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Keep IPv6 router announcements working with forwarding on

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With net.ipv6.conf.all.forwarding=1, Linux ignores router announcements
unless accept_ra is 2, so a server that gets its IPv6 route by SLAAC
(e.g. a Raspberry Pi at home) lost IPv6 once the route expired.

The sysctl file now also sets accept_ra=2 for the default and for every
network card and the IPv6 default-route interface, except where
accept_ra is 0. "update" rewrites the file, which fixes existing
installs. A new health check warns while the uplink still has
accept_ra=1.
This commit is contained in:
Daniel Redetzke
2026-10-05 00:10:13 +03:00
parent ebd3ceacd7
commit 9ecc188269
4 changed files with 106 additions and 11 deletions
Download Patch File Download Diff File Expand all files Collapse all files
main_test.go
+33
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@@ -12,6 +12,7 @@ import (
"net/netip"
"os"
"path/filepath"
"slices"
"strings"
"testing"
"time"
@@ -376,6 +377,38 @@ func TestUnitFile(t *testing.T) {
}
}
func TestSysctlConf(t *testing.T) {
dir := t.TempDir()
conf, sys := filepath.Join(dir, "conf"), filepath.Join(dir, "net")
for name, ra := range map[string]string{"eth0": "1", "wlan0": "2", "eth1": "0", "br0": "1", "veth1": "1", "lo": "1"} {
_ = os.MkdirAll(filepath.Join(conf, name), 0o755)
_ = os.WriteFile(filepath.Join(conf, name, "accept_ra"), []byte(ra+"\n"), 0o644)
}
for _, name := range []string{"eth0", "wlan0", "eth1"} { // network cards
_ = os.MkdirAll(filepath.Join(sys, name, "device"), 0o755)
}
_ = os.MkdirAll(filepath.Join(sys, "veth1"), 0o755)
// br0 carries the default route; the lo line is the kernel's unreachable route.
routes := filepath.Join(dir, "ipv6_route")
_ = os.WriteFile(routes, []byte(
"00000000000000000000000000000000 00 00000000000000000000000000000000 00 fe800000000000000000000000000001 00000400 00000001 00000000 00000003 br0\n"+
"00000000000000000000000000000000 00 00000000000000000000000000000000 00 00000000000000000000000000000000 ffffffff 00000001 00000000 00200200 lo\n"), 0o644)
got := raInterfaces(conf, sys, routes)
if want := []string{"br0", "eth0", "wlan0"}; !slices.Equal(got, want) {
t.Fatalf("raInterfaces = %v, want %v", got, want)
}
c := sysctlConf(got)
for _, want := range []string{"net.ipv6.conf.all.forwarding=1\n", "net.ipv6.conf.default.accept_ra=2\n", "net.ipv6.conf.eth0.accept_ra=2\n", "net.ipv6.conf.br0.accept_ra=2\n"} {
if !strings.Contains(c, want) {
t.Errorf("sysctl conf lacks %q:\n%s", want, c)
}
}
if strings.Contains(c, "eth1") || strings.Contains(c, "veth1") {
t.Errorf("sysctl conf names eth1 (accept_ra 0) or veth1 (virtual):\n%s", c)
}
}
func TestWriteIfChanged(t *testing.T) {
p := filepath.Join(t.TempDir(), "x.conf")
if ch, err := writeIfChanged(p, "a\n", 0o644); !ch || err != nil {