test-network: add test for advertised hop limit

For issue #28437.

test/test-network/systemd-networkd-tests.py

@@ -5288,6 +5288,37 @@ class NetworkdRATests(unittest.TestCase, Utilities):
         self.assertIn('2002:da8:1:0:b47e:7975:fc7a:7d6e', output)
         self.assertIn('2002:da8:2:0:f689:561a:8eda:7443', output)
 
+    def check_router_hop_limit(self, hop_limit):
+        self.wait_route('client', rf'default via fe80::1034:56ff:fe78:9a99 proto ra .* hoplimit {hop_limit}', ipv='-6', timeout_sec=10)
+
+        output = check_output('ip -6 route show dev client default via fe80::1034:56ff:fe78:9a99')
+        print(output)
+        self.assertIn(f'hoplimit {hop_limit}', output)
+
+        self.check_ipv6_sysctl_attr('client', 'hop_limit', f'{hop_limit}')
+
+    def test_router_hop_limit(self):
+        copy_network_unit('25-veth-client.netdev',
+                          '25-veth-router.netdev',
+                          '26-bridge.netdev',
+                          '25-veth-bridge.network',
+                          '25-veth-client.network',
+                          '25-veth-router-hop-limit.network',
+                          '25-bridge99.network')
+        start_networkd()
+        self.wait_online('client-p:enslaved',
+                         'router:degraded', 'router-p:enslaved',
+                         'bridge99:routable')
+
+        self.check_router_hop_limit(42)
+
+        with open(os.path.join(network_unit_dir, '25-veth-router-hop-limit.network'), mode='a', encoding='utf-8') as f:
+            f.write('\n[IPv6SendRA]\nHopLimit=43\n')
+
+        networkctl_reload()
+
+        self.check_router_hop_limit(43)
+
     def test_router_preference(self):
         copy_network_unit('25-veth-client.netdev',
                           '25-veth-router-high.netdev',