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net/dns: make MagicDNS IPv6 registration opt-out now, not opt-in

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This adds a new ControlKnob to make MagicDNS IPv6 registration
(telling systemd/etc) opt-out rather than opt-in.

Updates #15404

Change-Id: If008e1cb046b792c6aff7bb1d7c58638f7d650b1
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
This commit is contained in:
Brad Fitzpatrick
2026-02-16 18:56:51 -10:00
committed by Brad Fitzpatrick
parent a6390ca008
commit a7a864419d
5 changed files with 91 additions and 34 deletions
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16
control/controlknobs/controlknobs.go
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@@ -113,6 +113,14 @@ type Knobs struct {
// resolver on Windows or when the host is domain-joined and its primary domain
// takes precedence over MagicDNS. As of 2026-02-13, it is only used on Windows.
DisableHostsFileUpdates atomic.Bool
// ForceRegisterMagicDNSIPv4Only is whether the node should only register
// its IPv4 MagicDNS service IP and not its IPv6 one. The IPv6 one,
// tsaddr.TailscaleServiceIPv6String, still works in either case. This knob
// controls only whether we tell systemd/etc about the IPv6 one.
// See https://github.com/tailscale/tailscale/issues/15404.
// TODO(bradfitz): remove this a few releases after 2026-02-16.
ForceRegisterMagicDNSIPv4Only atomic.Bool
}
// UpdateFromNodeAttributes updates k (if non-nil) based on the provided self
@@ -144,6 +152,7 @@ func (k *Knobs) UpdateFromNodeAttributes(capMap tailcfg.NodeCapMap) {
disableCaptivePortalDetection = has(tailcfg.NodeAttrDisableCaptivePortalDetection)
disableSkipStatusQueue = has(tailcfg.NodeAttrDisableSkipStatusQueue)
disableHostsFileUpdates = has(tailcfg.NodeAttrDisableHostsFileUpdates)
forceRegisterMagicDNSIPv4Only = has(tailcfg.NodeAttrForceRegisterMagicDNSIPv4Only)
)
if has(tailcfg.NodeAttrOneCGNATEnable) {
@@ -171,6 +180,7 @@ func (k *Knobs) UpdateFromNodeAttributes(capMap tailcfg.NodeCapMap) {
k.DisableCaptivePortalDetection.Store(disableCaptivePortalDetection)
k.DisableSkipStatusQueue.Store(disableSkipStatusQueue)
k.DisableHostsFileUpdates.Store(disableHostsFileUpdates)
k.ForceRegisterMagicDNSIPv4Only.Store(forceRegisterMagicDNSIPv4Only)
// If both attributes are present, then "enable" should win. This reflects
// the history of seamless key renewal.
@@ -210,3 +220,9 @@ func (k *Knobs) AsDebugJSON() map[string]any {
}
return ret
}
// ShouldForceRegisterMagicDNSIPv4Only reports the value of
// ForceRegisterMagicDNSIPv4Only, or false if k is nil.
func (k *Knobs) ShouldForceRegisterMagicDNSIPv4Only() bool {
return k != nil && k.ForceRegisterMagicDNSIPv4Only.Load()
}