Merge pull request #1859 from fjl/fix-discover-refresh-race

p2p/discover: fix race involving the seed node iterator

6 files changed, 199 insertions, 183 deletions

diff --git a/p2p/discover/database.go b/p2p/discover/database.go
index d5c594364..e8e3371ff 100644
--- a/p2p/discover/database.go
+++ b/p2p/discover/database.go
@@ -21,6 +21,7 @@ package discover
 
 import (
 	"bytes"
+	"crypto/rand"
 	"encoding/binary"
 	"os"
 	"sync"
@@ -46,11 +47,8 @@ var (
 
 // nodeDB stores all nodes we know about.
 type nodeDB struct {
-	lvl    *leveldb.DB       // Interface to the database itself
-	seeder iterator.Iterator // Iterator for fetching possible seed nodes
-
-	self NodeID // Own node id to prevent adding it into the database
-
+	lvl    *leveldb.DB   // Interface to the database itself
+	self   NodeID        // Own node id to prevent adding it into the database
 	runner sync.Once     // Ensures we can start at most one expirer
 	quit   chan struct{} // Channel to signal the expiring thread to stop
 }
@@ -302,52 +300,70 @@ func (db *nodeDB) updateFindFails(id NodeID, fails int) error {
 	return db.storeInt64(makeKey(id, nodeDBDiscoverFindFails), int64(fails))
 }
 
-// querySeeds retrieves a batch of nodes to be used as potential seed servers
-// during bootstrapping the node into the network.
-//
-// Ideal seeds are the most recently seen nodes (highest probability to be still
-// alive), but yet untried. However, since leveldb only supports dumb iteration
-// we will instead start pulling in potential seeds that haven't been yet pinged
-// since the start of the boot procedure.
-//
-// If the database runs out of potential seeds, we restart the startup counter
-// and start iterating over the peers again.
-func (db *nodeDB) querySeeds(n int) []*Node {
-	// Create a new seed iterator if none exists
-	if db.seeder == nil {
-		db.seeder = db.lvl.NewIterator(nil, nil)
+// querySeeds retrieves random nodes to be used as potential seed nodes
+// for bootstrapping.
+func (db *nodeDB) querySeeds(n int, maxAge time.Duration) []*Node {
+	var (
+		now   = time.Now()
+		nodes = make([]*Node, 0, n)
+		it    = db.lvl.NewIterator(nil, nil)
+		id    NodeID
+	)
+	defer it.Release()
+
+seek:
+	for seeks := 0; len(nodes) < n && seeks < n*5; seeks++ {
+		// Seek to a random entry. The first byte is incremented by a
+		// random amount each time in order to increase the likelihood
+		// of hitting all existing nodes in very small databases.
+		ctr := id[0]
+		rand.Read(id[:])
+		id[0] = ctr + id[0]%16
+		it.Seek(makeKey(id, nodeDBDiscoverRoot))
+
+		n := nextNode(it)
+		if n == nil {
+			id[0] = 0
+			continue seek // iterator exhausted
+		}
+		if n.ID == db.self {
+			continue seek
+		}
+		if now.Sub(db.lastPong(n.ID)) > maxAge {
+			continue seek
+		}
+		for i := range nodes {
+			if nodes[i].ID == n.ID {
+				continue seek // duplicate
+			}
+		}
+		nodes = append(nodes, n)
 	}
-	// Iterate over the nodes and find suitable seeds
-	nodes := make([]*Node, 0, n)
-	for len(nodes) < n && db.seeder.Next() {
-		// Iterate until a discovery node is found
-		id, field := splitKey(db.seeder.Key())
+	return nodes
+}
+
+// reads the next node record from the iterator, skipping over other
+// database entries.
+func nextNode(it iterator.Iterator) *Node {
+	for end := false; !end; end = !it.Next() {
+		id, field := splitKey(it.Key())
 		if field != nodeDBDiscoverRoot {
 			continue
 		}
-		// Dump it if its a self reference
-		if bytes.Compare(id[:], db.self[:]) == 0 {
-			db.deleteNode(id)
+		var n Node
+		if err := rlp.DecodeBytes(it.Value(), &n); err != nil {
+			if glog.V(logger.Warn) {
+				glog.Errorf("invalid node %x: %v", id, err)
+			}
 			continue
 		}
-		// Load it as a potential seed
-		if node := db.node(id); node != nil {
-			nodes = append(nodes, node)
-		}
-	}
-	// Release the iterator if we reached the end
-	if len(nodes) == 0 {
-		db.seeder.Release()
-		db.seeder = nil
+		return &n
 	}
-	return nodes
+	return nil
 }
 
 // close flushes and closes the database files.
 func (db *nodeDB) close() {
-	if db.seeder != nil {
-		db.seeder.Release()
-	}
 	close(db.quit)
 	db.lvl.Close()
 }
diff --git a/p2p/discover/database_test.go b/p2p/discover/database_test.go
index 569585903..80c1a6ff2 100644
--- a/p2p/discover/database_test.go
+++ b/p2p/discover/database_test.go
@@ -162,9 +162,33 @@ var nodeDBSeedQueryNodes = []struct {
 	node *Node
 	pong time.Time
 }{
+	// This one should not be in the result set because its last
+	// pong time is too far in the past.
 	{
 		node: newNode(
-			MustHexID("0x01d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
+			MustHexID("0x84d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
+			net.IP{127, 0, 0, 3},
+			30303,
+			30303,
+		),
+		pong: time.Now().Add(-3 * time.Hour),
+	},
+	// This one shouldn't be in in the result set because its
+	// nodeID is the local node's ID.
+	{
+		node: newNode(
+			MustHexID("0x57d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
+			net.IP{127, 0, 0, 3},
+			30303,
+			30303,
+		),
+		pong: time.Now().Add(-4 * time.Second),
+	},
+
+	// These should be in the result set.
+	{
+		node: newNode(
+			MustHexID("0x22d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
 			net.IP{127, 0, 0, 1},
 			30303,
 			30303,
@@ -173,7 +197,7 @@ var nodeDBSeedQueryNodes = []struct {
 	},
 	{
 		node: newNode(
-			MustHexID("0x02d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
+			MustHexID("0x44d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
 			net.IP{127, 0, 0, 2},
 			30303,
 			30303,
@@ -182,7 +206,7 @@ var nodeDBSeedQueryNodes = []struct {
 	},
 	{
 		node: newNode(
-			MustHexID("0x03d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
+			MustHexID("0xe2d9d65c4552b5eb43d5ad55a2ee3f56c6cbc1c64a5c8d659f51fcd51bace24351232b8d7821617d2b29b54b81cdefb9b3e9c37d7fd5f63270bcc9e1a6f6a439"),
 			net.IP{127, 0, 0, 3},
 			30303,
 			30303,
@@ -192,7 +216,7 @@ var nodeDBSeedQueryNodes = []struct {
 }
 
 func TestNodeDBSeedQuery(t *testing.T) {
-	db, _ := newNodeDB("", Version, NodeID{})
+	db, _ := newNodeDB("", Version, nodeDBSeedQueryNodes[1].node.ID)
 	defer db.close()
 
 	// Insert a batch of nodes for querying
@@ -200,20 +224,24 @@ func TestNodeDBSeedQuery(t *testing.T) {
 		if err := db.updateNode(seed.node); err != nil {
 			t.Fatalf("node %d: failed to insert: %v", i, err)
 		}
+		if err := db.updateLastPong(seed.node.ID, seed.pong); err != nil {
+			t.Fatalf("node %d: failed to insert lastPong: %v", i, err)
+		}
 	}
+
 	// Retrieve the entire batch and check for duplicates
-	seeds := db.querySeeds(2 * len(nodeDBSeedQueryNodes))
-	if len(seeds) != len(nodeDBSeedQueryNodes) {
-		t.Errorf("seed count mismatch: have %v, want %v", len(seeds), len(nodeDBSeedQueryNodes))
-	}
+	seeds := db.querySeeds(len(nodeDBSeedQueryNodes)*2, time.Hour)
 	have := make(map[NodeID]struct{})
 	for _, seed := range seeds {
 		have[seed.ID] = struct{}{}
 	}
 	want := make(map[NodeID]struct{})
-	for _, seed := range nodeDBSeedQueryNodes {
+	for _, seed := range nodeDBSeedQueryNodes[2:] {
 		want[seed.node.ID] = struct{}{}
 	}
+	if len(seeds) != len(want) {
+		t.Errorf("seed count mismatch: have %v, want %v", len(seeds), len(want))
+	}
 	for id, _ := range have {
 		if _, ok := want[id]; !ok {
 			t.Errorf("extra seed: %v", id)
@@ -224,63 +252,6 @@ func TestNodeDBSeedQuery(t *testing.T) {
 			t.Errorf("missing seed: %v", id)
 		}
 	}
-	// Make sure the next batch is empty (seed EOF)
-	seeds = db.querySeeds(2 * len(nodeDBSeedQueryNodes))
-	if len(seeds) != 0 {
-		t.Errorf("seed count mismatch: have %v, want %v", len(seeds), 0)
-	}
-}
-
-func TestNodeDBSeedQueryContinuation(t *testing.T) {
-	db, _ := newNodeDB("", Version, NodeID{})
-	defer db.close()
-
-	// Insert a batch of nodes for querying
-	for i, seed := range nodeDBSeedQueryNodes {
-		if err := db.updateNode(seed.node); err != nil {
-			t.Fatalf("node %d: failed to insert: %v", i, err)
-		}
-	}
-	// Iteratively retrieve the batch, checking for an empty batch on reset
-	for i := 0; i < len(nodeDBSeedQueryNodes); i++ {
-		if seeds := db.querySeeds(1); len(seeds) != 1 {
-			t.Errorf("1st iteration %d: seed count mismatch: have %v, want %v", i, len(seeds), 1)
-		}
-	}
-	if seeds := db.querySeeds(1); len(seeds) != 0 {
-		t.Errorf("reset: seed count mismatch: have %v, want %v", len(seeds), 0)
-	}
-	for i := 0; i < len(nodeDBSeedQueryNodes); i++ {
-		if seeds := db.querySeeds(1); len(seeds) != 1 {
-			t.Errorf("2nd iteration %d: seed count mismatch: have %v, want %v", i, len(seeds), 1)
-		}
-	}
-}
-
-func TestNodeDBSelfSeedQuery(t *testing.T) {
-	// Assign a node as self to verify evacuation
-	self := nodeDBSeedQueryNodes[0].node.ID
-	db, _ := newNodeDB("", Version, self)
-	defer db.close()
-
-	// Insert a batch of nodes for querying
-	for i, seed := range nodeDBSeedQueryNodes {
-		if err := db.updateNode(seed.node); err != nil {
-			t.Fatalf("node %d: failed to insert: %v", i, err)
-		}
-	}
-	// Retrieve the entire batch and check that self was evacuated
-	seeds := db.querySeeds(2 * len(nodeDBSeedQueryNodes))
-	if len(seeds) != len(nodeDBSeedQueryNodes)-1 {
-		t.Errorf("seed count mismatch: have %v, want %v", len(seeds), len(nodeDBSeedQueryNodes)-1)
-	}
-	have := make(map[NodeID]struct{})
-	for _, seed := range seeds {
-		have[seed.ID] = struct{}{}
-	}
-	if _, ok := have[self]; ok {
-		t.Errorf("self not evacuated")
-	}
 }
 
 func TestNodeDBPersistency(t *testing.T) {
diff --git a/p2p/discover/table.go b/p2p/discover/table.go
index 972bc1077..c128c2ed1 100644
--- a/p2p/discover/table.go
+++ b/p2p/discover/table.go
@@ -44,6 +44,10 @@ const (
 
 	maxBondingPingPongs = 16
 	maxFindnodeFailures = 5
+
+	autoRefreshInterval = 1 * time.Hour
+	seedCount           = 30
+	seedMaxAge          = 5 * 24 * time.Hour
 )
 
 type Table struct {
@@ -52,6 +56,10 @@ type Table struct {
 	nursery []*Node           // bootstrap nodes
 	db      *nodeDB           // database of known nodes
 
+	refreshReq chan struct{}
+	closeReq   chan struct{}
+	closed     chan struct{}
+
 	bondmu    sync.Mutex
 	bonding   map[NodeID]*bondproc
 	bondslots chan struct{} // limits total number of active bonding processes
@@ -80,10 +88,7 @@ type transport interface {
 
 // bucket contains nodes, ordered by their last activity. the entry
 // that was most recently active is the first element in entries.
-type bucket struct {
-	lastLookup time.Time
-	entries    []*Node
-}
+type bucket struct{ entries []*Node }
 
 func newTable(t transport, ourID NodeID, ourAddr *net.UDPAddr, nodeDBPath string) *Table {
 	// If no node database was given, use an in-memory one
@@ -93,11 +98,14 @@ func newTable(t transport, ourID NodeID, ourAddr *net.UDPAddr, nodeDBPath string
 		db, _ = newNodeDB("", Version, ourID)
 	}
 	tab := &Table{
-		net:       t,
-		db:        db,
-		self:      newNode(ourID, ourAddr.IP, uint16(ourAddr.Port), uint16(ourAddr.Port)),
-		bonding:   make(map[NodeID]*bondproc),
-		bondslots: make(chan struct{}, maxBondingPingPongs),
+		net:        t,
+		db:         db,
+		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{}),
+		closeReq:   make(chan struct{}),
+		closed:     make(chan struct{}),
 	}
 	for i := 0; i < cap(tab.bondslots); i++ {
 		tab.bondslots <- struct{}{}
@@ -105,6 +113,7 @@ func newTable(t transport, ourID NodeID, ourAddr *net.UDPAddr, nodeDBPath string
 	for i := range tab.buckets {
 		tab.buckets[i] = new(bucket)
 	}
+	go tab.refreshLoop()
 	return tab
 }
 
@@ -163,10 +172,12 @@ func randUint(max uint32) uint32 {
 
 // Close terminates the network listener and flushes the node database.
 func (tab *Table) Close() {
-	if tab.net != nil {
-		tab.net.close()
+	select {
+	case <-tab.closed:
+		// already closed.
+	case tab.closeReq <- struct{}{}:
+		<-tab.closed // wait for refreshLoop to end.
 	}
-	tab.db.close()
 }
 
 // Bootstrap sets the bootstrap nodes. These nodes are used to connect
@@ -183,7 +194,7 @@ func (tab *Table) Bootstrap(nodes []*Node) {
 		tab.nursery = append(tab.nursery, &cpy)
 	}
 	tab.mutex.Unlock()
-	tab.refresh()
+	tab.requestRefresh()
 }
 
 // Lookup performs a network search for nodes close
@@ -204,15 +215,13 @@ func (tab *Table) Lookup(targetID NodeID) []*Node {
 	asked[tab.self.ID] = true
 
 	tab.mutex.Lock()
-	// update last lookup stamp (for refresh logic)
-	tab.buckets[logdist(tab.self.sha, target)].lastLookup = time.Now()
 	// generate initial result set
 	result := tab.closest(target, bucketSize)
 	tab.mutex.Unlock()
 
-	// If the result set is empty, all nodes were dropped, refresh
+	// If the result set is empty, all nodes were dropped, refresh.
 	if len(result.entries) == 0 {
-		tab.refresh()
+		tab.requestRefresh()
 		return nil
 	}
 
@@ -257,56 +266,86 @@ func (tab *Table) Lookup(targetID NodeID) []*Node {
 	return result.entries
 }
 
-// refresh performs a lookup for a random target to keep buckets full, or seeds
-// the table if it is empty (initial bootstrap or discarded faulty peers).
-func (tab *Table) refresh() {
-	seed := true
+func (tab *Table) requestRefresh() {
+	select {
+	case tab.refreshReq <- struct{}{}:
+	case <-tab.closed:
+	}
+}
 
-	// If the discovery table is empty, seed with previously known nodes
-	tab.mutex.Lock()
-	for _, bucket := range tab.buckets {
-		if len(bucket.entries) > 0 {
-			seed = false
-			break
+func (tab *Table) refreshLoop() {
+	defer func() {
+		tab.db.close()
+		if tab.net != nil {
+			tab.net.close()
 		}
-	}
-	tab.mutex.Unlock()
+		close(tab.closed)
+	}()
 
-	// If the table is not empty, try to refresh using the live entries
-	if !seed {
-		// The Kademlia paper specifies that the bucket refresh should
-		// perform a refresh in the least recently used bucket. We cannot
-		// adhere to this because the findnode target is a 512bit value
-		// (not hash-sized) and it is not easily possible to generate a
-		// sha3 preimage that falls into a chosen bucket.
-		//
-		// We perform a lookup with a random target instead.
-		var target NodeID
-		rand.Read(target[:])
-
-		result := tab.Lookup(target)
-		if len(result) == 0 {
-			// Lookup failed, seed after all
-			seed = true
+	timer := time.NewTicker(autoRefreshInterval)
+	var done chan struct{}
+	for {
+		select {
+		case <-timer.C:
+			if done == nil {
+				done = make(chan struct{})
+				go tab.doRefresh(done)
+			}
+		case <-tab.refreshReq:
+			if done == nil {
+				done = make(chan struct{})
+				go tab.doRefresh(done)
+			}
+		case <-done:
+			done = nil
+		case <-tab.closeReq:
+			if done != nil {
+				<-done
+			}
+			return
 		}
 	}
+}
 
-	if seed {
-		// Pick a batch of previously know seeds to lookup with
-		seeds := tab.db.querySeeds(10)
-		for _, seed := range seeds {
-			glog.V(logger.Debug).Infoln("Seeding network with", seed)
-		}
-		nodes := append(tab.nursery, seeds...)
+// doRefresh performs a lookup for a random target to keep buckets
+// full. seed nodes are inserted if the table is empty (initial
+// bootstrap or discarded faulty peers).
+func (tab *Table) doRefresh(done chan struct{}) {
+	defer close(done)
+
+	// The Kademlia paper specifies that the bucket refresh should
+	// perform a lookup in the least recently used bucket. We cannot
+	// adhere to this because the findnode target is a 512bit value
+	// (not hash-sized) and it is not easily possible to generate a
+	// sha3 preimage that falls into a chosen bucket.
+	// We perform a lookup with a random target instead.
+	var target NodeID
+	rand.Read(target[:])
+	result := tab.Lookup(target)
+	if len(result) > 0 {
+		return
+	}
 
-		// Bond with all the seed nodes (will pingpong only if failed recently)
-		bonded := tab.bondall(nodes)
-		if len(bonded) > 0 {
-			tab.Lookup(tab.self.ID)
+	// The table is empty. Load nodes from the database and insert
+	// them. This should yield a few previously seen nodes that are
+	// (hopefully) still alive.
+	seeds := tab.db.querySeeds(seedCount, seedMaxAge)
+	seeds = tab.bondall(append(seeds, tab.nursery...))
+	if glog.V(logger.Debug) {
+		if len(seeds) == 0 {
+			glog.Infof("no seed nodes found")
+		}
+		for _, n := range seeds {
+			age := time.Since(tab.db.lastPong(n.ID))
+			glog.Infof("seed node (age %v): %v", age, n)
 		}
-		// TODO: the Kademlia paper says that we're supposed to perform
-		// random lookups in all buckets further away than our closest neighbor.
 	}
+	tab.mutex.Lock()
+	tab.stuff(seeds)
+	tab.mutex.Unlock()
+
+	// Finally, do a self lookup to fill up the buckets.
+	tab.Lookup(tab.self.ID)
 }
 
 // closest returns the n nodes in the table that are closest to the
@@ -373,8 +412,9 @@ func (tab *Table) bond(pinged bool, id NodeID, addr *net.UDPAddr, tcpPort uint16
 	}
 	// If the node is unknown (non-bonded) or failed (remotely unknown), bond from scratch
 	var result error
-	if node == nil || fails > 0 {
-		glog.V(logger.Detail).Infof("Bonding %x: known=%v, fails=%v", id[:8], node != nil, fails)
+	age := time.Since(tab.db.lastPong(id))
+	if node == nil || fails > 0 || age > nodeDBNodeExpiration {
+		glog.V(logger.Detail).Infof("Bonding %x: known=%t, fails=%d age=%v", id[:8], node != nil, fails, age)
 
 		tab.bondmu.Lock()
 		w := tab.bonding[id]
@@ -435,13 +475,17 @@ func (tab *Table) pingpong(w *bondproc, pinged bool, id NodeID, addr *net.UDPAdd
 // ping a remote endpoint and wait for a reply, also updating the node
 // database accordingly.
 func (tab *Table) ping(id NodeID, addr *net.UDPAddr) error {
-	// Update the last ping and send the message
 	tab.db.updateLastPing(id, time.Now())
 	if err := tab.net.ping(id, addr); err != nil {
 		return err
 	}
-	// Pong received, update the database and return
 	tab.db.updateLastPong(id, time.Now())
+
+	// Start the background expiration goroutine after the first
+	// successful communication. Subsequent calls have no effect if it
+	// is already running. We do this here instead of somewhere else
+	// so that the search for seed nodes also considers older nodes
+	// that would otherwise be removed by the expiration.
 	tab.db.ensureExpirer()
 	return nil
 }
diff --git a/p2p/discover/table_test.go b/p2p/discover/table_test.go
index 426f4e9cc..84962a1a5 100644
--- a/p2p/discover/table_test.go
+++ b/p2p/discover/table_test.go
@@ -514,9 +514,6 @@ func (tn *preminedTestnet) findnode(toid NodeID, toaddr *net.UDPAddr, target Nod
 	if toaddr.Port == 0 {
 		panic("query to node at distance 0")
 	}
-	if target != tn.target {
-		panic("findnode with wrong target")
-	}
 	next := uint16(toaddr.Port) - 1
 	var result []*Node
 	for i, id := range tn.dists[toaddr.Port] {
diff --git a/p2p/discover/udp.go b/p2p/discover/udp.go
index afb31ee69..20f69cf08 100644
--- a/p2p/discover/udp.go
+++ b/p2p/discover/udp.go
@@ -39,7 +39,6 @@ var (
 	errPacketTooSmall   = errors.New("too small")
 	errBadHash          = errors.New("bad hash")
 	errExpired          = errors.New("expired")
-	errBadVersion       = errors.New("version mismatch")
 	errUnsolicitedReply = errors.New("unsolicited reply")
 	errUnknownNode      = errors.New("unknown node")
 	errTimeout          = errors.New("RPC timeout")
@@ -52,8 +51,6 @@ const (
 	respTimeout = 500 * time.Millisecond
 	sendTimeout = 500 * time.Millisecond
 	expiration  = 20 * time.Second
-
-	refreshInterval = 1 * time.Hour
 )
 
 // RPC packet types
@@ -312,10 +309,8 @@ func (t *udp) loop() {
 		plist       = list.New()
 		timeout     = time.NewTimer(0)
 		nextTimeout *pending // head of plist when timeout was last reset
-		refresh     = time.NewTicker(refreshInterval)
 	)
 	<-timeout.C // ignore first timeout
-	defer refresh.Stop()
 	defer timeout.Stop()
 
 	resetTimeout := func() {
@@ -344,9 +339,6 @@ func (t *udp) loop() {
 		resetTimeout()
 
 		select {
-		case <-refresh.C:
-			go t.refresh()
-
 		case <-t.closing:
 			for el := plist.Front(); el != nil; el = el.Next() {
 				el.Value.(*pending).errc <- errClosed
@@ -529,9 +521,6 @@ func (req *ping) handle(t *udp, from *net.UDPAddr, fromID NodeID, mac []byte) er
 	if expired(req.Expiration) {
 		return errExpired
 	}
-	if req.Version != Version {
-		return errBadVersion
-	}
 	t.send(from, pongPacket, pong{
 		To:         makeEndpoint(from, req.From.TCP),
 		ReplyTok:   mac,
diff --git a/p2p/discover/udp_test.go b/p2p/discover/udp_test.go
index a86d3737b..913199c26 100644
--- a/p2p/discover/udp_test.go
+++ b/p2p/discover/udp_test.go
@@ -122,7 +122,6 @@ func TestUDP_packetErrors(t *testing.T) {
 	defer test.table.Close()
 
 	test.packetIn(errExpired, pingPacket, &ping{From: testRemote, To: testLocalAnnounced, Version: Version})
-	test.packetIn(errBadVersion, pingPacket, &ping{From: testRemote, To: testLocalAnnounced, Version: 99, Expiration: futureExp})
 	test.packetIn(errUnsolicitedReply, pongPacket, &pong{ReplyTok: []byte{}, Expiration: futureExp})
 	test.packetIn(errUnknownNode, findnodePacket, &findnode{Expiration: futureExp})
 	test.packetIn(errUnsolicitedReply, neighborsPacket, &neighbors{Expiration: futureExp})