NAT: TCP MSS clamping

NAT plugin changes the MSS value in TCP SYN packets to avoid fragmentation.
If the negotiated MSS value is greater than the configured value it is changed
to the configured value. If the negotiated MSS value is smaller than the
configured value it remains unchanged.

Change-Id: Ic3c4f94a2f1b76e2bf79f50f3ad36a4097f3f188
Signed-off-by: Matus Fabian <matfabia@cisco.com>

1 files changed, 76 insertions, 0 deletions

diff --git a/src/plugins/nat/nat44_cli.c b/src/plugins/nat/nat44_cli.c
index 17a3827dee6..4f02896f4b9 100644
--- a/src/plugins/nat/nat44_cli.c
+++ b/src/plugins/nat/nat44_cli.c
@@ -292,6 +292,56 @@ nat44_show_alloc_addr_and_port_alg_command_fn (vlib_main_t * vm,
 }
 
 static clib_error_t *
+nat_set_mss_clamping_command_fn (vlib_main_t * vm, unformat_input_t * input,
+				 vlib_cli_command_t * cmd)
+{
+  unformat_input_t _line_input, *line_input = &_line_input;
+  snat_main_t *sm = &snat_main;
+  clib_error_t *error = 0;
+  u32 mss;
+
+  /* Get a line of input. */
+  if (!unformat_user (input, unformat_line_input, line_input))
+    return 0;
+
+  while (unformat_check_input (line_input) != UNFORMAT_END_OF_INPUT)
+    {
+      if (unformat (line_input, "disable"))
+	sm->mss_clamping = 0;
+      else if (unformat (line_input, "%d", &mss))
+	{
+	  sm->mss_clamping = (u16) mss;
+	  sm->mss_value_net = clib_host_to_net_u16 (sm->mss_clamping);
+	}
+      else
+	{
+	  error = clib_error_return (0, "unknown input '%U'",
+				     format_unformat_error, line_input);
+	  goto done;
+	}
+    }
+
+done:
+  unformat_free (line_input);
+
+  return error;
+}
+
+static clib_error_t *
+nat_show_mss_clamping_command_fn (vlib_main_t * vm, unformat_input_t * input,
+				  vlib_cli_command_t * cmd)
+{
+  snat_main_t *sm = &snat_main;
+
+  if (sm->mss_clamping)
+    vlib_cli_output (vm, "mss-clamping %d", sm->mss_clamping);
+  else
+    vlib_cli_output (vm, "mss-clamping disabled");
+
+  return 0;
+}
+
+static clib_error_t *
 add_address_command_fn (vlib_main_t * vm,
 			unformat_input_t * input, vlib_cli_command_t * cmd)
 {
@@ -1704,6 +1754,32 @@ VLIB_CLI_COMMAND (nat44_show_alloc_addr_and_port_alg_command, static) = {
 
 /*?
  * @cliexpar
+ * @cliexstart{nat mss-clamping}
+ * Set TCP MSS rewriting configuration
+ * To enable TCP MSS rewriting use:
+ *  vpp# nat mss-clamping 1452
+ * To disbale TCP MSS rewriting use:
+ *  vpp# nat mss-clamping disable
+?*/
+VLIB_CLI_COMMAND (nat_set_mss_clamping_command, static) = {
+    .path = "nat mss-clamping",
+    .short_help = "nat mss-clamping <mss-value>|disable",
+    .function = nat_set_mss_clamping_command_fn,
+};
+
+/*?
+ * @cliexpar
+ * @cliexstart{nat mss-clamping}
+ * Show TCP MSS rewriting configuration
+?*/
+VLIB_CLI_COMMAND (nat_show_mss_clamping_command, static) = {
+    .path = "show nat mss-clamping",
+    .short_help = "show nat mss-clamping",
+    .function = nat_show_mss_clamping_command_fn,
+};
+
+/*?
+ * @cliexpar
  * @cliexstart{show nat44 hash tables}
  * Show NAT44 hash tables
  * @cliexend