diff --git a/cmd/tailscale/cli/cli_test.go b/cmd/tailscale/cli/cli_test.go
index 3da21ba1d..266afbe9f 100644
--- a/cmd/tailscale/cli/cli_test.go
+++ b/cmd/tailscale/cli/cli_test.go
@@ -15,6 +15,7 @@
 	"inet.af/netaddr"
 	"tailscale.com/ipn"
 	"tailscale.com/ipn/ipnstate"
+	"tailscale.com/types/logger"
 	"tailscale.com/types/preftype"
 )
 
@@ -46,6 +47,7 @@ func TestCheckForAccidentalSettingReverts(t *testing.T) {
 			name:    "bare_up_means_up",
 			flagSet: f(),
 			curPrefs: &ipn.Prefs{
+				ControlURL:  ipn.DefaultControlURL,
 				WantRunning: false,
 				Hostname:    "foo",
 			},
@@ -61,15 +63,18 @@ func TestCheckForAccidentalSettingReverts(t *testing.T) {
 			name:    "losing_hostname",
 			flagSet: f("accept-dns"),
 			curPrefs: &ipn.Prefs{
+				ControlURL:  ipn.DefaultControlURL,
 				WantRunning: false,
 				Hostname:    "foo",
 				CorpDNS:     true,
 			},
 			mp: &ipn.MaskedPrefs{
 				Prefs: ipn.Prefs{
+					ControlURL:  ipn.DefaultControlURL,
 					WantRunning: true,
 					CorpDNS:     true,
 				},
+				ControlURLSet:  true,
 				WantRunningSet: true,
 				CorpDNSSet:     true,
 			},
@@ -79,14 +84,17 @@ func TestCheckForAccidentalSettingReverts(t *testing.T) {
 			name:    "hostname_changing_explicitly",
 			flagSet: f("hostname"),
 			curPrefs: &ipn.Prefs{
+				ControlURL:  ipn.DefaultControlURL,
 				WantRunning: false,
 				Hostname:    "foo",
 			},
 			mp: &ipn.MaskedPrefs{
 				Prefs: ipn.Prefs{
+					ControlURL:  ipn.DefaultControlURL,
 					WantRunning: true,
 					Hostname:    "bar",
 				},
+				ControlURLSet:  true,
 				WantRunningSet: true,
 				HostnameSet:    true,
 			},
@@ -96,14 +104,17 @@ func TestCheckForAccidentalSettingReverts(t *testing.T) {
 			name:    "hostname_changing_empty_explicitly",
 			flagSet: f("hostname"),
 			curPrefs: &ipn.Prefs{
+				ControlURL:  ipn.DefaultControlURL,
 				WantRunning: false,
 				Hostname:    "foo",
 			},
 			mp: &ipn.MaskedPrefs{
 				Prefs: ipn.Prefs{
+					ControlURL:  ipn.DefaultControlURL,
 					WantRunning: true,
 					Hostname:    "",
 				},
+				ControlURLSet:  true,
 				WantRunningSet: true,
 				HostnameSet:    true,
 			},
@@ -113,12 +124,27 @@ func TestCheckForAccidentalSettingReverts(t *testing.T) {
 			name:    "empty_slice_equals_nil_slice",
 			flagSet: f("hostname"),
 			curPrefs: &ipn.Prefs{
+				ControlURL:      ipn.DefaultControlURL,
 				AdvertiseRoutes: []netaddr.IPPrefix{},
 			},
 			mp: &ipn.MaskedPrefs{
 				Prefs: ipn.Prefs{
+					ControlURL:      ipn.DefaultControlURL,
 					AdvertiseRoutes: nil,
 				},
+				ControlURLSet: true,
+			},
+			want: "",
+		},
+		{
+			// Issue 1725: "tailscale up --authkey=..." (or other non-empty flags) works from
+			// a fresh server's initial prefs.
+			name:     "up_with_default_prefs",
+			flagSet:  f("authkey"),
+			curPrefs: ipn.NewPrefs(),
+			mp: &ipn.MaskedPrefs{
+				Prefs:          *defaultPrefsFromUpArgs(t),
+				WantRunningSet: true,
 			},
 			want: "",
 		},
@@ -136,6 +162,21 @@ func TestCheckForAccidentalSettingReverts(t *testing.T) {
 	}
 }
 
+func defaultPrefsFromUpArgs(t testing.TB) *ipn.Prefs {
+	upFlagSet.Parse(nil) // populates upArgs
+	if upFlagSet.Lookup("netfilter-mode") == nil && upArgs.netfilterMode == "" {
+		// This flag is not compiled on on-Linux platforms,
+		// but prefsFromUpArgs requires it be populated.
+		upArgs.netfilterMode = defaultNetfilterMode()
+	}
+	prefs, err := prefsFromUpArgs(upArgs, logger.Discard, new(ipnstate.Status), "linux")
+	if err != nil {
+		t.Fatalf("defaultPrefsFromUpArgs: %v", err)
+	}
+	prefs.WantRunning = true
+	return prefs
+}
+
 func TestPrefsFromUpArgs(t *testing.T) {
 	tests := []struct {
 		name     string
diff --git a/cmd/tailscale/cli/up.go b/cmd/tailscale/cli/up.go
index 0f399d260..30b4b1ac9 100644
--- a/cmd/tailscale/cli/up.go
+++ b/cmd/tailscale/cli/up.go
@@ -499,6 +499,10 @@ func checkForAccidentalSettingReverts(flagSet map[string]bool, curPrefs *ipn.Pre
 		// mean bringing the network up without any changes.
 		return nil
 	}
+	if curPrefs.ControlURL == "" {
+		// Don't validate things on initial "up" before a control URL has been set.
+		return nil
+	}
 	curWithExplicitEdits := curPrefs.Clone()
 	curWithExplicitEdits.ApplyEdits(mp)
 
diff --git a/ipn/fake_test.go b/ipn/fake_test.go
index cacb13caa..4f6c9273b 100644
--- a/ipn/fake_test.go
+++ b/ipn/fake_test.go
@@ -19,7 +19,7 @@ type FakeBackend struct {
 }
 
 func (b *FakeBackend) Start(opts Options) error {
-	b.serverURL = opts.Prefs.ControlURL
+	b.serverURL = opts.Prefs.ControlURLOrDefault()
 	if b.notify == nil {
 		panic("FakeBackend.Start: SetNotifyCallback not called")
 	}
diff --git a/ipn/handle.go b/ipn/handle.go
index 756dca5b0..7f1eb8ea3 100644
--- a/ipn/handle.go
+++ b/ipn/handle.go
@@ -156,7 +156,7 @@ func (h *Handle) Expiry() time.Time {
 }
 
 func (h *Handle) AdminPageURL() string {
-	return h.prefsCache.ControlURL + "/admin/machines"
+	return h.prefsCache.ControlURLOrDefault() + "/admin/machines"
 }
 
 func (h *Handle) StartLoginInteractive() {
diff --git a/ipn/ipnlocal/local.go b/ipn/ipnlocal/local.go
index 18d8b310f..6fa920c7f 100644
--- a/ipn/ipnlocal/local.go
+++ b/ipn/ipnlocal/local.go
@@ -436,6 +436,15 @@ func (b *LocalBackend) setClientStatus(st controlclient.Status) {
 	netMap := b.netMap
 	interact := b.interact
 
+	if prefs.ControlURL == "" {
+		// Once we get a message from the control plane, set
+		// our ControlURL pref explicitly. This causes a
+		// future "tailscale up" to start checking for
+		// implicit setting reverts, which it doesn't do when
+		// ControlURL is blank.
+		prefs.ControlURL = prefs.ControlURLOrDefault()
+		prefsChanged = true
+	}
 	if st.Persist != nil {
 		if !b.prefs.Persist.Equals(st.Persist) {
 			prefsChanged = true
@@ -637,7 +646,7 @@ func (b *LocalBackend) Start(opts ipn.Options) error {
 	}
 
 	b.inServerMode = b.prefs.ForceDaemon
-	b.serverURL = b.prefs.ControlURL
+	b.serverURL = b.prefs.ControlURLOrDefault()
 	hostinfo.RoutableIPs = append(hostinfo.RoutableIPs, b.prefs.AdvertiseRoutes...)
 	hostinfo.RequestTags = append(hostinfo.RequestTags, b.prefs.AdvertiseTags...)
 	if b.inServerMode || runtime.GOOS == "windows" {
diff --git a/ipn/prefs.go b/ipn/prefs.go
index 35b4a49b9..cd3cc2cda 100644
--- a/ipn/prefs.go
+++ b/ipn/prefs.go
@@ -33,6 +33,10 @@
 // Prefs are the user modifiable settings of the Tailscale node agent.
 type Prefs struct {
 	// ControlURL is the URL of the control server to use.
+	//
+	// If empty, the default for new installs, DefaultControlURL
+	// is used. It's set non-empty once the daemon has been started
+	// for the first time.
 	ControlURL string
 
 	// RouteAll specifies whether to accept subnets advertised by
@@ -340,12 +344,19 @@ func compareStrings(a, b []string) bool {
 	return true
 }
 
+// NewPrefs returns the default preferences to use.
 func NewPrefs() *Prefs {
+	// Provide default values for options which might be missing
+	// from the json data for any reason. The json can still
+	// override them to false.
 	return &Prefs{
-		// Provide default values for options which might be missing
-		// from the json data for any reason. The json can still
-		// override them to false.
-		ControlURL:       DefaultControlURL,
+		// ControlURL is explicitly not set to signal that
+		// it's not yet configured, which relaxes the CLI "up"
+		// safety net features. It will get set to DefaultControlURL
+		// on first up. Or, if not, DefaultControlURL will be used
+		// later anyway.
+		ControlURL: "",
+
 		RouteAll:         true,
 		AllowSingleHosts: true,
 		CorpDNS:          true,
@@ -354,6 +365,15 @@ func NewPrefs() *Prefs {
 	}
 }
 
+// ControlURLOrDefault returns the coordination server's URL base.
+// If not configured, DefaultControlURL is returned instead.
+func (p *Prefs) ControlURLOrDefault() string {
+	if p.ControlURL != "" {
+		return p.ControlURL
+	}
+	return DefaultControlURL
+}
+
 // PrefsFromBytes deserializes Prefs from a JSON blob. If
 // enforceDefaults is true, Prefs.RouteAll and Prefs.AllowSingleHosts
 // are forced on.