network: introduce per-interface IP forwarding settings

This deprecates IPForward= setting, which unconditionally controled
the global setting, even though it is a setting in .network file.

Instead, this introduces new IPv4Forwarding= and IPv6Forwarding=
settings both in .network and networkd.conf.
If these settings are specified in a .network file, then the
per-interface forwarding setting will be configured.
If specified in networkd.conf, then the global IP forwarding setting will
be configured.

Closes #30648.

test/test-network/conf/25-agent-client-peer.network

@@ -5,7 +5,7 @@ Name=client-peer
 [Network]
 Address=192.168.6.2/24
 DHCPServer=yes
-IPForward=ipv4
+IPv4Forwarding=yes
 IPv6AcceptRA=no
 
 [DHCPServer]

test/test-network/conf/25-agent-client.network

@@ -4,5 +4,5 @@ Name=client
 
 [Network]
 DHCP=yes
-IPForward=ipv4
+IPv4Forwarding=yes
 IPv6AcceptRA=no

test/test-network/conf/25-agent-server-peer.network

@@ -4,5 +4,5 @@ Name=server-peer
 
 [Network]
 Address=192.168.5.2/24
-IPForward=ipv4
+IPv4Forwarding=yes
 IPv6AcceptRA=no

test/test-network/conf/25-agent-server.network

@@ -4,7 +4,7 @@ Name=server
 
 [Network]
 Address=192.168.5.1/24
-IPForward=ipv4
+IPv4Forwarding=yes
 DHCPServer=yes
 IPv6AcceptRA=no
 

test/test-network/conf/25-ipv6-proxy-ndp.network

@@ -9,7 +9,6 @@ IPv6ProxyNDPAddress=2607:5300:203:5215:3::1
 IPv6ProxyNDPAddress=2607:5300:203:5215:2::1
 IPv6ProxyNDPAddress=2607:5300:203:5215:1::1
 IPv6AcceptRA=no
-IPForward=yes
 Address=66.70.129.136/32
 Address=66.70.129.142/32
 Address=66.70.129.143/32

test/test-network/conf/25-sysctl.network

@@ -3,7 +3,8 @@
 Name=dummy98
 
 [Network]
-IPForward=yes
+IPv4Forwarding=yes
+IPv6Forwarding=yes
 IPv6DuplicateAddressDetection=3
 IPv6HopLimit=5
 IPv4ProxyARP=yes

test/test-network/conf/26-bridge-vlan-master-issue-20373.network

@@ -4,7 +4,6 @@ Name=bridge99
 
 [Network]
 VLAN=vlan99
-IPForward=yes
 ConfigureWithoutCarrier=yes
 LLDP=yes
 IPv6AcceptRA=false

test/test-network/conf/26-bridge-vlan-slave-issue-20373.network

@@ -4,7 +4,6 @@ Name=test1
 
 [Network]
 IPv6AcceptRA=no
-IPForward=yes
 Bridge=bridge99
 LinkLocalAddressing=no
 EmitLLDP=nearest-bridge

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

@@ -5223,6 +5223,9 @@ class NetworkdRATests(unittest.TestCase, Utilities):
         start_networkd()
         self.wait_online('veth99:routable', 'veth-peer:degraded')
 
+        # IPv6SendRA=yes implies IPv6Forwarding.
+        self.check_ipv6_sysctl_attr('veth-peer', 'forwarding', '1')
+
         output = resolvectl('dns', 'veth99')
         print(output)
         self.assertRegex(output, 'fe80::')