network: use scope link for direct unicast routes by default

Strictly speaking, this breaks the backward compatibility, but I guess
in most cases people already sets Scope=link for such routes.

This behavior matches with how 'ip route' command adds such route by
default.

Prompted by https://twitter.com/jplitza/status/1480500562391179270.

4 files changed, 12 insertions, 7 deletions

diff --git a/man/systemd.network.xml b/man/systemd.network.xml
index 197e0dad1d..93c10b7755 100644
--- a/man/systemd.network.xml
+++ b/man/systemd.network.xml
@@ -1547,9 +1547,9 @@ Table=1234</programlisting></para>
 
           <para>For IPv4 route, defaults to <literal>host</literal> if <varname>Type=</varname> is
           <literal>local</literal> or <literal>nat</literal>, and <literal>link</literal> if
-          <varname>Type=</varname> is <literal>broadcast</literal>, <literal>multicast</literal>, or
-          <literal>anycast</literal>. In other cases, defaults to <literal>global</literal>. The value
-          is not used for IPv6.</para>
+          <varname>Type=</varname> is <literal>broadcast</literal>, <literal>multicast</literal>,
+          <literal>anycast</literal>, or direct <literal>unicast</literal> routes. In other cases,
+          defaults to <literal>global</literal>. The value is not used for IPv6.</para>
         </listitem>
       </varlistentry>
 
diff --git a/src/network/networkd-route.c b/src/network/networkd-route.c
index f0697a66af..00e64978d4 100644
--- a/src/network/networkd-route.c
+++ b/src/network/networkd-route.c
@@ -2846,6 +2846,12 @@ static int route_section_verify(Route *route, Network *network) {
                         route->scope = RT_SCOPE_HOST;
                 else if (IN_SET(route->type, RTN_BROADCAST, RTN_ANYCAST, RTN_MULTICAST))
                         route->scope = RT_SCOPE_LINK;
+                else if (IN_SET(route->type, RTN_UNICAST, RTN_UNSPEC) &&
+                         !route->gateway_from_dhcp_or_ra &&
+                         !in_addr_is_set(route->gw_family, &route->gw) &&
+                         ordered_set_isempty(route->multipath_routes) &&
+                         route->nexthop_id == 0)
+                        route->scope = RT_SCOPE_LINK;
         }
 
         if (route->scope != RT_SCOPE_UNIVERSE && route->family == AF_INET6) {
diff --git a/test/test-network/conf/25-route-static.network b/test/test-network/conf/25-route-static.network
index 8f242bd1fe..6aa3ec66dc 100644
--- a/test/test-network/conf/25-route-static.network
+++ b/test/test-network/conf/25-route-static.network
@@ -24,7 +24,6 @@ Gateway=fe80::222:4dff:ff:ff:ff:ff
 
 [Route]
 Destination=149.10.124.64
-Scope=link
 
 [Route]
 Gateway=149.10.124.64
diff --git a/test/test-network/systemd-networkd-tests.py b/test/test-network/systemd-networkd-tests.py
index 5613398757..2207f36245 100755
--- a/test/test-network/systemd-networkd-tests.py
+++ b/test/test-network/systemd-networkd-tests.py
@@ -2542,9 +2542,9 @@ class NetworkdNetworkTests(unittest.TestCase, Utilities):
         self.assertIn('149.10.124.48/28 proto kernel scope link src 149.10.124.58', output)
         self.assertIn('149.10.124.64 proto static scope link', output)
         self.assertIn('169.254.0.0/16 proto static scope link metric 2048', output)
-        self.assertIn('192.168.1.1 proto static initcwnd 20', output)
-        self.assertIn('192.168.1.2 proto static initrwnd 30', output)
-        self.assertIn('192.168.1.3 proto static advmss 30', output)
+        self.assertIn('192.168.1.1 proto static scope link initcwnd 20', output)
+        self.assertIn('192.168.1.2 proto static scope link initrwnd 30', output)
+        self.assertIn('192.168.1.3 proto static scope link advmss 30', output)
         self.assertIn('multicast 149.10.123.4 proto static', output)
 
         print('### ip -4 route show dev dummy98 default')