The host says what filters the machine, with owners, and keeps the found firewall retired on every converged apply (hq ADR 0168)

Every table and chain that refuses traffic is reported with whose it is:
the mesh's, the found firewall's, the container runtime's own, a ban, or
other — the runtime's user chain is other, which is where both predecessors
kept their rules, in the legacy filter on one machine and invisible to the
mesh. Adoption's threshold does not move; a converged machine's report
grows by its filters and its found firewall's state.

Convergence is a state the host keeps: a found firewall enabled again is
retired again and said; a reconcile that finds it inactive records that it
was found so, never that the mesh did it; a step skipped after a failed
apply is said. A retirement the mesh began and did not finish is finished.

Fixtures are rulesets captured from three machines of the first mesh.

cmd/mesh-host/main.go

@@ -1432,7 +1432,7 @@ func applyAndKeep(ctx context.Context, opts options, raw []byte, signed *store.D
 	// (novox/hq ADR 0140). Reported whatever the node's mode: a converged node's filter needs it,
 	// and an adopted one becomes converged without a further round trip. A machine that cannot read
 	// its own routing table says nothing rather than guessing, and is sent no filter.
-	if links, err := outward.Links(""); err != nil {
+	if links, err := outward.Links("", ""); err != nil {
 		fmt.Fprintf(os.Stderr, "mesh-host: applied, and could not read which links face outside: %v\n", err)
 	} else {
 		report.Outward = links

internal/outward/links.go

@@ -29,17 +29,32 @@ import (
 // routing table without one.
 const ProcNet = "/proc/net"
 
-// Links are the interfaces carrying a default route, for both address families, sorted and without
-// repeats.
+// SysClassNet is where the kernel lists the machine's network interfaces, one directory each. A
+// parameter for the same reason.
+const SysClassNet = "/sys/class/net"
+
+// Links are the interfaces carrying a default route, for both address families, and every interface
+// backed by a physical device, sorted and without repeats.
+//
+// **A physical link faces outside whether or not it is up** (novox/hq issue 197). The filter accepts
+// whatever did not arrive on a link named here, so a link left out of this list is not filtered at
+// all. A cable unplugged when the machine last reported carries no default route, and was left out:
+// plugged in, everything arriving on it was accepted until the next report and the next push — and a
+// second physical link that never carries the default route was never filtered. A physical device is
+// read from the kernel's own list, where it has a `device` entry; a bridge, a veth, the tunnel and the
+// loopback have none, and stay what they are, this machine's own.
 //
 // A machine may have more than one: a laptop with a cable and a radio has two, and both face
 // outside. A machine with none — no route off itself — returns nothing, and the mesh refuses to
 // compose a filter for it rather than writing a rule around a link with no name, which would be a
 // rule set that does not load and a machine filtering nothing while its unit reports success.
-func Links(procNet string) ([]string, error) {
+func Links(procNet, sysClassNet string) ([]string, error) {
 	if procNet == "" {
 		procNet = ProcNet
 	}
+	if sysClassNet == "" {
+		sysClassNet = SysClassNet
+	}
 	seen := map[string]bool{}
 
 	four, err := defaultsV4(filepath.Join(procNet, "route"))
@@ -50,7 +65,11 @@ func Links(procNet string) ([]string, error) {
 	if err != nil {
 		return nil, err
 	}
-	for _, name := range append(four, six...) {
+	devices, err := physical(sysClassNet)
+	if err != nil {
+		return nil, err
+	}
+	for _, name := range append(append(four, six...), devices...) {
 		if name != "" && name != "lo" {
 			seen[name] = true
 		}
@@ -64,6 +83,25 @@ func Links(procNet string) ([]string, error) {
 	return out, nil
 }
 
+// physical is every interface the kernel lists with a device behind it. A list that is not there is
+// not an error — a machine without sysfs mounted reports what its routing table says, as before.
+func physical(sysClassNet string) ([]string, error) {
+	entries, err := os.ReadDir(sysClassNet)
+	if os.IsNotExist(err) {
+		return nil, nil
+	}
+	if err != nil {
+		return nil, err
+	}
+	var out []string
+	for _, e := range entries {
+		if _, err := os.Stat(filepath.Join(sysClassNet, e.Name(), "device")); err == nil {
+			out = append(out, e.Name())
+		}
+	}
+	return out, nil
+}
+
 // defaultsV4 reads /proc/net/route, whose columns are
 //
 //	Iface Destination Gateway Flags RefCnt Use Metric Mask ...

internal/outward/links_test.go

@@ -32,7 +32,7 @@ func TestLinksAreTheOnesCarryingADefaultRoute(t *testing.T) {
 	write(t, dir, "route", routeV4)
 	write(t, dir, "ipv6_route", routeV6)
 
-	got, err := Links(dir)
+	got, err := Links(dir, t.TempDir())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -52,7 +52,7 @@ func TestAZeroDestinationWithAMaskIsNotADefaultRoute(t *testing.T) {
 	write(t, dir, "route", `Iface	Destination	Gateway 	Flags	RefCnt	Use	Metric	Mask		MTU	Window	IRTT
 br-abc	00000000	00000000	0001	0	0	0	00FFFFFF	0	0	0
 `)
-	got, err := Links(dir)
+	got, err := Links(dir, t.TempDir())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -67,7 +67,7 @@ br-abc	00000000	00000000	0001	0	0	0	00FFFFFF	0	0	0
 func TestNoDefaultRouteIsNoLinks(t *testing.T) {
 	dir := t.TempDir()
 	write(t, dir, "route", "Iface\tDestination\tGateway \tFlags\tRefCnt\tUse\tMetric\tMask\t\tMTU\tWindow\tIRTT\n")
-	got, err := Links(dir)
+	got, err := Links(dir, t.TempDir())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -81,7 +81,7 @@ func TestNoDefaultRouteIsNoLinks(t *testing.T) {
 func TestAMissingTableIsNotAFailure(t *testing.T) {
 	dir := t.TempDir()
 	write(t, dir, "route", routeV4)
-	got, err := Links(dir)
+	got, err := Links(dir, t.TempDir())
 	if err != nil {
 		t.Fatalf("a missing v6 table should not fail: %v", err)
 	}
@@ -97,7 +97,7 @@ func TestALinkIsReportedOnce(t *testing.T) {
 	write(t, dir, "ipv6_route",
 		"00000000000000000000000000000000 00 00000000000000000000000000000000 00 "+
 			"fe800000000000000000000000000001 00000400 00000001 00000000 00000003     enp9s0\n")
-	got, err := Links(dir)
+	got, err := Links(dir, t.TempDir())
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -109,7 +109,7 @@ func TestALinkIsReportedOnce(t *testing.T) {
 // Against this machine's own routing table, so the parse is held to what the kernel actually writes
 // and not only to a fixture written to agree with it.
 func TestAgainstThisMachinesOwnTable(t *testing.T) {
-	got, err := Links("")
+	got, err := Links("", "")
 	if err != nil {
 		t.Fatal(err)
 	}
@@ -118,3 +118,39 @@ func TestAgainstThisMachinesOwnTable(t *testing.T) {
 	}
 	t.Logf("this machine's outward links: %v", got)
 }
+
+// sysNet is a /sys/class/net: each name a directory, with a `device` entry when a device backs it.
+func sysNet(t *testing.T, physical []string, virtual []string) string {
+	t.Helper()
+	dir := t.TempDir()
+	for _, name := range physical {
+		if err := os.MkdirAll(filepath.Join(dir, name, "device"), 0o755); err != nil {
+			t.Fatal(err)
+		}
+	}
+	for _, name := range virtual {
+		if err := os.MkdirAll(filepath.Join(dir, name), 0o755); err != nil {
+			t.Fatal(err)
+		}
+	}
+	return dir
+}
+
+// **A physical link faces outside whether or not it carries the default route** (novox/hq issue
+// 197). A machine on its radio with its cable unplugged reported only the radio, and the filter then
+// accepted everything arriving on the cable the moment it was plugged in. Bridges, veths, the tunnel
+// and the loopback have no device behind them and stay this machine's own.
+func TestEveryPhysicalLinkFacesOutsideUpOrDown(t *testing.T) {
+	proc := t.TempDir()
+	write(t, proc, "route", `Iface	Destination	Gateway 	Flags	RefCnt	Use	Metric	Mask		MTU	Window	IRTT
+wlp5s0	00000000	01FEA8C0	0003	0	0	600	00000000	0	0	0
+`)
+	sys := sysNet(t, []string{"wlp5s0", "enp6s0"}, []string{"lo", "docker0", "br-0123456789ab", "veth1", "mesh0"})
+	got, err := Links(proc, sys)
+	if err != nil {
+		t.Fatal(err)
+	}
+	if want := []string{"enp6s0", "wlp5s0"}; !reflect.DeepEqual(got, want) {
+		t.Fatalf("outward links are %v, want %v", got, want)
+	}
+}