Merge branch 'FRRouting:master' into master

Author: ton31337

tests/.gitignore

@@ -15,6 +15,7 @@ frr_northbound*
 /isisd/test_fuzz_isis_tlv
 /isisd/test_fuzz_isis_tlv_tests.h
 /isisd/test_isis_lspdb
+/isisd/test_isis_remove_excess_adjs
 /isisd/test_isis_spf
 /isisd/test_isis_vertex_queue
 /lib/cli/test_cli

tests/topotests/zebra_mtu_ipv6_change/__init__.py

@@ -0,0 +1,13 @@
+!
+interface r1-eth0
+ ip address 10.0.0.1/30
+!
+router bgp 65000
+ no bgp ebgp-requires-policy
+ neighbor 10.0.0.2 remote-as 65000
+ neighbor 10.0.0.2 timers 1 3
+ neighbor 10.0.0.2 timers connect 1
+ address-family ipv6 unicast
+  neighbor 10.0.0.2 activate
+ exit-address-family
+!

tests/topotests/zebra_mtu_ipv6_change/r1/frr.conf

@@ -0,0 +1,16 @@
+!
+interface r2-eth0
+ ip address 10.0.0.2/30
+!
+router bgp 65000
+ no bgp ebgp-requires-policy
+ neighbor 10.0.0.1 remote-as 65000
+ neighbor 10.0.0.1 timers 1 3
+ neighbor 10.0.0.1 timers connect 1
+ address-family ipv6 unicast
+  network fdfd::/64
+  neighbor 10.0.0.1 activate
+ exit-address-family
+!
+ipv6 route fdfd::/64 blackhole
+!

tests/topotests/zebra_mtu_ipv6_change/r2/frr.conf

@@ -0,0 +1,91 @@
+#!/usr/bin/env python
+# SPDX-License-Identifier: ISC
+#
+# Copyright (c) 2026 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 setup_module(mod):
+    topodef = {"s1": ("r1", "r2")}
+    tgen = Topogen(topodef, 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_zebra_mtu_ipv6_change():
+    tgen = get_topogen()
+
+    if tgen.routers_have_failure():
+        pytest.skip(tgen.errors)
+
+    r1 = tgen.gears["r1"]
+
+    step("Wait for BGP to converge and fdfd::/64 to be installed")
+
+    def _bgp_route_installed():
+        output = json.loads(r1.vtysh_cmd("show bgp ipv6 unicast fdfd::/64 json"))
+        expected = {"prefix": "fdfd::/64", "paths": [{"valid": True}]}
+        return topotest.json_cmp(output, expected)
+
+    _, result = topotest.run_and_expect(_bgp_route_installed, None, count=60, wait=1)
+    assert result is None, "fdfd::/64 not installed initially"
+
+    def _kernel_route_installed():
+        output = json.loads(r1.run("ip -6 -j route show fdfd::/64"))
+        return topotest.json_cmp(
+            output, [{"dst": "fdfd::/64", "dev": "r1-eth0", "protocol": "bgp"}]
+        )
+
+    _, result = topotest.run_and_expect(_kernel_route_installed, None, count=30, wait=1)
+    assert result is None, "fdfd::/64 not in kernel initially"
+
+    step("Set MTU below IPv6 minimum (1280) — disables IPv6 on the interface")
+    r1.run("ip link set r1-eth0 mtu 1200")
+
+    def _kernel_route_gone():
+        output = json.loads(r1.run("ip -6 -j route show fdfd::/64"))
+        if len(output) == 0:
+            return None
+        return "fdfd::/64 still in kernel after MTU drop"
+
+    _, result = topotest.run_and_expect(_kernel_route_gone, None, count=30, wait=1)
+    assert result is None, "fdfd::/64 was not removed from kernel after MTU drop"
+
+    step("Restore MTU above IPv6 minimum — zebra must reinstall the BGP route")
+    r1.run("ip link set r1-eth0 mtu 1500")
+
+    _, result = topotest.run_and_expect(_kernel_route_installed, None, count=60, wait=1)
+    assert result is None, "fdfd::/64 was NOT reinstalled after MTU was restored"
+
+
+if __name__ == "__main__":
+    args = ["-s"] + sys.argv[1:]
+    sys.exit(pytest.main(args))