network/sysctl: logs when per-link IPMasquerade= setting changes the global IPv6Forwa...

All other cases, settings on different interfaces are completely
independent. But IPMasquerade=yes on an interface enables the global
IPv6Forwarding= setting, and hence affects other interfaces.
Let's log about that.

Prompted by https://github.com/systemd/systemd/issues/39304#issuecomment-3430382233.

diff --git a/src/network/networkd-sysctl.c b/src/network/networkd-sysctl.c
index 6433a77a5e635206971a6307548d3631bf01bcfb..b29d49d79db330d522ed016c0fe4ed3bed63345f 100644 (file)
--- a/src/network/networkd-sysctl.c
+++ b/src/network/networkd-sysctl.c
@@ -377,6 +377,8 @@ static int link_set_ip_forwarding(Link *link, int family) {
         if (FLAGS_SET(link->network->ip_masquerade, AF_TO_ADDRESS_FAMILY(family)) &&
             link->manager->ip_forwarding[family == AF_INET6] < 0) {
 
+                log_link_notice(link, "IPMasquerade= is enabled on the interface, enabling the global IPv6Forwarding= setting, which may affect NDisc and DHCPv6 client on other interfaces.");
+
                 link->manager->ip_forwarding[family == AF_INET6] = true;
                 manager_set_ip_forwarding(link->manager, family);