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_reass.h>
#include <nat/nat_inlines.h>
#include <nat/nat_syslog.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;
}

vlib_node_registration_t snat_out2in_node;
vlib_node_registration_t snat_out2in_fast_node;
vlib_node_registration_t nat44_out2in_reass_node;

#define foreach_snat_out2in_error                       \
_(UNSUPPORTED_PROTOCOL, "unsupported protocol")         \
_(OUT2IN_PACKETS, "good out2in packets processed")      \
_(OUT_OF_PORTS, "out of ports")                         \
_(BAD_ICMP_TYPE, "unsupported ICMP type")               \
_(NO_TRANSLATION, "no translation")                     \
_(MAX_SESSIONS_EXCEEDED, "maximum sessions exceeded")   \
_(DROP_FRAGMENT, "drop fragment")                       \
_(MAX_REASS, "maximum reassemblies exceeded")           \
_(MAX_FRAG, "maximum fragments per reassembly exceeded")\
_(TCP_PACKETS, "TCP packets")                           \
_(UDP_PACKETS, "UDP packets")                           \
_(ICMP_PACKETS, "ICMP packets")                         \
_(OTHER_PACKETS, "other protocol packets")              \
_(FRAGMENTS, "fragments")                               \
_(CACHED_FRAGMENTS, "cached fragments")                 \
_(PROCESSED_FRAGMENTS, "processed fragments")

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_NEXT_REASS,
  SNAT_OUT2IN_N_NEXT,
} snat_out2in_next_t;

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)
    {
      s_kv.key = s->in2out.as_u64;
      if (clib_bihash_add_del_8_8 (&tsm->in2out, &s_kv, 0))
        nat_log_warn ("out2in key del failed");

      snat_ipfix_logging_nat44_ses_delete (s->in2out.addr.as_u32,
                                           s->out2in.addr.as_u32,
                                           s->in2out.protocol,
                                           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->in2out.protocol);

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

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

  return 0;
}

/**
 * @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,
                                   snat_session_key_t in2out,
                                   snat_session_key_t out2in,
                                   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 (maximum_sessions_exceeded (sm, thread_index)))
    {
      b0->error = node->errors[SNAT_OUT2IN_ERROR_MAX_SESSIONS_EXCEEDED];
      nat_log_notice ("maximum sessions exceeded");
      return 0;
    }

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

  u =
    nat_user_get_or_create (sm, &in2out.addr, in2out.fib_index, thread_index);
  if (!u)
    {
      nat_log_warn ("create NAT user failed");
      return 0;
    }

  s = nat_session_alloc_or_recycle (sm, u, thread_index);
  if (!s)
    {
      nat44_delete_user_with_no_session (sm, u, thread_index);
      nat_log_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 = in2out;
  s->out2in = out2in;
  s->in2out.protocol = out2in.protocol;

  /* Add to translation hashes */
  ctx0.now = now;
  ctx0.thread_index = thread_index;
  kv0.key = s->in2out.as_u64;
  kv0.value = 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_log_notice ("in2out key add failed");

  kv0.key = s->out2in.as_u64;

  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_log_notice ("out2in key add failed");

  /* log NAT event */
  snat_ipfix_logging_nat44_ses_create (s->in2out.addr.as_u32,
                                       s->out2in.addr.as_u32,
                                       s->in2out.protocol,
                                       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->in2out.protocol);

  return s;
}

static_always_inline
  snat_out2in_error_t icmp_get_key (ip4_header_t * ip0,
                                    snat_session_key_t * p_key0)
{
  icmp46_header_t *icmp0;
  snat_session_key_t key0;
  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_is_error_message (icmp0))
    {
      key0.protocol = SNAT_PROTOCOL_ICMP;
      key0.addr = ip0->dst_address;
      key0.port = echo0->identifier;
    }
  else
    {
      inner_ip0 = (ip4_header_t *) (echo0 + 1);
      l4_header = ip4_next_header (inner_ip0);
      key0.protocol = ip_proto_to_snat_proto (inner_ip0->protocol);
      key0.addr = inner_ip0->src_address;
      switch (key0.protocol)
        {
        case SNAT_PROTOCOL_ICMP:
          inner_icmp0 = (icmp46_header_t *) l4_header;
          inner_echo0 = (icmp_echo_header_t *) (inner_icmp0 + 1);
          key0.port = inner_echo0->identifier;
          break;
        case SNAT_PROTOCOL_UDP:
        case SNAT_PROTOCOL_TCP:
          key0.port = ((tcp_udp_header_t *) l4_header)->src_port;
          break;
        default:
          return SNAT_OUT2IN_ERROR_UNSUPPORTED_PROTOCOL;
        }
    }
  *p_key0 = key0;
  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[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, u8 * p_proto,
                        snat_session_key_t * p_value,
                        u8 * p_dont_translate, void *d, void *e)
{
  icmp46_header_t *icmp0;
  u32 sw_if_index0;
  u32 rx_fib_index0;
  snat_session_key_t key0;
  snat_session_key_t sm0;
  snat_session_t *s0 = 0;
  u8 dont_translate = 0;
  clib_bihash_kv_8_8_t kv0, value0;
  u8 is_addr_only;
  u32 next0 = ~0;
  int err;
  u8 identity_nat;

  icmp0 = (icmp46_header_t *) ip4_next_header (ip0);
  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);

  key0.protocol = 0;

  err = icmp_get_key (ip0, &key0);
  if (err != -1)
    {
      b0->error = node->errors[SNAT_OUT2IN_ERROR_UNSUPPORTED_PROTOCOL];
      next0 = SNAT_OUT2IN_NEXT_DROP;
      goto out;
    }
  key0.fib_index = rx_fib_index0;

  kv0.key = key0.as_u64;

  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, key0, &sm0, 1, &is_addr_only, 0, 0, 0, &identity_nat))
        {
          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 (icmp0->type != ICMP4_echo_reply &&
                         (icmp0->type != 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, sm0, key0,
                                              node, thread_index,
                                              vlib_time_now (sm->vlib_main));

      if (!s0)
        {
          next0 = SNAT_OUT2IN_NEXT_DROP;
          goto out;
        }
    }
  else
    {
      if (PREDICT_FALSE (icmp0->type != ICMP4_echo_reply &&
                         icmp0->type != ICMP4_echo_request &&
                         !icmp_is_error_message (icmp0)))
        {
          b0->error = node->errors[SNAT_OUT2IN_ERROR_BAD_ICMP_TYPE];
          next0 = SNAT_OUT2IN_NEXT_DROP;
          goto out;
        }

      s0 = pool_elt_at_index (sm->per_thread_data[thread_index].sessions,
                              value0.value);
    }

out:
  *p_proto = key0.protocol;
  if (s0)
    *p_value = s0->in2out;
  *p_dont_translate = dont_translate;
  if (d)
    *(snat_session_t **) d = s0;
  return next0;
}

/**
 * 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[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, u8 * p_proto,
                        snat_session_key_t * p_value,
                        u8 * p_dont_translate, void *d, void *e)
{
  icmp46_header_t *icmp0;
  u32 sw_if_index0;
  u32 rx_fib_index0;
  snat_session_key_t key0;
  snat_session_key_t sm0;
  u8 dont_translate = 0;
  u8 is_addr_only;
  u32 next0 = ~0;
  int err;

  icmp0 = (icmp46_header_t *) ip4_next_header (ip0);
  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 (ip0, &key0);
  if (err != -1)
    {
      b0->error = node->errors[err];
      next0 = SNAT_OUT2IN_NEXT_DROP;
      goto out2;
    }
  key0.fib_index = rx_fib_index0;

  if (snat_static_mapping_match
      (sm, key0, &sm0, 1, &is_addr_only, 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 (icmp0->type != ICMP4_echo_reply &&
                     (icmp0->type != ICMP4_echo_request || !is_addr_only) &&
                     !icmp_is_error_message (icmp0)))
    {
      b0->error = node->errors[SNAT_OUT2IN_ERROR_BAD_ICMP_TYPE];
      next0 = SNAT_OUT2IN_NEXT_DROP;
      goto out;
    }

out:
  *p_value = sm0;
out2:
  *p_proto = key0.protocol;
  *p_dont_translate = dont_translate;
  return next0;
}

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)
{
  snat_session_key_t sm0;
  u8 protocol;
  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;

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

  next0_tmp = sm->icmp_match_out2in_cb (sm, node, thread_index, b0, ip0,
                                        &protocol, &sm0, &dont_translate, d,
                                        e);
  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 (sm->vlib_main, 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 = sm0.addr.as_u32;
  vnet_buffer (b0)->sw_if_index[VLIB_TX] = sm0.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 (icmp0->checksum == 0)
    icmp0->checksum = 0xffff;

  if (!icmp_is_error_message (icmp0))
    {
      new_id0 = sm0.port;
      if (PREDICT_FALSE (new_id0 != echo0->identifier))
        {
          old_id0 = echo0->identifier;
          new_id0 = sm0.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 = sm0.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 (protocol)
        {
        case SNAT_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 = sm0.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 SNAT_PROTOCOL_UDP:
        case SNAT_PROTOCOL_TCP:
          old_id0 = ((tcp_udp_header_t *) l4_header)->src_port;
          new_id0 = sm0.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;
}


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)
{
  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
                                     (sm->vlib_main, b0));
      /* 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;
  snat_session_key_t m_key;
  u32 old_addr, new_addr;
  ip_csum_t sum;

  m_key.addr = ip->dst_address;
  m_key.port = 0;
  m_key.protocol = 0;
  m_key.fib_index = 0;
  kv.key = m_key.as_u64;
  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;
}

static uword
snat_out2in_node_fn (vlib_main_t * vm,
                     vlib_node_runtime_t * node, vlib_frame_t * frame)
{
  u32 n_left_from, *from, *to_next;
  snat_out2in_next_t next_index;
  u32 pkts_processed = 0;
  snat_main_t *sm = &snat_main;
  f64 now = vlib_time_now (vm);
  u32 thread_index = vm->thread_index;
  u32 tcp_packets = 0, udp_packets = 0, icmp_packets = 0, other_packets =
    0, fragments = 0;

  from = vlib_frame_vector_args (frame);
  n_left_from = frame->n_vectors;
  next_index = node->cached_next_index;

  while (n_left_from > 0)
    {
      u32 n_left_to_next;

      vlib_get_next_frame (vm, node, next_index, to_next, n_left_to_next);

      while (n_left_from >= 4 && n_left_to_next >= 2)
        {
          u32 bi0, bi1;
          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;
          snat_session_key_t key0, key1, sm0, sm1;
          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;

          /* Prefetch next iteration. */
          {
            vlib_buffer_t *p2, *p3;

            p2 = vlib_get_buffer (vm, from[2]);
            p3 = vlib_get_buffer (vm, from[3]);

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

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

          /* speculatively enqueue b0 and b1 to the current next frame */
          to_next[0] = bi0 = from[0];
          to_next[1] = bi1 = from[1];
          from += 2;
          to_next += 2;
          n_left_from -= 2;
          n_left_to_next -= 2;

          b0 = vlib_get_buffer (vm, bi0);
          b1 = vlib_get_buffer (vm, bi1);

          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_snat_proto (ip0->protocol);

          if (PREDICT_FALSE (proto0 == ~0))
            {
              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;
                    }
                }
              other_packets++;
              goto trace0;
            }

          if (PREDICT_FALSE (ip4_is_fragment (ip0)))
            {
              next0 = SNAT_OUT2IN_NEXT_REASS;
              fragments++;
              goto trace0;
            }

          if (PREDICT_FALSE (proto0 == SNAT_PROTOCOL_ICMP))
            {
              next0 = icmp_out2in_slow_path
                (sm, b0, ip0, icmp0, sw_if_index0, rx_fib_index0, node,
                 next0, now, thread_index, &s0);
              icmp_packets++;
              goto trace0;
            }

          key0.addr = ip0->dst_address;
          key0.port = udp0->dst_port;
          key0.protocol = proto0;
          key0.fib_index = rx_fib_index0;

          kv0.key = key0.as_u64;

          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, key0, &sm0, 1, 0, 0, 0, 0, &identity_nat0))
                {
                  /*
                   * 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 == SNAT_PROTOCOL_UDP
                                     && (udp0->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, sm0, key0, node,
                                                      thread_index, now);
              if (!s0)
                {
                  next0 = SNAT_OUT2IN_NEXT_DROP;
                  goto trace0;
                }
            }
          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 == SNAT_PROTOCOL_TCP))
            {
              old_port0 = tcp0->dst_port;
              tcp0->dst_port = s0->in2out.port;
              new_port0 = tcp0->dst_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);
              tcp_packets++;
            }
          else
            {
              old_port0 = udp0->dst_port;
              udp0->dst_port = s0->in2out.port;
              udp0->checksum = 0;
              udp_packets++;
            }

          /* Accounting */
          nat44_session_update_counters (s0, now,
                                         vlib_buffer_length_in_chain (vm,
                                                                      b0));
          /* 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;
            }

          pkts_processed += next0 == SNAT_OUT2IN_NEXT_LOOKUP;


          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_snat_proto (ip1->protocol);

          if (PREDICT_FALSE (proto1 == ~0))
            {
              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;
                    }
                }
              other_packets++;
              goto trace1;
            }

          if (PREDICT_FALSE (ip4_is_fragment (ip1)))
            {
              next1 = SNAT_OUT2IN_NEXT_REASS;
              fragments++;
              goto trace1;
            }

          if (PREDICT_FALSE (proto1 == SNAT_PROTOCOL_ICMP))
            {
              next1 = icmp_out2in_slow_path
                (sm, b1, ip1, icmp1, sw_if_index1, rx_fib_index1, node,
                 next1, now, thread_index, &s1);
              icmp_packets++;
              goto trace1;
            }

          key1.addr = ip1->dst_address;
          key1.port = udp1->dst_port;
          key1.protocol = proto1;
          key1.fib_index = rx_fib_index1;

          kv1.key = key1.as_u64;

          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, key1, &sm1, 1, 0, 0, 0, 0, &identity_nat1))
                {
                  /*
                   * 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 == SNAT_PROTOCOL_UDP
                                     && (udp1->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, sm1, key1, 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 == SNAT_PROTOCOL_TCP))
            {
              old_port1 = tcp1->dst_port;
              tcp1->dst_port = s1->in2out.port;
              new_port1 = tcp1->dst_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);
              tcp_packets++;
            }
          else
            {
              old_port1 = udp1->dst_port;
              udp1->dst_port = s1->in2out.port;
              udp1->checksum = 0;
              udp_packets++;
            }

          /* Accounting */
          nat44_session_update_counters (s1, now,
                                         vlib_buffer_length_in_chain (vm,
                                                                      b1));
          /* 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;
            }

          pkts_processed += next1 == SNAT_OUT2IN_NEXT_LOOKUP;

          /* verify speculative enqueues, maybe switch current next frame */
          vlib_validate_buffer_enqueue_x2 (vm, node, next_index,
                                           to_next, n_left_to_next,
                                           bi0, bi1, next0, next1);
        }

      while (n_left_from > 0 && n_left_to_next > 0)
        {
          u32 bi0;
          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;
          snat_session_key_t key0, sm0;
          u32 rx_fib_index0;
          u32 proto0;
          snat_session_t *s0 = 0;
          clib_bihash_kv_8_8_t kv0, value0;
          u8 identity_nat0;

          /* speculatively enqueue b0 to the current next frame */
          bi0 = from[0];
          to_next[0] = bi0;
          from += 1;
          to_next += 1;
          n_left_from -= 1;
          n_left_to_next -= 1;

          b0 = vlib_get_buffer (vm, bi0);

          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_snat_proto (ip0->protocol);

          if (PREDICT_FALSE (proto0 == ~0))
            {
              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;
                    }
                }
              other_packets++;
              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 (ip4_is_fragment (ip0)))
            {
              next0 = SNAT_OUT2IN_NEXT_REASS;
              fragments++;
              goto trace00;
            }

          if (PREDICT_FALSE (proto0 == SNAT_PROTOCOL_ICMP))
            {
              next0 = icmp_out2in_slow_path
                (sm, b0, ip0, icmp0, sw_if_index0, rx_fib_index0, node,
                 next0, now, thread_index, &s0);
              icmp_packets++;
              goto trace00;
            }

          key0.addr = ip0->dst_address;
          key0.port = udp0->dst_port;
          key0.protocol = proto0;
          key0.fib_index = rx_fib_index0;

          kv0.key = key0.as_u64;

          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, key0, &sm0, 1, 0, 0, 0, 0, &identity_nat0))
                {
                  /*
                   * 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 == SNAT_PROTOCOL_UDP
                                     && (udp0->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, sm0, key0, 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 == SNAT_PROTOCOL_TCP))
            {
              old_port0 = tcp0->dst_port;
              tcp0->dst_port = s0->in2out.port;
              new_port0 = tcp0->dst_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);
              tcp_packets++;
            }
          else
            {
              old_port0 = udp0->dst_port;
              udp0->dst_port = s0->in2out.port;
              udp0->checksum = 0;
              udp_packets++;
            }

          /* Accounting */
          nat44_session_update_counters (s0, now,
                                         vlib_buffer_length_in_chain (vm,
                                                                      b0));
          /* 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;
            }

          pkts_processed += next0 == SNAT_OUT2IN_NEXT_LOOKUP;

          /* verify speculative enqueue, maybe switch current next frame */
          vlib_validate_buffer_enqueue_x1 (vm, node, next_index,
                                           to_next, n_left_to_next,
                                           bi0, next0);
        }

      vlib_put_next_frame (vm, node, next_index, n_left_to_next);
    }

  vlib_node_increment_counter (vm, snat_out2in_node.index,
                               SNAT_OUT2IN_ERROR_OUT2IN_PACKETS,
                               pkts_processed);
  vlib_node_increment_counter (vm, snat_out2in_node.index,
                               SNAT_OUT2IN_ERROR_TCP_PACKETS, tcp_packets);
  vlib_node_increment_counter (vm, snat_out2in_node.index,
                               SNAT_OUT2IN_ERROR_UDP_PACKETS, udp_packets);
  vlib_node_increment_counter (vm, snat_out2in_node.index,
                               SNAT_OUT2IN_ERROR_ICMP_PACKETS, icmp_packets);
  vlib_node_increment_counter (vm, snat_out2in_node.index,
                               SNAT_OUT2IN_ERROR_OTHER_PACKETS,
                               other_packets);
  vlib_node_increment_counter (vm, snat_out2in_node.index,
                               SNAT_OUT2IN_ERROR_FRAGMENTS, fragments);

  return frame->n_vectors;
}

/* *INDENT-OFF* */
VLIB_REGISTER_NODE (snat_out2in_node) = {
  .function = snat_out2in_node_fn,
  .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",
    [SNAT_OUT2IN_NEXT_REASS] = "nat44-out2in-reass",
  },
};
/* *INDENT-ON* */

VLIB_NODE_FUNCTION_MULTIARCH (snat_out2in_node, snat_out2in_node_fn);

static uword
nat44_out2in_reass_node_fn (vlib_main_t * vm,
                            vlib_node_runtime_t * node, vlib_frame_t * frame)
{
  u32 n_left_from, *from, *to_next;
  snat_out2in_next_t next_index;
  u32 pkts_processed = 0, cached_fragments = 0;
  snat_main_t *sm = &snat_main;
  f64 now = vlib_time_now (vm);
  u32 thread_index = vm->thread_index;
  snat_main_per_thread_data_t *per_thread_data =
    &sm->per_thread_data[thread_index];
  u32 *fragments_to_drop = 0;
  u32 *fragments_to_loopback = 0;

  from = vlib_frame_vector_args (frame);
  n_left_from = frame->n_vectors;
  next_index = node->cached_next_index;

  while (n_left_from > 0)
    {
      u32 n_left_to_next;

      vlib_get_next_frame (vm, node, next_index, to_next, n_left_to_next);

      while (n_left_from > 0 && n_left_to_next > 0)
        {
          u32 bi0, sw_if_index0, proto0, rx_fib_index0, new_addr0, old_addr0;
          vlib_buffer_t *b0;
          u32 next0;
          u8 cached0 = 0;
          ip4_header_t *ip0;
          nat_reass_ip4_t *reass0;
          udp_header_t *udp0;
          tcp_header_t *tcp0;
          icmp46_header_t *icmp0;
          snat_session_key_t key0, sm0;
          clib_bihash_kv_8_8_t kv0, value0;
          snat_session_t *s0 = 0;
          u16 old_port0, new_port0;
          ip_csum_t sum0;
          u8 identity_nat0;

          /* speculatively enqueue b0 to the current next frame */
          bi0 = from[0];
          to_next[0] = bi0;
          from += 1;
          to_next += 1;
          n_left_from -= 1;
          n_left_to_next -= 1;

          b0 = vlib_get_buffer (vm, bi0);
          next0 = SNAT_OUT2IN_NEXT_LOOKUP;

          sw_if_index0 = vnet_buffer (b0)->sw_if_index[VLIB_RX];
          rx_fib_index0 =
            fib_table_get_index_for_sw_if_index (FIB_PROTOCOL_IP4,
                                                 sw_if_index0);

          if (PREDICT_FALSE (nat_reass_is_drop_frag (0)))
            {
              next0 = SNAT_OUT2IN_NEXT_DROP;
              b0->error = node->errors[SNAT_OUT2IN_ERROR_DROP_FRAGMENT];
              goto trace0;
            }

          ip0 = (ip4_header_t *) vlib_buffer_get_current (b0);
          udp0 = ip4_next_header (ip0);
          tcp0 = (tcp_header_t *) udp0;
          icmp0 = (icmp46_header_t *) udp0;
          proto0 = ip_proto_to_snat_proto (ip0->protocol);

          reass0 = nat_ip4_reass_find_or_create (ip0->src_address,
                                                 ip0->dst_address,
                                                 ip0->fragment_id,
                                                 ip0->protocol,
                                                 1, &fragments_to_drop);

          if (PREDICT_FALSE (!reass0))
            {
              next0 = SNAT_OUT2IN_NEXT_DROP;
              b0->error = node->errors[SNAT_OUT2IN_ERROR_MAX_REASS];
              nat_log_notice ("maximum reassemblies exceeded");
              goto trace0;
            }

          if (PREDICT_FALSE (ip4_is_first_fragment (ip0)))
            {
              if (PREDICT_FALSE (proto0 == SNAT_PROTOCOL_ICMP))
                {
                  next0 = icmp_out2in_slow_path
                    (sm, b0, ip0, icmp0, sw_if_index0, rx_fib_index0, node,
                     next0, now, thread_index, &s0);

                  if (PREDICT_TRUE (next0 != SNAT_OUT2IN_NEXT_DROP))
                    {
                      if (s0)
                        reass0->sess_index = s0 - per_thread_data->sessions;
                      else
                        reass0->flags |= NAT_REASS_FLAG_ED_DONT_TRANSLATE;
                      reass0->thread_index = thread_index;
                      nat_ip4_reass_get_frags (reass0,
                                               &fragments_to_loopback);
                    }

                  goto trace0;
                }

              key0.addr = ip0->dst_address;
              key0.port = udp0->dst_port;
              key0.protocol = proto0;
              key0.fib_index = rx_fib_index0;
              kv0.key = key0.as_u64;

              if (clib_bihash_search_8_8
                  (&per_thread_data->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, key0, &sm0, 1, 0, 0, 0, 0, &identity_nat0))
                    {
                      /*
                       * 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 == SNAT_PROTOCOL_UDP
                                         && (udp0->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;
                        }
                      else
                        {
                          reass0->flags |= NAT_REASS_FLAG_ED_DONT_TRANSLATE;
                          nat_ip4_reass_get_frags (reass0,
                                                   &fragments_to_loopback);
                        }
                      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, sm0, key0,
                                                       node, thread_index,
                                                       now);
                  if (!s0)
                    {
                      b0->error =
                        node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
                      next0 = SNAT_OUT2IN_NEXT_DROP;
                      goto trace0;
                    }
                  reass0->sess_index = s0 - per_thread_data->sessions;
                  reass0->thread_index = thread_index;
                }
              else
                {
                  s0 = pool_elt_at_index (per_thread_data->sessions,
                                          value0.value);
                  reass0->sess_index = value0.value;
                }
              nat_ip4_reass_get_frags (reass0, &fragments_to_loopback);
            }
          else
            {
              if (reass0->flags & NAT_REASS_FLAG_ED_DONT_TRANSLATE)
                goto trace0;
              if (PREDICT_FALSE (reass0->sess_index == (u32) ~ 0))
                {
                  if (nat_ip4_reass_add_fragment
                      (reass0, bi0, &fragments_to_drop))
                    {
                      b0->error = node->errors[SNAT_OUT2IN_ERROR_MAX_FRAG];
                      nat_log_notice
                        ("maximum fragments per reassembly exceeded");
                      next0 = SNAT_OUT2IN_NEXT_DROP;
                      goto trace0;
                    }
                  cached0 = 1;
                  goto trace0;
                }
              s0 = pool_elt_at_index (per_thread_data->sessions,
                                      reass0->sess_index);
            }

          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_FALSE (ip4_is_first_fragment (ip0)))
            {
              if (PREDICT_TRUE (proto0 == SNAT_PROTOCOL_TCP))
                {
                  old_port0 = tcp0->dst_port;
                  tcp0->dst_port = s0->in2out.port;
                  new_port0 = tcp0->dst_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);
                }
              else
                {
                  old_port0 = udp0->dst_port;
                  udp0->dst_port = s0->in2out.port;
                  udp0->checksum = 0;
                }
            }

          /* Accounting */
          nat44_session_update_counters (s0, now,
                                         vlib_buffer_length_in_chain (vm,
                                                                      b0));
          /* 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)))
            {
              nat44_reass_trace_t *t =
                vlib_add_trace (vm, node, b0, sizeof (*t));
              t->cached = cached0;
              t->sw_if_index = sw_if_index0;
              t->next_index = next0;
            }

          if (cached0)
            {
              n_left_to_next++;
              to_next--;
              cached_fragments++;
            }
          else
            {
              pkts_processed += next0 != SNAT_OUT2IN_NEXT_DROP;

              /* verify speculative enqueue, maybe switch current next frame */
              vlib_validate_buffer_enqueue_x1 (vm, node, next_index,
                                               to_next, n_left_to_next,
                                               bi0, next0);
            }

          if (n_left_from == 0 && vec_len (fragments_to_loopback))
            {
              from = vlib_frame_vector_args (frame);
              u32 len = vec_len (fragments_to_loopback);
              if (len <= VLIB_FRAME_SIZE)
                {
                  clib_memcpy_fast (from, fragments_to_loopback,
                                    sizeof (u32) * len);
                  n_left_from = len;
                  vec_reset_length (fragments_to_loopback);
                }
              else
                {
                  clib_memcpy_fast (from, fragments_to_loopback +
                                    (len - VLIB_FRAME_SIZE),
                                    sizeof (u32) * VLIB_FRAME_SIZE);
                  n_left_from = VLIB_FRAME_SIZE;
                  _vec_len (fragments_to_loopback) = len - VLIB_FRAME_SIZE;
                }
            }
        }

      vlib_put_next_frame (vm, node, next_index, n_left_to_next);
    }

  vlib_node_increment_counter (vm, nat44_out2in_reass_node.index,
                               SNAT_OUT2IN_ERROR_PROCESSED_FRAGMENTS,
                               pkts_processed);
  vlib_node_increment_counter (vm, nat44_out2in_reass_node.index,
                               SNAT_OUT2IN_ERROR_CACHED_FRAGMENTS,
                               cached_fragments);

  nat_send_all_to_node (vm, fragments_to_drop, node,
                        &node->errors[SNAT_OUT2IN_ERROR_DROP_FRAGMENT],
                        SNAT_OUT2IN_NEXT_DROP);

  vec_free (fragments_to_drop);
  vec_free (fragments_to_loopback);
  return frame->n_vectors;
}

/* *INDENT-OFF* */
VLIB_REGISTER_NODE (nat44_out2in_reass_node) = {
  .function = nat44_out2in_reass_node_fn,
  .name = "nat44-out2in-reass",
  .vector_size = sizeof (u32),
  .format_trace = format_nat44_reass_trace,
  .type = VLIB_NODE_TYPE_INTERNAL,

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

  .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",
    [SNAT_OUT2IN_NEXT_REASS] = "nat44-out2in-reass",
  },
};
/* *INDENT-ON* */

VLIB_NODE_FUNCTION_MULTIARCH (nat44_out2in_reass_node,
                              nat44_out2in_reass_node_fn);

static uword
snat_out2in_fast_node_fn (vlib_main_t * vm,
                          vlib_node_runtime_t * node, vlib_frame_t * frame)
{
  u32 n_left_from, *from, *to_next;
  snat_out2in_next_t next_index;
  u32 pkts_processed = 0;
  snat_main_t *sm = &snat_main;

  from = vlib_frame_vector_args (frame);
  n_left_from = frame->n_vectors;
  next_index = node->cached_next_index;

  while (n_left_from > 0)
    {
      u32 n_left_to_next;

      vlib_get_next_frame (vm, node, next_index, to_next, n_left_to_next);

      while (n_left_from > 0 && n_left_to_next > 0)
        {
          u32 bi0;
          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;
          snat_session_key_t key0, sm0;
          u32 proto0;
          u32 rx_fib_index0;

          /* speculatively enqueue b0 to the current next frame */
          bi0 = from[0];
          to_next[0] = bi0;
          from += 1;
          to_next += 1;
          n_left_from -= 1;
          n_left_to_next -= 1;

          b0 = vlib_get_buffer (vm, bi0);

          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_snat_proto (ip0->protocol);

          if (PREDICT_FALSE (proto0 == ~0))
            goto trace00;

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

          key0.addr = ip0->dst_address;
          key0.port = udp0->dst_port;
          key0.fib_index = rx_fib_index0;

          if (snat_static_mapping_match (sm, key0, &sm0, 1, 0, 0, 0, 0, 0))
            {
              b0->error = node->errors[SNAT_OUT2IN_ERROR_NO_TRANSLATION];
              goto trace00;
            }

          new_addr0 = sm0.addr.as_u32;
          new_port0 = sm0.port;
          vnet_buffer (b0)->sw_if_index[VLIB_TX] = sm0.fib_index;
          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))
            {
              if (PREDICT_TRUE (proto0 == SNAT_PROTOCOL_TCP))
                {
                  old_port0 = tcp0->dst_port;
                  tcp0->dst_port = new_port0;

                  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
                {
                  old_port0 = udp0->dst_port;
                  udp0->dst_port = new_port0;
                  udp0->checksum = 0;
                }
            }
          else
            {
              if (PREDICT_TRUE (proto0 == SNAT_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);
                }
            }

        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;
            }

          pkts_processed += next0 != SNAT_OUT2IN_NEXT_DROP;

          /* verify speculative enqueue, maybe switch current next frame */
          vlib_validate_buffer_enqueue_x1 (vm, node, next_index,
                                           to_next, n_left_to_next,
                                           bi0, next0);
        }

      vlib_put_next_frame (vm, node, next_index, n_left_to_next);
    }

  vlib_node_increment_counter (vm, snat_out2in_fast_node.index,
                               SNAT_OUT2IN_ERROR_OUT2IN_PACKETS,
                               pkts_processed);
  return frame->n_vectors;
}

/* *INDENT-OFF* */
VLIB_REGISTER_NODE (snat_out2in_fast_node) = {
  .function = snat_out2in_fast_node_fn,
  .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",
    [SNAT_OUT2IN_NEXT_REASS] = "nat44-out2in-reass",
  },
};
/* *INDENT-ON* */

VLIB_NODE_FUNCTION_MULTIARCH (snat_out2in_fast_node,
                              snat_out2in_fast_node_fn);

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