diff --git a/eth/p2p/discovery.nim b/eth/p2p/discovery.nim
index 0c0000e..acff0ef 100644
--- a/eth/p2p/discovery.nim
+++ b/eth/p2p/discovery.nim
@@ -39,14 +39,6 @@ type
     bindIp: IpAddress
     bindPort: Port
 
-  CommandId = enum
-    cmdPing = 1
-    cmdPong = 2
-    cmdFindNode = 3
-    cmdNeighbours = 4
-    cmdENRRequest = 5
-    cmdENRResponse = 6
-
   DiscProtocolError* = object of CatchableError
 
   DiscResult*[T] = Result[T, cstring]
diff --git a/eth/p2p/kademlia.nim b/eth/p2p/kademlia.nim
index c75b502..2cf74d0 100644
--- a/eth/p2p/kademlia.nim
+++ b/eth/p2p/kademlia.nim
@@ -19,6 +19,9 @@ logScope:
   topics = "kademlia"
 
 type
+  # 32 bytes NodeId | 16 bytes ip | 1 byte mode
+  TimeKey = array[49, byte]
+
   KademliaProtocol* [Wire] = ref object
     wire: Wire
     thisNode: Node
@@ -27,6 +30,7 @@ type
     pingFutures: Table[Node, Future[bool]]
     neighboursCallbacks: Table[Node, proc(n: seq[Node]) {.gcsafe, raises: [Defect].}]
     rng: ref HmacDrbgContext
+    pingPongTime: OrderedTable[TimeKey, int64] # int64 -> unix time
 
   NodeId* = UInt256
 
@@ -44,12 +48,21 @@ type
     replacementCache: seq[Node]
     lastUpdated: float # epochTime
 
+  CommandId* = enum
+    cmdPing = 1
+    cmdPong = 2
+    cmdFindNode = 3
+    cmdNeighbours = 4
+    cmdENRRequest = 5
+    cmdENRResponse = 6
+
 const
   BUCKET_SIZE = 16
   BITS_PER_HOP = 8
   REQUEST_TIMEOUT = chronos.milliseconds(5000) # timeout of message round trips
   FIND_CONCURRENCY = 3                  # parallel find node lookups
   ID_SIZE = 256
+  BOND_EXPIRATION = initDuration(hours = 12)
 
 proc toNodeId*(pk: PublicKey): NodeId =
   readUintBE[256](keccak256.digest(pk.toRaw()).data)
@@ -81,6 +94,68 @@ proc hash*(n: Node): hashes.Hash = hash(n.node.pubkey.toRaw)
 proc `==`*(a, b: Node): bool = (a.isNil and b.isNil) or
   (not a.isNil and not b.isNil and a.node.pubkey == b.node.pubkey)
 
+proc timeKey(id: NodeId, ip: IpAddress, cmd: CommandId): TimeKey =
+  result[0..31] = id.toByteArrayBE()[0..31]
+  case ip.family
+  of IpAddressFamily.IPv6:
+    result[32..47] = ip.address_v6[0..15]
+  of IpAddressFamily.IPv4:
+    result[32..35] = ip.address_v4[0..3]
+  result[48] = cmd.byte
+
+proc ip(n: Node): IpAddress =
+  n.node.address.ip
+
+proc timeKeyPong(n: Node): TimeKey =
+  timeKey(n.id, n.ip, cmdPong)
+
+proc timeKeyPing(n: Node): TimeKey =
+  timeKey(n.id, n.ip, cmdPing)
+
+proc lastPingReceived(k: KademliaProtocol, n: Node): Time =
+  k.pingPongTime.getOrDefault(n.timeKeyPing, 0'i64).fromUnix
+
+proc lastPongReceived(k: KademliaProtocol, n: Node): Time =
+  k.pingPongTime.getOrDefault(n.timeKeyPong, 0'i64).fromUnix
+
+proc cmp(x, y: (TimeKey, int64)): int =
+  if x[1] < y[1]: return -1
+  if x[1] > y[1]: return 1
+  0
+
+proc removeTooOldPingPongTime(k: KademliaProtocol) =
+  const
+    MaxEntries = 128
+    MaxRC = 5
+
+  if k.pingPongTime.len < MaxEntries:
+    return
+
+  k.pingPongTime.sort(cmp, order = SortOrder.Descending)
+  var
+    num = 0
+    rc: array[MaxRC, TimeKey]
+
+  for v in keys(k.pingPongTime):
+    if num < MaxRC:
+      rc[num] = v
+      inc num
+
+  for i in 0..<num:
+    k.pingPongTime.del(rc[i])
+
+proc updateLastPingReceived(k: KademliaProtocol, n: Node, t: Time) =
+  k.removeTooOldPingPongTime()
+  k.pingPongTime[n.timeKeyPing] = t.toUnix
+
+proc updateLastPongReceived(k: KademliaProtocol, n: Node, t: Time) =
+  k.removeTooOldPingPongTime()
+  k.pingPongTime[n.timeKeyPong] = t.toUnix
+
+# checkBond checks if the given node has a recent enough endpoint proof.
+proc checkBond(k: KademliaProtocol, n: Node): bool =
+  getTime() - k.lastPongReceived(n) < BOND_EXPIRATION
+
 proc newKBucket(istart, iend: NodeId): KBucket =
   result.new()
   result.istart = istart
@@ -496,16 +571,37 @@ proc recvPong*(k: KademliaProtocol, n: Node, token: seq[byte]) =
   var future: Future[bool]
   if k.pongFutures.take(pingid, future):
     future.complete(true)
+  k.updateLastPongReceived(n, getTime())
 
 proc recvPing*(k: KademliaProtocol, n: Node, msgHash: any)
     {.raises: [ValueError, Defect].} =
   trace "<<< ping from ", n
-  k.updateRoutingTable(n)
   k.wire.sendPong(n, msgHash)
 
+  if getTime() - k.lastPongReceived(n) > BOND_EXPIRATION:
+    let pingId = pingId(n, k.ping(n))
+
+    let fut = if pingId in k.pongFutures:
+                k.pongFutures[pingId]
+              else:
+                k.waitPong(n, pingId)
+
+    let cb = proc(data: pointer) {.gcsafe.} =
+               # fut.read == true if pingid exists
+               try:
+                 if fut.completed and fut.read:
+                   k.updateRoutingTable(n)
+               except CatchableError as ex:
+                 error "recvPing:WaitPong exception", msg=ex.msg
+
+    fut.addCallback cb
+  else:
+    k.updateRoutingTable(n)
+
   var future: Future[bool]
   if k.pingFutures.take(n, future):
     future.complete(true)
+  k.updateLastPingReceived(n, getTime())
 
 proc recvNeighbours*(k: KademliaProtocol, remote: Node, neighbours: seq[Node]) =
   ## Process a neighbours response.