T8302: This PR adds Router Advertisement (RA) base-interface support for IPv6 wildcard prefix derivation and includes validation and smoketests.

Included changes:
- Add `base-interface` under:
  - `service router-advert interface <lan-if> prefix ::/64 base-interface <wan-if>`
- Render `Base6Interface <wan-if>;` in `radvd.conf` when configured.
- Add validation guard:
  - `base-interface` is only allowed with wildcard prefix `::/64`.
- Extend smoketests:
  - Positive case: `::/64` + `base-interface` commits and renders correctly.
  - Negative case: non-`::/64` prefix with `base-interface` fails commit.

1 files changed, 14 insertions, 0 deletions

diff --git a/smoketest/scripts/cli/test_service_router-advert.py b/smoketest/scripts/cli/test_service_router-advert.py
index 54133b5c7..52f0db4ab 100755
--- a/smoketest/scripts/cli/test_service_router-advert.py
+++ b/smoketest/scripts/cli/test_service_router-advert.py
@@ -376,5 +376,19 @@ class TestServiceRADVD(VyOSUnitTestSHIM.TestCase):
         tmp = f'autoignoreprefixes' + ' {'
         self.assertNotIn(tmp, config)
 
+    def test_base_interface(self):
+        self.cli_set(base_path + ['prefix', '::/64'])
+        self.cli_set(base_path + ['prefix', '::/64', 'base-interface', 'eth0'])
+        self.cli_commit()
+
+        config = read_file(RADVD_CONF)
+        self.assertIn('Base6Interface eth0;', config)
+
+        self.cli_set(base_path + ['prefix', '2001:db8:1234::/64'])
+        self.cli_set(
+            base_path + ['prefix', '2001:db8:1234::/64', 'base-interface', 'eth0']
+        )
+        with self.assertRaises(ConfigSessionError):
+            self.cli_commit()
 if __name__ == '__main__':
     unittest.main(verbosity=2, failfast=VyOSUnitTestSHIM.TestCase.debug_on())