tests: Add a test that shows the v6 recursive nexthop problem

Currently FRR does not handle v6 recurisive resolution properly
when the route being recursed through changes and the most
significant bits of the route are not changed.

Signed-off-by: Donald Sharp <sharpd@nvidia.com>
(cherry picked from commit 73ab6a46c5)

tests/topotests/v6_nexthop_group_recursive_resolution/r1/frr.conf

@@ -0,0 +1,4 @@
+int r1-eth0
+  ipv6 address fc00::1/64
+
+ipv6 route 1::1/128 fc00::2

tests/topotests/v6_nexthop_group_recursive_resolution/test_v6_nexthop_group_recursive_resolution.py

@@ -0,0 +1,189 @@
+#!/usr/bin/env python
+# SPDX-License-Identifier: ISC
+
+#
+# Copyright (c) 2024 by Nvidia Corporation
+# Donald Sharp
+#
+
+"""
+Check that the v6 nexthop recursive resolution works when it changes
+"""
+
+import os
+import sys
+import json
+import pytest
+import functools
+
+CWD = os.path.dirname(os.path.realpath(__file__))
+sys.path.append(os.path.join(CWD, "../"))
+
+# pylint: disable=C0413
+from lib import topotest
+from lib.topogen import Topogen, TopoRouter, get_topogen
+from lib.common_config import step
+
+pytestmark = [pytest.mark.staticd]
+
+
+def build_topo(tgen):
+
+    tgen.add_router("r1")
+
+    switch = tgen.add_switch("s1")
+    switch.add_link(tgen.gears["r1"])
+
+
+def setup_module(mod):
+    tgen = Topogen(build_topo, mod.__name__)
+    tgen.start_topology()
+
+    router_list = tgen.routers()
+
+    for rname, router in router_list.items():
+        router.load_frr_config(os.path.join(CWD, "{}/frr.conf".format(rname)),
+                               [(TopoRouter.RD_MGMTD, None),
+                                (TopoRouter.RD_ZEBRA, None),
+                                (TopoRouter.RD_STATIC, None),
+                                (TopoRouter.RD_SHARP, None)])
+
+    tgen.start_router()
+
+
+def teardown_module(mod):
+    tgen = get_topogen()
+    tgen.stop_topology()
+
+
+def test_recursive_v6_nexthop_generation():
+    tgen = get_topogen()
+
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    step("Testing v6 nexthop resolution")
+
+    #assert False
+    router = tgen.gears["r1"]
+
+    def _v6_converge_1_1_initial():
+        output = json.loads(
+            router.vtysh_cmd("show ipv6 route 1::1 json"))
+
+        expected = {
+            "1::1/128":[
+                {
+                    "prefix":"1::1/128",
+                    "prefixLen":128,
+                    "protocol":"static",
+                    "vrfName":"default",
+                    "selected":True,
+                    "destSelected":True,
+                    "distance":1,
+                    "metric":0,
+                    "installed":True,
+                    "table":254,
+                    "nexthops":[
+                        {
+                            "fib":True,
+                            "ip":"fc00::2",
+                            "afi":"ipv6",
+                            "interfaceName":"r1-eth0",
+                            "active":True,
+                            "weight":1
+                        }
+                    ]
+                }
+            ]
+        }
+
+        return topotest.json_cmp(output, expected)
+
+    test_func = functools.partial(_v6_converge_1_1_initial)
+    _, result = topotest.run_and_expect(test_func, None, count=60, wait=0.5)
+    assert result is None, "Failed to install v6 1::1 route"
+
+    router.vtysh_cmd("sharp install routes 2::2 nexthop 1::1 1")
+    router.vtysh_cmd("conf\nipv6 route 1::1/128 fc00::3\nno ipv6 route 1::1/128 fc00::2")
+
+    def _v6_converge_1_1_post():
+        output = json.loads(
+            router.vtysh_cmd("show ipv6 route 1::1 json"))
+
+        expected = {
+            "1::1/128":[
+                {
+                    "prefix":"1::1/128",
+                    "prefixLen":128,
+                    "protocol":"static",
+                    "vrfName":"default",
+                    "selected":True,
+                    "destSelected":True,
+                    "distance":1,
+                    "metric":0,
+                    "installed":True,
+                    "table":254,
+                    "nexthops":[
+                        {
+                            "fib":True,
+                            "ip":"fc00::3",
+                            "afi":"ipv6",
+                            "interfaceName":"r1-eth0",
+                            "active":True,
+                            "weight":1
+                        }
+                    ]
+                }
+            ]
+        }
+
+        return topotest.json_cmp(output, expected)
+
+    test_func = functools.partial(_v6_converge_1_1_post)
+    _, result = topotest.run_and_expect(test_func, None, count=60, wait=0.5)
+    assert result is None, "Failed to change v6 1::1 route"
+
+    router.vtysh_cmd("sharp install routes 2::2 nexthop 1::1 1")
+
+    def _v6_change_2_2_post():
+        output = json.loads(
+            router.vtysh_cmd("show ipv6 route 2::2 json"))
+
+        expected = {
+            "2::2/128":[
+                {
+                    "prefix":"2::2/128",
+                    "prefixLen":128,
+                    "protocol":"sharp",
+                    "vrfName":"default",
+                    "selected":True,
+                    "destSelected":True,
+                    "distance":150,
+                    "metric":0,
+                    "installed":True,
+                    "table":254,
+                    "nexthops":[
+                        {
+                            "fib":True,
+                            "ip":"fc00::3",
+                            "afi":"ipv6",
+                            "interfaceName":"r1-eth0",
+                            "active":True,
+                            "weight":1
+                        }
+                    ]
+                }
+            ]
+        }
+
+        return topotest.json_cmp(output, expected)
+
+    test_func = functools.partial(_v6_change_2_2_post)
+    _, result = topotest.run_and_expect(test_func, None, count=60, wait=0.5)
+    assert result is None, "Failed to see sharpd route correctly"
+
+
+if __name__ == "__main__":
+    args = ["-s"] + sys.argv[1:]
+    sys.exit(pytest.main(args))