frrender: T9054: keep PPPoE/DHCP default route when "protocols static" is deleted

Deleting "protocols static" set config_dict['static'] to a dict object shared
by reference across every deleted protocol. Merging the PPPoE/DHCP default-route
data into it left the "deleted" marker in place, so the entire staticd section -
including the just-merged default route - was skipped during FRR rendering,
dropping the default route from the RIB/FIB.

Copy the shared deleted-protocol marker before mutating it, and clear the marker
once DHCP/PPPoE content has been merged in so the section is still rendered.

2 files changed, 58 insertions, 2 deletions

diff --git a/python/vyos/frrender.py b/python/vyos/frrender.py
index 7c9a72c50..a905c9a00 100644
--- a/python/vyos/frrender.py
+++ b/python/vyos/frrender.py
@@ -467,7 +467,9 @@ def get_frrender_dict(conf: Config, argv=None) -> dict:
                                   no_tag_node_value_mangle=True)
         dict.update({'static' : static})
     elif conf.exists_effective(static_cli_path):
-        dict.update({'static' : deleted_protocol})
+        # Use a copy - static.dhcp/static.pppoe below may be merged in,
+        # and deleted_protocol is shared by reference with other protocols
+        dict.update({'static' : deleted_protocol.copy()})
 
     # We need to check the CLI if the NHRP node is present and thus load in all the default
     # values present on the CLI - that's why we have if conf.exists()
@@ -488,6 +490,12 @@ def get_frrender_dict(conf: Config, argv=None) -> dict:
     tmp = get_pppoe_interfaces(conf)
     if tmp: dict_set_nested('static.pppoe', tmp, dict)
 
+    # T6991/T9054: "protocols static" may have been deleted while a DHCP or
+    # PPPoE interface still contributes a default route - in that case the
+    # static section must still be rendered, so drop the deletion marker
+    if 'static' in dict and ('dhcp' in dict['static'] or 'pppoe' in dict['static']):
+        dict['static'].pop('deleted', None)
+
     # keep a re-usable list of dependent VRFs
     dependent_vrfs_default = {}
     if 'bgp' in dict:
@@ -615,7 +623,9 @@ def get_frrender_dict(conf: Config, argv=None) -> dict:
                                               no_tag_node_value_mangle=True)
                 dict_set_nested(f'{protocol_dict_path}.static', static, vrf)
             elif conf.exists_effective(static_vrf_path):
-                dict_set_nested(f'{protocol_dict_path}.static', deleted_protocol, vrf)
+                # Use a copy - static.dhcp/static.pppoe below may be merged in,
+                # and deleted_protocol is shared by reference with other protocols
+                dict_set_nested(f'{protocol_dict_path}.static', deleted_protocol.copy(), vrf)
 
             # T3680 - get a list of all interfaces currently configured to use DHCP
             tmp = get_dhcp_interfaces(conf, vrf_name)
@@ -624,6 +634,14 @@ def get_frrender_dict(conf: Config, argv=None) -> dict:
             tmp = get_pppoe_interfaces(conf, vrf_name)
             if tmp: dict_set_nested(f'name.{vrf_name}.protocols.static.pppoe', tmp, vrf)
 
+            # T6991/T9054: "protocols static" may have been deleted while a
+            # DHCP or PPPoE interface still contributes a default route - in
+            # that case the static section must still be rendered, so drop
+            # the deletion marker
+            static_dict = dict_search(f'{protocol_dict_path}.static', vrf)
+            if static_dict and ('dhcp' in static_dict or 'pppoe' in static_dict):
+                static_dict.pop('deleted', None)
+
             vrf_vni_path = ['vrf', 'name', vrf_name, 'vni']
             if conf.exists(vrf_vni_path):
                 vrf_config.update({'vni': conf.return_value(vrf_vni_path)})
diff --git a/smoketest/scripts/cli/test_interfaces_pppoe.py b/smoketest/scripts/cli/test_interfaces_pppoe.py
index b8b0429a8..2c240d20e 100755
--- a/smoketest/scripts/cli/test_interfaces_pppoe.py
+++ b/smoketest/scripts/cli/test_interfaces_pppoe.py
@@ -416,5 +416,43 @@ class PPPoEInterfaceTest(VyOSUnitTestSHIM.TestCase):
             # Validate and verify assigned IP addresses
             self._verify_interface_address(interface)
 
+    def test_pppoe_default_route_survives_static_deletion(self):
+        # T6991/T9054: The PPPoE default route must not be withdrawn from FRR
+        # when "protocols static" is deleted - only the statically configured
+        # routes must disappear, the PPPoE-sourced default route must stay.
+        interface = self._interfaces[0]
+        (user, passwd) = self.u_p_dict[interface]
+        static_base_path = ['protocols', 'static']
+
+        self.cli_set(base_path + [interface, 'authentication', 'username', user])
+        self.cli_set(base_path + [interface, 'authentication', 'password', passwd])
+        self.cli_set(base_path + [interface, 'source-interface', self._source_interface])
+        self.cli_commit()
+
+        self.assertTrue(wait_for_interface(interface),
+                        msg=f'Interface {interface} not found after {connect_timeout} seconds!')
+
+        default_route = rf'ip route 0.0.0.0/0 {interface} tag 210'
+        frrconfig = self.getFRRconfig('')
+        self.assertIn(default_route, frrconfig)
+
+        # Add an unrelated static route - this is what triggers "protocols
+        # static" to exist on the CLI in the first place
+        self.cli_set(static_base_path + ['route', '10.0.0.0/8', 'blackhole'])
+        self.cli_commit()
+
+        frrconfig = self.getFRRconfig('')
+        self.assertIn(default_route, frrconfig)
+        self.assertIn(r'ip route 10.0.0.0/8 blackhole', frrconfig)
+
+        # Now delete "protocols static" entirely - the PPPoE default route
+        # must remain in the FRR configuration (and thus in the RIB/FIB)
+        self.cli_delete(static_base_path)
+        self.cli_commit()
+
+        frrconfig = self.getFRRconfig('')
+        self.assertNotIn(r'ip route 10.0.0.0/8 blackhole', frrconfig)
+        self.assertIn(default_route, frrconfig)
+
 if __name__ == '__main__':
     unittest.main(verbosity=2, failfast=VyOSUnitTestSHIM.TestCase.debug_on())