Guard only packets addressed to this machine, and order the guard's unit before the network and against shutdown (hq ADR 0103)

internal/catalogue/adoption.go

@@ -146,8 +146,9 @@ func Published(resources []map[string]any) map[string]map[int]int {
 //
 // It passes everything by default and holds nothing but a refusal, so it cannot close anything
 // the machine serves; and it is the mesh's own table, so the found firewall reloading does not
-// touch it. It refuses the ports except from the machine itself — its loopback and the container
-// runtime's own networks — and from the private network, known by the interface a packet arrives
+// touch it. It refuses only packets addressed to this machine, and the ports except from the
+// machine itself — its loopback and the container runtime's own networks — and from the private
+// network, known by the interface a packet arrives
 // on and never by its source address. At prerouting, ahead of the runtime's destination
 // translation, so it matches the port the packet was sent to; in the inet family, so both address
 // families.
@@ -166,8 +167,11 @@ func AsGuard(ports []int) string {
 	b.WriteString("table inet mesh_guard {\n")
 	b.WriteString("\tchain prerouting {\n")
 	b.WriteString("\t\ttype filter hook prerouting priority raw; policy accept;\n")
-	fmt.Fprintf(&b, "\t\tiifname != \"lo\" iifname != \"docker0\" iifname != \"br-*\" "+
-		"iifname != \"mesh0\" tcp dport { %s } drop\n", strings.Join(listed, ", "))
+	// Only packets addressed to this machine: traffic it routes for others — a predecessor's hub,
+	// say — is never the guard's business (novox/hq ADR 0103).
+	fmt.Fprintf(&b, "\t\tfib daddr type local iifname != \"lo\" iifname != \"docker0\" "+
+		"iifname != \"br-*\" iifname != \"mesh0\" tcp dport { %s } drop\n",
+		strings.Join(listed, ", "))
 	b.WriteString("\t}\n")
 	b.WriteString("}\n")
 	return b.String()
@@ -178,8 +182,12 @@ func AsGuard(ports []int) string {
 func GuardUnitText() string {
 	return "[Unit]\n" +
 		"Description=The mesh's guard: refuses its own ports from outside (novox/hq ADR 0100)\n" +
-		"Before=network-pre.target\n" +
+		// Early, before the network is up, and without the default dependencies that would
+		// order it after the network; stopped at shutdown like any unit.
+		"DefaultDependencies=no\n" +
 		"Wants=network-pre.target\n" +
+		"Before=network-pre.target shutdown.target\n" +
+		"Conflicts=shutdown.target\n" +
 		"\n" +
 		"[Service]\n" +
 		"Type=oneshot\n" +

internal/catalogue/adoption_test.go

@@ -200,13 +200,33 @@ delete table inet mesh_guard
 table inet mesh_guard {
 	chain prerouting {
 		type filter hook prerouting priority raw; policy accept;
-		iifname != "lo" iifname != "docker0" iifname != "br-*" iifname != "mesh0" tcp dport { 5432, 15672 } drop
+		fib daddr type local iifname != "lo" iifname != "docker0" iifname != "br-*" iifname != "mesh0" tcp dport { 5432, 15672 } drop
 	}
 }
 `
 	if got := AsGuard([]int{15672, 5432}); got != golden {
 		t.Fatalf("the guard changed:\n%s", got)
 	}
+	const unit = `[Unit]
+Description=The mesh's guard: refuses its own ports from outside (novox/hq ADR 0100)
+DefaultDependencies=no
+Wants=network-pre.target
+Before=network-pre.target shutdown.target
+Conflicts=shutdown.target
+
+[Service]
+Type=oneshot
+RemainAfterExit=yes
+ExecStart=nft -f /etc/mesh/guard.nft
+ExecReload=nft -f /etc/mesh/guard.nft
+ExecStop=nft delete table inet mesh_guard
+
+[Install]
+WantedBy=multi-user.target
+`
+	if got := GuardUnitText(); got != unit {
+		t.Fatalf("the guard's unit changed:\n%s", got)
+	}
 	if GuardResources(nil) != nil {
 		t.Fatal("a guard with nothing to guard is an empty set nft refuses to load")
 	}