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diff --git a/src/plugins/snat/snat_det.c b/src/plugins/snat/snat_det.c
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+/*
+ * snat_det.c - deterministic NAT
+ *
+ * Copyright (c) 2017 Cisco and/or its affiliates.
+ * Licensed under the Apache License, Version 2.0 (the "License");
+ * you may not use this file except in compliance with the License.
+ * You may obtain a copy of the License at:
+ *
+ * http://www.apache.org/licenses/LICENSE-2.0
+ *
+ * Unless required by applicable law or agreed to in writing, software
+ * distributed under the License is distributed on an "AS IS" BASIS,
+ * WITHOUT WARRANTIES OR CONDITIONS OF ANY KIND, either express or implied.
+ * See the License for the specific language governing permissions and
+ * limitations under the License.
+ */
+/**
+ * @file
+ * @brief deterministic NAT
+ */
+
+#include <snat/snat_det.h>
+
+
+/**
+ * @brief Add/delete deterministic NAT mapping.
+ *
+ * Create bijective mapping of inside address to outside address and port range
+ * pairs, with the purpose of enabling deterministic NAT to reduce logging in
+ * CGN deployments.
+ *
+ * @param sm SNAT main.
+ * @param in_addr Inside network address.
+ * @param in_plen Inside network prefix length.
+ * @param out_addr Outside network address.
+ * @param out_plen Outside network prefix length.
+ * @param is_add If 0 delete, otherwise add.
+ */
+int
+snat_det_add_map (snat_main_t * sm, ip4_address_t * in_addr, u8 in_plen,
+ ip4_address_t * out_addr, u8 out_plen, int is_add)
+{
+ snat_det_map_t *det_map;
+ static snat_det_session_t empty_snat_det_session = { 0 };
+ snat_interface_t *i;
+
+ pool_get (sm->det_maps, det_map);
+ memset (det_map, 0, sizeof (*det_map));
+ det_map->in_addr.as_u32 = in_addr->as_u32 & ip4_main.fib_masks[in_plen];
+ det_map->in_plen = in_plen;
+ det_map->out_addr.as_u32 = out_addr->as_u32 & ip4_main.fib_masks[out_plen];
+ det_map->out_plen = out_plen;
+ det_map->sharing_ratio = (1 << (32 - in_plen)) / (1 << (32 - out_plen));
+ det_map->ports_per_host = (65535 - 1023) / det_map->sharing_ratio;
+
+ vec_validate_init_empty (det_map->sessions,
+ SNAT_DET_SES_PER_USER * (1 << (32 - in_plen)) - 1,
+ empty_snat_det_session);
+
+ /* Add/del external address range to FIB */
+ /* *INDENT-OFF* */
+ pool_foreach (i, sm->interfaces,
+ ({
+ if (i->is_inside)
+ continue;
+
+ snat_add_del_addr_to_fib(out_addr, out_plen, i->sw_if_index, is_add);
+ break;
+ }));
+ /* *INDENT-ON* */
+ return 0;
+}
+
+/**
+ * @brief The 'snat-det-expire-walk' process's main loop.
+ *
+ * Check expire time for active sessions.
+ */
+static uword
+snat_det_expire_walk_fn (vlib_main_t * vm, vlib_node_runtime_t * rt,
+ vlib_frame_t * f)
+{
+ snat_main_t *sm = &snat_main;
+ snat_det_map_t *dm;
+ snat_det_session_t *ses;
+
+ while (sm->deterministic)
+ {
+ vlib_process_wait_for_event_or_clock (vm, 10.0);
+ vlib_process_get_events (vm, NULL);
+ u32 now = (u32) vlib_time_now (vm);
+ /* *INDENT-OFF* */
+ pool_foreach (dm, sm->det_maps,
+ ({
+ vec_foreach(ses, dm->sessions)
+ {
+ /* Delete if session expired */
+ if (ses->in_port && (ses->expire < now))
+ snat_det_ses_close (dm, ses);
+ }
+ }));
+ /* *INDENT-ON* */
+ }
+
+ return 0;
+}
+
+static vlib_node_registration_t snat_det_expire_walk_node;
+
+/* *INDENT-OFF* */
+VLIB_REGISTER_NODE (snat_det_expire_walk_node, static) = {
+ .function = snat_det_expire_walk_fn,
+ .type = VLIB_NODE_TYPE_PROCESS,
+ .name =
+ "snat-det-expire-walk",
+};
+/* *INDENT-ON* */
+
+/*
+ * fd.io coding-style-patch-verification: ON
+ *
+ * Local Variables:
+ * eval: (c-set-style "gnu")
+ * End:
+ */