Merge pull request #1925 from fjl/p2p-dial-resolve

p2p: resolve incomplete dial targets

10 files changed, 444 insertions, 208 deletions

diff --git a/p2p/dial.go b/p2p/dial.go
index 0fd3a4cf5..c0e703d7d 100644
--- a/p2p/dial.go
+++ b/p2p/dial.go
@@ -36,6 +36,10 @@ const (
 	// Discovery lookups are throttled and can only run
 	// once every few seconds.
 	lookupInterval = 4 * time.Second
+
+	// Endpoint resolution is throttled with bounded backoff.
+	initialResolveDelay = 60 * time.Second
+	maxResolveDelay     = time.Hour
 )
 
 // dialstate schedules dials and discovery lookups.
@@ -46,19 +50,17 @@ type dialstate struct {
 	ntab        discoverTable
 
 	lookupRunning bool
-	bootstrapped  bool
-
-	dialing     map[discover.NodeID]connFlag
-	lookupBuf   []*discover.Node // current discovery lookup results
-	randomNodes []*discover.Node // filled from Table
-	static      map[discover.NodeID]*discover.Node
-	hist        *dialHistory
+	dialing       map[discover.NodeID]connFlag
+	lookupBuf     []*discover.Node // current discovery lookup results
+	randomNodes   []*discover.Node // filled from Table
+	static        map[discover.NodeID]*dialTask
+	hist          *dialHistory
 }
 
 type discoverTable interface {
 	Self() *discover.Node
 	Close()
-	Bootstrap([]*discover.Node)
+	Resolve(target discover.NodeID) *discover.Node
 	Lookup(target discover.NodeID) []*discover.Node
 	ReadRandomNodes([]*discover.Node) int
 }
@@ -76,21 +78,20 @@ type task interface {
 	Do(*Server)
 }
 
-// A dialTask is generated for each node that is dialed.
+// A dialTask is generated for each node that is dialed. Its
+// fields cannot be accessed while the task is running.
 type dialTask struct {
-	flags connFlag
-	dest  *discover.Node
+	flags        connFlag
+	dest         *discover.Node
+	lastResolved time.Time
+	resolveDelay time.Duration
 }
 
 // discoverTask runs discovery table operations.
 // Only one discoverTask is active at any time.
-//
-// If bootstrap is true, the task runs Table.Bootstrap,
-// otherwise it performs a random lookup and leaves the
-// results in the task.
+// discoverTask.Do performs a random lookup.
 type discoverTask struct {
-	bootstrap bool
-	results   []*discover.Node
+	results []*discover.Node
 }
 
 // A waitExpireTask is generated if there are no other tasks
@@ -103,26 +104,31 @@ func newDialState(static []*discover.Node, ntab discoverTable, maxdyn int) *dial
 	s := &dialstate{
 		maxDynDials: maxdyn,
 		ntab:        ntab,
-		static:      make(map[discover.NodeID]*discover.Node),
+		static:      make(map[discover.NodeID]*dialTask),
 		dialing:     make(map[discover.NodeID]connFlag),
 		randomNodes: make([]*discover.Node, maxdyn/2),
 		hist:        new(dialHistory),
 	}
 	for _, n := range static {
-		s.static[n.ID] = n
+		s.addStatic(n)
 	}
 	return s
 }
 
 func (s *dialstate) addStatic(n *discover.Node) {
-	s.static[n.ID] = n
+	// This overwites the task instead of updating an existing
+	// entry, giving users the opportunity to force a resolve operation.
+	s.static[n.ID] = &dialTask{flags: staticDialedConn, dest: n}
 }
 
 func (s *dialstate) newTasks(nRunning int, peers map[discover.NodeID]*Peer, now time.Time) []task {
 	var newtasks []task
+	isDialing := func(id discover.NodeID) bool {
+		_, found := s.dialing[id]
+		return found || peers[id] != nil || s.hist.contains(id)
+	}
 	addDial := func(flag connFlag, n *discover.Node) bool {
-		_, dialing := s.dialing[n.ID]
-		if dialing || peers[n.ID] != nil || s.hist.contains(n.ID) {
+		if isDialing(n.ID) {
 			return false
 		}
 		s.dialing[n.ID] = flag
@@ -147,14 +153,17 @@ func (s *dialstate) newTasks(nRunning int, peers map[discover.NodeID]*Peer, now
 	s.hist.expire(now)
 
 	// Create dials for static nodes if they are not connected.
-	for _, n := range s.static {
-		addDial(staticDialedConn, n)
+	for id, t := range s.static {
+		if !isDialing(id) {
+			s.dialing[id] = t.flags
+			newtasks = append(newtasks, t)
+		}
 	}
 
 	// Use random nodes from the table for half of the necessary
 	// dynamic dials.
 	randomCandidates := needDynDials / 2
-	if randomCandidates > 0 && s.bootstrapped {
+	if randomCandidates > 0 {
 		n := s.ntab.ReadRandomNodes(s.randomNodes)
 		for i := 0; i < randomCandidates && i < n; i++ {
 			if addDial(dynDialedConn, s.randomNodes[i]) {
@@ -171,12 +180,10 @@ func (s *dialstate) newTasks(nRunning int, peers map[discover.NodeID]*Peer, now
 		}
 	}
 	s.lookupBuf = s.lookupBuf[:copy(s.lookupBuf, s.lookupBuf[i:])]
-	// Launch a discovery lookup if more candidates are needed. The
-	// first discoverTask bootstraps the table and won't return any
-	// results.
+	// Launch a discovery lookup if more candidates are needed.
 	if len(s.lookupBuf) < needDynDials && !s.lookupRunning {
 		s.lookupRunning = true
-		newtasks = append(newtasks, &discoverTask{bootstrap: !s.bootstrapped})
+		newtasks = append(newtasks, &discoverTask{})
 	}
 
 	// Launch a timer to wait for the next node to expire if all
@@ -196,35 +203,79 @@ func (s *dialstate) taskDone(t task, now time.Time) {
 		s.hist.add(t.dest.ID, now.Add(dialHistoryExpiration))
 		delete(s.dialing, t.dest.ID)
 	case *discoverTask:
-		if t.bootstrap {
-			s.bootstrapped = true
-		}
 		s.lookupRunning = false
 		s.lookupBuf = append(s.lookupBuf, t.results...)
 	}
 }
 
 func (t *dialTask) Do(srv *Server) {
-	addr := &net.TCPAddr{IP: t.dest.IP, Port: int(t.dest.TCP)}
-	glog.V(logger.Debug).Infof("dialing %v\n", t.dest)
+	if t.dest.Incomplete() {
+		if !t.resolve(srv) {
+			return
+		}
+	}
+	success := t.dial(srv, t.dest)
+	// Try resolving the ID of static nodes if dialing failed.
+	if !success && t.flags&staticDialedConn != 0 {
+		if t.resolve(srv) {
+			t.dial(srv, t.dest)
+		}
+	}
+}
+
+// resolve attempts to find the current endpoint for the destination
+// using discovery.
+//
+// Resolve operations are throttled with backoff to avoid flooding the
+// discovery network with useless queries for nodes that don't exist.
+// The backoff delay resets when the node is found.
+func (t *dialTask) resolve(srv *Server) bool {
+	if srv.ntab == nil {
+		glog.V(logger.Debug).Infof("can't resolve node %x: discovery is disabled", t.dest.ID[:6])
+		return false
+	}
+	if t.resolveDelay == 0 {
+		t.resolveDelay = initialResolveDelay
+	}
+	if time.Since(t.lastResolved) < t.resolveDelay {
+		return false
+	}
+	resolved := srv.ntab.Resolve(t.dest.ID)
+	t.lastResolved = time.Now()
+	if resolved == nil {
+		t.resolveDelay *= 2
+		if t.resolveDelay > maxResolveDelay {
+			t.resolveDelay = maxResolveDelay
+		}
+		glog.V(logger.Debug).Infof("resolving node %x failed (new delay: %v)", t.dest.ID[:6], t.resolveDelay)
+		return false
+	}
+	// The node was found.
+	t.resolveDelay = initialResolveDelay
+	t.dest = resolved
+	glog.V(logger.Debug).Infof("resolved node %x: %v:%d", t.dest.ID[:6], t.dest.IP, t.dest.TCP)
+	return true
+}
+
+// dial performs the actual connection attempt.
+func (t *dialTask) dial(srv *Server, dest *discover.Node) bool {
+	addr := &net.TCPAddr{IP: dest.IP, Port: int(dest.TCP)}
+	glog.V(logger.Debug).Infof("dial tcp %v (%x)\n", addr, dest.ID[:6])
 	fd, err := srv.Dialer.Dial("tcp", addr.String())
 	if err != nil {
-		glog.V(logger.Detail).Infof("dial error: %v", err)
-		return
+		glog.V(logger.Detail).Infof("%v", err)
+		return false
 	}
 	mfd := newMeteredConn(fd, false)
-
-	srv.setupConn(mfd, t.flags, t.dest)
+	srv.setupConn(mfd, t.flags, dest)
+	return true
 }
+
 func (t *dialTask) String() string {
 	return fmt.Sprintf("%v %x %v:%d", t.flags, t.dest.ID[:8], t.dest.IP, t.dest.TCP)
 }
 
 func (t *discoverTask) Do(srv *Server) {
-	if t.bootstrap {
-		srv.ntab.Bootstrap(srv.BootstrapNodes)
-		return
-	}
 	// newTasks generates a lookup task whenever dynamic dials are
 	// necessary. Lookups need to take some time, otherwise the
 	// event loop spins too fast.
@@ -238,12 +289,8 @@ func (t *discoverTask) Do(srv *Server) {
 	t.results = srv.ntab.Lookup(target)
 }
 
-func (t *discoverTask) String() (s string) {
-	if t.bootstrap {
-		s = "discovery bootstrap"
-	} else {
-		s = "discovery lookup"
-	}
+func (t *discoverTask) String() string {
+	s := "discovery lookup"
 	if len(t.results) > 0 {
 		s += fmt.Sprintf(" (%d results)", len(t.results))
 	}
diff --git a/p2p/dial_test.go b/p2p/dial_test.go
index d24e03e29..3447660a3 100644
--- a/p2p/dial_test.go
+++ b/p2p/dial_test.go
@@ -18,6 +18,7 @@ package p2p
 
 import (
 	"encoding/binary"
+	"net"
 	"reflect"
 	"testing"
 	"time"
@@ -76,15 +77,11 @@ func runDialTest(t *testing.T, test dialtest) {
 
 type fakeTable []*discover.Node
 
-func (t fakeTable) Self() *discover.Node       { return new(discover.Node) }
-func (t fakeTable) Close()                     {}
-func (t fakeTable) Bootstrap([]*discover.Node) {}
-func (t fakeTable) Lookup(target discover.NodeID) []*discover.Node {
-	return nil
-}
-func (t fakeTable) ReadRandomNodes(buf []*discover.Node) int {
-	return copy(buf, t)
-}
+func (t fakeTable) Self() *discover.Node                     { return new(discover.Node) }
+func (t fakeTable) Close()                                   {}
+func (t fakeTable) Lookup(discover.NodeID) []*discover.Node  { return nil }
+func (t fakeTable) Resolve(discover.NodeID) *discover.Node   { return nil }
+func (t fakeTable) ReadRandomNodes(buf []*discover.Node) int { return copy(buf, t) }
 
 // This test checks that dynamic dials are launched from discovery results.
 func TestDialStateDynDial(t *testing.T) {
@@ -98,7 +95,7 @@ func TestDialStateDynDial(t *testing.T) {
 					{rw: &conn{flags: dynDialedConn, id: uintID(1)}},
 					{rw: &conn{flags: dynDialedConn, id: uintID(2)}},
 				},
-				new: []task{&discoverTask{bootstrap: true}},
+				new: []task{&discoverTask{}},
 			},
 			// Dynamic dials are launched when it completes.
 			{
@@ -108,7 +105,7 @@ func TestDialStateDynDial(t *testing.T) {
 					{rw: &conn{flags: dynDialedConn, id: uintID(2)}},
 				},
 				done: []task{
-					&discoverTask{bootstrap: true, results: []*discover.Node{
+					&discoverTask{results: []*discover.Node{
 						{ID: uintID(2)}, // this one is already connected and not dialed.
 						{ID: uintID(3)},
 						{ID: uintID(4)},
@@ -118,9 +115,9 @@ func TestDialStateDynDial(t *testing.T) {
 					}},
 				},
 				new: []task{
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(3)}},
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(4)}},
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(5)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(3)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(4)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(5)}},
 				},
 			},
 			// Some of the dials complete but no new ones are launched yet because
@@ -134,8 +131,8 @@ func TestDialStateDynDial(t *testing.T) {
 					{rw: &conn{flags: dynDialedConn, id: uintID(4)}},
 				},
 				done: []task{
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(3)}},
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(4)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(3)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(4)}},
 				},
 			},
 			// No new dial tasks are launched in the this round because
@@ -150,7 +147,7 @@ func TestDialStateDynDial(t *testing.T) {
 					{rw: &conn{flags: dynDialedConn, id: uintID(5)}},
 				},
 				done: []task{
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(5)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(5)}},
 				},
 				new: []task{
 					&waitExpireTask{Duration: 14 * time.Second},
@@ -167,7 +164,7 @@ func TestDialStateDynDial(t *testing.T) {
 					{rw: &conn{flags: dynDialedConn, id: uintID(5)}},
 				},
 				new: []task{
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(6)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(6)}},
 				},
 			},
 			// More peers (3,4) drop off and dial for ID 6 completes.
@@ -180,10 +177,10 @@ func TestDialStateDynDial(t *testing.T) {
 					{rw: &conn{flags: dynDialedConn, id: uintID(5)}},
 				},
 				done: []task{
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(6)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(6)}},
 				},
 				new: []task{
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(7)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(7)}},
 					&discoverTask{},
 				},
 			},
@@ -198,7 +195,7 @@ func TestDialStateDynDial(t *testing.T) {
 					{rw: &conn{flags: dynDialedConn, id: uintID(7)}},
 				},
 				done: []task{
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(7)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(7)}},
 				},
 			},
 			// Finish the running node discovery with an empty set. A new lookup
@@ -238,22 +235,15 @@ func TestDialStateDynDialFromTable(t *testing.T) {
 	runDialTest(t, dialtest{
 		init: newDialState(nil, table, 10),
 		rounds: []round{
-			// Discovery bootstrap is launched.
-			{
-				new: []task{&discoverTask{bootstrap: true}},
-			},
 			// 5 out of 8 of the nodes returned by ReadRandomNodes are dialed.
 			{
-				done: []task{
-					&discoverTask{bootstrap: true},
-				},
 				new: []task{
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(1)}},
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(2)}},
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(3)}},
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(4)}},
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(5)}},
-					&discoverTask{bootstrap: false},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(1)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(2)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(3)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(4)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(5)}},
+					&discoverTask{},
 				},
 			},
 			// Dialing nodes 1,2 succeeds. Dials from the lookup are launched.
@@ -263,8 +253,8 @@ func TestDialStateDynDialFromTable(t *testing.T) {
 					{rw: &conn{flags: dynDialedConn, id: uintID(2)}},
 				},
 				done: []task{
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(1)}},
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(2)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(1)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(2)}},
 					&discoverTask{results: []*discover.Node{
 						{ID: uintID(10)},
 						{ID: uintID(11)},
@@ -272,10 +262,10 @@ func TestDialStateDynDialFromTable(t *testing.T) {
 					}},
 				},
 				new: []task{
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(10)}},
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(11)}},
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(12)}},
-					&discoverTask{bootstrap: false},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(10)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(11)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(12)}},
+					&discoverTask{},
 				},
 			},
 			// Dialing nodes 3,4,5 fails. The dials from the lookup succeed.
@@ -288,12 +278,12 @@ func TestDialStateDynDialFromTable(t *testing.T) {
 					{rw: &conn{flags: dynDialedConn, id: uintID(12)}},
 				},
 				done: []task{
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(3)}},
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(4)}},
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(5)}},
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(10)}},
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(11)}},
-					&dialTask{dynDialedConn, &discover.Node{ID: uintID(12)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(3)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(4)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(5)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(10)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(11)}},
+					&dialTask{flags: dynDialedConn, dest: &discover.Node{ID: uintID(12)}},
 				},
 			},
 			// Waiting for expiry. No waitExpireTask is launched because the
@@ -344,9 +334,9 @@ func TestDialStateStaticDial(t *testing.T) {
 					{rw: &conn{flags: dynDialedConn, id: uintID(2)}},
 				},
 				new: []task{
-					&dialTask{staticDialedConn, &discover.Node{ID: uintID(3)}},
-					&dialTask{staticDialedConn, &discover.Node{ID: uintID(4)}},
-					&dialTask{staticDialedConn, &discover.Node{ID: uintID(5)}},
+					&dialTask{flags: staticDialedConn, dest: &discover.Node{ID: uintID(3)}},
+					&dialTask{flags: staticDialedConn, dest: &discover.Node{ID: uintID(4)}},
+					&dialTask{flags: staticDialedConn, dest: &discover.Node{ID: uintID(5)}},
 				},
 			},
 			// No new tasks are launched in this round because all static
@@ -358,7 +348,7 @@ func TestDialStateStaticDial(t *testing.T) {
 					{rw: &conn{flags: staticDialedConn, id: uintID(3)}},
 				},
 				done: []task{
-					&dialTask{staticDialedConn, &discover.Node{ID: uintID(3)}},
+					&dialTask{flags: staticDialedConn, dest: &discover.Node{ID: uintID(3)}},
 				},
 			},
 			// No new dial tasks are launched because all static
@@ -372,8 +362,8 @@ func TestDialStateStaticDial(t *testing.T) {
 					{rw: &conn{flags: staticDialedConn, id: uintID(5)}},
 				},
 				done: []task{
-					&dialTask{staticDialedConn, &discover.Node{ID: uintID(4)}},
-					&dialTask{staticDialedConn, &discover.Node{ID: uintID(5)}},
+					&dialTask{flags: staticDialedConn, dest: &discover.Node{ID: uintID(4)}},
+					&dialTask{flags: staticDialedConn, dest: &discover.Node{ID: uintID(5)}},
 				},
 				new: []task{
 					&waitExpireTask{Duration: 14 * time.Second},
@@ -398,8 +388,8 @@ func TestDialStateStaticDial(t *testing.T) {
 					{rw: &conn{flags: staticDialedConn, id: uintID(5)}},
 				},
 				new: []task{
-					&dialTask{staticDialedConn, &discover.Node{ID: uintID(2)}},
-					&dialTask{staticDialedConn, &discover.Node{ID: uintID(4)}},
+					&dialTask{flags: staticDialedConn, dest: &discover.Node{ID: uintID(2)}},
+					&dialTask{flags: staticDialedConn, dest: &discover.Node{ID: uintID(4)}},
 				},
 			},
 		},
@@ -422,9 +412,9 @@ func TestDialStateCache(t *testing.T) {
 			{
 				peers: nil,
 				new: []task{
-					&dialTask{staticDialedConn, &discover.Node{ID: uintID(1)}},
-					&dialTask{staticDialedConn, &discover.Node{ID: uintID(2)}},
-					&dialTask{staticDialedConn, &discover.Node{ID: uintID(3)}},
+					&dialTask{flags: staticDialedConn, dest: &discover.Node{ID: uintID(1)}},
+					&dialTask{flags: staticDialedConn, dest: &discover.Node{ID: uintID(2)}},
+					&dialTask{flags: staticDialedConn, dest: &discover.Node{ID: uintID(3)}},
 				},
 			},
 			// No new tasks are launched in this round because all static
@@ -435,8 +425,8 @@ func TestDialStateCache(t *testing.T) {
 					{rw: &conn{flags: staticDialedConn, id: uintID(2)}},
 				},
 				done: []task{
-					&dialTask{staticDialedConn, &discover.Node{ID: uintID(1)}},
-					&dialTask{staticDialedConn, &discover.Node{ID: uintID(2)}},
+					&dialTask{flags: staticDialedConn, dest: &discover.Node{ID: uintID(1)}},
+					&dialTask{flags: staticDialedConn, dest: &discover.Node{ID: uintID(2)}},
 				},
 			},
 			// A salvage task is launched to wait for node 3's history
@@ -447,7 +437,7 @@ func TestDialStateCache(t *testing.T) {
 					{rw: &conn{flags: dynDialedConn, id: uintID(2)}},
 				},
 				done: []task{
-					&dialTask{staticDialedConn, &discover.Node{ID: uintID(3)}},
+					&dialTask{flags: staticDialedConn, dest: &discover.Node{ID: uintID(3)}},
 				},
 				new: []task{
 					&waitExpireTask{Duration: 14 * time.Second},
@@ -467,13 +457,40 @@ func TestDialStateCache(t *testing.T) {
 					{rw: &conn{flags: dynDialedConn, id: uintID(2)}},
 				},
 				new: []task{
-					&dialTask{staticDialedConn, &discover.Node{ID: uintID(3)}},
+					&dialTask{flags: staticDialedConn, dest: &discover.Node{ID: uintID(3)}},
 				},
 			},
 		},
 	})
 }
 
+func TestDialResolve(t *testing.T) {
+	resolved := discover.NewNode(uintID(1), net.IP{127, 0, 55, 234}, 3333, 4444)
+	table := &resolveMock{answer: resolved}
+	state := newDialState(nil, table, 0)
+
+	// Check that the task is generated with an incomplete ID.
+	dest := discover.NewNode(uintID(1), nil, 0, 0)
+	state.addStatic(dest)
+	tasks := state.newTasks(0, nil, time.Time{})
+	if !reflect.DeepEqual(tasks, []task{&dialTask{flags: staticDialedConn, dest: dest}}) {
+		t.Fatalf("expected dial task, got %#v", tasks)
+	}
+
+	// Now run the task, it should resolve the ID once.
+	srv := &Server{ntab: table, Dialer: &net.Dialer{Deadline: time.Now().Add(-5 * time.Minute)}}
+	tasks[0].Do(srv)
+	if !reflect.DeepEqual(table.resolveCalls, []discover.NodeID{dest.ID}) {
+		t.Fatalf("wrong resolve calls, got %v", table.resolveCalls)
+	}
+
+	// Report it as done to the dialer, which should update the static node record.
+	state.taskDone(tasks[0], time.Now())
+	if state.static[uintID(1)].dest != resolved {
+		t.Fatalf("state.dest not updated")
+	}
+}
+
 // compares task lists but doesn't care about the order.
 func sametasks(a, b []task) bool {
 	if len(a) != len(b) {
@@ -496,3 +513,20 @@ func uintID(i uint32) discover.NodeID {
 	binary.BigEndian.PutUint32(id[:], i)
 	return id
 }
+
+// implements discoverTable for TestDialResolve
+type resolveMock struct {
+	resolveCalls []discover.NodeID
+	answer       *discover.Node
+}
+
+func (t *resolveMock) Resolve(id discover.NodeID) *discover.Node {
+	t.resolveCalls = append(t.resolveCalls, id)
+	return t.answer
+}
+
+func (t *resolveMock) Self() *discover.Node                     { return new(discover.Node) }
+func (t *resolveMock) Close()                                   {}
+func (t *resolveMock) Bootstrap([]*discover.Node)               {}
+func (t *resolveMock) Lookup(discover.NodeID) []*discover.Node  { return nil }
+func (t *resolveMock) ReadRandomNodes(buf []*discover.Node) int { return 0 }
diff --git a/p2p/discover/database_test.go b/p2p/discover/database_test.go
index 80c1a6ff2..5a729f02b 100644
--- a/p2p/discover/database_test.go
+++ b/p2p/discover/database_test.go
@@ -102,7 +102,7 @@ func TestNodeDBInt64(t *testing.T) {
 }
 
 func TestNodeDBFetchStore(t *testing.T) {
-	node := newNode(
+	node := NewNode(
 		MustHexID("0x1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
 		net.IP{192, 168, 0, 1},
 		30303,
@@ -165,7 +165,7 @@ var nodeDBSeedQueryNodes = []struct {
 	// This one should not be in the result set because its last
 	// pong time is too far in the past.
 	{
-		node: newNode(
+		node: NewNode(
 			MustHexID("0x84d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
 			net.IP{127, 0, 0, 3},
 			30303,
@@ -176,7 +176,7 @@ var nodeDBSeedQueryNodes = []struct {
 	// This one shouldn't be in in the result set because its
 	// nodeID is the local node's ID.
 	{
-		node: newNode(
+		node: NewNode(
 			MustHexID("0x57d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
 			net.IP{127, 0, 0, 3},
 			30303,
@@ -187,7 +187,7 @@ var nodeDBSeedQueryNodes = []struct {
 
 	// These should be in the result set.
 	{
-		node: newNode(
+		node: NewNode(
 			MustHexID("0x22d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
 			net.IP{127, 0, 0, 1},
 			30303,
@@ -196,7 +196,7 @@ var nodeDBSeedQueryNodes = []struct {
 		pong: time.Now().Add(-2 * time.Second),
 	},
 	{
-		node: newNode(
+		node: NewNode(
 			MustHexID("0x44d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
 			net.IP{127, 0, 0, 2},
 			30303,
@@ -205,7 +205,7 @@ var nodeDBSeedQueryNodes = []struct {
 		pong: time.Now().Add(-3 * time.Second),
 	},
 	{
-		node: newNode(
+		node: NewNode(
 			MustHexID("0xe2d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
 			net.IP{127, 0, 0, 3},
 			30303,
@@ -303,7 +303,7 @@ var nodeDBExpirationNodes = []struct {
 	exp  bool
 }{
 	{
-		node: newNode(
+		node: NewNode(
 			MustHexID("0x01d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
 			net.IP{127, 0, 0, 1},
 			30303,
@@ -312,7 +312,7 @@ var nodeDBExpirationNodes = []struct {
 		pong: time.Now().Add(-nodeDBNodeExpiration + time.Minute),
 		exp:  false,
 	}, {
-		node: newNode(
+		node: NewNode(
 			MustHexID("0x02d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
 			net.IP{127, 0, 0, 2},
 			30303,
diff --git a/p2p/discover/node.go b/p2p/discover/node.go
index dd19df3a2..c4a3b5011 100644
--- a/p2p/discover/node.go
+++ b/p2p/discover/node.go
@@ -26,6 +26,7 @@ import (
 	"math/rand"
 	"net"
 	"net/url"
+	"regexp"
 	"strconv"
 	"strings"
 
@@ -37,6 +38,7 @@ import (
 const nodeIDBits = 512
 
 // Node represents a host on the network.
+// The fields of Node may not be modified.
 type Node struct {
 	IP       net.IP // len 4 for IPv4 or 16 for IPv6
 	UDP, TCP uint16 // port numbers
@@ -54,7 +56,9 @@ type Node struct {
 	contested bool
 }
 
-func newNode(id NodeID, ip net.IP, udpPort, tcpPort uint16) *Node {
+// NewNode creates a new node. It is mostly meant to be used for
+// testing purposes.
+func NewNode(id NodeID, ip net.IP, udpPort, tcpPort uint16) *Node {
 	if ipv4 := ip.To4(); ipv4 != nil {
 		ip = ipv4
 	}
@@ -71,31 +75,65 @@ func (n *Node) addr() *net.UDPAddr {
 	return &net.UDPAddr{IP: n.IP, Port: int(n.UDP)}
 }
 
+// Incomplete returns true for nodes with no IP address.
+func (n *Node) Incomplete() bool {
+	return n.IP == nil
+}
+
+// checks whether n is a valid complete node.
+func (n *Node) validateComplete() error {
+	if n.Incomplete() {
+		return errors.New("incomplete node")
+	}
+	if n.UDP == 0 {
+		return errors.New("missing UDP port")
+	}
+	if n.TCP == 0 {
+		return errors.New("missing TCP port")
+	}
+	if n.IP.IsMulticast() || n.IP.IsUnspecified() {
+		return errors.New("invalid IP (multicast/unspecified)")
+	}
+	_, err := n.ID.Pubkey() // validate the key (on curve, etc.)
+	return err
+}
+
 // The string representation of a Node is a URL.
 // Please see ParseNode for a description of the format.
 func (n *Node) String() string {
-	addr := net.TCPAddr{IP: n.IP, Port: int(n.TCP)}
-	u := url.URL{
-		Scheme: "enode",
-		User:   url.User(fmt.Sprintf("%x", n.ID[:])),
-		Host:   addr.String(),
-	}
-	if n.UDP != n.TCP {
-		u.RawQuery = "discport=" + strconv.Itoa(int(n.UDP))
+	u := url.URL{Scheme: "enode"}
+	if n.Incomplete() {
+		u.Host = fmt.Sprintf("%x", n.ID[:])
+	} else {
+		addr := net.TCPAddr{IP: n.IP, Port: int(n.TCP)}
+		u.User = url.User(fmt.Sprintf("%x", n.ID[:]))
+		u.Host = addr.String()
+		if n.UDP != n.TCP {
+			u.RawQuery = "discport=" + strconv.Itoa(int(n.UDP))
+		}
 	}
 	return u.String()
 }
 
-// ParseNode parses a node URL.
+var incompleteNodeURL = regexp.MustCompile("(?i)^(?:enode://)?([0-9a-f]+)$")
+
+// ParseNode parses a node designator.
+//
+// There are two basic forms of node designators
+//   - incomplete nodes, which only have the public key (node ID)
+//   - complete nodes, which contain the public key and IP/Port information
+//
+// For incomplete nodes, the designator must look like one of these
 //
-// A node URL has scheme "enode".
+//    enode://<hex node id>
+//    <hex node id>
 //
-// The hexadecimal node ID is encoded in the username portion of the
-// URL, separated from the host by an @ sign. The hostname can only be
-// given as an IP address, DNS domain names are not allowed. The port
-// in the host name section is the TCP listening port. If the TCP and
-// UDP (discovery) ports differ, the UDP port is specified as query
-// parameter "discport".
+// For complete nodes, the node ID is encoded in the username portion
+// of the URL, separated from the host by an @ sign. The hostname can
+// only be given as an IP address, DNS domain names are not allowed.
+// The port in the host name section is the TCP listening port. If the
+// TCP and UDP (discovery) ports differ, the UDP port is specified as
+// query parameter "discport".
 //
 // In the following example, the node URL describes
 // a node with IP address 10.3.58.6, TCP listening port 30303
@@ -103,12 +141,26 @@ func (n *Node) String() string {
 //
 //    enode://<hex node id>@10.3.58.6:30303?discport=30301
 func ParseNode(rawurl string) (*Node, error) {
+	if m := incompleteNodeURL.FindStringSubmatch(rawurl); m != nil {
+		id, err := HexID(m[1])
+		if err != nil {
+			return nil, fmt.Errorf("invalid node ID (%v)", err)
+		}
+		return NewNode(id, nil, 0, 0), nil
+	}
+	return parseComplete(rawurl)
+}
+
+func parseComplete(rawurl string) (*Node, error) {
 	var (
 		id               NodeID
 		ip               net.IP
 		tcpPort, udpPort uint64
 	)
 	u, err := url.Parse(rawurl)
+	if err != nil {
+		return nil, err
+	}
 	if u.Scheme != "enode" {
 		return nil, errors.New("invalid URL scheme, want \"enode\"")
 	}
@@ -143,7 +195,7 @@ func ParseNode(rawurl string) (*Node, error) {
 			return nil, errors.New("invalid discport in query")
 		}
 	}
-	return newNode(id, ip, uint16(udpPort), uint16(tcpPort)), nil
+	return NewNode(id, ip, uint16(udpPort), uint16(tcpPort)), nil
 }
 
 // MustParseNode parses a node URL. It panics if the URL is not valid.
@@ -180,7 +232,7 @@ func HexID(in string) (NodeID, error) {
 	if err != nil {
 		return id, err
 	} else if len(b) != len(id) {
-		return id, fmt.Errorf("wrong length, need %d hex bytes", len(id))
+		return id, fmt.Errorf("wrong length, want %d hex chars", len(id)*2)
 	}
 	copy(id[:], b)
 	return id, nil
@@ -215,7 +267,7 @@ func (id NodeID) Pubkey() (*ecdsa.PublicKey, error) {
 	p.X.SetBytes(id[:half])
 	p.Y.SetBytes(id[half:])
 	if !p.Curve.IsOnCurve(p.X, p.Y) {
-		return nil, errors.New("not a point on the S256 curve")
+		return nil, errors.New("id is invalid secp256k1 curve point")
 	}
 	return p, nil
 }
diff --git a/p2p/discover/node_test.go b/p2p/discover/node_test.go
index e523e12d2..3d1662d0b 100644
--- a/p2p/discover/node_test.go
+++ b/p2p/discover/node_test.go
@@ -17,10 +17,12 @@
 package discover
 
 import (
+	"fmt"
 	"math/big"
 	"math/rand"
 	"net"
 	"reflect"
+	"strings"
 	"testing"
 	"testing/quick"
 	"time"
@@ -29,6 +31,27 @@ import (
 	"github.com/ethereum/go-ethereum/crypto"
 )
 
+func ExampleNewNode() {
+	id := MustHexID("1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439")
+
+	// Complete nodes contain UDP and TCP endpoints:
+	n1 := NewNode(id, net.ParseIP("2001:db8:3c4d:15::abcd:ef12"), 52150, 30303)
+	fmt.Println("n1:", n1)
+	fmt.Println("n1.Incomplete() ->", n1.Incomplete())
+
+	// An incomplete node can be created by passing zero values
+	// for all parameters except id.
+	n2 := NewNode(id, nil, 0, 0)
+	fmt.Println("n2:", n2)
+	fmt.Println("n2.Incomplete() ->", n2.Incomplete())
+
+	// Output:
+	// n1: enode://1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439@[2001:db8:3c4d:15::abcd:ef12]:30303?discport=52150
+	// n1.Incomplete() -> false
+	// n2: enode://1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439
+	// n2.Incomplete() -> true
+}
+
 var parseNodeTests = []struct {
 	rawurl     string
 	wantError  string
@@ -39,13 +62,10 @@ var parseNodeTests = []struct {
 		wantError: `invalid URL scheme, want "enode"`,
 	},
 	{
-		rawurl:    "enode://foobar",
-		wantError: `does not contain node ID`,
-	},
-	{
 		rawurl:    "enode://01010101@123.124.125.126:3",
-		wantError: `invalid node ID (wrong length, need 64 hex bytes)`,
+		wantError: `invalid node ID (wrong length, want 128 hex chars)`,
 	},
+	// Complete nodes with IP address.
 	{
 		rawurl:    "enode://1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439@hostname:3",
 		wantError: `invalid IP address`,
@@ -60,7 +80,7 @@ var parseNodeTests = []struct {
 	},
 	{
 		rawurl: "enode://1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439@127.0.0.1:52150",
-		wantResult: newNode(
+		wantResult: NewNode(
 			MustHexID("0x1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
 			net.IP{0x7f, 0x0, 0x0, 0x1},
 			52150,
@@ -69,7 +89,7 @@ var parseNodeTests = []struct {
 	},
 	{
 		rawurl: "enode://1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439@[::]:52150",
-		wantResult: newNode(
+		wantResult: NewNode(
 			MustHexID("0x1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
 			net.ParseIP("::"),
 			52150,
@@ -78,7 +98,7 @@ var parseNodeTests = []struct {
 	},
 	{
 		rawurl: "enode://1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439@[2001:db8:3c4d:15::abcd:ef12]:52150",
-		wantResult: newNode(
+		wantResult: NewNode(
 			MustHexID("0x1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
 			net.ParseIP("2001:db8:3c4d:15::abcd:ef12"),
 			52150,
@@ -87,33 +107,62 @@ var parseNodeTests = []struct {
 	},
 	{
 		rawurl: "enode://1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439@127.0.0.1:52150?discport=22334",
-		wantResult: newNode(
+		wantResult: NewNode(
 			MustHexID("0x1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
 			net.IP{0x7f, 0x0, 0x0, 0x1},
 			22334,
 			52150,
 		),
 	},
+	// Incomplete nodes with no address.
+	{
+		rawurl: "1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439",
+		wantResult: NewNode(
+			MustHexID("0x1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
+			nil, 0, 0,
+		),
+	},
+	{
+		rawurl: "enode://1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439",
+		wantResult: NewNode(
+			MustHexID("0x1dd9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
+			nil, 0, 0,
+		),
+	},
+	// Invalid URLs
+	{
+		rawurl:    "01010101",
+		wantError: `invalid node ID (wrong length, want 128 hex chars)`,
+	},
+	{
+		rawurl:    "enode://01010101",
+		wantError: `invalid node ID (wrong length, want 128 hex chars)`,
+	},
+	{
+		// This test checks that errors from url.Parse are handled.
+		rawurl:    "://foo",
+		wantError: `parse ://foo: missing protocol scheme`,
+	},
 }
 
 func TestParseNode(t *testing.T) {
-	for i, test := range parseNodeTests {
+	for _, test := range parseNodeTests {
 		n, err := ParseNode(test.rawurl)
 		if test.wantError != "" {
 			if err == nil {
-				t.Errorf("test %d: got nil error, expected %#q", i, test.wantError)
+				t.Errorf("test %q:\n  got nil error, expected %#q", test.rawurl, test.wantError)
 				continue
 			} else if err.Error() != test.wantError {
-				t.Errorf("test %d: got error %#q, expected %#q", i, err.Error(), test.wantError)
+				t.Errorf("test %q:\n  got error %#q, expected %#q", test.rawurl, err.Error(), test.wantError)
 				continue
 			}
 		} else {
 			if err != nil {
-				t.Errorf("test %d: unexpected error: %v", i, err)
+				t.Errorf("test %q:\n  unexpected error: %v", test.rawurl, err)
 				continue
 			}
 			if !reflect.DeepEqual(n, test.wantResult) {
-				t.Errorf("test %d: result mismatch:\ngot:  %#v, want: %#v", i, n, test.wantResult)
+				t.Errorf("test %q:\n  result mismatch:\ngot:  %#v, want: %#v", test.rawurl, n, test.wantResult)
 			}
 		}
 	}
@@ -121,12 +170,11 @@ func TestParseNode(t *testing.T) {
 
 func TestNodeString(t *testing.T) {
 	for i, test := range parseNodeTests {
-		if test.wantError != "" {
-			continue
-		}
-		str := test.wantResult.String()
-		if str != test.rawurl {
-			t.Errorf("test %d: Node.String() mismatch:\ngot:  %s\nwant: %s", i, str, test.rawurl)
+		if test.wantError == "" && strings.HasPrefix(test.rawurl, "enode://") {
+			str := test.wantResult.String()
+			if str != test.rawurl {
+				t.Errorf("test %d: Node.String() mismatch:\ngot:  %s\nwant: %s", i, str, test.rawurl)
+			}
 		}
 	}
 }
diff --git a/p2p/discover/table.go b/p2p/discover/table.go
index 298ba3fa6..abb7980f8 100644
--- a/p2p/discover/table.go
+++ b/p2p/discover/table.go
@@ -25,6 +25,7 @@ package discover
 import (
 	"crypto/rand"
 	"encoding/binary"
+	"fmt"
 	"net"
 	"sort"
 	"sync"
@@ -56,7 +57,7 @@ type Table struct {
 	nursery []*Node           // bootstrap nodes
 	db      *nodeDB           // database of known nodes
 
-	refreshReq chan struct{}
+	refreshReq chan chan struct{}
 	closeReq   chan struct{}
 	closed     chan struct{}
 
@@ -99,10 +100,10 @@ func newTable(t transport, ourID NodeID, ourAddr *net.UDPAddr, nodeDBPath string
 	tab := &Table{
 		net:        t,
 		db:         db,
-		self:       newNode(ourID, ourAddr.IP, uint16(ourAddr.Port), uint16(ourAddr.Port)),
+		self:       NewNode(ourID, ourAddr.IP, uint16(ourAddr.Port), uint16(ourAddr.Port)),
 		bonding:    make(map[NodeID]*bondproc),
 		bondslots:  make(chan struct{}, maxBondingPingPongs),
-		refreshReq: make(chan struct{}),
+		refreshReq: make(chan chan struct{}),
 		closeReq:   make(chan struct{}),
 		closed:     make(chan struct{}),
 	}
@@ -179,21 +180,49 @@ func (tab *Table) Close() {
 	}
 }
 
-// Bootstrap sets the bootstrap nodes. These nodes are used to connect
-// to the network if the table is empty. Bootstrap will also attempt to
-// fill the table by performing random lookup operations on the
-// network.
-func (tab *Table) Bootstrap(nodes []*Node) {
+// SetFallbackNodes sets the initial points of contact. These nodes
+// are used to connect to the network if the table is empty and there
+// are no known nodes in the database.
+func (tab *Table) SetFallbackNodes(nodes []*Node) error {
+	for _, n := range nodes {
+		if err := n.validateComplete(); err != nil {
+			return fmt.Errorf("bad bootstrap/fallback node %q (%v)", n, err)
+		}
+	}
 	tab.mutex.Lock()
-	// TODO: maybe filter nodes with bad fields (nil, etc.) to avoid strange crashes
 	tab.nursery = make([]*Node, 0, len(nodes))
 	for _, n := range nodes {
 		cpy := *n
+		// Recompute cpy.sha because the node might not have been
+		// created by NewNode or ParseNode.
 		cpy.sha = crypto.Sha3Hash(n.ID[:])
 		tab.nursery = append(tab.nursery, &cpy)
 	}
 	tab.mutex.Unlock()
-	tab.requestRefresh()
+	tab.refresh()
+	return nil
+}
+
+// Resolve searches for a specific node with the given ID.
+// It returns nil if the node could not be found.
+func (tab *Table) Resolve(targetID NodeID) *Node {
+	// If the node is present in the local table, no
+	// network interaction is required.
+	hash := crypto.Sha3Hash(targetID[:])
+	tab.mutex.Lock()
+	cl := tab.closest(hash, 1)
+	tab.mutex.Unlock()
+	if len(cl.entries) > 0 && cl.entries[0].ID == targetID {
+		return cl.entries[0]
+	}
+	// Otherwise, do a network lookup.
+	result := tab.Lookup(targetID)
+	for _, n := range result {
+		if n.ID == targetID {
+			return n
+		}
+	}
+	return nil
 }
 
 // Lookup performs a network search for nodes close
@@ -202,26 +231,36 @@ func (tab *Table) Bootstrap(nodes []*Node) {
 // The given target does not need to be an actual node
 // identifier.
 func (tab *Table) Lookup(targetID NodeID) []*Node {
+	return tab.lookup(targetID, true)
+}
+
+func (tab *Table) lookup(targetID NodeID, refreshIfEmpty bool) []*Node {
 	var (
 		target         = crypto.Sha3Hash(targetID[:])
 		asked          = make(map[NodeID]bool)
 		seen           = make(map[NodeID]bool)
 		reply          = make(chan []*Node, alpha)
 		pendingQueries = 0
+		result         *nodesByDistance
 	)
 	// don't query further if we hit ourself.
 	// unlikely to happen often in practice.
 	asked[tab.self.ID] = true
 
-	tab.mutex.Lock()
-	// generate initial result set
-	result := tab.closest(target, bucketSize)
-	tab.mutex.Unlock()
-
-	// If the result set is empty, all nodes were dropped, refresh.
-	if len(result.entries) == 0 {
-		tab.requestRefresh()
-		return nil
+	for {
+		tab.mutex.Lock()
+		// generate initial result set
+		result = tab.closest(target, bucketSize)
+		tab.mutex.Unlock()
+		if len(result.entries) > 0 || !refreshIfEmpty {
+			break
+		}
+		// The result set is empty, all nodes were dropped, refresh.
+		// We actually wait for the refresh to complete here. The very
+		// first query will hit this case and run the bootstrapping
+		// logic.
+		<-tab.refresh()
+		refreshIfEmpty = false
 	}
 
 	for {
@@ -265,24 +304,24 @@ func (tab *Table) Lookup(targetID NodeID) []*Node {
 	return result.entries
 }
 
-func (tab *Table) requestRefresh() {
+func (tab *Table) refresh() <-chan struct{} {
+	done := make(chan struct{})
 	select {
-	case tab.refreshReq <- struct{}{}:
+	case tab.refreshReq <- done:
 	case <-tab.closed:
+		close(done)
 	}
+	return done
 }
 
+// refreshLoop schedules doRefresh runs and coordinates shutdown.
 func (tab *Table) refreshLoop() {
-	defer func() {
-		tab.db.close()
-		if tab.net != nil {
-			tab.net.close()
-		}
-		close(tab.closed)
-	}()
-
-	timer := time.NewTicker(autoRefreshInterval)
-	var done chan struct{}
+	var (
+		timer   = time.NewTicker(autoRefreshInterval)
+		waiting []chan struct{} // accumulates waiting callers while doRefresh runs
+		done    chan struct{}   // where doRefresh reports completion
+	)
+loop:
 	for {
 		select {
 		case <-timer.C:
@@ -290,20 +329,34 @@ func (tab *Table) refreshLoop() {
 				done = make(chan struct{})
 				go tab.doRefresh(done)
 			}
-		case <-tab.refreshReq:
+		case req := <-tab.refreshReq:
+			waiting = append(waiting, req)
 			if done == nil {
 				done = make(chan struct{})
 				go tab.doRefresh(done)
 			}
 		case <-done:
+			for _, ch := range waiting {
+				close(ch)
+			}
+			waiting = nil
 			done = nil
 		case <-tab.closeReq:
-			if done != nil {
-				<-done
-			}
-			return
+			break loop
 		}
 	}
+
+	if tab.net != nil {
+		tab.net.close()
+	}
+	if done != nil {
+		<-done
+	}
+	for _, ch := range waiting {
+		close(ch)
+	}
+	tab.db.close()
+	close(tab.closed)
 }
 
 // doRefresh performs a lookup for a random target to keep buckets
@@ -320,7 +373,7 @@ func (tab *Table) doRefresh(done chan struct{}) {
 	// We perform a lookup with a random target instead.
 	var target NodeID
 	rand.Read(target[:])
-	result := tab.Lookup(target)
+	result := tab.lookup(target, false)
 	if len(result) > 0 {
 		return
 	}
@@ -344,7 +397,7 @@ func (tab *Table) doRefresh(done chan struct{}) {
 	tab.mutex.Unlock()
 
 	// Finally, do a self lookup to fill up the buckets.
-	tab.Lookup(tab.self.ID)
+	tab.lookup(tab.self.ID, false)
 }
 
 // closest returns the n nodes in the table that are closest to the
@@ -466,7 +519,7 @@ func (tab *Table) pingpong(w *bondproc, pinged bool, id NodeID, addr *net.UDPAdd
 		tab.net.waitping(id)
 	}
 	// Bonding succeeded, update the node database.
-	w.n = newNode(id, addr.IP, uint16(addr.Port), tcpPort)
+	w.n = NewNode(id, addr.IP, uint16(addr.Port), tcpPort)
 	tab.db.updateNode(w.n)
 	close(w.done)
 }
diff --git a/p2p/discover/table_test.go b/p2p/discover/table_test.go
index 13effaed6..30a418f44 100644
--- a/p2p/discover/table_test.go
+++ b/p2p/discover/table_test.go
@@ -36,7 +36,7 @@ func TestTable_pingReplace(t *testing.T) {
 		transport := newPingRecorder()
 		tab, _ := newTable(transport, NodeID{}, &net.UDPAddr{}, "")
 		defer tab.Close()
-		pingSender := newNode(MustHexID("a502af0f59b2aab7746995408c79e9ca312d2793cc997e44fc55eda62f0150bbb8c59a6f9269ba3a081518b62699ee807c7c19c20125ddfccca872608af9e370"), net.IP{}, 99, 99)
+		pingSender := NewNode(MustHexID("a502af0f59b2aab7746995408c79e9ca312d2793cc997e44fc55eda62f0150bbb8c59a6f9269ba3a081518b62699ee807c7c19c20125ddfccca872608af9e370"), net.IP{}, 99, 99)
 
 		// fill up the sender's bucket.
 		last := fillBucket(tab, 253)
@@ -287,7 +287,7 @@ func TestTable_Lookup(t *testing.T) {
 		t.Fatalf("lookup on empty table returned %d results: %#v", len(results), results)
 	}
 	// seed table with initial node (otherwise lookup will terminate immediately)
-	seed := newNode(lookupTestnet.dists[256][0], net.IP{}, 256, 0)
+	seed := NewNode(lookupTestnet.dists[256][0], net.IP{}, 256, 0)
 	tab.stuff([]*Node{seed})
 
 	results := tab.Lookup(lookupTestnet.target)
@@ -517,7 +517,7 @@ func (tn *preminedTestnet) findnode(toid NodeID, toaddr *net.UDPAddr, target Nod
 	next := uint16(toaddr.Port) - 1
 	var result []*Node
 	for i, id := range tn.dists[toaddr.Port] {
-		result = append(result, newNode(id, net.ParseIP("127.0.0.1"), next, uint16(i)))
+		result = append(result, NewNode(id, net.ParseIP("127.0.0.1"), next, uint16(i)))
 	}
 	return result, nil
 }
diff --git a/p2p/discover/udp.go b/p2p/discover/udp.go
index fc7fa737c..72b2a45e5 100644
--- a/p2p/discover/udp.go
+++ b/p2p/discover/udp.go
@@ -114,13 +114,11 @@ func makeEndpoint(addr *net.UDPAddr, tcpPort uint16) rpcEndpoint {
 	return rpcEndpoint{IP: ip, UDP: uint16(addr.Port), TCP: tcpPort}
 }
 
-func nodeFromRPC(rn rpcNode) (n *Node, valid bool) {
+func nodeFromRPC(rn rpcNode) (*Node, error) {
 	// TODO: don't accept localhost, LAN addresses from internet hosts
-	// TODO: check public key is on secp256k1 curve
-	if rn.IP.IsMulticast() || rn.IP.IsUnspecified() || rn.UDP == 0 {
-		return nil, false
-	}
-	return newNode(rn.ID, rn.IP, rn.UDP, rn.TCP), true
+	n := NewNode(rn.ID, rn.IP, rn.UDP, rn.TCP)
+	err := n.validateComplete()
+	return n, err
 }
 
 func nodeToRPC(n *Node) rpcNode {
@@ -271,7 +269,7 @@ func (t *udp) findnode(toid NodeID, toaddr *net.UDPAddr, target NodeID) ([]*Node
 		reply := r.(*neighbors)
 		for _, rn := range reply.Nodes {
 			nreceived++
-			if n, valid := nodeFromRPC(rn); valid {
+			if n, err := nodeFromRPC(rn); err == nil {
 				nodes = append(nodes, n)
 			}
 		}
diff --git a/p2p/discover/udp_test.go b/p2p/discover/udp_test.go
index 944e73d6e..8ed12b8ec 100644
--- a/p2p/discover/udp_test.go
+++ b/p2p/discover/udp_test.go
@@ -167,16 +167,17 @@ func TestUDP_responseTimeouts(t *testing.T) {
 		binary.BigEndian.PutUint64(p.from[:], uint64(i))
 		if p.ptype <= 128 {
 			p.errc = timeoutErr
+			test.udp.addpending <- p
 			nTimeouts++
 		} else {
 			p.errc = nilErr
+			test.udp.addpending <- p
 			time.AfterFunc(randomDuration(60*time.Millisecond), func() {
 				if !test.udp.handleReply(p.from, p.ptype, nil) {
 					t.Logf("not matched: %v", p)
 				}
 			})
 		}
-		test.udp.addpending <- p
 		time.Sleep(randomDuration(30 * time.Millisecond))
 	}
 
@@ -243,7 +244,7 @@ func TestUDP_findnode(t *testing.T) {
 
 	// ensure there's a bond with the test node,
 	// findnode won't be accepted otherwise.
-	test.table.db.updateNode(newNode(
+	test.table.db.updateNode(NewNode(
 		PubkeyID(&test.remotekey.PublicKey),
 		test.remoteaddr.IP,
 		uint16(test.remoteaddr.Port),
diff --git a/p2p/server.go b/p2p/server.go
index 7991585f1..52d1be677 100644
--- a/p2p/server.go
+++ b/p2p/server.go
@@ -334,6 +334,9 @@ func (srv *Server) Start() (err error) {
 		if err != nil {
 			return err
 		}
+		if err := ntab.SetFallbackNodes(srv.BootstrapNodes); err != nil {
+			return err
+		}
 		srv.ntab = ntab
 	}