From 72ca0cae4b690555edc7612be9d4ca8564337017 Mon Sep 17 00:00:00 2001
From: Brad Fitzpatrick <bradfitz@tailscale.com>
Date: Thu, 9 Jul 2026 14:58:15 +0000
Subject: [PATCH] wgengine/wgcfg,wgengine,ipn/ipnlocal: remove Peers from
 wgcfg.Config

The wireguard-go device now learns its peer set solely from the live
per-peer config source that LocalBackend installs with
Engine.SetPeerConfigFunc, backed by the route manager. Peers are
created lazily on first packet and converged per peer with
Engine.SyncDevicePeer, so the full-peer-list snapshot in wgcfg.Config
and the diff-and-reconfigure machinery around it (wgcfg.Peer,
ReconfigDevice, and the engine's full device sync in
maybeReconfigWireguardLocked) are dead weight: they duplicated state
that the route manager already owns and forced every netmap change to
rebuild and rehash the entire peer list.

Delete the Peers field and the Peer type from wgcfg, along with
ReconfigDevice and maybeReconfigWireguardLocked. Engine.Reconfig no
longer does any device peer work; it only manages the private key,
addresses, and the non-peer subsystems. Full-netmap application converges the device by
syncing exactly the peers whose routes the route manager reports as
changed or removed.

Updates #12542

Change-Id: Ic776e42cfaa5be6b9329b3d381d5cbde17d7078b
Signed-off-by: Brad Fitzpatrick <bradfitz@tailscale.com>
---
 ipn/ipnlocal/local.go                 |  30 +++---
 ipn/ipnlocal/local_test.go            |   6 ++
 ipn/ipnlocal/node_backend.go          |  12 +--
 ipn/ipnlocal/node_backend_test.go     |  18 ++--
 ipn/ipnlocal/state_test.go            |  81 ++++++++--------
 tsnet/tsnet_test.go                   |   4 +-
 util/deephash/tailscale_types_test.go |   5 -
 wgengine/bench/wg.go                  |  28 +++---
 wgengine/magicsock/magicsock_test.go  | 127 +++++++++++++++-----------
 wgengine/userspace.go                 |  77 +++-------------
 wgengine/userspace_test.go            |  50 ++--------
 wgengine/wgcfg/config.go              |  47 ++--------
 wgengine/wgcfg/config_test.go         |  17 +---
 wgengine/wgcfg/device.go              |  66 -------------
 wgengine/wgcfg/device_test.go         |  81 +++++-----------
 wgengine/wgcfg/nmcfg/nmcfg.go         |  19 ++--
 wgengine/wgcfg/wgcfg_clone.go         |  36 --------
 17 files changed, 227 insertions(+), 477 deletions(-)

diff --git a/ipn/ipnlocal/local.go b/ipn/ipnlocal/local.go
index 4b60ed2f7..3e84e9268 100644
--- a/ipn/ipnlocal/local.go
+++ b/ipn/ipnlocal/local.go
@@ -6144,13 +6144,14 @@ func (b *LocalBackend) authReconfigLocked() {
 		return
 	}
 
-	oneCGNATRoute := shouldUseOneCGNATRoute(b.logf, b.sys.NetMon.Get(), b.sys.ControlKnobs(), version.OS())
+	// Note: b.goos (set only by tests) speaks runtime.GOOS while
+	// version.OS is Tailscale-style ("macOS", "iOS"); they agree for
+	// the values tests pin ("linux", "windows"), which is all the
+	// override needs.
+	oneCGNATRoute := shouldUseOneCGNATRoute(b.logf, b.sys.NetMon.Get(), b.sys.ControlKnobs(), cmp.Or(b.goos, version.OS()))
 	// Sync the WireGuard device for any peers whose allowed source
 	// prefixes changed with the new prefs, such as the old and new
-	// exit node when the selection changes. The Reconfig below still
-	// converges every peer via its full device sync, but this
-	// incremental sync is what will remain once the full reconfig is
-	// gated on actual router/DNS changes.
+	// exit node when the selection changes.
 	changedAllowedIPs := cn.updateRouteManagerPrefs(routePrefs{
 		ExitNodeID:       prefs.ExitNodeID(),
 		ExitNodeSelected: prefs.ExitNodeID() != "" || prefs.ExitNodeIP().IsValid(),
@@ -6168,21 +6169,12 @@ func (b *LocalBackend) authReconfigLocked() {
 	// allowed source prefixes (including for lazily created peers)
 	// while keeping them out of the OS route set, because the
 	// expected extension (features/conn25) does not want these routes
-	// installed on the OS. This runs after routerConfigLocked above
-	// for the same reason: rcfg is derived from cfg.Peers, which must
-	// not yet include the extras.
+	// installed on the OS.
 	// See also [Hooks.ExtraWireGuardAllowedIPs].
 	if extraAllowedIPsFn, ok := b.extHost.hooks.ExtraWireGuardAllowedIPs.GetOk(); ok {
 		for k := range cn.updateRouteManagerExtras(extraAllowedIPsFn) {
 			b.e.SyncDevicePeer(k)
 		}
-		// Also append the extras to cfg.Peers so the full SyncPeers
-		// in Reconfig below doesn't strip them from active peers.
-		// This loop goes away when cfg.Peers does.
-		for i := range cfg.Peers {
-			extras := extraAllowedIPsFn(cfg.Peers[i].PublicKey)
-			cfg.Peers[i].AllowedIPs = extras.AppendTo(cfg.Peers[i].AllowedIPs)
-		}
 	}
 	// The prefs and extras commits above can both change the outbound
 	// table (such as installing the selected exit node's /0 routes),
@@ -7342,7 +7334,7 @@ func (b *LocalBackend) setNetMapLocked(nm *netmap.NetworkMap) {
 	if nm != nil {
 		login = cmp.Or(profileFromView(nm.UserProfiles[nm.User()]).LoginName, "<missing-profile>")
 	}
-	discoChanged := b.currentNode().SetNetMap(nm)
+	discoChanged, routeChanged := b.currentNode().SetNetMap(nm)
 	b.setDataPlanePeerRoutes()
 	if ms, ok := b.sys.MagicSock.GetOK(); ok {
 		if nm != nil {
@@ -7361,6 +7353,12 @@ func (b *LocalBackend) setNetMapLocked(nm *netmap.NetworkMap) {
 	for _, k := range discoChanged {
 		b.e.ResetDevicePeer(k)
 	}
+	// Converge the wireguard-go device for peers whose routes changed
+	// (or that were removed) in the full-netmap resync above; peers not
+	// in routeChanged are already up to date.
+	for k := range routeChanged {
+		b.e.SyncDevicePeer(k)
+	}
 	if login != b.activeLogin {
 		b.logf("active login: %v", login)
 		b.activeLogin = login
diff --git a/ipn/ipnlocal/local_test.go b/ipn/ipnlocal/local_test.go
index 7644e178f..1751792e1 100644
--- a/ipn/ipnlocal/local_test.go
+++ b/ipn/ipnlocal/local_test.go
@@ -5367,6 +5367,12 @@ func withAddresses(addresses ...netip.Prefix) peerOptFunc {
 	}
 }
 
+func withAllowedIPs(prefixes ...netip.Prefix) peerOptFunc {
+	return func(n *tailcfg.Node) {
+		n.AllowedIPs = append(n.AllowedIPs, prefixes...)
+	}
+}
+
 func deterministicRegionForTest(t testing.TB, want views.Slice[int], use int) selectRegionFunc {
 	t.Helper()
 
diff --git a/ipn/ipnlocal/node_backend.go b/ipn/ipnlocal/node_backend.go
index 811d0802f..2098ebadd 100644
--- a/ipn/ipnlocal/node_backend.go
+++ b/ipn/ipnlocal/node_backend.go
@@ -594,7 +594,7 @@ func (nb *nodeBackend) netMapWithPeers() *netmap.NetworkMap {
 	return nm
 }
 
-func (nb *nodeBackend) SetNetMap(nm *netmap.NetworkMap) (discoChanged []key.NodePublic) {
+func (nb *nodeBackend) SetNetMap(nm *netmap.NetworkMap) (discoChanged []key.NodePublic, routeChanged routemanager.PeersWithRouteChanges) {
 	nb.mu.Lock()
 	defer nb.mu.Unlock()
 	nb.netMap = nm
@@ -602,7 +602,7 @@ func (nb *nodeBackend) SetNetMap(nm *netmap.NetworkMap) (discoChanged []key.Node
 	nb.updateNodeByKeyLocked()
 	nb.updateNodeByStableIDLocked()
 	nb.updateNodeByNameLocked()
-	discoChanged = nb.updatePeersLocked()
+	discoChanged, routeChanged = nb.updatePeersLocked()
 	nb.signalKeyWaitersForTestLocked()
 	if nm != nil {
 		nb.userProfiles = maps.Clone(nm.UserProfiles)
@@ -615,7 +615,7 @@ func (nb *nodeBackend) SetNetMap(nm *netmap.NetworkMap) (discoChanged []key.Node
 		nb.packetFilter = nil
 		nb.derpMapViewPub.Publish(tailcfg.DERPMapView{})
 	}
-	return discoChanged
+	return discoChanged, routeChanged
 }
 
 // AwaitNodeKeyForTest returns a channel that is closed once a peer with the
@@ -796,7 +796,7 @@ func (nb *nodeBackend) ExtraDNSByName(hostname string) (_ netip.Addr, ok bool) {
 	return ip, ok
 }
 
-func (nb *nodeBackend) updatePeersLocked() (discoChanged []key.NodePublic) {
+func (nb *nodeBackend) updatePeersLocked() (discoChanged []key.NodePublic, routeChanged routemanager.PeersWithRouteChanges) {
 	nm := nb.netMap
 	oldIDs := slices.Collect(maps.Keys(nb.peers))
 
@@ -843,8 +843,8 @@ func (nb *nodeBackend) updatePeersLocked() (discoChanged []key.NodePublic) {
 	for _, p := range nb.peers {
 		rt.UpsertPeer(p)
 	}
-	rt.Commit()
-	return discoChanged
+	res := rt.Commit()
+	return discoChanged, res.AllowedIPs
 }
 
 // recordTSMPLearnedDisco notes that a peer's new disco key was learned via
diff --git a/ipn/ipnlocal/node_backend_test.go b/ipn/ipnlocal/node_backend_test.go
index b8eb98479..adad0c32b 100644
--- a/ipn/ipnlocal/node_backend_test.go
+++ b/ipn/ipnlocal/node_backend_test.go
@@ -390,31 +390,31 @@ func TestNodeBackendDiscoChanged(t *testing.T) {
 
 	// A brand-new peer is not a disco change.
 	d1 := newDisco()
-	if got := nb.SetNetMap(mkNetMap(d1)); len(got) != 0 {
+	if got, _ := nb.SetNetMap(mkNetMap(d1)); len(got) != 0 {
 		t.Errorf("SetNetMap(new peer) discoChanged = %v; want none", got)
 	}
 
 	// A changed disco key requires a session reset.
 	d2 := newDisco()
-	if got := nb.SetNetMap(mkNetMap(d2)); !slices.Contains(got, nk) {
+	if got, _ := nb.SetNetMap(mkNetMap(d2)); !slices.Contains(got, nk) {
 		t.Errorf("SetNetMap(changed disco) discoChanged = %v; want %v", got, nk)
 	}
 
 	// An unchanged disco key does not.
-	if got := nb.SetNetMap(mkNetMap(d2)); len(got) != 0 {
+	if got, _ := nb.SetNetMap(mkNetMap(d2)); len(got) != 0 {
 		t.Errorf("SetNetMap(same disco) discoChanged = %v; want none", got)
 	}
 
 	// A change already learned via TSMP is suppressed...
 	d3 := newDisco()
 	nb.recordTSMPLearnedDisco(nk, d3)
-	if got := nb.SetNetMap(mkNetMap(d3)); len(got) != 0 {
+	if got, _ := nb.SetNetMap(mkNetMap(d3)); len(got) != 0 {
 		t.Errorf("SetNetMap(TSMP-learned disco) discoChanged = %v; want none", got)
 	}
 
 	// ...but the TSMP entry is consumed, so the next change resets again.
 	d4 := newDisco()
-	if got := nb.SetNetMap(mkNetMap(d4)); !slices.Contains(got, nk) {
+	if got, _ := nb.SetNetMap(mkNetMap(d4)); !slices.Contains(got, nk) {
 		t.Errorf("SetNetMap(after TSMP entry consumed) discoChanged = %v; want %v", got, nk)
 	}
 
@@ -423,7 +423,7 @@ func TestNodeBackendDiscoChanged(t *testing.T) {
 	before := metricTSMPLearnedKeyMismatch.Value()
 	nb.recordTSMPLearnedDisco(nk, newDisco())
 	d5 := newDisco()
-	if got := nb.SetNetMap(mkNetMap(d5)); !slices.Contains(got, nk) {
+	if got, _ := nb.SetNetMap(mkNetMap(d5)); !slices.Contains(got, nk) {
 		t.Errorf("SetNetMap(TSMP mismatch) discoChanged = %v; want %v", got, nk)
 	}
 	if delta := metricTSMPLearnedKeyMismatch.Value() - before; delta != 1 {
@@ -436,15 +436,15 @@ func TestNodeBackendDiscoChanged(t *testing.T) {
 	nb.recordTSMPLearnedDisco(nk, d6)
 	nb.SetNetMap(&netmap.NetworkMap{})
 	nb.SetNetMap(mkNetMap(d5))
-	if got := nb.SetNetMap(mkNetMap(d6)); !slices.Contains(got, nk) {
+	if got, _ := nb.SetNetMap(mkNetMap(d6)); !slices.Contains(got, nk) {
 		t.Errorf("SetNetMap(after TSMP entry GC) discoChanged = %v; want %v", got, nk)
 	}
 
 	// Transitions to or from a zero disco key never reset.
-	if got := nb.SetNetMap(mkNetMap(key.DiscoPublic{})); len(got) != 0 {
+	if got, _ := nb.SetNetMap(mkNetMap(key.DiscoPublic{})); len(got) != 0 {
 		t.Errorf("SetNetMap(to zero disco) discoChanged = %v; want none", got)
 	}
-	if got := nb.SetNetMap(mkNetMap(d1)); len(got) != 0 {
+	if got, _ := nb.SetNetMap(mkNetMap(d1)); len(got) != 0 {
 		t.Errorf("SetNetMap(from zero disco) discoChanged = %v; want none", got)
 	}
 }
diff --git a/ipn/ipnlocal/state_test.go b/ipn/ipnlocal/state_test.go
index d8b045c00..3ce554fac 100644
--- a/ipn/ipnlocal/state_test.go
+++ b/ipn/ipnlocal/state_test.go
@@ -1238,10 +1238,10 @@ func TestEngineReconfigOnStateChange(t *testing.T) {
 	connect := &ipn.MaskedPrefs{Prefs: ipn.Prefs{WantRunning: true}, WantRunningSet: true}
 	disconnect := &ipn.MaskedPrefs{Prefs: ipn.Prefs{WantRunning: false}, WantRunningSet: true}
 	node1 := buildNetmapWithPeers(
-		makePeer(1, withName("node-1"), withAddresses(netip.MustParsePrefix("100.64.1.1/32"))),
+		makePeer(1, withName("node-1"), withAddresses(netip.MustParsePrefix("100.64.1.1/32")), withAllowedIPs(netip.MustParsePrefix("100.64.1.1/32"))),
 	)
 	node2 := buildNetmapWithPeers(
-		makePeer(2, withName("node-2"), withAddresses(netip.MustParsePrefix("100.64.1.2/32"))),
+		makePeer(2, withName("node-2"), withAddresses(netip.MustParsePrefix("100.64.1.2/32")), withAllowedIPs(netip.MustParsePrefix("100.64.1.2/32"))),
 	)
 	node3 := buildNetmapWithPeers(
 		makePeer(3, withName("node-3"), withAddresses(netip.MustParsePrefix("100.64.1.3/32"))),
@@ -1257,6 +1257,7 @@ func TestEngineReconfigOnStateChange(t *testing.T) {
 		steps         func(*testing.T, *LocalBackend, func() *mockControl)
 		wantState     ipn.State
 		wantCfg       *wgcfg.Config
+		wantPeers     []key.NodePublic
 		wantRouterCfg *router.Config
 		wantDNSCfg    *dns.Config
 	}{
@@ -1301,7 +1302,6 @@ func TestEngineReconfigOnStateChange(t *testing.T) {
 			// After the auth is completed, the configs must be updated to reflect the node's netmap.
 			wantState: ipn.Starting,
 			wantCfg: &wgcfg.Config{
-				Peers:     []wgcfg.Peer{},
 				Addresses: node1.SelfNode.Addresses().AsSlice(),
 			},
 			wantRouterCfg: &router.Config{
@@ -1359,7 +1359,6 @@ func TestEngineReconfigOnStateChange(t *testing.T) {
 			// Once the auth is completed, the configs must be updated to reflect the node's netmap.
 			wantState: ipn.Starting,
 			wantCfg: &wgcfg.Config{
-				Peers:     []wgcfg.Peer{},
 				Addresses: node2.SelfNode.Addresses().AsSlice(),
 			},
 			wantRouterCfg: &router.Config{
@@ -1409,7 +1408,6 @@ func TestEngineReconfigOnStateChange(t *testing.T) {
 			// must be updated to reflect the node's netmap.
 			wantState: ipn.Starting,
 			wantCfg: &wgcfg.Config{
-				Peers:     []wgcfg.Peer{},
 				Addresses: node1.SelfNode.Addresses().AsSlice(),
 			},
 			wantRouterCfg: &router.Config{
@@ -1434,23 +1432,17 @@ func TestEngineReconfigOnStateChange(t *testing.T) {
 			},
 			wantState: ipn.Starting,
 			wantCfg: &wgcfg.Config{
-				Peers: []wgcfg.Peer{
-					{
-						PublicKey: node1.SelfNode.Key(),
-						DiscoKey:  node1.SelfNode.DiscoKey(),
-					},
-					{
-						PublicKey: node2.SelfNode.Key(),
-						DiscoKey:  node2.SelfNode.DiscoKey(),
-					},
-				},
 				Addresses: node3.SelfNode.Addresses().AsSlice(),
 			},
+			wantPeers: []key.NodePublic{
+				node1.SelfNode.Key(),
+				node2.SelfNode.Key(),
+			},
 			wantRouterCfg: &router.Config{
 				SNATSubnetRoutes: true,
 				NetfilterMode:    preftype.NetfilterOn,
 				LocalAddrs:       node3.SelfNode.Addresses().AsSlice(),
-				Routes:           routesWithQuad100(),
+				Routes:           routesWithQuad100(netip.MustParsePrefix("100.64.1.1/32"), netip.MustParsePrefix("100.64.1.2/32")),
 			},
 			wantDNSCfg: &dns.Config{
 				AcceptDNS:             true,
@@ -1490,7 +1482,6 @@ func TestEngineReconfigOnStateChange(t *testing.T) {
 			// Starting a reauth should leave everything up:
 			wantState: ipn.Starting,
 			wantCfg: &wgcfg.Config{
-				Peers:     []wgcfg.Peer{},
 				Addresses: node1.SelfNode.Addresses().AsSlice(),
 			},
 			wantRouterCfg: &router.Config{
@@ -1522,7 +1513,6 @@ func TestEngineReconfigOnStateChange(t *testing.T) {
 			},
 			wantState: ipn.Starting,
 			wantCfg: &wgcfg.Config{
-				Peers:     []wgcfg.Peer{},
 				Addresses: node1.SelfNode.Addresses().AsSlice(),
 			},
 			wantRouterCfg: &router.Config{
@@ -1571,13 +1561,12 @@ func TestEngineReconfigOnStateChange(t *testing.T) {
 				t.Errorf("State: got %v; want %v", gotState, tt.wantState)
 			}
 
-			if engine.Config() != nil {
-				for _, p := range engine.Config().Peers {
-					pKey := p.PublicKey.UntypedHexString()
-					_, err := lb.MagicConn().ParseEndpoint(pKey)
-					if err != nil {
-						t.Errorf("ParseEndpoint(%q) failed: %v", pKey, err)
-					}
+			// Peers are not part of wgcfg.Config; the engine learns
+			// them from the config source installed by LocalBackend
+			// via SetPeerConfigFunc.
+			for _, k := range tt.wantPeers {
+				if _, ok := engine.PeerAllowedIPs(k); !ok {
+					t.Errorf("PeerAllowedIPs(%v) = false; want peer known", k.ShortString())
 				}
 			}
 
@@ -1597,7 +1586,10 @@ func TestEngineReconfigOnStateChange(t *testing.T) {
 	}
 }
 
-func TestEngineReconfigOnPeerRouteDelta(t *testing.T) {
+// TestPeerConfigUpdatedOnPeerRouteDelta tests that a netmap delta that
+// changes a peer's allowed IPs is visible through the live per-peer
+// config source that LocalBackend installs on the engine.
+func TestPeerConfigUpdatedOnPeerRouteDelta(t *testing.T) {
 	connect := &ipn.MaskedPrefs{Prefs: ipn.Prefs{WantRunning: true}, WantRunningSet: true}
 	peerAddr := netip.MustParsePrefix("100.64.1.1/32")
 	vipAddr := netip.MustParsePrefix("100.99.99.99/32")
@@ -1623,20 +1615,13 @@ func TestEngineReconfigOnPeerRouteDelta(t *testing.T) {
 		t.Fatal("UpdateNetmapDelta = false, want true")
 	}
 
-	cfg := engine.Config()
-	if cfg == nil {
-		t.Fatal("engine config is nil")
+	ips, ok := engine.PeerAllowedIPs(replacement.Key)
+	if !ok {
+		t.Fatalf("peer config source missing peer %v", replacement.Key.ShortString())
 	}
-	for _, peer := range cfg.Peers {
-		if peer.PublicKey != replacement.Key {
-			continue
-		}
-		if !slices.Contains(peer.AllowedIPs, vipAddr) {
-			t.Fatalf("peer AllowedIPs = %v; want %v", peer.AllowedIPs, vipAddr)
-		}
-		return
+	if !slices.Contains(ips, vipAddr) {
+		t.Fatalf("peer AllowedIPs = %v; want %v", ips, vipAddr)
 	}
-	t.Fatalf("engine config missing peer %v", replacement.Key.ShortString())
 }
 
 // TestSendPreservesAuthURL tests that wgengine updates arriving in the middle of
@@ -1900,6 +1885,8 @@ type mockEngine struct {
 
 	filter, jailedFilter *filter.Filter
 
+	peerConfigFn func(key.NodePublic) (allowedIPs []netip.Prefix, ok bool)
+
 	statusCb wgengine.StatusCallback
 }
 
@@ -2005,8 +1992,24 @@ func (e *mockEngine) InstallCaptureHook(packet.CaptureCallback) {}
 
 func (e *mockEngine) SetPeerByIPPacketFunc(func(netip.Addr) (_ key.NodePublic, ok bool)) {}
 func (e *mockEngine) SetPeerForIPFunc(func(netip.Addr) (_ wgengine.PeerForIP, ok bool))  {}
-func (e *mockEngine) SetPeerConfigFunc(func(key.NodePublic) (allowedIPs []netip.Prefix, ok bool)) {
+func (e *mockEngine) SetPeerConfigFunc(fn func(key.NodePublic) (allowedIPs []netip.Prefix, ok bool)) {
+	e.mu.Lock()
+	defer e.mu.Unlock()
+	e.peerConfigFn = fn
 }
+
+// PeerAllowedIPs looks up a peer's allowed IPs via the live per-peer
+// config source installed by LocalBackend with SetPeerConfigFunc.
+func (e *mockEngine) PeerAllowedIPs(k key.NodePublic) (_ []netip.Prefix, ok bool) {
+	e.mu.Lock()
+	fn := e.peerConfigFn
+	e.mu.Unlock()
+	if fn == nil {
+		return nil, false
+	}
+	return fn(k)
+}
+
 func (e *mockEngine) SyncDevicePeer(key.NodePublic)  {}
 func (e *mockEngine) ResetDevicePeer(key.NodePublic) {}
 func (e *mockEngine) SetPeerSessionStateFunc(func(key.NodePublic, wgengine.PeerWireGuardState)) {
diff --git a/tsnet/tsnet_test.go b/tsnet/tsnet_test.go
index 906008b06..ca3ed035e 100644
--- a/tsnet/tsnet_test.go
+++ b/tsnet/tsnet_test.go
@@ -1746,7 +1746,7 @@ func TestFallbackTCPHandler(t *testing.T) {
 // Before aa5da2e5f22a, every peer change rebuilt a full netmap on
 // the engine, so [wgengine.Engine.SetNetworkMap] kept the engine's
 // cached netmap fresh and [wgengine.Engine.Reconfig] kept wgdev and
-// e.lastCfgFull fresh. After that refactor, peer adds and removes
+// e.lastCfg fresh. After that refactor, peer adds and removes
 // ride the delta path and only mutate [nodeBackend]; the engine's
 // cached netmap and wireguard config stayed stale, and
 // [wgengine.Engine.PeerForIP] / [wgengine.Engine.Ping] / wgdev's
@@ -1925,7 +1925,7 @@ func TestPingSubnetRouteOfDeltaPeer(t *testing.T) {
 	// outbound wgdev encryption, magicsock transport. The receiving
 	// side (s2's tstun.Wrapper) intercepts TSMP regardless of dst
 	// IP and replies with a pong. So this catches both halves of
-	// the bug: a stale BART / lastCfgFull (PeerForIP / lookupPeerByIP
+	// the bug: a stale BART / lastCfg (PeerForIP / lookupPeerByIP
 	// miss) AND a stale wgdev PeerLookupFunc closure (peer's noise
 	// key not yet registered for outbound encryption).
 	pingCtx, cancelPing := pingTimeout(ctx)
diff --git a/util/deephash/tailscale_types_test.go b/util/deephash/tailscale_types_test.go
index 7e803c841..7cff5335c 100644
--- a/util/deephash/tailscale_types_test.go
+++ b/util/deephash/tailscale_types_test.go
@@ -86,11 +86,6 @@ func getVal() *tailscaleTypes {
 	return &tailscaleTypes{
 		&wgcfg.Config{
 			Addresses: []netip.Prefix{netip.PrefixFrom(netip.AddrFrom16([16]byte{3: 3}).Unmap(), 5)},
-			Peers: []wgcfg.Peer{
-				{
-					PublicKey: key.NodePublic{},
-				},
-			},
 		},
 		&router.Config{
 			Routes: []netip.Prefix{
diff --git a/wgengine/bench/wg.go b/wgengine/bench/wg.go
index 1e28707e2..0e96a7b61 100644
--- a/wgengine/bench/wg.go
+++ b/wgengine/bench/wg.go
@@ -83,8 +83,8 @@ func setupWGTest(b *testing.B, logf logger.Logf, traf *TrafficGen, a1, a2 netip.
 	e2.SetFilter(filter.NewAllowAllForTest(l2))
 
 	// There is no LocalBackend in this benchmark, so install trivial
-	// outbound peer lookups; without one, outbound packets can't
-	// lazily create their WireGuard peer.
+	// outbound peer lookups and per-peer config sources; without them,
+	// outbound packets can't lazily create their WireGuard peer.
 	k1pub, k2pub := k1.Public(), k2.Public()
 	e1.SetPeerByIPPacketFunc(func(dst netip.Addr) (_ key.NodePublic, ok bool) {
 		return k2pub, a2.Contains(dst)
@@ -92,6 +92,18 @@ func setupWGTest(b *testing.B, logf logger.Logf, traf *TrafficGen, a1, a2 netip.
 	e2.SetPeerByIPPacketFunc(func(dst netip.Addr) (_ key.NodePublic, ok bool) {
 		return k1pub, a1.Contains(dst)
 	})
+	e1.SetPeerConfigFunc(func(pubk key.NodePublic) (_ []netip.Prefix, ok bool) {
+		if pubk == k2pub {
+			return []netip.Prefix{a2}, true
+		}
+		return nil, false
+	})
+	e2.SetPeerConfigFunc(func(pubk key.NodePublic) (_ []netip.Prefix, ok bool) {
+		if pubk == k1pub {
+			return []netip.Prefix{a1}, true
+		}
+		return nil, false
+	})
 
 	var wait sync.WaitGroup
 	wait.Add(2)
@@ -107,12 +119,6 @@ func setupWGTest(b *testing.B, logf logger.Logf, traf *TrafficGen, a1, a2 netip.
 		logf("e1 status: %v", *st)
 
 		e2.SetSelfNode(tailcfg.NodeView{})
-
-		p := wgcfg.Peer{
-			PublicKey:  c1.PrivateKey.Public(),
-			AllowedIPs: []netip.Prefix{a1},
-		}
-		c2.Peers = []wgcfg.Peer{p}
 		e2.Reconfig(&c2, &router.Config{}, new(dns.Config))
 		e1waitDoneOnce.Do(wait.Done)
 	})
@@ -128,12 +134,6 @@ func setupWGTest(b *testing.B, logf logger.Logf, traf *TrafficGen, a1, a2 netip.
 		logf("e2 status: %v", *st)
 
 		e1.SetSelfNode(tailcfg.NodeView{})
-
-		p := wgcfg.Peer{
-			PublicKey:  c2.PrivateKey.Public(),
-			AllowedIPs: []netip.Prefix{a2},
-		}
-		c1.Peers = []wgcfg.Peer{p}
 		e1.Reconfig(&c1, &router.Config{}, new(dns.Config))
 		e2waitDoneOnce.Do(wait.Done)
 	})
diff --git a/wgengine/magicsock/magicsock_test.go b/wgengine/magicsock/magicsock_test.go
index 4286b6028..63876bc51 100644
--- a/wgengine/magicsock/magicsock_test.go
+++ b/wgengine/magicsock/magicsock_test.go
@@ -246,50 +246,71 @@ func newMagicStackWithKey(t testing.TB, logf logger.Logf, ln nettype.PacketListe
 	}
 }
 
-// Reconfig applies cfg to the stack's device and tun layer. peers,
-// if non-nil, are the tailcfg nodes that cfg was derived from; the
-// tun layer's per-peer data-plane attributes (masquerade addresses,
-// jailed classification) are derived from them with a real
-// [routemanager.RouteManager], exactly as LocalBackend does in
-// production, so this helper cannot drift from the production
-// derivation. Tests whose hand-built configs carry no such
-// attributes may pass nil.
+// Reconfig applies cfg and peers to the stack's WireGuard device and
+// tun-layer data plane. In production these flow from LocalBackend
+// (via [tailscale.com/wgengine.Engine.Reconfig] and the live per-peer
+// config source installed with Engine.SetPeerConfigFunc); tests that
+// bypass LocalBackend replicate that wiring here, deriving everything
+// from a real [routemanager.RouteManager] fed the given peers,
+// exactly as LocalBackend does in production, so this helper cannot
+// drift from the production derivation.
 func (s *magicStack) Reconfig(cfg *wgcfg.Config, peers []tailcfg.NodeView) error {
 	s.tsTun.SetWGConfig(cfg)
 
-	if peers != nil {
-		rm := routemanager.New(nil)
-		mut := rm.Begin()
-		// Mirror the netmap.AllowSubnetRoutes flag the tests pass to
-		// nmcfg.WGCfg.
-		mut.SetPrefs(routemanager.Prefs{RouteAll: true})
-		for _, n := range peers {
-			mut.UpsertPeer(n)
+	rm := routemanager.New(nil)
+	mut := rm.Begin()
+	// Mirror the netmap.AllowSubnetRoutes flag the tests pass to
+	// nmcfg.WGCfg.
+	mut.SetPrefs(routemanager.Prefs{RouteAll: true})
+	// idByKey stands in for nodeBackend's public-key-to-node-ID
+	// index, which LocalBackend uses to serve the engine's per-peer
+	// config source.
+	idByKey := make(map[key.NodePublic]tailcfg.NodeID, len(peers))
+	for _, n := range peers {
+		idByKey[n.Key()] = n.ID()
+		mut.UpsertPeer(n)
+	}
+	mut.Commit()
+	peerAllowedIPs := func(k key.NodePublic) ([]netip.Prefix, bool) {
+		id, ok := idByKey[k]
+		if !ok {
+			return nil, false
 		}
-		mut.Commit()
-		native4, native6 := tsaddr.FirstTailscaleAddrs(slices.All(cfg.Addresses))
-		s.tsTun.SetPeerRoutes(native4, native6, rm.Outbound())
+		return rm.PeerAllowedIPs(id)
 	}
 
-	// In production, LocalBackend installs a PeerByIPPacketFunc via
-	// Engine.SetPeerByIPPacketFunc. Tests that bypass LocalBackend need
-	// to install one here for outbound packet routing.
-	ipToPeer := make(map[netip.Addr]device.NoisePublicKey, len(cfg.Peers))
-	for _, p := range cfg.Peers {
-		pk := p.PublicKey.Raw32()
-		for _, pfx := range p.AllowedIPs {
-			if pfx.IsSingleIP() {
-				ipToPeer[pfx.Addr()] = pk
+	// The tun-layer per-peer route attributes (masquerade, jailed).
+	native4, native6 := tsaddr.FirstTailscaleAddrs(slices.All(cfg.Addresses))
+	s.tsTun.SetPeerRoutes(native4, native6, rm.Outbound())
+
+	// Outbound packet routing, as LocalBackend's lookupPeerByIP does
+	// via the outbound table.
+	s.dev.SetPeerByIPPacketFunc(func(_, dst netip.Addr, _ []byte) (device.NoisePublicKey, bool) {
+		if pr, ok := rm.Outbound().Lookup(dst); ok {
+			return pr.Key.Raw32(), true
+		}
+		return device.NoisePublicKey{}, false
+	})
+
+	// The live per-peer config source backing lazy peer creation, as
+	// LocalBackend's peerAllowedIPs does via PeerAllowedIPs, and the
+	// per-peer device convergence that Engine.SyncDevicePeer does.
+	s.dev.SetPeerLookupFunc(wgcfg.NewPeerLookupFunc(s.conn.Bind(), s.conn.logf, func(pubk device.NoisePublicKey) ([]netip.Prefix, bool) {
+		return peerAllowedIPs(key.NodePublicFromRaw32(mem.B(pubk[:])))
+	}))
+	s.dev.SetPrivateKey(key.NodePrivateAs[device.NoisePrivateKey](cfg.PrivateKey))
+	s.dev.RemoveMatchingPeers(func(pk device.NoisePublicKey) bool {
+		_, ok := peerAllowedIPs(key.NodePublicFromRaw32(mem.B(pk[:])))
+		return !ok
+	})
+	for _, n := range peers {
+		if peer, ok := s.dev.LookupActivePeer(n.Key().Raw32()); ok {
+			if ips, ok := peerAllowedIPs(n.Key()); ok {
+				peer.SetAllowedIPs(ips)
 			}
 		}
 	}
-	s.dev.SetPeerByIPPacketFunc(func(_, dst netip.Addr, _ []byte) (device.NoisePublicKey, bool) {
-		pk, ok := ipToPeer[dst]
-		return pk, ok
-	})
-
-	s.dev.SetPrivateKey(key.NodePrivateAs[device.NoisePrivateKey](cfg.PrivateKey))
-	return wgcfg.ReconfigDevice(s.dev, cfg, s.conn.logf)
+	return nil
 }
 
 func (s *magicStack) String() string {
@@ -1203,30 +1224,32 @@ func testTwoDevicePing(t *testing.T, d *devices) {
 	m1cfg := &wgcfg.Config{
 		PrivateKey: m1.privateKey,
 		Addresses:  []netip.Prefix{netip.MustParsePrefix("1.0.0.1/32")},
-		Peers: []wgcfg.Peer{
-			{
-				PublicKey:  m2.privateKey.Public(),
-				DiscoKey:   m2.conn.DiscoPublicKey(),
-				AllowedIPs: []netip.Prefix{netip.MustParsePrefix("1.0.0.2/32")},
-			},
-		},
 	}
+	m1peers := nodeViews([]*tailcfg.Node{{
+		ID:         2,
+		Key:        m2.privateKey.Public(),
+		DiscoKey:   m2.conn.DiscoPublicKey(),
+		HomeDERP:   1,
+		Addresses:  []netip.Prefix{netip.MustParsePrefix("1.0.0.2/32")},
+		AllowedIPs: []netip.Prefix{netip.MustParsePrefix("1.0.0.2/32")},
+	}})
 	m2cfg := &wgcfg.Config{
 		PrivateKey: m2.privateKey,
 		Addresses:  []netip.Prefix{netip.MustParsePrefix("1.0.0.2/32")},
-		Peers: []wgcfg.Peer{
-			{
-				PublicKey:  m1.privateKey.Public(),
-				DiscoKey:   m1.conn.DiscoPublicKey(),
-				AllowedIPs: []netip.Prefix{netip.MustParsePrefix("1.0.0.1/32")},
-			},
-		},
 	}
+	m2peers := nodeViews([]*tailcfg.Node{{
+		ID:         1,
+		Key:        m1.privateKey.Public(),
+		DiscoKey:   m1.conn.DiscoPublicKey(),
+		HomeDERP:   1,
+		Addresses:  []netip.Prefix{netip.MustParsePrefix("1.0.0.1/32")},
+		AllowedIPs: []netip.Prefix{netip.MustParsePrefix("1.0.0.1/32")},
+	}})
 
-	if err := m1.Reconfig(m1cfg, nil); err != nil {
+	if err := m1.Reconfig(m1cfg, m1peers); err != nil {
 		t.Fatal(err)
 	}
-	if err := m2.Reconfig(m2cfg, nil); err != nil {
+	if err := m2.Reconfig(m2cfg, m2peers); err != nil {
 		t.Fatal(err)
 	}
 
@@ -1350,7 +1373,7 @@ func testTwoDevicePing(t *testing.T, d *devices) {
 	t.Run("no-op-dev1-reconfig", func(t *testing.T) {
 		setT(t)
 		defer setT(outerT)
-		if err := m1.Reconfig(m1cfg, nil); err != nil {
+		if err := m1.Reconfig(m1cfg, m1peers); err != nil {
 			t.Fatal(err)
 		}
 		ping1(t)
diff --git a/wgengine/userspace.go b/wgengine/userspace.go
index f36d16620..e2b1b85c0 100644
--- a/wgengine/userspace.go
+++ b/wgengine/userspace.go
@@ -94,8 +94,6 @@ type userspaceEngine struct {
 	// feature/bird package is not linked into the binary.
 	bird Bird
 
-	testMaybeReconfigHook func() // for tests; if non-nil, fires if maybeReconfigWireguardLocked called
-
 	// isLocalAddr reports the whether an IP is assigned to the local
 	// tunnel interface. It's used to reflect local packets
 	// incorrectly sent to us.
@@ -118,7 +116,7 @@ type userspaceEngine struct {
 	// no longer install per-config lookup closures.
 	peerConfigFn atomic.Pointer[func(key.NodePublic) (allowedIPs []netip.Prefix, ok bool)]
 
-	lastCfgFull    wgcfg.Config
+	lastCfg        wgcfg.Config
 	lastRouter     *router.Config
 	lastDNSConfig  dns.ConfigView // or invalid if none
 	reconfigureVPN func() error   // or nil
@@ -678,59 +676,6 @@ func (e *userspaceEngine) handleLocalPackets(p *packet.Parsed, t *tstun.Wrapper)
 	return filter.Accept
 }
 
-// maybeReconfigWireguardLocked reconfigures wireguard-go with the current
-// full config, installing a PeerLookupFunc for on-demand peer creation.
-//
-// e.wgLock must be held.
-func (e *userspaceEngine) maybeReconfigWireguardLocked() error {
-	if hook := e.testMaybeReconfigHook; hook != nil {
-		hook()
-		return nil
-	}
-
-	full := e.lastCfgFull
-	// The wireguard-go peer set may have changed; drop the cached
-	// peer-string rewrites so the next log line re-resolves them
-	// against the current lookup.
-	e.wgLogger.Invalidate()
-
-	e.logf("wgengine: Reconfig: configuring userspace WireGuard config (with %d peers)", len(full.Peers))
-	if e.peerConfigFn.Load() != nil {
-		// The device has a long-lived PeerLookupFunc backed by the
-		// live config source, so only the peer set needs syncing;
-		// there is no per-config lookup closure to (re)install, and
-		// no removed peer can be resurrected with stale state.
-		//
-		// TODO(bradfitz): remove this O(n peers) sync. It's redundant
-		// with the incremental SyncDevicePeer calls that LocalBackend
-		// makes for exactly the peers whose allowed IPs changed. It
-		// only remains because peer changes still force a full
-		// Reconfig; once that's gated on actual router/DNS changes,
-		// this sync (and full-config peer syncing generally) can go.
-		peers := make(map[device.NoisePublicKey][]netip.Prefix, len(full.Peers))
-		for _, p := range full.Peers {
-			peers[p.PublicKey.Raw32()] = p.AllowedIPs
-		}
-		e.wgdev.RemoveMatchingPeers(func(pk device.NoisePublicKey) bool {
-			_, exists := peers[pk]
-			return !exists
-		})
-		// Update AllowedIPs on any already-active peers whose config
-		// may have changed. Peers that don't exist yet will get the
-		// correct AllowedIPs from the device's PeerLookupFunc when
-		// they are lazily created.
-		for pk, allowedIPs := range peers {
-			if peer, ok := e.wgdev.LookupActivePeer(pk); ok {
-				peer.SetAllowedIPs(allowedIPs)
-			}
-		}
-	} else if err := wgcfg.ReconfigDevice(e.wgdev, &full, e.logf); err != nil {
-		e.logf("wgdev.Reconfig: %v", err)
-		return err
-	}
-	return nil
-}
-
 // SetPeerConfigFunc implements [Engine.SetPeerConfigFunc]. It stores
 // fn and installs a single wgdev PeerLookupFunc wrapping it, so
 // lazily-created peers always get current allowed IPs and the lookup
@@ -753,6 +698,9 @@ func (e *userspaceEngine) SyncDevicePeer(k key.NodePublic) {
 	}
 	e.wgLock.Lock()
 	defer e.wgLock.Unlock()
+	// The peer set may be about to change; drop the wgLogger's cached
+	// peer-string rewrites so the next log line re-resolves them.
+	e.wgLogger.Invalidate()
 	allowedIPs, ok := (*fn)(k)
 	if !ok {
 		e.wgdev.RemovePeer(k.Raw32())
@@ -767,6 +715,7 @@ func (e *userspaceEngine) SyncDevicePeer(k key.NodePublic) {
 func (e *userspaceEngine) ResetDevicePeer(k key.NodePublic) {
 	e.wgLock.Lock()
 	defer e.wgLock.Unlock()
+	e.wgLogger.Invalidate()
 	e.wgdev.RemovePeer(k.Raw32())
 }
 
@@ -878,7 +827,7 @@ func (e *userspaceEngine) Reconfig(cfg *wgcfg.Config, routerCfg *router.Config,
 		birdChanged = e.bird.Reconfig(self)
 	}
 
-	engineChanged := !e.lastCfgFull.Equal(cfg)
+	engineChanged := !e.lastCfg.Equal(cfg)
 	routerChanged := checkchange.Update(&e.lastRouter, routerCfg)
 	dnsChanged := buildfeatures.HasDNS && !e.lastDNSConfig.Equal(dnsCfg.View())
 	if dnsChanged {
@@ -910,7 +859,7 @@ func (e *userspaceEngine) Reconfig(cfg *wgcfg.Config, routerCfg *router.Config,
 		e.isDNSIPOverTailscale.Store(ipset.NewContainsIPFunc(views.SliceOf(dnsIPsOverTailscale(dnsCfg, routerCfg))))
 	}
 
-	if !e.lastCfgFull.PrivateKey.Equal(cfg.PrivateKey) {
+	if !e.lastCfg.PrivateKey.Equal(cfg.PrivateKey) {
 		// Tell magicsock about the new (or initial) private key
 		// (which is needed by DERP) before wgdev gets it, as wgdev
 		// will start trying to handshake, which we want to be able to
@@ -924,16 +873,16 @@ func (e *userspaceEngine) Reconfig(cfg *wgcfg.Config, routerCfg *router.Config,
 		}
 	}
 
-	e.lastCfgFull = *cfg.Clone()
+	e.lastCfg = *cfg.Clone()
 
 	e.magicConn.SetPreferredPort(listenPort)
 	e.magicConn.UpdatePMTUD()
 
-	if engineChanged {
-		if err := e.maybeReconfigWireguardLocked(); err != nil {
-			return err
-		}
-	}
+	// Note: no wireguard-go device reconfig happens here. The device
+	// learns its peer set from the live config source installed via
+	// [Engine.SetPeerConfigFunc] (peers are lazily created and synced
+	// per peer by [Engine.SyncDevicePeer]), and its private key is set
+	// above when it changes.
 
 	if routerChanged {
 		e.logf("wgengine: Reconfig: configuring router")
diff --git a/wgengine/userspace_test.go b/wgengine/userspace_test.go
index 890a9cb0b..fc1c89403 100644
--- a/wgengine/userspace_test.go
+++ b/wgengine/userspace_test.go
@@ -90,7 +90,7 @@ func TestUserspaceEngineReconfig(t *testing.T) {
 
 	routerCfg := &router.Config{}
 
-	for _, nodeHex := range []string{
+	for i, nodeHex := range []string{
 		"aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa",
 		"bbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbbb",
 	} {
@@ -102,18 +102,9 @@ func TestUserspaceEngineReconfig(t *testing.T) {
 				},
 			}),
 		}
-		nk, err := key.ParseNodePublicUntyped(mem.S(nodeHex))
-		if err != nil {
-			t.Fatal(err)
-		}
 		cfg := &wgcfg.Config{
-			Peers: []wgcfg.Peer{
-				{
-					PublicKey: nk,
-					AllowedIPs: []netip.Prefix{
-						netip.PrefixFrom(netaddr.IPv4(100, 100, 99, 1), 32),
-					},
-				},
+			Addresses: []netip.Prefix{
+				netip.PrefixFrom(netaddr.IPv4(100, 100, 99, byte(1+i)), 32),
 			},
 		}
 
@@ -156,18 +147,9 @@ func TestUserspaceEnginePortReconfig(t *testing.T) {
 	t.Cleanup(ue.Close)
 
 	startingPort := ue.magicConn.LocalPort()
-	nodeKey, err := key.ParseNodePublicUntyped(mem.S("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"))
-	if err != nil {
-		t.Fatal(err)
-	}
 	cfg := &wgcfg.Config{
-		Peers: []wgcfg.Peer{
-			{
-				PublicKey: nodeKey,
-				AllowedIPs: []netip.Prefix{
-					netip.PrefixFrom(netaddr.IPv4(100, 100, 99, 1), 32),
-				},
-			},
+		Addresses: []netip.Prefix{
+			netip.PrefixFrom(netaddr.IPv4(100, 100, 99, 1), 32),
 		},
 	}
 	routerCfg := &router.Config{}
@@ -238,18 +220,9 @@ func TestUserspaceEnginePeerMTUReconfig(t *testing.T) {
 	t.Logf("Info: OS default don't fragment bit(s) setting: %v", osDefaultDF)
 
 	// Build a set of configs to use as we change the peer MTU settings.
-	nodeKey, err := key.ParseNodePublicUntyped(mem.S("aaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaaa"))
-	if err != nil {
-		t.Fatal(err)
-	}
 	cfg := &wgcfg.Config{
-		Peers: []wgcfg.Peer{
-			{
-				PublicKey: nodeKey,
-				AllowedIPs: []netip.Prefix{
-					netip.PrefixFrom(netaddr.IPv4(100, 100, 99, 1), 32),
-				},
-			},
+		Addresses: []netip.Prefix{
+			netip.PrefixFrom(netaddr.IPv4(100, 100, 99, 1), 32),
 		},
 	}
 	routerCfg := &router.Config{}
@@ -315,14 +288,7 @@ func TestTSMPKeyAdvertisement(t *testing.T) {
 		}).View(),
 	}
 	cfg := &wgcfg.Config{
-		Peers: []wgcfg.Peer{
-			{
-				PublicKey: nodeKey,
-				AllowedIPs: []netip.Prefix{
-					netip.PrefixFrom(netaddr.IPv4(100, 100, 99, 1), 32),
-				},
-			},
-		},
+		Addresses: nm.SelfNode.Addresses().AsSlice(),
 	}
 
 	ue.SetSelfNode(nm.SelfNode)
diff --git a/wgengine/wgcfg/config.go b/wgengine/wgcfg/config.go
index bd37c19f3..d613f0fc5 100644
--- a/wgengine/wgcfg/config.go
+++ b/wgengine/wgcfg/config.go
@@ -11,14 +11,17 @@
 	"tailscale.com/types/key"
 )
 
-//go:generate go run tailscale.com/cmd/cloner -type=Config,Peer
+//go:generate go run tailscale.com/cmd/cloner -type=Config
 
 // Config is a WireGuard configuration.
 // It only supports the set of things Tailscale uses.
+//
+// Peers are not part of the config: wireguard-go learns the peer set
+// and each peer's allowed IPs from the live per-peer config source
+// installed via [tailscale.com/wgengine.Engine.SetPeerConfigFunc].
 type Config struct {
 	PrivateKey key.NodePrivate
 	Addresses  []netip.Prefix
-	Peers      []Peer
 }
 
 func (c *Config) Equal(o *Config) bool {
@@ -26,43 +29,5 @@ func (c *Config) Equal(o *Config) bool {
 		return c == o
 	}
 	return c.PrivateKey.Equal(o.PrivateKey) &&
-		slices.Equal(c.Addresses, o.Addresses) &&
-		slices.EqualFunc(c.Peers, o.Peers, Peer.Equal)
-}
-
-type Peer struct {
-	PublicKey           key.NodePublic
-	DiscoKey            key.DiscoPublic // present only so we can handle restarts within wgengine, not passed to WireGuard
-	AllowedIPs          []netip.Prefix
-	V4MasqAddr          *netip.Addr // if non-nil, masquerade IPv4 traffic to this peer using this address
-	V6MasqAddr          *netip.Addr // if non-nil, masquerade IPv6 traffic to this peer using this address
-	IsJailed            bool        // if true, this peer is jailed and cannot initiate connections
-	PersistentKeepalive uint16      // in seconds between keep-alives; 0 to disable
-}
-
-func addrPtrEq(a, b *netip.Addr) bool {
-	if a == nil || b == nil {
-		return a == b
-	}
-	return *a == *b
-}
-
-func (p Peer) Equal(o Peer) bool {
-	return p.PublicKey == o.PublicKey &&
-		p.DiscoKey == o.DiscoKey &&
-		slices.Equal(p.AllowedIPs, o.AllowedIPs) &&
-		p.IsJailed == o.IsJailed &&
-		p.PersistentKeepalive == o.PersistentKeepalive &&
-		addrPtrEq(p.V4MasqAddr, o.V4MasqAddr) &&
-		addrPtrEq(p.V6MasqAddr, o.V6MasqAddr)
-}
-
-// PeerWithKey returns the Peer with key k and reports whether it was found.
-func (config Config) PeerWithKey(k key.NodePublic) (Peer, bool) {
-	for _, p := range config.Peers {
-		if p.PublicKey == k {
-			return p, true
-		}
-	}
-	return Peer{}, false
+		slices.Equal(c.Addresses, o.Addresses)
 }
diff --git a/wgengine/wgcfg/config_test.go b/wgengine/wgcfg/config_test.go
index fc8fdcbbb..64ffc8041 100644
--- a/wgengine/wgcfg/config_test.go
+++ b/wgengine/wgcfg/config_test.go
@@ -14,25 +14,10 @@ func TestConfigEqual(t *testing.T) {
 	rt := reflect.TypeFor[Config]()
 	for sf := range rt.Fields() {
 		switch sf.Name {
-		case "Name", "NodeID", "PrivateKey", "Addresses", "Peers":
+		case "Name", "NodeID", "PrivateKey", "Addresses":
 			// These are compared in [Config.Equal].
 		default:
 			t.Errorf("Have you added field %q to Config.Equal? Do so if not, and then update TestConfigEqual", sf.Name)
 		}
 	}
 }
-
-// Tests that [Peer.Equal] tests all fields of [Peer], even ones
-// that might get added in the future.
-func TestPeerEqual(t *testing.T) {
-	rt := reflect.TypeFor[Peer]()
-	for sf := range rt.Fields() {
-		switch sf.Name {
-		case "PublicKey", "DiscoKey", "AllowedIPs", "IsJailed",
-			"PersistentKeepalive", "V4MasqAddr", "V6MasqAddr":
-			// These are compared in [Peer.Equal].
-		default:
-			t.Errorf("Have you added field %q to Peer.Equal? Do so if not, and then update TestPeerEqual", sf.Name)
-		}
-	}
-}
diff --git a/wgengine/wgcfg/device.go b/wgengine/wgcfg/device.go
index 554cc9c1e..c5d39ea3d 100644
--- a/wgengine/wgcfg/device.go
+++ b/wgengine/wgcfg/device.go
@@ -38,69 +38,3 @@ func NewPeerLookupFunc(bind conn.Bind, logf logger.Logf, allowedIPs func(device.
 		}, true
 	}
 }
-
-// ReconfigDevice replaces the existing device configuration with cfg.
-//
-// Instead of using the UAPI text protocol, it uses the wireguard-go direct API
-// to install a [device.PeerLookupFunc] callback that creates peers on demand.
-//
-// The caller is responsible for:
-//   - calling [device.Device.SetPrivateKey] when the key changes
-//   - installing a [device.PeerByIPPacketFunc] on the device for outbound
-//     packet routing (e.g. via [tailscale.com/wgengine.Engine.SetPeerByIPPacketFunc])
-func ReconfigDevice(d *device.Device, cfg *Config, logf logger.Logf) (err error) {
-	defer func() {
-		if err != nil {
-			logf("wgcfg.Reconfig failed: %v", err)
-		}
-	}()
-
-	// Build peer map: public key → allowed IPs.
-	peers := make(map[device.NoisePublicKey][]netip.Prefix, len(cfg.Peers))
-	for _, p := range cfg.Peers {
-		peers[p.PublicKey.Raw32()] = p.AllowedIPs
-	}
-
-	// Remove peers not in the new config.
-	d.RemoveMatchingPeers(func(pk device.NoisePublicKey) bool {
-		_, exists := peers[pk]
-		return !exists
-	})
-
-	// Update AllowedIPs on any already-active peers whose config may have
-	// changed. Peers that don't exist yet will get the correct AllowedIPs
-	// from PeerLookupFunc when they are lazily created.
-	for pk, allowedIPs := range peers {
-		if peer, ok := d.LookupActivePeer(pk); ok {
-			peer.SetAllowedIPs(allowedIPs)
-		}
-	}
-
-	// Install callback for lazy peer creation (incoming packets).
-	bind := d.Bind()
-	d.SetPeerLookupFunc(func(pubk device.NoisePublicKey) (_ *device.NewPeerConfig, ok bool) {
-		allowedIPs, ok := peers[pubk]
-		if !ok {
-			return nil, false
-		}
-		ep, err := bind.ParseEndpoint(fmt.Sprintf("%x", pubk[:]))
-		if err != nil {
-			logf("wgcfg: failed to parse endpoint for peer %x: %v", pubk[:8], err)
-			return nil, false
-		}
-		return &device.NewPeerConfig{
-			AllowedIPs: allowedIPs,
-			Endpoint:   ep,
-		}, true
-	})
-
-	// RemoveMatchingPeers _again_, now that SetPeerLookupFunc is installed,
-	// lest any removed peers got re-created before the new SetPeerLookupFunc
-	// func was installed.
-	d.RemoveMatchingPeers(func(pk device.NoisePublicKey) bool {
-		_, exists := peers[pk]
-		return !exists
-	})
-
-	return nil
-}
diff --git a/wgengine/wgcfg/device_test.go b/wgengine/wgcfg/device_test.go
index 07eb41adb..c07e14702 100644
--- a/wgengine/wgcfg/device_test.go
+++ b/wgengine/wgcfg/device_test.go
@@ -15,76 +15,47 @@
 	"tailscale.com/types/key"
 )
 
-func TestReconfigDevice(t *testing.T) {
-	k1, pk1 := newK()
-	ip1 := netip.MustParsePrefix("10.0.0.1/32")
+func TestNewPeerLookupFunc(t *testing.T) {
+	k1, _ := newK()
 
 	k2, _ := newK()
 	ip2 := netip.MustParsePrefix("10.0.0.2/32")
 
 	k3, _ := newK()
-	ip3 := netip.MustParsePrefix("10.0.0.3/32")
-
-	cfg1 := &Config{
-		PrivateKey: pk1,
-		Peers: []Peer{
-			{PublicKey: k2, AllowedIPs: []netip.Prefix{ip2}},
-		},
-	}
 
 	dev := NewDevice(newNilTun(), new(noopBind), device.NewLogger(device.LogLevelError, "test"))
 	defer dev.Close()
 
-	t.Run("initial-config", func(t *testing.T) {
-		if err := ReconfigDevice(dev, cfg1, t.Logf); err != nil {
-			t.Fatal(err)
-		}
-		// Peer should be creatable on demand via LookupPeer.
-		peer := dev.LookupPeer(k2.Raw32())
-		if peer == nil {
+	// peers is the live per-peer config source, standing in for what
+	// LocalBackend provides via wgengine.Engine.SetPeerConfigFunc.
+	peers := map[device.NoisePublicKey][]netip.Prefix{
+		k2.Raw32(): {ip2},
+	}
+	dev.SetPeerLookupFunc(NewPeerLookupFunc(dev.Bind(), t.Logf, func(pubk device.NoisePublicKey) ([]netip.Prefix, bool) {
+		ips, ok := peers[pubk]
+		return ips, ok
+	}))
+
+	t.Run("lazy-creation", func(t *testing.T) {
+		// A peer known to the config source should be creatable on
+		// demand via LookupPeer.
+		if p := dev.LookupPeer(k2.Raw32()); p == nil {
 			t.Fatal("expected peer k2 to exist via LookupPeer")
 		}
-		// Unknown peer should not be found.
-		peer = dev.LookupPeer(k3.Raw32())
-		if peer != nil {
+		// An unknown peer should not be found.
+		if p := dev.LookupPeer(k3.Raw32()); p != nil {
 			t.Fatal("expected unknown peer k3 to not exist")
 		}
 	})
 
-	t.Run("add-peer", func(t *testing.T) {
-		cfg1.Peers = append(cfg1.Peers, Peer{
-			PublicKey:  k3,
-			AllowedIPs: []netip.Prefix{ip3},
-		})
-		if err := ReconfigDevice(dev, cfg1, t.Logf); err != nil {
-			t.Fatal(err)
-		}
-		// Both peers should now be discoverable.
-		if p := dev.LookupPeer(k2.Raw32()); p == nil {
-			t.Fatal("expected peer k2 to exist")
-		}
-		if p := dev.LookupPeer(k3.Raw32()); p == nil {
-			t.Fatal("expected peer k3 to exist")
-		}
-	})
-
 	t.Run("remove-peer", func(t *testing.T) {
-		cfg2 := &Config{
-			PrivateKey: pk1,
-			Peers: []Peer{
-				{PublicKey: k2, AllowedIPs: []netip.Prefix{ip2}},
-			},
-		}
-		if err := ReconfigDevice(dev, cfg2, t.Logf); err != nil {
-			t.Fatal(err)
-		}
-		// k2 should still be discoverable.
-		if p := dev.LookupPeer(k2.Raw32()); p == nil {
-			t.Fatal("expected peer k2 to exist")
-		}
-		// k3 should no longer be discoverable.
-		if p := dev.LookupPeer(k3.Raw32()); p != nil {
-			t.Fatal("expected peer k3 to not exist after removal")
+		delete(peers, k2.Raw32())
+		dev.RemoveMatchingPeers(func(pk device.NoisePublicKey) bool {
+			_, ok := peers[pk]
+			return !ok
+		})
+		if p := dev.LookupPeer(k2.Raw32()); p != nil {
+			t.Fatal("expected peer k2 to not exist after removal")
 		}
 	})
 
@@ -94,8 +65,6 @@ func TestReconfigDevice(t *testing.T) {
 			t.Fatal("expected own key to not be a peer")
 		}
 	})
-
-	_ = ip1 // suppress unused
 }
 
 func newK() (key.NodePublic, key.NodePrivate) {
diff --git a/wgengine/wgcfg/nmcfg/nmcfg.go b/wgengine/wgcfg/nmcfg/nmcfg.go
index 7f633e4b5..da4d038db 100644
--- a/wgengine/wgcfg/nmcfg/nmcfg.go
+++ b/wgengine/wgcfg/nmcfg/nmcfg.go
@@ -45,11 +45,16 @@ func cidrIsSubnet(node tailcfg.NodeView, cidr netip.Prefix) bool {
 }
 
 // WGCfg returns the NetworkMaps's WireGuard configuration.
+//
+// The config does not include peers; wireguard-go gets those from the
+// live per-peer config source installed via
+// [tailscale.com/wgengine.Engine.SetPeerConfigFunc], fed by the route
+// manager. WGCfg still walks the peers to log which ones are not
+// routable and why, mirroring the route manager's filtering.
 func WGCfg(pk key.NodePrivate, nm *netmap.NetworkMap, logf logger.Logf, flags netmap.WGConfigFlags, exitNode tailcfg.StableNodeID) (*wgcfg.Config, error) {
 	cfg := &wgcfg.Config{
 		PrivateKey: pk,
 		Addresses:  nm.GetAddresses().AsSlice(),
-		Peers:      make([]wgcfg.Peer, 0, len(nm.Peers)),
 	}
 
 	var skippedExitNode, skippedSubnetRouter, skippedExpired []tailcfg.NodeView
@@ -69,16 +74,7 @@ func WGCfg(pk key.NodePrivate, nm *netmap.NetworkMap, logf logger.Logf, flags ne
 			continue
 		}
 
-		cfg.Peers = append(cfg.Peers, wgcfg.Peer{
-			PublicKey: peer.Key(),
-			DiscoKey:  peer.DiscoKey(),
-		})
-		cpeer := &cfg.Peers[len(cfg.Peers)-1]
-
 		didExitNodeLog := false
-		cpeer.V4MasqAddr = peer.SelfNodeV4MasqAddrForThisPeer().Clone()
-		cpeer.V6MasqAddr = peer.SelfNodeV6MasqAddrForThisPeer().Clone()
-		cpeer.IsJailed = peer.IsJailed()
 		for _, allowedIP := range peer.AllowedIPs().All() {
 			if allowedIP.Bits() == 0 && peer.StableID() != exitNode {
 				if didExitNodeLog {
@@ -87,14 +83,11 @@ func WGCfg(pk key.NodePrivate, nm *netmap.NetworkMap, logf logger.Logf, flags ne
 				}
 				didExitNodeLog = true
 				skippedExitNode = append(skippedExitNode, peer)
-				continue
 			} else if cidrIsSubnet(peer, allowedIP) {
 				if (flags & netmap.AllowSubnetRoutes) == 0 {
 					skippedSubnetRouter = append(skippedSubnetRouter, peer)
-					continue
 				}
 			}
-			cpeer.AllowedIPs = append(cpeer.AllowedIPs, allowedIP)
 		}
 	}
 
diff --git a/wgengine/wgcfg/wgcfg_clone.go b/wgengine/wgcfg/wgcfg_clone.go
index 32e7e31e5..7b56729c4 100644
--- a/wgengine/wgcfg/wgcfg_clone.go
+++ b/wgengine/wgcfg/wgcfg_clone.go
@@ -20,12 +20,6 @@ func (src *Config) Clone() *Config {
 	dst := new(Config)
 	*dst = *src
 	dst.Addresses = append(src.Addresses[:0:0], src.Addresses...)
-	if src.Peers != nil {
-		dst.Peers = make([]Peer, len(src.Peers))
-		for i := range dst.Peers {
-			dst.Peers[i] = *src.Peers[i].Clone()
-		}
-	}
 	return dst
 }
 
@@ -33,34 +27,4 @@ func (src *Config) Clone() *Config {
 var _ConfigCloneNeedsRegeneration = Config(struct {
 	PrivateKey key.NodePrivate
 	Addresses  []netip.Prefix
-	Peers      []Peer
-}{})
-
-// Clone makes a deep copy of Peer.
-// The result aliases no memory with the original.
-func (src *Peer) Clone() *Peer {
-	if src == nil {
-		return nil
-	}
-	dst := new(Peer)
-	*dst = *src
-	dst.AllowedIPs = append(src.AllowedIPs[:0:0], src.AllowedIPs...)
-	if dst.V4MasqAddr != nil {
-		dst.V4MasqAddr = new(*src.V4MasqAddr)
-	}
-	if dst.V6MasqAddr != nil {
-		dst.V6MasqAddr = new(*src.V6MasqAddr)
-	}
-	return dst
-}
-
-// A compilation failure here means this code must be regenerated, with the command at the top of this file.
-var _PeerCloneNeedsRegeneration = Peer(struct {
-	PublicKey           key.NodePublic
-	DiscoKey            key.DiscoPublic
-	AllowedIPs          []netip.Prefix
-	V4MasqAddr          *netip.Addr
-	V6MasqAddr          *netip.Addr
-	IsJailed            bool
-	PersistentKeepalive uint16
 }{})