nat: pick outside addr based on local addr

Use outside addresses more evenly by using local address to pick from
pool of addresses. This ensures stability from POV of remote host -
an internal host always gets translated using the same outside address,
so it doesn't appear to be "hopping". Also, this avoids all hosts
being translated using the first address, which helps avoid needless
recaptchas and the like.

Exact assignment depends on internal ordering of addresses - local address
is used to pick an offset into internal vector. If that address cannot be
used, a linear search is performed as a fallback mechanism to find a possible
translation.

Type: improvement
Signed-off-by: Klement Sekera <ksekera@cisco.com>
Change-Id: I7ccb1da1dda5537f5d30d2f4cb48024f4b51c1a4

1 files changed, 92 insertions, 71 deletions

diff --git a/src/plugins/nat/nat44-ed/nat44_ed_in2out.c b/src/plugins/nat/nat44-ed/nat44_ed_in2out.c
index b99b3367329..59355e49ccd 100644
--- a/src/plugins/nat/nat44-ed/nat44_ed_in2out.c
+++ b/src/plugins/nat/nat44-ed/nat44_ed_in2out.c
@@ -165,91 +165,112 @@ snat_not_translate_fast (snat_main_t *sm, vlib_node_runtime_t *node,
 }
 
 static int
-nat_ed_alloc_addr_and_port (snat_main_t *sm, u32 rx_fib_index, u32 nat_proto,
-			    u32 thread_index, ip4_address_t r_addr, u16 r_port,
-			    u8 proto, u16 port_per_thread,
-			    u32 snat_thread_index, snat_session_t *s,
-			    ip4_address_t *outside_addr, u16 *outside_port)
+nat_ed_alloc_addr_and_port_with_snat_address (
+  snat_main_t *sm, u32 nat_proto, u32 thread_index, snat_address_t *a,
+  u16 port_per_thread, u32 snat_thread_index, snat_session_t *s,
+  ip4_address_t *outside_addr, u16 *outside_port)
 {
-  int i;
-  snat_address_t *a, *ga = 0;
-
   const u16 port_thread_offset = (port_per_thread * snat_thread_index) + 1024;
 
-  for (i = 0; i < vec_len (sm->addresses); i++)
+  s->o2i.match.daddr = a->addr;
+  /* first try port suggested by caller */
+  u16 port = clib_net_to_host_u16 (*outside_port);
+  u16 port_offset = port - port_thread_offset;
+  if (port <= port_thread_offset ||
+      port > port_thread_offset + port_per_thread)
+    {
+      /* need to pick a different port, suggested port doesn't fit in
+       * this thread's port range */
+      port_offset = snat_random_port (0, port_per_thread - 1);
+      port = port_thread_offset + port_offset;
+    }
+  u16 attempts = ED_PORT_ALLOC_ATTEMPTS;
+  do
     {
-      a = sm->addresses + i;
-      switch (nat_proto)
+      if (NAT_PROTOCOL_ICMP == nat_proto)
 	{
-#define _(N, j, n, unused)                                                    \
+	  s->o2i.match.sport = clib_host_to_net_u16 (port);
+	}
+      s->o2i.match.dport = clib_host_to_net_u16 (port);
+      if (0 == nat_ed_ses_o2i_flow_hash_add_del (sm, thread_index, s, 2))
+	{
+#define _(N, i, n, s)                                                         \
   case NAT_PROTOCOL_##N:                                                      \
-    if (a->fib_index == rx_fib_index)                                         \
-      {                                                                       \
-	s->o2i.match.daddr = a->addr;                                         \
-	/* first try port suggested by caller */                              \
-	u16 port = clib_net_to_host_u16 (*outside_port);                      \
-	u16 port_offset = port - port_thread_offset;                          \
-	if (port <= port_thread_offset ||                                     \
-	    port > port_thread_offset + port_per_thread)                      \
-	  {                                                                   \
-	    /* need to pick a different port, suggested port doesn't fit in   \
-	     * this thread's port range */                                    \
-	    port_offset = snat_random_port (0, port_per_thread - 1);          \
-	    port = port_thread_offset + port_offset;                          \
-	  }                                                                   \
-	u16 attempts = ED_PORT_ALLOC_ATTEMPTS;                                \
-	do                                                                    \
-	  {                                                                   \
-	    if (NAT_PROTOCOL_ICMP == nat_proto)                               \
-	      {                                                               \
-		s->o2i.match.sport = clib_host_to_net_u16 (port);             \
-	      }                                                               \
-	    s->o2i.match.dport = clib_host_to_net_u16 (port);                 \
-	    if (0 ==                                                          \
-		nat_ed_ses_o2i_flow_hash_add_del (sm, thread_index, s, 2))    \
-	      {                                                               \
-		++a->busy_##n##_port_refcounts[port];                         \
-		a->busy_##n##_ports_per_thread[thread_index]++;               \
-		a->busy_##n##_ports++;                                        \
-		*outside_addr = a->addr;                                      \
-		*outside_port = clib_host_to_net_u16 (port);                  \
-		return 0;                                                     \
-	      }                                                               \
-	    port_offset = snat_random_port (0, port_per_thread - 1);          \
-	    port = port_thread_offset + port_offset;                          \
-	    --attempts;                                                       \
-	  }                                                                   \
-	while (attempts > 0);                                                 \
-      }                                                                       \
-    else if (a->fib_index == ~0)                                              \
-      {                                                                       \
-	ga = a;                                                               \
-      }                                                                       \
+    ++a->busy_##n##_port_refcounts[port];                                     \
+    a->busy_##n##_ports_per_thread[thread_index]++;                           \
+    a->busy_##n##_ports++;                                                    \
     break;
-
-	  foreach_nat_protocol;
-	default:
-	  nat_elog_info (sm, "unknown protocol");
-	  return 1;
+	  switch (nat_proto)
+	    {
+	      foreach_nat_protocol;
+	    default:
+	      nat_elog_info (sm, "unknown protocol");
+	      return 1;
+	    }
+#undef _
+	  *outside_addr = a->addr;
+	  *outside_port = clib_host_to_net_u16 (port);
+	  return 0;
 	}
+      port_offset = snat_random_port (0, port_per_thread - 1);
+      port = port_thread_offset + port_offset;
+      --attempts;
     }
+  while (attempts > 0);
+  return 1;
+}
 
-  if (ga)
+static int
+nat_ed_alloc_addr_and_port (snat_main_t *sm, u32 rx_fib_index, u32 nat_proto,
+			    u32 thread_index, ip4_address_t s_addr,
+			    u16 port_per_thread, u32 snat_thread_index,
+			    snat_session_t *s, ip4_address_t *outside_addr,
+			    u16 *outside_port)
+{
+  int i;
+  snat_address_t *a, *ga = 0;
+
+  if (vec_len (sm->addresses) > 0)
     {
-      /* fake fib_index to reuse macro */
-      rx_fib_index = ~0;
-      a = ga;
-      switch (nat_proto)
+      int s_addr_offset = s_addr.as_u32 % vec_len (sm->addresses);
+
+      for (i = s_addr_offset; i < vec_len (sm->addresses); ++i)
 	{
-	  foreach_nat_protocol;
-	default:
-	  nat_elog_info (sm, "unknown protocol");
-	  return 1;
+	  a = sm->addresses + i;
+	  if (a->fib_index == rx_fib_index)
+	    {
+	      return nat_ed_alloc_addr_and_port_with_snat_address (
+		sm, nat_proto, thread_index, a, port_per_thread,
+		snat_thread_index, s, outside_addr, outside_port);
+	    }
+	  else if (a->fib_index == ~0)
+	    {
+	      ga = a;
+	    }
 	}
-    }
 
-#undef _
+      for (i = 0; i < s_addr_offset; ++i)
+	{
+	  a = sm->addresses + i;
+	  if (a->fib_index == rx_fib_index)
+	    {
+	      return nat_ed_alloc_addr_and_port_with_snat_address (
+		sm, nat_proto, thread_index, a, port_per_thread,
+		snat_thread_index, s, outside_addr, outside_port);
+	    }
+	  else if (a->fib_index == ~0)
+	    {
+	      ga = a;
+	    }
+	}
 
+      if (ga)
+	{
+	  return nat_ed_alloc_addr_and_port_with_snat_address (
+	    sm, nat_proto, thread_index, a, port_per_thread, snat_thread_index,
+	    s, outside_addr, outside_port);
+	}
+    }
   /* Totally out of translations to use... */
   nat_ipfix_logging_addresses_exhausted (thread_index, 0);
   return 1;
@@ -423,7 +444,7 @@ slow_path_ed (snat_main_t *sm, vlib_buffer_t *b, ip4_address_t l_addr,
       nat_6t_flow_txfib_rewrite_set (&s->o2i, rx_fib_index);
 
       if (nat_ed_alloc_addr_and_port (
-	    sm, rx_fib_index, nat_proto, thread_index, daddr, dport, proto,
+	    sm, rx_fib_index, nat_proto, thread_index, l_addr,
 	    sm->port_per_thread, tsm->snat_thread_index, s, &outside_addr,
 	    &outside_port))
 	{