tests: Check if Link-Local Next Hop capability works

Signed-off-by: Donatas Abraitis <donatas@opensourcerouting.org>

tests/topotests/bgp_ipv6_link_local_capability/r1/frr.conf

@@ -0,0 +1,15 @@
+!
+int lo
+ ip address 10.0.0.1/32
+!
+router bgp 65001
+ no bgp ebgp-requires-policy
+ no bgp network import-check
+ bgp default link-local-capability
+ neighbor r1-eth0 interface remote-as auto
+ address-family ipv6 unicast
+  network 2001:db8::1/128
+  neighbor r1-eth0 activate
+ exit-address-family
+ !
+!

tests/topotests/bgp_ipv6_link_local_capability/r2/frr.conf

@@ -0,0 +1,13 @@
+!
+int lo
+ ip address 10.0.0.2/32
+!
+router bgp 65002
+ no bgp ebgp-requires-policy
+ bgp default link-local-capability
+ neighbor r2-eth0 interface remote-as auto
+ address-family ipv6 unicast
+  neighbor r2-eth0 activate
+ exit-address-family
+ !
+!

tests/topotests/bgp_ipv6_link_local_capability/test_bgp_ipv6_link_local_capability.py

@@ -0,0 +1,110 @@
+#!/usr/bin/env python
+# SPDX-License-Identifier: ISC
+#
+# Copyright (c) 2024 by
+# Donatas Abraitis <donatas@opensourcerouting.org>
+#
+
+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, get_topogen
+from lib.common_config import step
+
+pytestmark = [pytest.mark.bgpd]
+
+
+def build_topo(tgen):
+    tgen.add_router("r1")
+    tgen.add_router("r2")
+
+    switch = tgen.add_switch("s1")
+    switch.add_link(tgen.gears["r1"])
+    switch.add_link(tgen.gears["r2"])
+
+
+def setup_module(mod):
+    tgen = Topogen(build_topo, mod.__name__)
+    tgen.start_topology()
+
+    router_list = tgen.routers()
+
+    for _, (rname, router) in enumerate(router_list.items(), 1):
+        router.load_frr_config(os.path.join(CWD, "{}/frr.conf".format(rname)))
+
+    tgen.start_router()
+
+
+def teardown_module(mod):
+    tgen = get_topogen()
+    tgen.stop_topology()
+
+
+def test_bgp_ipv6_link_local_capability():
+    tgen = get_topogen()
+
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    r2 = tgen.gears["r2"]
+
+    def _bgp_converge():
+        output = json.loads(r2.vtysh_cmd("show bgp neighbor json"))
+        expected = {
+            "r2-eth0": {
+                "neighborCapabilities": {
+                    "linkLocalNextHop": {
+                        "advertised": True,
+                        "received": True,
+                    }
+                }
+            }
+        }
+        return topotest.json_cmp(output, expected)
+
+    test_func = functools.partial(_bgp_converge)
+    _, result = topotest.run_and_expect(test_func, None, count=30, wait=1)
+    assert result is None, "Can't converge initially"
+
+    def _bgp_check_received_nexthops():
+        output = json.loads(r2.vtysh_cmd("show bgp 2001:db8::1/128 json"))
+        expected = {
+            "paths": [
+                {
+                    "valid": True,
+                    "nexthops": [
+                        {
+                            "hostname": "r1",
+                            "afi": "ipv6",
+                            "scope": "global",
+                            "length": 16,
+                            "accessible": True,
+                        }
+                    ],
+                    "peer": {
+                        "routerId": "10.0.0.1",
+                        "hostname": "r1",
+                        "interface": "r2-eth0",
+                        "type": "external",
+                    },
+                }
+            ]
+        }
+        return topotest.json_cmp(output, expected)
+
+    test_func = functools.partial(_bgp_check_received_nexthops)
+    _, result = topotest.run_and_expect(test_func, None, count=30, wait=1)
+    assert result is None, "Can't see 2001:db8::1/128"
+
+
+if __name__ == "__main__":
+    args = ["-s"] + sys.argv[1:]
+    sys.exit(pytest.main(args))