diff --git a/wgengine/magicsock/debugknobs.go b/wgengine/magicsock/debugknobs.go
new file mode 100644
index 000000000..1476b28f4
--- /dev/null
+++ b/wgengine/magicsock/debugknobs.go
@@ -0,0 +1,53 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+//go:build !ios
+// +build !ios
+
+package magicsock
+
+import (
+	"os"
+	"strconv"
+)
+
+// Various debugging and experimental tweakables, set by environment
+// variable.
+var (
+	// logPacketDests prints the known addresses for a peer every time
+	// they change, in the legacy (non-discovery) endpoint code only.
+	logPacketDests, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_LOG_PACKET_DESTS"))
+	// debugDisco prints verbose logs of active discovery events as
+	// they happen.
+	debugDisco, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_DISCO"))
+	// debugOmitLocalAddresses removes all local interface addresses
+	// from magicsock's discovered local endpoints. Used in some tests.
+	debugOmitLocalAddresses, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_OMIT_LOCAL_ADDRS"))
+	// debugUseDerpRoute temporarily (2020-03-22) controls whether DERP
+	// reverse routing is enabled (Issue 150). It will become always true
+	// later.
+	debugUseDerpRouteEnv = os.Getenv("TS_DEBUG_ENABLE_DERP_ROUTE")
+	debugUseDerpRoute, _ = strconv.ParseBool(debugUseDerpRouteEnv)
+	// logDerpVerbose logs all received DERP packets, including their
+	// full payload.
+	logDerpVerbose, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_DERP"))
+	// debugReSTUNStopOnIdle unconditionally enables the "shut down
+	// STUN if magicsock is idle" behavior that normally only triggers
+	// on mobile devices, lowers the shutdown interval, and logs more
+	// verbosely about idle measurements.
+	debugReSTUNStopOnIdle, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_RESTUN_STOP_ON_IDLE"))
+	// debugAlwaysDERP disables the use of UDP, forcing all peer communication over DERP.
+	debugAlwaysDERP, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_ALWAYS_USE_DERP"))
+)
+
+// inTest reports whether the running program is a test that set the
+// IN_TS_TEST environment variable.
+//
+// Unlike the other debug tweakables above, this one needs to be
+// checked every time at runtime, because tests set this after program
+// startup.
+func inTest() bool {
+	inTest, _ := strconv.ParseBool(os.Getenv("IN_TS_TEST"))
+	return inTest
+}
diff --git a/wgengine/magicsock/debugknobs_ios.go b/wgengine/magicsock/debugknobs_ios.go
new file mode 100644
index 000000000..1ebad76b3
--- /dev/null
+++ b/wgengine/magicsock/debugknobs_ios.go
@@ -0,0 +1,20 @@
+// Copyright (c) 2021 Tailscale Inc & AUTHORS All rights reserved.
+// Use of this source code is governed by a BSD-style
+// license that can be found in the LICENSE file.
+
+package magicsock
+
+// All knobs are disabled on iOS.
+// Further, they're const, so the toolchain can produce smaller binaries.
+const (
+	logPacketDests          = false
+	debugDisco              = false
+	debugOmitLocalAddresses = false
+	debugUseDerpRouteEnv    = ""
+	debugUseDerpRoute       = false
+	logDerpVerbose          = false
+	debugReSTUNStopOnIdle   = false
+	debugAlwaysDERP         = false
+)
+
+func inTest() bool { return false }
diff --git a/wgengine/magicsock/magicsock.go b/wgengine/magicsock/magicsock.go
index 107df0388..2e753c06a 100644
--- a/wgengine/magicsock/magicsock.go
+++ b/wgengine/magicsock/magicsock.go
@@ -59,35 +59,6 @@ import (
 	"tailscale.com/wgengine/wgcfg"
 )
 
-// Various debugging and experimental tweakables, set by environment
-// variable.
-var (
-	// logPacketDests prints the known addresses for a peer every time
-	// they change, in the legacy (non-discovery) endpoint code only.
-	logPacketDests, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_LOG_PACKET_DESTS"))
-	// debugDisco prints verbose logs of active discovery events as
-	// they happen.
-	debugDisco, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_DISCO"))
-	// debugOmitLocalAddresses removes all local interface addresses
-	// from magicsock's discovered local endpoints. Used in some tests.
-	debugOmitLocalAddresses, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_OMIT_LOCAL_ADDRS"))
-	// debugUseDerpRoute temporarily (2020-03-22) controls whether DERP
-	// reverse routing is enabled (Issue 150). It will become always true
-	// later.
-	debugUseDerpRouteEnv = os.Getenv("TS_DEBUG_ENABLE_DERP_ROUTE")
-	debugUseDerpRoute, _ = strconv.ParseBool(debugUseDerpRouteEnv)
-	// logDerpVerbose logs all received DERP packets, including their
-	// full payload.
-	logDerpVerbose, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_DERP"))
-	// debugReSTUNStopOnIdle unconditionally enables the "shut down
-	// STUN if magicsock is idle" behavior that normally only triggers
-	// on mobile devices, lowers the shutdown interval, and logs more
-	// verbosely about idle measurements.
-	debugReSTUNStopOnIdle, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_RESTUN_STOP_ON_IDLE"))
-	// debugAlwaysDERP disables the use of UDP, forcing all peer communication over DERP.
-	debugAlwaysDERP, _ = strconv.ParseBool(os.Getenv("TS_DEBUG_ALWAYS_USE_DERP"))
-)
-
 // useDerpRoute reports whether magicsock should enable the DERP
 // return path optimization (Issue 150).
 func useDerpRoute() bool {
@@ -101,17 +72,6 @@ func useDerpRoute() bool {
 	return false
 }
 
-// inTest reports whether the running program is a test that set the
-// IN_TS_TEST environment variable.
-//
-// Unlike the other debug tweakables above, this one needs to be
-// checked every time at runtime, because tests set this after program
-// startup.
-func inTest() bool {
-	inTest, _ := strconv.ParseBool(os.Getenv("IN_TS_TEST"))
-	return inTest
-}
-
 // A Conn routes UDP packets and actively manages a list of its endpoints.
 // It implements wireguard/conn.Bind.
 type Conn struct {