out2in.c

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/*
 * Copyright (c) 2016 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 NAT44 endpoint-dependent outside to inside network translation
 */

#include <vlib/vlib.h>
#include <vnet/vnet.h>
#include <vnet/pg/pg.h>

#include <vnet/ip/ip.h>
#include <vnet/udp/udp.h>
#include <vnet/ethernet/ethernet.h>
#include <vnet/fib/ip4_fib.h>
#include <nat/nat.h>
#include <nat/nat_ipfix_logging.h>
#include <nat/nat_inlines.h>
#include <nat/nat44/inlines.h>
#include <nat/nat_syslog.h>
#include <nat/nat_ha.h>

#include <vppinfra/hash.h>
#include <vppinfra/error.h>
#include <vppinfra/elog.h>

typedef struct
{
  u32 sw_if_index;
  u32 next_index;
  u32 session_index;
} snat_out2in_trace_t;

/* packet trace format function */
static u8 *
format_snat_out2in_trace (u8 * s, va_list * args)
{
  CLIB_UNUSED (vlib_main_t * vm) = va_arg (*args, vlib_main_t *);
  CLIB_UNUSED (vlib_node_t * node) = va_arg (*args, vlib_node_t *);
  snat_out2in_trace_t *t = va_arg (*args, snat_out2in_trace_t *);

  s =
    format (s,
            "NAT44_OUT2IN: sw_if_index %d, next index %d, session index %d",
            t->sw_if_index, t->next_index, t->session_index);
  return s;
}

static u8 *
format_snat_out2in_fast_trace (u8 * s, va_list * args)
{
  CLIB_UNUSED (vlib_main_t * vm) = va_arg (*args, vlib_main_t *);
  CLIB_UNUSED (vlib_node_t * node) = va_arg (*args, vlib_node_t *);
  snat_out2in_trace_t *t = va_arg (*args, snat_out2in_trace_t *);

  s = format (s, "NAT44_OUT2IN_FAST: sw_if_index %d, next index %d",
              t->sw_if_index, t->next_index);
  return s;
}

#define foreach_snat_out2in_error                       \
_(UNSUPPORTED_PROTOCOL, "unsupported protocol")         \
_(OUT_OF_PORTS, "out of ports")                         \
_(BAD_ICMP_TYPE, "unsupported ICMP type")               \
_(NO_TRANSLATION, "no translation")                     \
_(MAX_SESSIONS_EXCEEDED, "maximum sessions exceeded")   \
_(CANNOT_CREATE_USER, "cannot create NAT user")

typedef enum
{
#define _(sym,str) SNAT_OUT2IN_ERROR_##sym,
  foreach_snat_out2in_error
#undef _
    SNAT_OUT2IN_N_ERROR,
} snat_out2in_error_t;

static char *snat_out2in_error_strings[] = {
#define _(sym,string) string,
  foreach_snat_out2in_error
#undef _
};

typedef enum
{
  SNAT_OUT2IN_NEXT_DROP,
  SNAT_OUT2IN_NEXT_LOOKUP,
  SNAT_OUT2IN_NEXT_ICMP_ERROR,
  SNAT_OUT2IN_N_NEXT,
} snat_out2in_next_t;

#ifndef CLIB_MARCH_VARIANT
int
nat44_o2i_is_idle_session_cb (clib_bihash_kv_8_8_t * kv, void *arg)
{
  snat_main_t *sm = &snat_main;
  nat44_is_idle_session_ctx_t *ctx = arg;
  snat_session_t *s;
  u64 sess_timeout_time;
  snat_main_per_thread_data_t *tsm = vec_elt_at_index (sm->per_thread_data,
                                                       ctx->thread_index);
  clib_bihash_kv_8_8_t s_kv;

  s = pool_elt_at_index (tsm->sessions, kv->value);
  sess_timeout_time = s->last_heard + (f64) nat44_session_get_timeout (sm, s);
  if (ctx->now >= sess_timeout_time)
    {
      init_nat_i2o_k (&s_kv, s);
      if (clib_bihash_add_del_8_8 (&tsm->in2out, &s_kv, 0))
        nat_elog_warn ("out2in key del failed");

      snat_ipfix_logging_nat44_ses_delete (ctx->thread_index,
                                           s->in2out.addr.as_u32,
                                           s->out2in.addr.as_u32,
                                           s->nat_proto,
                                           s->in2out.port,
                                           s->out2in.port,
                                           s->in2out.fib_index);

      nat_syslog_nat44_apmdel (s->user_index, s->in2out.fib_index,
                               &s->in2out.addr, s->in2out.port,
                               &s->out2in.addr, s->out2in.port, s->nat_proto);

      nat_ha_sdel (&s->out2in.addr, s->out2in.port, &s->ext_host_addr,
                   s->ext_host_port, s->nat_proto, s->out2in.fib_index,
                   ctx->thread_index);

      if (!snat_is_session_static (s))
        snat_free_outside_address_and_port (sm->addresses, ctx->thread_index,
                                            &s->out2in.addr, s->out2in.port,
                                            s->nat_proto);

      nat44_delete_session (sm, s, ctx->thread_index);
      return 1;
    }

  return 0;
}
#endif

/**
 * @brief Create session for static mapping.
 *
 * Create NAT session initiated by host from external network with static
 * mapping.
 *
 * @param sm     NAT main.
 * @param b0     Vlib buffer.
 * @param in2out In2out NAT44 session key.
 * @param out2in Out2in NAT44 session key.
 * @param node   Vlib node.
 *
 * @returns SNAT session if successfully created otherwise 0.
 */
static inline snat_session_t *
create_session_for_static_mapping (snat_main_t * sm,
                                   vlib_buffer_t * b0,
                                   ip4_address_t i2o_addr,
                                   u16 i2o_port,
                                   u32 i2o_fib_index,
                                   ip4_address_t o2i_addr,
                                   u16 o2i_port,
                                   u32 o2i_fib_index,
                                   nat_protocol_t proto,
                                   vlib_node_runtime_t * node,
                                   u32 thread_index, f64 now)
{
  snat_user_t *u;
  snat_session_t *s;
  clib_bihash_kv_8_8_t kv0;
  ip4_header_t *ip0;
  udp_header_t *udp0;
  nat44_is_idle_session_ctx_t ctx0;

  if (PREDICT_FALSE (nat44_maximum_sessions_exceeded (sm, thread_index)))
    {
      b0->error = node->errors[SNAT_OUT2IN_ERROR_MAX_SESSIONS_EXCEEDED];
      nat_elog_notice ("maximum sessions exceeded");
      return 0;
    }

  ip0 = vlib_buffer_get_current (b0);
  udp0 = ip4_next_header (ip0);

  u = nat_user_get_or_create (sm, &i2o_addr, i2o_fib_index, thread_index);
  if (!u)
    {
      b0->error = node->errors[SNAT_OUT2IN_ERROR_CANNOT_CREATE_USER];
      return 0;
    }

  s = nat_session_alloc_or_recycle (sm, u, thread_index, now);
  if (!s)
    {
      nat44_delete_user_with_no_session (sm, u, thread_index);
      nat_elog_warn ("create NAT session failed");
      return 0;
    }

  s->flags |= SNAT_SESSION_FLAG_STATIC_MAPPING;
  s->ext_host_addr.as_u32 = ip0->src_address.as_u32;
  s->ext_host_port = udp0->src_port;
  user_session_increment (sm, u, 1 /* static */ );
  s->in2out.addr = i2o_addr;
  s->in2out.port = i2o_port;
  s->in2out.fib_index = i2o_fib_index;
  s->out2in.addr = o2i_addr;
  s->out2in.port = o2i_port;
  s->out2in.fib_index = o2i_fib_index;
  s->nat_proto = proto;

  /* Add to translation hashes */
  ctx0.now = now;
  ctx0.thread_index = thread_index;
  init_nat_i2o_kv (&kv0, s, s - sm->per_thread_data[thread_index].sessions);
  if (clib_bihash_add_or_overwrite_stale_8_8
      (&sm->per_thread_data[thread_index].in2out, &kv0,
       nat44_i2o_is_idle_session_cb, &ctx0))
    nat_elog_notice ("in2out key add failed");

  init_nat_o2i_kv (&kv0, s, s - sm->per_thread_data[thread_index].sessions);
  if (clib_bihash_add_or_overwrite_stale_8_8
      (&sm->per_thread_data[thread_index].out2in, &kv0,
       nat44_o2i_is_idle_session_cb, &ctx0))
    nat_elog_notice ("out2in key add failed");

  /* log NAT event */
  snat_ipfix_logging_nat44_ses_create (thread_index,
                                       s->in2out.addr.as_u32,
                                       s->out2in.addr.as_u32,
                                       s->nat_proto,
                                       s->in2out.port,
                                       s->out2in.port, s->in2out.fib_index);

  nat_syslog_nat44_apmadd (s->user_index, s->in2out.fib_index,
                           &s->in2out.addr, s->in2out.port, &s->out2in.addr,
                           s->out2in.port, s->nat_proto);

  nat_ha_sadd (&s->in2out.addr, s->in2out.port, &s->out2in.addr,
               s->out2in.port, &s->ext_host_addr, s->ext_host_port,
               &s->ext_host_nat_addr, s->ext_host_nat_port,
               s->nat_proto, s->in2out.fib_index, s->flags, thread_index, 0);

  return s;
}

#ifndef CLIB_MARCH_VARIANT
static_always_inline snat_out2in_error_t
icmp_get_key (vlib_buffer_t * b, ip4_header_t * ip0,
              ip4_address_t * addr, u16 * port, nat_protocol_t * nat_proto)
{
  icmp46_header_t *icmp0;
  icmp_echo_header_t *echo0, *inner_echo0 = 0;
  ip4_header_t *inner_ip0;
  void *l4_header = 0;
  icmp46_header_t *inner_icmp0;

  icmp0 = (icmp46_header_t *) ip4_next_header (ip0);
  echo0 = (icmp_echo_header_t *) (icmp0 + 1);

  if (!icmp_type_is_error_message
      (vnet_buffer (b)->ip.reass.icmp_type_or_tcp_flags))
    {
      *nat_proto = NAT_PROTOCOL_ICMP;
      *addr = ip0->dst_address;
      *port = vnet_buffer (b)->ip.reass.l4_src_port;
    }
  else
    {
      inner_ip0 = (ip4_header_t *) (echo0 + 1);
      l4_header = ip4_next_header (inner_ip0);
      *nat_proto = ip_proto_to_nat_proto (inner_ip0->protocol);
      *addr = inner_ip0->src_address;
      switch (*nat_proto)
        {
        case NAT_PROTOCOL_ICMP:
          inner_icmp0 = (icmp46_header_t *) l4_header;
          inner_echo0 = (icmp_echo_header_t *) (inner_icmp0 + 1);
          *port = inner_echo0->identifier;
          break;
        case NAT_PROTOCOL_UDP:
        case NAT_PROTOCOL_TCP:
          *port = ((tcp_udp_header_t *) l4_header)->src_port;
          break;
        default:
          return SNAT_OUT2IN_ERROR_UNSUPPORTED_PROTOCOL;
        }
    }
  return -1;                    /* success */
}

/**
 * Get address and port values to be used for ICMP packet translation
 * and create session if needed
 *
 * @param[in,out] sm             NAT main
 * @param[in,out] node           NAT node runtime
 * @param[in] thread_index       thread index
 * @param[in,out] b0             buffer containing packet to be translated
 * @param[in,out] ip0            ip header
 * @param[out] p_proto           protocol used for matching
 * @param[out] p_value           address and port after NAT translation
 * @param[out] p_dont_translate  if packet should not be translated
 * @param d                      optional parameter
 * @param e                      optional parameter
 */
u32
icmp_match_out2in_slow (snat_main_t * sm, vlib_node_runtime_t * node,
                        u32 thread_index, vlib_buffer_t * b0,
                        ip4_header_t * ip0, ip4_address_t * addr,
                        u16 * port, u32 * fib_index,
                        nat_protocol_t * proto, void *d, void *e,
                        u8 * dont_translate)
{
  snat_main_per_thread_data_t *tsm = &sm->per_thread_data[thread_index];
  u32 sw_if_index0;
  snat_session_t *s0 = 0;
  clib_bihash_kv_8_8_t kv0, value0;
  u8 is_addr_only;
  u32 next0 = ~0;
  int err;
  u8 identity_nat;
  vlib_main_t *vm = vlib_get_main ();
  *dont_translate = 0;

  sw_if_index0 = vnet_buffer (b0)->sw_if_index[VLIB_RX];
  *fib_index = ip4_fib_table_get_index_for_sw_if_index (sw_if_index0);

  *proto = 0;

  err = icmp_get_key (b0, ip0, addr, port, proto);
  if (err != -1)
    {
      b0->error = node->errors[SNAT_OUT2IN_ERROR_UNSUPPORTED_PROTOCOL];
      next0 = SNAT_OUT2IN_NEXT_DROP;
      goto out;
    }

  ip4_address_t mapping_addr;
  u16 mapping_port;
  u32 mapping_fib_index;

  init_nat_k (&kv0, *addr, *port, *fib_index, *proto);
  if (clib_bihash_search_8_8 (&tsm->out2in, &kv0, &value0))
    {
      /* Try to match static mapping by external address and port,
         destination address and port in packet */
      if (snat_static_mapping_match
          (sm, *addr, *port, *fib_index, *proto,
           &mapping_addr, &mapping_port, &mapping_fib_index, 1, &is_addr_only,
           0, 0, 0, &identity_nat, 0))
        {
          if (!sm->forwarding_enabled)
            {
              /* Don't NAT packet aimed at the intfc address */
              if (PREDICT_FALSE (is_interface_addr (sm, node, sw_if_index0,
                                                    ip0->dst_address.as_u32)))
                {
                  *dont_translate = 1;
                  goto out;
                }
              b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
              next0 = SNAT_OUT2IN_NEXT_DROP;
              goto out;
            }
          else
            {
              *dont_translate = 1;
              goto out;
            }
        }

      if (PREDICT_FALSE
          (vnet_buffer (b0)->ip.reass.icmp_type_or_tcp_flags !=
           ICMP4_echo_reply
           && (vnet_buffer (b0)->ip.reass.icmp_type_or_tcp_flags !=
               ICMP4_echo_request || !is_addr_only)))
        {
          b0->error = node->errors[SNAT_OUT2IN_ERROR_BAD_ICMP_TYPE];
          next0 = SNAT_OUT2IN_NEXT_DROP;
          goto out;
        }

      if (PREDICT_FALSE (identity_nat))
        {
          *dont_translate = 1;
          goto out;
        }
      /* Create session initiated by host from external network */
      s0 =
        create_session_for_static_mapping (sm, b0, mapping_addr, mapping_port,
                                           mapping_fib_index, *addr, *port,
                                           *fib_index, *proto, node,
                                           thread_index, vlib_time_now (vm));

      if (!s0)
        {
          next0 = SNAT_OUT2IN_NEXT_DROP;
          goto out;
        }
    }
  else
    {
      if (PREDICT_FALSE
          (vnet_buffer (b0)->ip.reass.icmp_type_or_tcp_flags !=
           ICMP4_echo_reply
           && vnet_buffer (b0)->ip.reass.icmp_type_or_tcp_flags !=
           ICMP4_echo_request
           && !icmp_type_is_error_message (vnet_buffer (b0)->ip.
                                           reass.icmp_type_or_tcp_flags)))
        {
          b0->error = node->errors[SNAT_OUT2IN_ERROR_BAD_ICMP_TYPE];
          next0 = SNAT_OUT2IN_NEXT_DROP;
          goto out;
        }

      s0 = pool_elt_at_index (tsm->sessions, value0.value);
    }

out:
  if (s0)
    {
      *addr = s0->in2out.addr;
      *port = s0->in2out.port;
      *fib_index = s0->in2out.fib_index;
    }
  if (d)
    *(snat_session_t **) d = s0;
  return next0;
}
#endif

#ifndef CLIB_MARCH_VARIANT
/**
 * Get address and port values to be used for ICMP packet translation
 *
 * @param[in] sm                 NAT main
 * @param[in,out] node           NAT node runtime
 * @param[in] thread_index       thread index
 * @param[in,out] b0             buffer containing packet to be translated
 * @param[in,out] ip0            ip header
 * @param[out] p_proto           protocol used for matching
 * @param[out] p_value           address and port after NAT translation
 * @param[out] p_dont_translate  if packet should not be translated
 * @param d                      optional parameter
 * @param e                      optional parameter
 */
u32
icmp_match_out2in_fast (snat_main_t * sm, vlib_node_runtime_t * node,
                        u32 thread_index, vlib_buffer_t * b0,
                        ip4_header_t * ip0, ip4_address_t * mapping_addr,
                        u16 * mapping_port, u32 * mapping_fib_index,
                        nat_protocol_t * proto, void *d, void *e,
                        u8 * dont_translate)
{
  u32 sw_if_index0;
  u32 rx_fib_index0;
  u8 is_addr_only;
  u32 next0 = ~0;
  int err;
  ip4_address_t addr;
  u16 port;
  *dont_translate = 0;

  sw_if_index0 = vnet_buffer (b0)->sw_if_index[VLIB_RX];
  rx_fib_index0 = ip4_fib_table_get_index_for_sw_if_index (sw_if_index0);

  err = icmp_get_key (b0, ip0, &addr, &port, proto);
  if (err != -1)
    {
      b0->error = node->errors[err];
      next0 = SNAT_OUT2IN_NEXT_DROP;
      goto out;
    }
  if (snat_static_mapping_match
      (sm, addr, port, rx_fib_index0, *proto, mapping_addr, mapping_port,
       mapping_fib_index, 1, &is_addr_only, 0, 0, 0, 0, 0))
    {
      /* Don't NAT packet aimed at the intfc address */
      if (is_interface_addr (sm, node, sw_if_index0, ip0->dst_address.as_u32))
        {
          *dont_translate = 1;
          goto out;
        }
      b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
      next0 = SNAT_OUT2IN_NEXT_DROP;
      goto out;
    }

  if (PREDICT_FALSE
      (vnet_buffer (b0)->ip.reass.icmp_type_or_tcp_flags != ICMP4_echo_reply
       && (vnet_buffer (b0)->ip.reass.icmp_type_or_tcp_flags !=
           ICMP4_echo_request || !is_addr_only)
       && !icmp_type_is_error_message (vnet_buffer (b0)->ip.
                                       reass.icmp_type_or_tcp_flags)))
    {
      b0->error = node->errors[SNAT_OUT2IN_ERROR_BAD_ICMP_TYPE];
      next0 = SNAT_OUT2IN_NEXT_DROP;
      goto out;
    }

out:
  return next0;
}
#endif

#ifndef CLIB_MARCH_VARIANT
u32
icmp_out2in (snat_main_t * sm,
             vlib_buffer_t * b0,
             ip4_header_t * ip0,
             icmp46_header_t * icmp0,
             u32 sw_if_index0,
             u32 rx_fib_index0,
             vlib_node_runtime_t * node,
             u32 next0, u32 thread_index, void *d, void *e)
{
  icmp_echo_header_t *echo0, *inner_echo0 = 0;
  ip4_header_t *inner_ip0 = 0;
  void *l4_header = 0;
  icmp46_header_t *inner_icmp0;
  u8 dont_translate;
  u32 new_addr0, old_addr0;
  u16 old_id0, new_id0;
  ip_csum_t sum0;
  u16 checksum0;
  u32 next0_tmp;
  vlib_main_t *vm = vlib_get_main ();
  ip4_address_t addr;
  u16 port;
  u32 fib_index;
  nat_protocol_t proto;

  echo0 = (icmp_echo_header_t *) (icmp0 + 1);

  next0_tmp = sm->icmp_match_out2in_cb (sm, node, thread_index, b0, ip0,
                                        &addr, &port, &fib_index, &proto,
                                        d, e, &dont_translate);
  if (next0_tmp != ~0)
    next0 = next0_tmp;
  if (next0 == SNAT_OUT2IN_NEXT_DROP || dont_translate)
    goto out;

  if (PREDICT_TRUE (!ip4_is_fragment (ip0)))
    {
      sum0 =
        ip_incremental_checksum_buffer (vm, b0,
                                        (u8 *) icmp0 -
                                        (u8 *) vlib_buffer_get_current (b0),
                                        ntohs (ip0->length) -
                                        ip4_header_bytes (ip0), 0);
      checksum0 = ~ip_csum_fold (sum0);
      if (checksum0 != 0 && checksum0 != 0xffff)
        {
          next0 = SNAT_OUT2IN_NEXT_DROP;
          goto out;
        }
    }

  old_addr0 = ip0->dst_address.as_u32;
  new_addr0 = ip0->dst_address.as_u32 = addr.as_u32;
  vnet_buffer (b0)->sw_if_index[VLIB_TX] = fib_index;

  sum0 = ip0->checksum;
  sum0 = ip_csum_update (sum0, old_addr0, new_addr0, ip4_header_t,
                         dst_address /* changed member */ );
  ip0->checksum = ip_csum_fold (sum0);


  if (!vnet_buffer (b0)->ip.reass.is_non_first_fragment)
    {
      if (icmp0->checksum == 0)
        icmp0->checksum = 0xffff;

      if (!icmp_type_is_error_message (icmp0->type))
        {
          new_id0 = port;
          if (PREDICT_FALSE (new_id0 != echo0->identifier))
            {
              old_id0 = echo0->identifier;
              new_id0 = port;
              echo0->identifier = new_id0;

              sum0 = icmp0->checksum;
              sum0 =
                ip_csum_update (sum0, old_id0, new_id0, icmp_echo_header_t,
                                identifier /* changed member */ );
              icmp0->checksum = ip_csum_fold (sum0);
            }
        }
      else
        {
          inner_ip0 = (ip4_header_t *) (echo0 + 1);
          l4_header = ip4_next_header (inner_ip0);

          if (!ip4_header_checksum_is_valid (inner_ip0))
            {
              next0 = SNAT_OUT2IN_NEXT_DROP;
              goto out;
            }

          old_addr0 = inner_ip0->src_address.as_u32;
          inner_ip0->src_address = addr;
          new_addr0 = inner_ip0->src_address.as_u32;

          sum0 = icmp0->checksum;
          sum0 = ip_csum_update (sum0, old_addr0, new_addr0, ip4_header_t,
                                 src_address /* changed member */ );
          icmp0->checksum = ip_csum_fold (sum0);

          switch (proto)
            {
            case NAT_PROTOCOL_ICMP:
              inner_icmp0 = (icmp46_header_t *) l4_header;
              inner_echo0 = (icmp_echo_header_t *) (inner_icmp0 + 1);

              old_id0 = inner_echo0->identifier;
              new_id0 = port;
              inner_echo0->identifier = new_id0;

              sum0 = icmp0->checksum;
              sum0 =
                ip_csum_update (sum0, old_id0, new_id0, icmp_echo_header_t,
                                identifier);
              icmp0->checksum = ip_csum_fold (sum0);
              break;
            case NAT_PROTOCOL_UDP:
            case NAT_PROTOCOL_TCP:
              old_id0 = ((tcp_udp_header_t *) l4_header)->src_port;
              new_id0 = port;
              ((tcp_udp_header_t *) l4_header)->src_port = new_id0;

              sum0 = icmp0->checksum;
              sum0 = ip_csum_update (sum0, old_id0, new_id0, tcp_udp_header_t,
                                     src_port);
              icmp0->checksum = ip_csum_fold (sum0);
              break;
            default:
              ASSERT (0);
            }
        }
    }

out:
  return next0;
}
#endif

static inline u32
icmp_out2in_slow_path (snat_main_t * sm,
                       vlib_buffer_t * b0,
                       ip4_header_t * ip0,
                       icmp46_header_t * icmp0,
                       u32 sw_if_index0,
                       u32 rx_fib_index0,
                       vlib_node_runtime_t * node,
                       u32 next0, f64 now,
                       u32 thread_index, snat_session_t ** p_s0)
{
  vlib_main_t *vm = vlib_get_main ();

  next0 = icmp_out2in (sm, b0, ip0, icmp0, sw_if_index0, rx_fib_index0, node,
                       next0, thread_index, p_s0, 0);
  snat_session_t *s0 = *p_s0;
  if (PREDICT_TRUE (next0 != SNAT_OUT2IN_NEXT_DROP && s0))
    {
      /* Accounting */
      nat44_session_update_counters (s0, now,
                                     vlib_buffer_length_in_chain
                                     (vm, b0), thread_index);
      /* Per-user LRU list maintenance */
      nat44_session_update_lru (sm, s0, thread_index);
    }
  return next0;
}

static int
nat_out2in_sm_unknown_proto (snat_main_t * sm,
                             vlib_buffer_t * b,
                             ip4_header_t * ip, u32 rx_fib_index)
{
  clib_bihash_kv_8_8_t kv, value;
  snat_static_mapping_t *m;
  u32 old_addr, new_addr;
  ip_csum_t sum;

  init_nat_k (&kv, ip->dst_address, 0, 0, 0);
  if (clib_bihash_search_8_8 (&sm->static_mapping_by_external, &kv, &value))
    return 1;

  m = pool_elt_at_index (sm->static_mappings, value.value);

  old_addr = ip->dst_address.as_u32;
  new_addr = ip->dst_address.as_u32 = m->local_addr.as_u32;
  sum = ip->checksum;
  sum = ip_csum_update (sum, old_addr, new_addr, ip4_header_t, dst_address);
  ip->checksum = ip_csum_fold (sum);

  vnet_buffer (b)->sw_if_index[VLIB_TX] = m->fib_index;
  return 0;
}

VLIB_NODE_FN (snat_out2in_node) (vlib_main_t * vm,
                                 vlib_node_runtime_t * node,
                                 vlib_frame_t * frame)
{
  u32 n_left_from, *from;
  snat_main_t *sm = &snat_main;
  f64 now = vlib_time_now (vm);
  u32 thread_index = vm->thread_index;
  snat_main_per_thread_data_t *tsm = &sm->per_thread_data[thread_index];

  from = vlib_frame_vector_args (frame);
  n_left_from = frame->n_vectors;

  vlib_buffer_t *bufs[VLIB_FRAME_SIZE], **b = bufs;
  u16 nexts[VLIB_FRAME_SIZE], *next = nexts;
  vlib_get_buffers (vm, from, b, n_left_from);

  while (n_left_from >= 2)
    {
      vlib_buffer_t *b0, *b1;
      u32 next0 = SNAT_OUT2IN_NEXT_LOOKUP;
      u32 next1 = SNAT_OUT2IN_NEXT_LOOKUP;
      u32 sw_if_index0, sw_if_index1;
      ip4_header_t *ip0, *ip1;
      ip_csum_t sum0, sum1;
      u32 new_addr0, old_addr0;
      u16 new_port0, old_port0;
      u32 new_addr1, old_addr1;
      u16 new_port1, old_port1;
      udp_header_t *udp0, *udp1;
      tcp_header_t *tcp0, *tcp1;
      icmp46_header_t *icmp0, *icmp1;
      u32 rx_fib_index0, rx_fib_index1;
      u32 proto0, proto1;
      snat_session_t *s0 = 0, *s1 = 0;
      clib_bihash_kv_8_8_t kv0, kv1, value0, value1;
      u8 identity_nat0, identity_nat1;
      ip4_address_t sm_addr0, sm_addr1;
      u16 sm_port0, sm_port1;
      u32 sm_fib_index0, sm_fib_index1;

      b0 = *b;
      b++;
      b1 = *b;
      b++;

      /* Prefetch next iteration. */
      if (PREDICT_TRUE (n_left_from >= 4))
        {
          vlib_buffer_t *p2, *p3;

          p2 = *b;
          p3 = *(b + 1);

          vlib_prefetch_buffer_header (p2, LOAD);
          vlib_prefetch_buffer_header (p3, LOAD);

          CLIB_PREFETCH (p2->data, CLIB_CACHE_LINE_BYTES, LOAD);
          CLIB_PREFETCH (p3->data, CLIB_CACHE_LINE_BYTES, LOAD);
        }

      vnet_buffer (b0)->snat.flags = 0;
      vnet_buffer (b1)->snat.flags = 0;

      ip0 = vlib_buffer_get_current (b0);
      udp0 = ip4_next_header (ip0);
      tcp0 = (tcp_header_t *) udp0;
      icmp0 = (icmp46_header_t *) udp0;

      sw_if_index0 = vnet_buffer (b0)->sw_if_index[VLIB_RX];
      rx_fib_index0 = vec_elt (sm->ip4_main->fib_index_by_sw_if_index,
                               sw_if_index0);

      if (PREDICT_FALSE (ip0->ttl == 1))
        {
          vnet_buffer (b0)->sw_if_index[VLIB_TX] = (u32) ~ 0;
          icmp4_error_set_vnet_buffer (b0, ICMP4_time_exceeded,
                                       ICMP4_time_exceeded_ttl_exceeded_in_transit,
                                       0);
          next0 = SNAT_OUT2IN_NEXT_ICMP_ERROR;
          goto trace0;
        }

      proto0 = ip_proto_to_nat_proto (ip0->protocol);

      if (PREDICT_FALSE (proto0 == NAT_PROTOCOL_OTHER))
        {
          if (nat_out2in_sm_unknown_proto (sm, b0, ip0, rx_fib_index0))
            {
              if (!sm->forwarding_enabled)
                {
                  b0->error =
                    node->errors[SNAT_OUT2IN_ERROR_UNSUPPORTED_PROTOCOL];
                  next0 = SNAT_OUT2IN_NEXT_DROP;
                }
            }
          vlib_increment_simple_counter (&sm->counters.slowpath.out2in.other,
                                         thread_index, sw_if_index0, 1);

          goto trace0;
        }

      if (PREDICT_FALSE (proto0 == NAT_PROTOCOL_ICMP))
        {
          next0 = icmp_out2in_slow_path
            (sm, b0, ip0, icmp0, sw_if_index0, rx_fib_index0, node,
             next0, now, thread_index, &s0);
          vlib_increment_simple_counter (&sm->counters.slowpath.out2in.icmp,
                                         thread_index, sw_if_index0, 1);
          goto trace0;
        }

      init_nat_k (&kv0, ip0->dst_address,
                  vnet_buffer (b0)->ip.reass.l4_dst_port, rx_fib_index0,
                  proto0);
      if (clib_bihash_search_8_8
          (&sm->per_thread_data[thread_index].out2in, &kv0, &value0))
        {
          /* Try to match static mapping by external address and port,
             destination address and port in packet */
          if (snat_static_mapping_match
              (sm, ip0->dst_address,
               vnet_buffer (b0)->ip.reass.l4_dst_port, rx_fib_index0,
               proto0, &sm_addr0, &sm_port0, &sm_fib_index0, 1, 0, 0, 0,
               0, &identity_nat0, 0))
            {
              /*
               * Send DHCP packets to the ipv4 stack, or we won't
               * be able to use dhcp client on the outside interface
               */
              if (PREDICT_FALSE
                  (proto0 == NAT_PROTOCOL_UDP
                   && (vnet_buffer (b0)->ip.reass.l4_dst_port ==
                       clib_host_to_net_u16 (UDP_DST_PORT_dhcp_to_client))))
                {
                  vnet_feature_next (&next0, b0);
                  goto trace0;
                }

              if (!sm->forwarding_enabled)
                {
                  b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
                  next0 = SNAT_OUT2IN_NEXT_DROP;
                }
              goto trace0;
            }

          if (PREDICT_FALSE (identity_nat0))
            goto trace0;

          /* Create session initiated by host from external network */
          s0 = create_session_for_static_mapping (sm, b0,
                                                  sm_addr0, sm_port0,
                                                  sm_fib_index0,
                                                  ip0->dst_address,
                                                  vnet_buffer (b0)->ip.
                                                  reass.l4_dst_port,
                                                  rx_fib_index0, proto0, node,
                                                  thread_index, now);
          if (!s0)
            {
              next0 = SNAT_OUT2IN_NEXT_DROP;
              goto trace0;
            }
        }
      else
        s0 = pool_elt_at_index (tsm->sessions, value0.value);

      old_addr0 = ip0->dst_address.as_u32;
      ip0->dst_address = s0->in2out.addr;
      new_addr0 = ip0->dst_address.as_u32;
      vnet_buffer (b0)->sw_if_index[VLIB_TX] = s0->in2out.fib_index;

      sum0 = ip0->checksum;
      sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
                             ip4_header_t, dst_address /* changed member */ );
      ip0->checksum = ip_csum_fold (sum0);

      if (PREDICT_TRUE (proto0 == NAT_PROTOCOL_TCP))
        {
          if (!vnet_buffer (b0)->ip.reass.is_non_first_fragment)
            {
              old_port0 = vnet_buffer (b0)->ip.reass.l4_dst_port;
              new_port0 = udp0->dst_port = s0->in2out.port;
              sum0 = tcp0->checksum;
              sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
                                     ip4_header_t,
                                     dst_address /* changed member */ );

              sum0 = ip_csum_update (sum0, old_port0, new_port0,
                                     ip4_header_t /* cheat */ ,
                                     length /* changed member */ );
              tcp0->checksum = ip_csum_fold (sum0);
            }
          vlib_increment_simple_counter (&sm->counters.slowpath.out2in.tcp,
                                         thread_index, sw_if_index0, 1);
        }
      else
        {
          if (!vnet_buffer (b0)->ip.reass.is_non_first_fragment)
            {
              old_port0 = vnet_buffer (b0)->ip.reass.l4_dst_port;
              new_port0 = udp0->dst_port = s0->in2out.port;
              if (PREDICT_FALSE (udp0->checksum))
                {
                  sum0 = udp0->checksum;
                  sum0 = ip_csum_update (sum0, old_addr0, new_addr0, ip4_header_t, dst_address  /* changed member */
                    );
                  sum0 =
                    ip_csum_update (sum0, old_port0, new_port0,
                                    ip4_header_t /* cheat */ ,
                                    length /* changed member */ );
                  udp0->checksum = ip_csum_fold (sum0);
                }
            }
          vlib_increment_simple_counter (&sm->counters.slowpath.out2in.udp,
                                         thread_index, sw_if_index0, 1);
        }

      /* Accounting */
      nat44_session_update_counters (s0, now,
                                     vlib_buffer_length_in_chain (vm, b0),
                                     thread_index);
      /* Per-user LRU list maintenance */
      nat44_session_update_lru (sm, s0, thread_index);
    trace0:

      if (PREDICT_FALSE ((node->flags & VLIB_NODE_FLAG_TRACE)
                         && (b0->flags & VLIB_BUFFER_IS_TRACED)))
        {
          snat_out2in_trace_t *t = vlib_add_trace (vm, node, b0, sizeof (*t));
          t->sw_if_index = sw_if_index0;
          t->next_index = next0;
          t->session_index = ~0;
          if (s0)
            t->session_index =
              s0 - sm->per_thread_data[thread_index].sessions;
        }

      if (next0 == SNAT_OUT2IN_NEXT_DROP)
        {
          vlib_increment_simple_counter (&sm->counters.slowpath.out2in.drops,
                                         thread_index, sw_if_index0, 1);
        }


      ip1 = vlib_buffer_get_current (b1);
      udp1 = ip4_next_header (ip1);
      tcp1 = (tcp_header_t *) udp1;
      icmp1 = (icmp46_header_t *) udp1;

      sw_if_index1 = vnet_buffer (b1)->sw_if_index[VLIB_RX];
      rx_fib_index1 = vec_elt (sm->ip4_main->fib_index_by_sw_if_index,
                               sw_if_index1);

      if (PREDICT_FALSE (ip1->ttl == 1))
        {
          vnet_buffer (b1)->sw_if_index[VLIB_TX] = (u32) ~ 0;
          icmp4_error_set_vnet_buffer (b1, ICMP4_time_exceeded,
                                       ICMP4_time_exceeded_ttl_exceeded_in_transit,
                                       0);
          next1 = SNAT_OUT2IN_NEXT_ICMP_ERROR;
          goto trace1;
        }

      proto1 = ip_proto_to_nat_proto (ip1->protocol);

      if (PREDICT_FALSE (proto1 == NAT_PROTOCOL_OTHER))
        {
          if (nat_out2in_sm_unknown_proto (sm, b1, ip1, rx_fib_index1))
            {
              if (!sm->forwarding_enabled)
                {
                  b1->error =
                    node->errors[SNAT_OUT2IN_ERROR_UNSUPPORTED_PROTOCOL];
                  next1 = SNAT_OUT2IN_NEXT_DROP;
                }
            }
          vlib_increment_simple_counter (&sm->counters.slowpath.out2in.other,
                                         thread_index, sw_if_index1, 1);
          goto trace1;
        }

      if (PREDICT_FALSE (proto1 == NAT_PROTOCOL_ICMP))
        {
          next1 = icmp_out2in_slow_path
            (sm, b1, ip1, icmp1, sw_if_index1, rx_fib_index1, node,
             next1, now, thread_index, &s1);
          vlib_increment_simple_counter (&sm->counters.slowpath.out2in.icmp,
                                         thread_index, sw_if_index1, 1);
          goto trace1;
        }

      init_nat_k (&kv1, ip1->dst_address,
                  vnet_buffer (b1)->ip.reass.l4_dst_port, rx_fib_index1,
                  proto1);

      if (clib_bihash_search_8_8
          (&sm->per_thread_data[thread_index].out2in, &kv1, &value1))
        {
          /* Try to match static mapping by external address and port,
             destination address and port in packet */
          if (snat_static_mapping_match
              (sm, ip1->dst_address,
               vnet_buffer (b1)->ip.reass.l4_dst_port, proto1,
               rx_fib_index1, &sm_addr1, &sm_port1, &sm_fib_index1, 1, 0,
               0, 0, 0, &identity_nat1, 0))
            {
              /*
               * Send DHCP packets to the ipv4 stack, or we won't
               * be able to use dhcp client on the outside interface
               */
              if (PREDICT_FALSE
                  (proto1 == NAT_PROTOCOL_UDP
                   && (vnet_buffer (b1)->ip.reass.l4_dst_port ==
                       clib_host_to_net_u16 (UDP_DST_PORT_dhcp_to_client))))
                {
                  vnet_feature_next (&next1, b1);
                  goto trace1;
                }

              if (!sm->forwarding_enabled)
                {
                  b1->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
                  next1 = SNAT_OUT2IN_NEXT_DROP;
                }
              goto trace1;
            }

          if (PREDICT_FALSE (identity_nat1))
            goto trace1;

          /* Create session initiated by host from external network */
          s1 =
            create_session_for_static_mapping (sm, b1, sm_addr1, sm_port1,
                                               sm_fib_index1,
                                               ip1->dst_address,
                                               vnet_buffer (b1)->ip.
                                               reass.l4_dst_port,
                                               rx_fib_index1, proto1, node,
                                               thread_index, now);
          if (!s1)
            {
              next1 = SNAT_OUT2IN_NEXT_DROP;
              goto trace1;
            }
        }
      else
        s1 =
          pool_elt_at_index (sm->per_thread_data[thread_index].sessions,
                             value1.value);

      old_addr1 = ip1->dst_address.as_u32;
      ip1->dst_address = s1->in2out.addr;
      new_addr1 = ip1->dst_address.as_u32;
      vnet_buffer (b1)->sw_if_index[VLIB_TX] = s1->in2out.fib_index;

      sum1 = ip1->checksum;
      sum1 = ip_csum_update (sum1, old_addr1, new_addr1,
                             ip4_header_t, dst_address /* changed member */ );
      ip1->checksum = ip_csum_fold (sum1);

      if (PREDICT_TRUE (proto1 == NAT_PROTOCOL_TCP))
        {
          if (!vnet_buffer (b1)->ip.reass.is_non_first_fragment)
            {
              old_port1 = vnet_buffer (b1)->ip.reass.l4_dst_port;
              new_port1 = udp1->dst_port = s1->in2out.port;

              sum1 = tcp1->checksum;
              sum1 = ip_csum_update (sum1, old_addr1, new_addr1,
                                     ip4_header_t,
                                     dst_address /* changed member */ );

              sum1 = ip_csum_update (sum1, old_port1, new_port1,
                                     ip4_header_t /* cheat */ ,
                                     length /* changed member */ );
              tcp1->checksum = ip_csum_fold (sum1);
            }
          vlib_increment_simple_counter (&sm->counters.slowpath.out2in.tcp,
                                         thread_index, sw_if_index1, 1);
        }
      else
        {
          if (!vnet_buffer (b1)->ip.reass.is_non_first_fragment)
            {
              old_port1 = vnet_buffer (b1)->ip.reass.l4_dst_port;
              new_port1 = udp1->dst_port = s1->in2out.port;
              if (PREDICT_FALSE (udp1->checksum))
                {

                  sum1 = udp1->checksum;
                  sum1 =
                    ip_csum_update (sum1, old_addr1, new_addr1,
                                    ip4_header_t,
                                    dst_address /* changed member */ );
                  sum1 =
                    ip_csum_update (sum1, old_port1, new_port1,
                                    ip4_header_t /* cheat */ ,
                                    length /* changed member */ );
                  udp1->checksum = ip_csum_fold (sum1);
                }
            }
          vlib_increment_simple_counter (&sm->counters.slowpath.out2in.udp,
                                         thread_index, sw_if_index1, 1);
        }

      /* Accounting */
      nat44_session_update_counters (s1, now,
                                     vlib_buffer_length_in_chain (vm, b1),
                                     thread_index);
      /* Per-user LRU list maintenance */
      nat44_session_update_lru (sm, s1, thread_index);
    trace1:

      if (PREDICT_FALSE ((node->flags & VLIB_NODE_FLAG_TRACE)
                         && (b1->flags & VLIB_BUFFER_IS_TRACED)))
        {
          snat_out2in_trace_t *t = vlib_add_trace (vm, node, b1, sizeof (*t));
          t->sw_if_index = sw_if_index1;
          t->next_index = next1;
          t->session_index = ~0;
          if (s1)
            t->session_index =
              s1 - sm->per_thread_data[thread_index].sessions;
        }

      if (next1 == SNAT_OUT2IN_NEXT_DROP)
        {
          vlib_increment_simple_counter (&sm->counters.slowpath.out2in.drops,
                                         thread_index, sw_if_index1, 1);
        }

      n_left_from -= 2;
      next[0] = next0;
      next[1] = next1;
      next += 2;
    }

  while (n_left_from > 0)
    {
      vlib_buffer_t *b0;
      u32 next0 = SNAT_OUT2IN_NEXT_LOOKUP;
      u32 sw_if_index0;
      ip4_header_t *ip0;
      ip_csum_t sum0;
      u32 new_addr0, old_addr0;
      u16 new_port0, old_port0;
      udp_header_t *udp0;
      tcp_header_t *tcp0;
      icmp46_header_t *icmp0;
      u32 rx_fib_index0;
      u32 proto0;
      snat_session_t *s0 = 0;
      clib_bihash_kv_8_8_t kv0, value0;
      u8 identity_nat0;
      ip4_address_t sm_addr0;
      u16 sm_port0;
      u32 sm_fib_index0;

      b0 = *b;
      ++b;

      vnet_buffer (b0)->snat.flags = 0;

      ip0 = vlib_buffer_get_current (b0);
      udp0 = ip4_next_header (ip0);
      tcp0 = (tcp_header_t *) udp0;
      icmp0 = (icmp46_header_t *) udp0;

      sw_if_index0 = vnet_buffer (b0)->sw_if_index[VLIB_RX];
      rx_fib_index0 = vec_elt (sm->ip4_main->fib_index_by_sw_if_index,
                               sw_if_index0);

      proto0 = ip_proto_to_nat_proto (ip0->protocol);

      if (PREDICT_FALSE (proto0 == NAT_PROTOCOL_OTHER))
        {
          if (nat_out2in_sm_unknown_proto (sm, b0, ip0, rx_fib_index0))
            {
              if (!sm->forwarding_enabled)
                {
                  b0->error =
                    node->errors[SNAT_OUT2IN_ERROR_UNSUPPORTED_PROTOCOL];
                  next0 = SNAT_OUT2IN_NEXT_DROP;
                }
            }
          vlib_increment_simple_counter (&sm->counters.slowpath.out2in.other,
                                         thread_index, sw_if_index0, 1);
          goto trace00;
        }

      if (PREDICT_FALSE (ip0->ttl == 1))
        {
          vnet_buffer (b0)->sw_if_index[VLIB_TX] = (u32) ~ 0;
          icmp4_error_set_vnet_buffer (b0, ICMP4_time_exceeded,
                                       ICMP4_time_exceeded_ttl_exceeded_in_transit,
                                       0);
          next0 = SNAT_OUT2IN_NEXT_ICMP_ERROR;
          goto trace00;
        }

      if (PREDICT_FALSE (proto0 == NAT_PROTOCOL_ICMP))
        {
          next0 = icmp_out2in_slow_path
            (sm, b0, ip0, icmp0, sw_if_index0, rx_fib_index0, node,
             next0, now, thread_index, &s0);
          vlib_increment_simple_counter (&sm->counters.slowpath.out2in.icmp,
                                         thread_index, sw_if_index0, 1);
          goto trace00;
        }

      init_nat_k (&kv0, ip0->dst_address,
                  vnet_buffer (b0)->ip.reass.l4_dst_port, rx_fib_index0,
                  proto0);

      if (clib_bihash_search_8_8
          (&sm->per_thread_data[thread_index].out2in, &kv0, &value0))
        {
          /* Try to match static mapping by external address and port,
             destination address and port in packet */
          if (snat_static_mapping_match
              (sm, ip0->dst_address,
               vnet_buffer (b0)->ip.reass.l4_dst_port, rx_fib_index0,
               proto0, &sm_addr0, &sm_port0, &sm_fib_index0, 1, 0, 0, 0,
               0, &identity_nat0, 0))
            {
              /*
               * Send DHCP packets to the ipv4 stack, or we won't
               * be able to use dhcp client on the outside interface
               */
              if (PREDICT_FALSE
                  (proto0 == NAT_PROTOCOL_UDP
                   && (vnet_buffer (b0)->ip.reass.l4_dst_port ==
                       clib_host_to_net_u16 (UDP_DST_PORT_dhcp_to_client))))
                {
                  vnet_feature_next (&next0, b0);
                  goto trace00;
                }

              if (!sm->forwarding_enabled)
                {
                  b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
                  next0 = SNAT_OUT2IN_NEXT_DROP;
                }
              goto trace00;
            }

          if (PREDICT_FALSE (identity_nat0))
            goto trace00;

          /* Create session initiated by host from external network */
          s0 = create_session_for_static_mapping (sm, b0,
                                                  sm_addr0, sm_port0,
                                                  sm_fib_index0,
                                                  ip0->dst_address,
                                                  vnet_buffer (b0)->ip.
                                                  reass.l4_dst_port,
                                                  rx_fib_index0, proto0, node,
                                                  thread_index, now);
          if (!s0)
            {
              next0 = SNAT_OUT2IN_NEXT_DROP;
              goto trace00;
            }
        }
      else
        s0 =
          pool_elt_at_index (sm->per_thread_data[thread_index].sessions,
                             value0.value);

      old_addr0 = ip0->dst_address.as_u32;
      ip0->dst_address = s0->in2out.addr;
      new_addr0 = ip0->dst_address.as_u32;
      vnet_buffer (b0)->sw_if_index[VLIB_TX] = s0->in2out.fib_index;

      sum0 = ip0->checksum;
      sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
                             ip4_header_t, dst_address /* changed member */ );
      ip0->checksum = ip_csum_fold (sum0);

      if (PREDICT_TRUE (proto0 == NAT_PROTOCOL_TCP))
        {
          if (!vnet_buffer (b0)->ip.reass.is_non_first_fragment)
            {
              old_port0 = vnet_buffer (b0)->ip.reass.l4_dst_port;
              new_port0 = udp0->dst_port = s0->in2out.port;

              sum0 = tcp0->checksum;
              sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
                                     ip4_header_t,
                                     dst_address /* changed member */ );

              sum0 = ip_csum_update (sum0, old_port0, new_port0,
                                     ip4_header_t /* cheat */ ,
                                     length /* changed member */ );
              tcp0->checksum = ip_csum_fold (sum0);
            }
          vlib_increment_simple_counter (&sm->counters.slowpath.out2in.tcp,
                                         thread_index, sw_if_index0, 1);
        }
      else
        {
          if (!vnet_buffer (b0)->ip.reass.is_non_first_fragment)
            {
              old_port0 = vnet_buffer (b0)->ip.reass.l4_dst_port;
              new_port0 = udp0->dst_port = s0->in2out.port;
              if (PREDICT_FALSE (udp0->checksum))
                {
                  sum0 = udp0->checksum;
                  sum0 = ip_csum_update (sum0, old_addr0, new_addr0, ip4_header_t, dst_address  /* changed member */
                    );
                  sum0 =
                    ip_csum_update (sum0, old_port0, new_port0,
                                    ip4_header_t /* cheat */ ,
                                    length /* changed member */ );
                  udp0->checksum = ip_csum_fold (sum0);
                }
            }
          vlib_increment_simple_counter (&sm->counters.slowpath.out2in.udp,
                                         thread_index, sw_if_index0, 1);
        }

      /* Accounting */
      nat44_session_update_counters (s0, now,
                                     vlib_buffer_length_in_chain (vm, b0),
                                     thread_index);
      /* Per-user LRU list maintenance */
      nat44_session_update_lru (sm, s0, thread_index);
    trace00:

      if (PREDICT_FALSE ((node->flags & VLIB_NODE_FLAG_TRACE)
                         && (b0->flags & VLIB_BUFFER_IS_TRACED)))
        {
          snat_out2in_trace_t *t = vlib_add_trace (vm, node, b0, sizeof (*t));
          t->sw_if_index = sw_if_index0;
          t->next_index = next0;
          t->session_index = ~0;
          if (s0)
            t->session_index =
              s0 - sm->per_thread_data[thread_index].sessions;
        }

      if (next0 == SNAT_OUT2IN_NEXT_DROP)
        {
          vlib_increment_simple_counter (&sm->counters.slowpath.out2in.drops,
                                         thread_index, sw_if_index0, 1);
        }

      n_left_from--;
      next[0] = next0;
      next++;
    }

  vlib_buffer_enqueue_to_next (vm, node, from, (u16 *) nexts,
                               frame->n_vectors);

  return frame->n_vectors;
}

/* *INDENT-OFF* */
VLIB_REGISTER_NODE (snat_out2in_node) = {
  .name = "nat44-out2in",
  .vector_size = sizeof (u32),
  .format_trace = format_snat_out2in_trace,
  .type = VLIB_NODE_TYPE_INTERNAL,

  .n_errors = ARRAY_LEN(snat_out2in_error_strings),
  .error_strings = snat_out2in_error_strings,

  .runtime_data_bytes = sizeof (snat_runtime_t),

  .n_next_nodes = SNAT_OUT2IN_N_NEXT,

  /* edit / add dispositions here */
  .next_nodes = {
    [SNAT_OUT2IN_NEXT_DROP] = "error-drop",
    [SNAT_OUT2IN_NEXT_LOOKUP] = "ip4-lookup",
    [SNAT_OUT2IN_NEXT_ICMP_ERROR] = "ip4-icmp-error",
  },
};
/* *INDENT-ON* */

VLIB_NODE_FN (snat_out2in_fast_node) (vlib_main_t * vm,
                                      vlib_node_runtime_t * node,
                                      vlib_frame_t * frame)
{
  u32 n_left_from, *from;
  snat_main_t *sm = &snat_main;

  from = vlib_frame_vector_args (frame);
  n_left_from = frame->n_vectors;

  vlib_buffer_t *bufs[VLIB_FRAME_SIZE], **b = bufs;
  u16 nexts[VLIB_FRAME_SIZE], *next = nexts;
  vlib_get_buffers (vm, from, b, n_left_from);
  while (n_left_from > 0)
    {
      vlib_buffer_t *b0;
      u32 next0 = SNAT_OUT2IN_NEXT_DROP;
      u32 sw_if_index0;
      ip4_header_t *ip0;
      ip_csum_t sum0;
      u32 new_addr0, old_addr0;
      u16 new_port0, old_port0;
      udp_header_t *udp0;
      tcp_header_t *tcp0;
      icmp46_header_t *icmp0;
      u32 proto0;
      u32 rx_fib_index0;
      ip4_address_t sm_addr0;
      u16 sm_port0;
      u32 sm_fib_index0;

      b0 = *b;
      b++;

      ip0 = vlib_buffer_get_current (b0);
      udp0 = ip4_next_header (ip0);
      tcp0 = (tcp_header_t *) udp0;
      icmp0 = (icmp46_header_t *) udp0;

      sw_if_index0 = vnet_buffer (b0)->sw_if_index[VLIB_RX];
      rx_fib_index0 = ip4_fib_table_get_index_for_sw_if_index (sw_if_index0);

      vnet_feature_next (&next0, b0);

      if (PREDICT_FALSE (ip0->ttl == 1))
        {
          vnet_buffer (b0)->sw_if_index[VLIB_TX] = (u32) ~ 0;
          icmp4_error_set_vnet_buffer (b0, ICMP4_time_exceeded,
                                       ICMP4_time_exceeded_ttl_exceeded_in_transit,
                                       0);
          next0 = SNAT_OUT2IN_NEXT_ICMP_ERROR;
          goto trace00;
        }

      proto0 = ip_proto_to_nat_proto (ip0->protocol);

      if (PREDICT_FALSE (proto0 == NAT_PROTOCOL_OTHER))
        goto trace00;

      if (PREDICT_FALSE (proto0 == NAT_PROTOCOL_ICMP))
        {
          next0 = icmp_out2in (sm, b0, ip0, icmp0, sw_if_index0,
                               rx_fib_index0, node, next0, ~0, 0, 0);
          goto trace00;
        }

      if (snat_static_mapping_match
          (sm, ip0->dst_address, udp0->dst_port, rx_fib_index0, proto0,
           &sm_addr0, &sm_port0, &sm_fib_index0, 1, 0, 0, 0, 0, 0, 0))
        {
          b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
          goto trace00;
        }

      new_addr0 = sm_addr0.as_u32;
      new_port0 = sm_port0;
      vnet_buffer (b0)->sw_if_index[VLIB_TX] = sm_fib_index0;
      old_addr0 = ip0->dst_address.as_u32;
      ip0->dst_address.as_u32 = new_addr0;

      sum0 = ip0->checksum;
      sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
                             ip4_header_t, dst_address /* changed member */ );
      ip0->checksum = ip_csum_fold (sum0);

      if (PREDICT_FALSE (new_port0 != udp0->dst_port))
        {
          old_port0 = udp0->dst_port;
          udp0->dst_port = new_port0;

          if (PREDICT_TRUE (proto0 == NAT_PROTOCOL_TCP))
            {
              sum0 = tcp0->checksum;
              sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
                                     ip4_header_t,
                                     dst_address /* changed member */ );
              sum0 = ip_csum_update (sum0, old_port0, new_port0,
                                     ip4_header_t /* cheat */ ,
                                     length /* changed member */ );
              tcp0->checksum = ip_csum_fold (sum0);
            }
          else if (udp0->checksum)
            {
              sum0 = udp0->checksum;
              sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
                                     ip4_header_t,
                                     dst_address /* changed member */ );
              sum0 = ip_csum_update (sum0, old_port0, new_port0,
                                     ip4_header_t /* cheat */ ,
                                     length /* changed member */ );
              udp0->checksum = ip_csum_fold (sum0);
            }
        }
      else
        {
          if (PREDICT_TRUE (proto0 == NAT_PROTOCOL_TCP))
            {
              sum0 = tcp0->checksum;
              sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
                                     ip4_header_t,
                                     dst_address /* changed member */ );
              tcp0->checksum = ip_csum_fold (sum0);
            }
          else if (udp0->checksum)
            {
              sum0 = udp0->checksum;
              sum0 = ip_csum_update (sum0, old_addr0, new_addr0,
                                     ip4_header_t,
                                     dst_address /* changed member */ );
              udp0->checksum = ip_csum_fold (sum0);
            }
        }

    trace00:

      if (PREDICT_FALSE ((node->flags & VLIB_NODE_FLAG_TRACE)
                         && (b0->flags & VLIB_BUFFER_IS_TRACED)))
        {
          snat_out2in_trace_t *t = vlib_add_trace (vm, node, b0, sizeof (*t));
          t->sw_if_index = sw_if_index0;
          t->next_index = next0;
        }

      if (next0 == SNAT_OUT2IN_NEXT_DROP)
        {
          vlib_increment_simple_counter (&sm->counters.fastpath.out2in.drops,
                                         vm->thread_index, sw_if_index0, 1);
        }

      n_left_from--;
      next[0] = next0;
      next++;
    }

  vlib_buffer_enqueue_to_next (vm, node, from, (u16 *) nexts,
                               frame->n_vectors);

  return frame->n_vectors;
}

/* *INDENT-OFF* */
VLIB_REGISTER_NODE (snat_out2in_fast_node) = {
  .name = "nat44-out2in-fast",
  .vector_size = sizeof (u32),
  .format_trace = format_snat_out2in_fast_trace,
  .type = VLIB_NODE_TYPE_INTERNAL,

  .n_errors = ARRAY_LEN(snat_out2in_error_strings),
  .error_strings = snat_out2in_error_strings,

  .runtime_data_bytes = sizeof (snat_runtime_t),

  .n_next_nodes = SNAT_OUT2IN_N_NEXT,

  /* edit / add dispositions here */
  .next_nodes = {
    [SNAT_OUT2IN_NEXT_LOOKUP] = "ip4-lookup",
    [SNAT_OUT2IN_NEXT_DROP] = "error-drop",
    [SNAT_OUT2IN_NEXT_ICMP_ERROR] = "ip4-icmp-error",
  },
};
/* *INDENT-ON* */

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