset =
 	clib_host_to_net_u16 (IP4_HEADER_FLAG_MORE_FRAGMENTS);
       inner_ip4->ttl = inner_ip6->hop_limit;
       inner_ip4->protocol = inner_protocol;
       inner_ip4->checksum = ip4_header_checksum (inner_ip4);

       if (inner_ip4->protocol == IP_PROTOCOL_ICMP)
 	{
 	  //Recompute ICMP checksum
 	  icmp46_header_t *inner_icmp = (icmp46_header_t *) inner_l4;
 	  inner_icmp->checksum = 0;
 	  csum =
 	    ip_incremental_checksum (0, inner_icmp,
 				     clib_net_to_host_u16 (inner_ip4->length)
 				     - sizeof (*inner_ip4));
 	  inner_icmp->checksum = ~ip_csum_fold (csum);
 	}
       else
 	{
 	  //Update to new pseudo-header
 	  csum = *inner_L4_checksum;
 	  csum = ip_csum_add_even (csum, inner_ip4->src_address.as_u32);
 	  csum = ip_csum_add_even (csum, inner_ip4->dst_address.as_u32);
 	  *inner_L4_checksum = ip_csum_fold (csum);
 	}

       //Move up icmp header
       ip4 = (ip4_header_t *) u8_ptr_add (inner_l4, -2 * sizeof (*ip4) - 8);
       clib_memcpy (u8_ptr_add (inner_l4, -sizeof (*ip4) - 8), icmp, 8);
       icmp = (icmp46_header_t *) u8_ptr_add (inner_l4, -sizeof (*ip4) - 8);
     }
   else
     {
       //Only one header to translate
       ip4 = (ip4_header_t *) u8_ptr_add (ip6, sizeof (*ip6) - sizeof (*ip4));
     }

   vlib_buffer_advance (p, (u32) (((u8 *) ip4) - ((u8 *) ip6)));

   if ((rv = fn (ip6, ip4, ctx)) != 0)
     return rv;

   ip4->ip_version_and_header_length =
     IP4_VERSION_AND_HEADER_LENGTH_NO_OPTIONS;
   ip4->tos = ip6_translate_tos (ip6);
   ip4->fragment_id = 0;
   ip4->flags_and_fragment_offset = 0;
   ip4->ttl = ip6->hop_limit;
   ip4->protocol = IP_PROTOCOL_ICMP;
   //TODO fix the length depending on offset length
   ip4->length = u16_net_add (ip6->payload_length,
 			     (inner_ip6 ==
 			      NULL) ? sizeof (*ip4) : (2 * sizeof (*ip4) -
 						       sizeof (*ip6)));
   ip4->checksum = ip4_header_checksum (ip4);

   //Recompute ICMP checksum
   icmp->checksum = 0;
   csum =
     ip_incremental_checksum (0, icmp,
 			     clib_net_to_host_u16 (ip4->length) -
 			     sizeof (*ip4));
   icmp->checksum = ~ip_csum_fold (csum);

   return 0;
 }

 /**
  * @brief Translate IPv6 fragmented packet to IPv4.
  *
  * @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
 ip6_to_ip4_fragmented (vlib_buffer_t * p, ip6_to_ip4_set_fn_t fn, void *ctx)
 {
   ip6_header_t *ip6;
   ip6_frag_hdr_t *frag;
   ip4_header_t *ip4;
   u16 frag_id;
   u8 frag_more;
   u16 frag_offset;
   u8 l4_protocol;
   u16 l4_offset;
   int rv;

   ip6 = vlib_buffer_get_current (p);

   if (ip6_parse
       (ip6, p->current_length, &l4_protocol, &l4_offset, &frag_offset))
     return -1;

   frag = (ip6_frag_hdr_t *) u8_ptr_add (ip6, frag_offset);
   ip4 = (ip4_header_t *) u8_ptr_add (ip6, l4_offset - sizeof (*ip4));
   vlib_buffer_advance (p, l4_offset - sizeof (*ip4));

   frag_id = frag_id_6to4 (frag->identification);
   frag_more = ip6_frag_hdr_more (frag);
   frag_offset = ip6_frag_hdr_offset (frag);

   if ((rv = fn (ip6, ip4, ctx)) != 0)
     return rv;

   ip4->ip_version_and_header_length =
     IP4_VERSION_AND_HEADER_LENGTH_NO_OPTIONS;
   ip4->tos = ip6_translate_tos (ip6);
   ip4->length = u16_net_add (ip6->payload_length,
 			     sizeof (*ip4) - l4_offset + sizeof (*ip6));
   ip4->fragment_id = frag_id;
   ip4->flags_and_fragment_offset =
     clib_host_to_net_u16 (frag_offset |
 			  (frag_more ? IP4_HEADER_FLAG_MORE_FRAGMENTS : 0));
   ip4->ttl = ip6->hop_limit;
   ip4->protocol =
     (l4_protocol == IP_PROTOCOL_ICMP6) ? IP_PROTOCOL_ICMP : l4_protocol;
   ip4->checksum = ip4_header_checksum (ip4);

   return 0;
 }

 /**
  * @brief Translate IPv6 UDP/TCP packet to IPv4.
  *
  * @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
 ip6_to_ip4_tcp_udp (vlib_buffer_t * p, ip6_to_ip4_set_fn_t fn, void *ctx,
 		    u8 udp_checksum)
 {
   ip6_header_t *ip6;
   u16 *checksum;
   ip_csum_t csum = 0;
   ip4_header_t *ip4;
   u16 fragment_id;
   u16 flags;
   u16 frag_offset;
   u8 l4_protocol;
   u16 l4_offset;
   int rv;

   ip6 = vlib_buffer_get_current (p);

   if (ip6_parse
       (ip6, p->current_length, &l4_protocol, &l4_offset, &frag_offset))
     return -1;

   if (l4_protocol == IP_PROTOCOL_TCP)
     {
       tcp_header_t *tcp = ip6_next_header (ip6);
       checksum = &tcp->checksum;
     }
   else
     {
       udp_header_t *udp = ip6_next_header (ip6);
       checksum = &udp->checksum;
       //UDP checksum is optional over IPv4
       if (!udp_checksum)
 	goto no_csum;
     }

   csum = ip_csum_sub_even (*checksum, ip6->src_address.as_u64[0]);
   csum = ip_csum_sub_even (csum, ip6->src_address.as_u64[1]);
   csum = ip_csum_sub_even (csum, ip6->dst_address.as_u64[0]);
   csum = ip_csum_sub_even (csum, ip6->dst_address.as_u64[1]);
   *checksum = ip_csum_fold (csum);

 no_csum:
   ip4 = (ip4_header_t *) u8_ptr_add (ip6, l4_offset - sizeof (*ip4));

   vlib_buffer_advance (p, l4_offset - sizeof (*ip4));

   if (PREDICT_FALSE (frag_offset))
     {
       //Only the first fragment
       ip6_frag_hdr_t *hdr = (ip6_frag_hdr_t *) u8_ptr_add (ip6, frag_offset);
       fragment_id = frag_id_6to4 (hdr->identification);
       flags = clib_host_to_net_u16 (IP4_HEADER_FLAG_MORE_FRAGMENTS);
     }
   else
     {
       fragment_id = 0;
       flags = 0;
     }

   if ((rv = fn (ip6, ip4, ctx)) != 0)
     return rv;

   ip4->ip_version_and_header_length =
     IP4_VERSION_AND_HEADER_LENGTH_NO_OPTIONS;
   ip4->tos = ip6_translate_tos (ip6);
   ip4->length = u16_net_add (ip6->payload_length,
 			     sizeof (*ip4) + sizeof (*ip6) - l4_offset);
   ip4->fragment_id = fragment_id;
   ip4->flags_and_fragment_offset = flags;
   ip4->ttl = ip6->hop_limit;
   ip4->protocol = l4_protocol;
   ip4->checksum = ip4_header_checksum (ip4);

   //UDP checksum is optional over IPv4
   if (!udp_checksum && l4_protocol == IP_PROTOCOL_UDP)
     {
       *checksum = 0;
     }
   else
     {
       csum = ip_csum_add_even (*checksum, ip4->dst_address.as_u32);
       csum = ip_csum_add_even (csum, ip4->src_address.as_u32);
       *checksum = ip_csum_fold (csum);
     }

   return 0;
 }

 #endif /* __included_ip6_to_ip4_h__ */

 /*
  * fd.io coding-style-patch-verification: ON
  *
  * Local Variables:
  * eval: (c-set-style "gnu")
  * End:
  */
	/*
	* 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 IPv6 to IPv4 translation
	*/
	#ifndef __included_ip6_to_ip4_h__
	#define __included_ip6_to_ip4_h__

	#include <vnet/ip/ip.h>

	/**
	* IPv6 to IPv4 set call back function type
	*/
	typedef int (ip6_to_ip4_set_fn_t) (ip6_header_t ip6, ip4_header_t * ip4,
	void *ctx);

	/* INDENT-OFF */
	static u8 icmp6_to_icmp_updater_pointer_table[] =
	{ 0, 1, ~0, ~0,
	2, 2, 9, 8,
	12, 12, 12, 12,
	12, 12, 12, 12,
	12, 12, 12, 12,
	12, 12, 12, 12,
	24, 24, 24, 24,
	24, 24, 24, 24,
	24, 24, 24, 24,
	24, 24, 24, 24
	};
	/* INDENT-ON */

	#define frag_id_6to4(id) ((id) ^ ((id) >> 16))

	/**
	* @brief Parse some useful information from IPv6 header.
	*
	* @param ip6 IPv6 header.
	* @param buff_len Buffer length.
	* @param l4_protocol L4 protocol number.
	* @param l4_offset L4 header offset.
	* @param frag_hdr_offset Fragment header offset if present, 0 otherwise.
	*
	* @returns 0 on success, non-zero value otherwise.
	*/
	static_always_inline int
	ip6_parse (const ip6_header_t * ip6, u32 buff_len,
	u8 * l4_protocol, u16 * l4_offset, u16 * frag_hdr_offset)
	{
	if (ip6->protocol == IP_PROTOCOL_IPV6_FRAGMENTATION)
	{
	l4_protocol = ((ip6_frag_hdr_t ) (ip6 + 1))->next_hdr;
	frag_hdr_offset = sizeof (ip6);
	l4_offset = sizeof (ip6) + sizeof (ip6_frag_hdr_t);
	}
	else
	{
	*l4_protocol = ip6->protocol;
	*frag_hdr_offset = 0;
	l4_offset = sizeof (ip6);
	}

	return (buff_len < (*l4_offset + 4)) \|\|
	(clib_net_to_host_u16 (ip6->payload_length) <
	(l4_offset + 4 - sizeof (ip6)));
	}

	/**
	* @brief Get TCP/UDP port number or ICMP id from IPv6 packet.
	*
	* @param ip6 IPv6 header.
	* @param sender 1 get sender port, 0 get receiver port.
	* @param buffer_len Buffer length.
	*
	* @returns Port number on success, 0 otherwise.
	*/
	always_inline u16
	ip6_get_port (ip6_header_t * ip6, u8 sender, u16 buffer_len)
	{
	u8 l4_protocol;
	u16 l4_offset;
	u16 frag_offset;
	u8 *l4;

	if (ip6_parse (ip6, buffer_len, &l4_protocol, &l4_offset, &frag_offset))
	return 0;

	if (frag_offset &&
	ip6_frag_hdr_offset (((ip6_frag_hdr_t *)
	u8_ptr_add (ip6, frag_offset))))
	return 0; //Can't deal with non-first fragment for now

	l4 = u8_ptr_add (ip6, l4_offset);
	if (l4_protocol == IP_PROTOCOL_TCP \|\| l4_protocol == IP_PROTOCOL_UDP)
	{
	return (sender) ? ((udp_header_t *) (l4))->src_port : ((udp_header_t
	*)
	(l4))->dst_port;
	}
	else if (l4_protocol == IP_PROTOCOL_ICMP6)
	{
	icmp46_header_t icmp = (icmp46_header_t ) (l4);
	if (icmp->type == ICMP6_echo_request)
	{
	return (sender) ? ((u16 *) (icmp))[2] : -1;
	}
	else if (icmp->type == ICMP6_echo_reply)
	{
	return (sender) ? -1 : ((u16 *) (icmp))[2];
	}
	}
	return 0;
	}

	/**
	* @brief Convert type and code value from ICMP6 to ICMP4.
	*
	* @param icmp ICMP header.
	* @param inner_ip6 Inner IPv6 header if present, 0 otherwise.
	*
	* @returns 0 on success, non-zero value otherwise.
	*/
	static_always_inline int
	icmp6_to_icmp_header (icmp46_header_t * icmp, ip6_header_t ** inner_ip6)
	{
	*inner_ip6 = NULL;
	switch (icmp->type)
	{
	case ICMP6_echo_request:
	icmp->type = ICMP4_echo_request;
	break;
	case ICMP6_echo_reply:
	icmp->type = ICMP4_echo_reply;
	break;
	case ICMP6_destination_unreachable:
	inner_ip6 = (ip6_header_t ) u8_ptr_add (icmp, 8);

	switch (icmp->code)
	{
	case ICMP6_destination_unreachable_no_route_to_destination: //0
	case ICMP6_destination_unreachable_beyond_scope_of_source_address: //2
	case ICMP6_destination_unreachable_address_unreachable: //3
	icmp->type = ICMP4_destination_unreachable;
	icmp->code =
	ICMP4_destination_unreachable_destination_unreachable_host;
	break;
	case ICMP6_destination_unreachable_destination_administratively_prohibited: //1
	icmp->type =
	ICMP4_destination_unreachable;
	icmp->code =
	ICMP4_destination_unreachable_communication_administratively_prohibited;
	break;
	case ICMP6_destination_unreachable_port_unreachable:
	icmp->type = ICMP4_destination_unreachable;
	icmp->code = ICMP4_destination_unreachable_port_unreachable;
	break;
	default:
	return -1;
	}
	break;
	case ICMP6_packet_too_big:
	inner_ip6 = (ip6_header_t ) u8_ptr_add (icmp, 8);

	icmp->type = ICMP4_destination_unreachable;
	icmp->code = 4;
	{
	u32 advertised_mtu = clib_net_to_host_u32 (((u32 ) (icmp + 1)));
	advertised_mtu -= 20;
	//FIXME: = minimum(advertised MTU-20, MTU_of_IPv4_nexthop, (MTU_of_IPv6_nexthop)-20)
	((u16 *) (icmp))[3] = clib_host_to_net_u16 (advertised_mtu);
	}
	break;

	case ICMP6_time_exceeded:
	inner_ip6 = (ip6_header_t ) u8_ptr_add (icmp, 8);

	icmp->type = ICMP4_time_exceeded;
	break;

	case ICMP6_parameter_problem:
	inner_ip6 = (ip6_header_t ) u8_ptr_add (icmp, 8);

	switch (icmp->code)
	{
	case ICMP6_parameter_problem_erroneous_header_field:
	icmp->type = ICMP4_parameter_problem;
	icmp->code = ICMP4_parameter_problem_pointer_indicates_error;
	u32 pointer = clib_net_to_host_u32 (((u32 ) (icmp + 1)));
	if (pointer >= 40)
	return -1;

	((u8 *) (icmp + 1))[0] =
	icmp6_to_icmp_updater_pointer_table[pointer];
	break;
	case ICMP6_parameter_problem_unrecognized_next_header:
	icmp->type = ICMP4_destination_unreachable;
	icmp->code = ICMP4_destination_unreachable_port_unreachable;
	break;
	case ICMP6_parameter_problem_unrecognized_option:
	default:
	return -1;
	}
	break;
	default:
	return -1;
	break;
	}
	return 0;
	}

	/**
	* @brief Translate TOS value from IPv6 to IPv4.
	*
	* @param ip6 IPv6 header.
	*
	* @returns IPv4 TOS value.
	*/
	static_always_inline u8
	ip6_translate_tos (const ip6_header_t * ip6)
	{
	return (clib_net_to_host_u32 (ip6->ip_version_traffic_class_and_flow_label)
	& 0x0ff00000) >> 20;
	}

	/**
	* @brief Translate ICMP6 packet to ICMP4.
	*
	* @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
	icmp6_to_icmp (vlib_buffer_t * p, ip6_to_ip4_set_fn_t fn, void *ctx,
	ip6_to_ip4_set_fn_t inner_fn, void *inner_ctx)
	{
	ip6_header_t ip6, inner_ip6;
	ip4_header_t ip4, inner_ip4;
	u32 ip6_pay_len;
	icmp46_header_t *icmp;
	ip_csum_t csum;
	int rv;

	ip6 = vlib_buffer_get_current (p);
	ip6_pay_len = clib_net_to_host_u16 (ip6->payload_length);
	icmp = (icmp46_header_t *) (ip6 + 1);
	ASSERT (ip6_pay_len + sizeof (*ip6) <= p->current_length);

	//No extensions headers allowed here
	if (ip6->protocol != IP_PROTOCOL_ICMP6)
	return -1;

	//There are no fragmented ICMP messages, so no extension header for now
	if (icmp6_to_icmp_header (icmp, &inner_ip6))
	return -1;

	if (inner_ip6)
	{
	u16 *inner_L4_checksum, inner_l4_offset, inner_frag_offset,
	inner_frag_id;
	u8 *inner_l4, inner_protocol;

	//We have two headers to translate
	// FROM
	// [ IPv6 ]<- ext ->[IC][ IPv6 ]<- ext ->[L4 header ...
	// Handled cases:
	// [ IPv6 ][IC][ IPv6 ][L4 header ...
	// [ IPv6 ][IC][ IPv6 ][Fr][L4 header ...
	// TO
	// [ IPv4][IC][ IPv4][L4 header ...

	if (ip6_parse (inner_ip6, ip6_pay_len - 8,
	&inner_protocol, &inner_l4_offset, &inner_frag_offset))
	return -1;

	inner_l4 = u8_ptr_add (inner_ip6, inner_l4_offset);
	inner_ip4 =
	(ip4_header_t ) u8_ptr_add (inner_l4, -sizeof (inner_ip4));
	if (inner_frag_offset)
	{
	ip6_frag_hdr_t *inner_frag =
	(ip6_frag_hdr_t *) u8_ptr_add (inner_ip6, inner_frag_offset);
	inner_frag_id = frag_id_6to4 (inner_frag->identification);
	}
	else
	{
	inner_frag_id = 0;
	}

	//Do the translation of the inner packet
	if (inner_protocol == IP_PROTOCOL_TCP)
	{
	inner_L4_checksum = (u16 *) u8_ptr_add (inner_l4, 16);
	}
	else if (inner_protocol == IP_PROTOCOL_UDP)
	{
	inner_L4_checksum = (u16 *) u8_ptr_add (inner_l4, 6);
	}
	else if (inner_protocol == IP_PROTOCOL_ICMP6)
	{
	icmp46_header_t inner_icmp = (icmp46_header_t ) inner_l4;
	//It cannot be of a different type as ip6_icmp_to_icmp6_in_place succeeded
	inner_icmp->type = (inner_icmp->type == ICMP6_echo_request) ?
	ICMP4_echo_request : ICMP4_echo_reply;
	inner_protocol = IP_PROTOCOL_ICMP; //Will be copied to ip6 later
	inner_L4_checksum = &inner_icmp->checksum;
	}
	else
	{
	return -1;
	}

	csum = *inner_L4_checksum;
	csum = ip_csum_sub_even (csum, inner_ip6->src_address.as_u64[0]);
	csum = ip_csum_sub_even (csum, inner_ip6->src_address.as_u64[1]);
	csum = ip_csum_sub_even (csum, inner_ip6->dst_address.as_u64[0]);
	csum = ip_csum_sub_even (csum, inner_ip6->dst_address.as_u64[1]);
	*inner_L4_checksum = ip_csum_fold (csum);

	if ((rv = inner_fn (inner_ip6, inner_ip4, inner_ctx)) != 0)
	return rv;

	inner_ip4->ip_version_and_header_length =
	IP4_VERSION_AND_HEADER_LENGTH_NO_OPTIONS;
	inner_ip4->tos = ip6_translate_tos (inner_ip6);
	inner_ip4->length =
	u16_net_add (inner_ip6->payload_length,
	sizeof (ip4) + sizeof (ip6) - inner_l4_offset);
	inner_ip4->fragment_id = inner_frag_id;
	inner_ip4->flags_and_fragment_offset =
	clib_host_to_net_u16 (IP4_HEADER_FLAG_MORE_FRAGMENTS);
	inner_ip4->ttl = inner_ip6->hop_limit;
	inner_ip4->protocol = inner_protocol;
	inner_ip4->checksum = ip4_header_checksum (inner_ip4);

	if (inner_ip4->protocol == IP_PROTOCOL_ICMP)
	{
	//Recompute ICMP checksum
	icmp46_header_t inner_icmp = (icmp46_header_t ) inner_l4;
	inner_icmp->checksum = 0;
	csum =
	ip_incremental_checksum (0, inner_icmp,
	clib_net_to_host_u16 (inner_ip4->length)
	- sizeof (*inner_ip4));
	inner_icmp->checksum = ~ip_csum_fold (csum);
	}
	else
	{
	//Update to new pseudo-header
	csum = *inner_L4_checksum;
	csum = ip_csum_add_even (csum, inner_ip4->src_address.as_u32);
	csum = ip_csum_add_even (csum, inner_ip4->dst_address.as_u32);
	*inner_L4_checksum = ip_csum_fold (csum);
	}

	//Move up icmp header
	ip4 = (ip4_header_t ) u8_ptr_add (inner_l4, -2 sizeof (*ip4) - 8);
	clib_memcpy (u8_ptr_add (inner_l4, -sizeof (*ip4) - 8), icmp, 8);
	icmp = (icmp46_header_t ) u8_ptr_add (inner_l4, -sizeof (ip4) - 8);
	}
	else
	{
	//Only one header to translate
	ip4 = (ip4_header_t ) u8_ptr_add (ip6, sizeof (ip6) - sizeof (*ip4));
	}

	vlib_buffer_advance (p, (u32) (((u8 ) ip4) - ((u8 ) ip6)));

	if ((rv = fn (ip6, ip4, ctx)) != 0)
	return rv;

	ip4->ip_version_and_header_length =
	IP4_VERSION_AND_HEADER_LENGTH_NO_OPTIONS;
	ip4->tos = ip6_translate_tos (ip6);
	ip4->fragment_id = 0;
	ip4->flags_and_fragment_offset = 0;
	ip4->ttl = ip6->hop_limit;
	ip4->protocol = IP_PROTOCOL_ICMP;
	//TODO fix the length depending on offset length
	ip4->length = u16_net_add (ip6->payload_length,
	(inner_ip6 ==
	NULL) ? sizeof (ip4) : (2 sizeof (*ip4) -
	sizeof (*ip6)));
	ip4->checksum = ip4_header_checksum (ip4);

	//Recompute ICMP checksum
	icmp->checksum = 0;
	csum =
	ip_incremental_checksum (0, icmp,
	clib_net_to_host_u16 (ip4->length) -
	sizeof (*ip4));
	icmp->checksum = ~ip_csum_fold (csum);

	return 0;
	}

	/**
	* @brief Translate IPv6 fragmented packet to IPv4.
	*
	* @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
	ip6_to_ip4_fragmented (vlib_buffer_t * p, ip6_to_ip4_set_fn_t fn, void *ctx)
	{
	ip6_header_t *ip6;
	ip6_frag_hdr_t *frag;
	ip4_header_t *ip4;
	u16 frag_id;
	u8 frag_more;
	u16 frag_offset;
	u8 l4_protocol;
	u16 l4_offset;
	int rv;

	ip6 = vlib_buffer_get_current (p);

	if (ip6_parse
	(ip6, p->current_length, &l4_protocol, &l4_offset, &frag_offset))
	return -1;

	frag = (ip6_frag_hdr_t *) u8_ptr_add (ip6, frag_offset);
	ip4 = (ip4_header_t ) u8_ptr_add (ip6, l4_offset - sizeof (ip4));
	vlib_buffer_advance (p, l4_offset - sizeof (*ip4));

	frag_id = frag_id_6to4 (frag->identification);
	frag_more = ip6_frag_hdr_more (frag);
	frag_offset = ip6_frag_hdr_offset (frag);

	if ((rv = fn (ip6, ip4, ctx)) != 0)
	return rv;

	ip4->ip_version_and_header_length =
	IP4_VERSION_AND_HEADER_LENGTH_NO_OPTIONS;
	ip4->tos = ip6_translate_tos (ip6);
	ip4->length = u16_net_add (ip6->payload_length,
	sizeof (ip4) - l4_offset + sizeof (ip6));
	ip4->fragment_id = frag_id;
	ip4->flags_and_fragment_offset =
	clib_host_to_net_u16 (frag_offset \|
	(frag_more ? IP4_HEADER_FLAG_MORE_FRAGMENTS : 0));
	ip4->ttl = ip6->hop_limit;
	ip4->protocol =
	(l4_protocol == IP_PROTOCOL_ICMP6) ? IP_PROTOCOL_ICMP : l4_protocol;
	ip4->checksum = ip4_header_checksum (ip4);

	return 0;
	}

	/**
	* @brief Translate IPv6 UDP/TCP packet to IPv4.
	*
	* @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
	ip6_to_ip4_tcp_udp (vlib_buffer_t * p, ip6_to_ip4_set_fn_t fn, void *ctx,
	u8 udp_checksum)
	{
	ip6_header_t *ip6;
	u16 *checksum;
	ip_csum_t csum = 0;
	ip4_header_t *ip4;
	u16 fragment_id;
	u16 flags;
	u16 frag_offset;
	u8 l4_protocol;
	u16 l4_offset;
	int rv;

	ip6 = vlib_buffer_get_current (p);

	if (ip6_parse
	(ip6, p->current_length, &l4_protocol, &l4_offset, &frag_offset))
	return -1;

	if (l4_protocol == IP_PROTOCOL_TCP)
	{
	tcp_header_t *tcp = ip6_next_header (ip6);
	checksum = &tcp->checksum;
	}
	else
	{
	udp_header_t *udp = ip6_next_header (ip6);
	checksum = &udp->checksum;
	//UDP checksum is optional over IPv4
	if (!udp_checksum)
	goto no_csum;
	}

	csum = ip_csum_sub_even (*checksum, ip6->src_address.as_u64[0]);
	csum = ip_csum_sub_even (csum, ip6->src_address.as_u64[1]);
	csum = ip_csum_sub_even (csum, ip6->dst_address.as_u64[0]);
	csum = ip_csum_sub_even (csum, ip6->dst_address.as_u64[1]);
	*checksum = ip_csum_fold (csum);

	no_csum:
	ip4 = (ip4_header_t ) u8_ptr_add (ip6, l4_offset - sizeof (ip4));

	vlib_buffer_advance (p, l4_offset - sizeof (*ip4));

	if (PREDICT_FALSE (frag_offset))
	{
	//Only the first fragment
	ip6_frag_hdr_t hdr = (ip6_frag_hdr_t ) u8_ptr_add (ip6, frag_offset);
	fragment_id = frag_id_6to4 (hdr->identification);
	flags = clib_host_to_net_u16 (IP4_HEADER_FLAG_MORE_FRAGMENTS);
	}
	else
	{
	fragment_id = 0;
	flags = 0;
	}

	if ((rv = fn (ip6, ip4, ctx)) != 0)
	return rv;

	ip4->ip_version_and_header_length =
	IP4_VERSION_AND_HEADER_LENGTH_NO_OPTIONS;
	ip4->tos = ip6_translate_tos (ip6);
	ip4->length = u16_net_add (ip6->payload_length,
	sizeof (ip4) + sizeof (ip6) - l4_offset);
	ip4->fragment_id = fragment_id;
	ip4->flags_and_fragment_offset = flags;
	ip4->ttl = ip6->hop_limit;
	ip4->protocol = l4_protocol;
	ip4->checksum = ip4_header_checksum (ip4);

	//UDP checksum is optional over IPv4
	if (!udp_checksum && l4_protocol == IP_PROTOCOL_UDP)
	{
	*checksum = 0;
	}
	else
	{
	csum = ip_csum_add_even (*checksum, ip4->dst_address.as_u32);
	csum = ip_csum_add_even (csum, ip4->src_address.as_u32);
	*checksum = ip_csum_fold (csum);
	}

	return 0;
	}

	#endif /* __included_ip6_to_ip4_h__ */

	/*
	* fd.io coding-style-patch-verification: ON
	*
	* Local Variables:
	* eval: (c-set-style "gnu")
	* End:
	*/