topotests: isis-lfa add a switchover test after BFD down

Add a switchover test that consists in:
- Setting up ISIS BFD between rt1 and rt2
- The no link-detect setting on rt1 eth-rt2 is still present so that
  zebra does not take account linkdown events on this interface.
- Shutting down rt1 eth-rt2 from the switch side
- Wait for BFD to comes down

Check that the switchover between primary and backup happens before the
SPF re-computation.

Signed-off-by: Louis Scalbert <louis.scalbert@6wind.com>

tests/topotests/isis_lfa_topo1/rt1/bfdd.conf

@@ -0,0 +1,6 @@
+hostname rt1
+!
+bfd
+ peer 2001:db8:1000::2 multihop local-address 2001:db8:1000::1
+ !
+!

tests/topotests/isis_lfa_topo1/rt2/bfdd.conf

@@ -0,0 +1,6 @@
+hostname rt2
+!
+bfd
+ peer 2001:db8:1000::1 multihop local-address 2001:db8:1000::2
+ !
+!

tests/topotests/isis_lfa_topo1/test_isis_lfa_topo1.py

@@ -175,6 +175,9 @@ def setup_module(mod):
         router.load_config(
             TopoRouter.RD_ISIS, os.path.join(CWD, "{}/isisd.conf".format(rname))
         )
+        router.load_config(
+            TopoRouter.RD_BFD, os.path.join(CWD, "/dev/null".format(rname))
+        )
 
     tgen.start_router()
 
@@ -902,6 +905,109 @@ def test_rib_ipv6_step22():
         )
 
 
+#
+# Step 23
+#
+# Action(s):
+# - Setting spf-delay-ietf init-delay of 15s
+#
+# Expected changes:
+# - No routing table change
+# - At the end of test, SPF reacts to a failure in 15s
+#
+def test_rib_ipv6_step23():
+    logger.info("Test (step 23): verify IPv6 RIB")
+    tgen = get_topogen()
+
+    # Skip if previous fatal error condition is raised
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    logger.info("Setup BFD on rt1 and rt2")
+    for rname in ["rt1", "rt2"]:
+        conf_file = os.path.join(CWD, "{}/bfdd.conf".format(rname))
+        tgen.net[rname].cmd("vtysh -f {}".format(conf_file))
+
+    rname = "rt1"
+    expect = '[{"multihop":true,"peer":"2001:db8:1000::2","local":"2001:db8:1000::1","status":"up"}]'
+    router_compare_json_output(rname, "show bfd peers json", expect)
+
+    logger.info("Set ISIS BFD")
+    tgen.net["rt1"].cmd('vtysh -c "conf t" -c "int eth-rt2" -c "isis bfd"')
+    tgen.net["rt2"].cmd('vtysh -c "conf t" -c "int eth-rt1" -c "isis bfd"')
+
+    router_compare_json_output(
+        rname,
+        "show ipv6 route isis json",
+        outputs[rname][14]["show_ipv6_route.ref"],
+    )
+
+
+#
+# Step 24
+#
+# Action(s):
+# - shut the eth-rt2 interface on rt1
+#
+# Expected changes:
+# - Route switchover of routes via eth-rt2
+#
+def test_rib_ipv6_step24():
+    logger.info("Test (step 24): verify IPv6 RIB")
+    tgen = get_topogen()
+
+    # Skip if previous fatal error condition is raised
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    logger.info("Shut the interface to rt2 from the switch side and check fast-reroute")
+    tgen.net.cmd_raises("ip link set %s down" % tgen.net["s1"].intfs[0])
+
+    rname = "rt1"
+    expect = '[{"multihop":true,"peer":"2001:db8:1000::2","local":"2001:db8:1000::1","status":"down"}]'
+    router_compare_json_output(
+        rname,
+        "show bfd peers json",
+        expect,
+        count=20,
+        wait=0.05,
+    )
+
+    router_compare_json_output(
+        rname,
+        "show ipv6 route isis json",
+        outputs[rname][15]["show_ipv6_route.ref"],
+        count=2,
+        wait=0.05,
+    )
+
+
+#
+# Step 25
+#
+# Action(s): wait for the convergence and SPF computation on rt1
+#
+# Expected changes:
+# - convergence of IPv6 RIB
+#
+def test_rib_ipv6_step25():
+    logger.info("Test (step 25): verify IPv6 RIB")
+    tgen = get_topogen()
+
+    # Skip if previous fatal error condition is raised
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    logger.info("Check SPF convergence")
+
+    for rname in ["rt1"]:
+        router_compare_json_output(
+            rname,
+            "show ipv6 route isis json",
+            outputs[rname][16]["show_ipv6_route.ref"],
+        )
+
+
 # Memory leak test template
 def test_memory_leak():
     "Run the memory leak test and report results."