bfd: reset peer discriminator on timeout

More RFC compliance.

Ticket: VPP-1816 BFD: peer discriminator not reset on timeout
Type: fix

Change-Id: I68063c18097d282b3527e3fb485c1d0d1fd1b0c8
Signed-off-by: Klement Sekera <ksekera@cisco.com>

src/vnet/bfd/bfd_main.c

@@ -1054,6 +1054,19 @@ bfd_check_rx_timeout (bfd_main_t * bm, bfd_session_t * bs, u64 now,
       now + bm->wheel_inaccuracy)
     {
       BFD_DBG ("Rx timeout, session goes down");
+      /*
+       * RFC 5880 6.8.1. State Variables
+
+       * bfd.RemoteDiscr
+
+       * The remote discriminator for this BFD session.  This is the
+       * discriminator chosen by the remote system, and is totally opaque
+       * to the local system.  This MUST be initialized to zero.  If a
+       * period of a Detection Time passes without the receipt of a valid,
+       * authenticated BFD packet from the remote system, this variable
+       * MUST be set to zero.
+       */
+      bs->remote_discr = 0;
       bfd_set_diag (bs, BFD_DIAG_CODE_det_time_exp);
       bfd_set_state (bm, bs, BFD_STATE_down, handling_wakeup);
       /*

test/test_bfd.py

@@ -831,6 +831,16 @@ class BFD4TestCase(VppTestCase):
         e = self.vapi.wait_for_event(1, "bfd_udp_session_details")
         verify_event(self, e, expected_state=BFDState.down)
 
+    def test_peer_discr_reset_sess_down(self):
+        """ peer discriminator reset after session goes down """
+        bfd_session_up(self)
+        detection_time = self.test_session.detect_mult *\
+            self.vpp_session.required_min_rx / USEC_IN_SEC
+        self.sleep(detection_time, "waiting for BFD session time-out")
+        self.test_session.my_discriminator = 0
+        wait_for_bfd_packet(self,
+                            pcap_time_min=time.time() - self.vpp_clock_offset)
+
     @unittest.skipUnless(running_extended_tests, "part of extended tests")
     def test_large_required_min_rx(self):
         """ large remote required min rx interval """
@@ -2129,6 +2139,7 @@ class BFDSHA1TestCase(VppTestCase):
         self.test_session.vpp_seq_number = None
         # now throw away any pending packets
         self.pg0.enable_capture()
+        self.test_session.my_discriminator = 0
         bfd_session_up(self)