diff --git a/examples/app/app.nim b/examples/app/app.nim
index 81d0be1..6f0805c 100644
--- a/examples/app/app.nim
+++ b/examples/app/app.nim
@@ -22,6 +22,8 @@ type
     sock: AsyncSocket
     outMessages: TableRef[string, Future[string]]
     peerNotifications: FutureStream[string]
+    probedIp: IpAddress
+    probedPorts: seq[Port]
 
   # Punchd messages
   ProgressTcpSyniConnect* = object
@@ -152,36 +154,50 @@ proc punchHole(punchdConn: PunchdConnection, serverConn: ServerConnection,
       future.fail(e)
     except ValueError as e:
       future.fail(e)
-  let myPorts = &"{1234},{1234},{1234}"
+  let myPorts = (@[Port(1234)] & serverConn.probedPorts).join(",")
   let peerPorts = peerInfo.ports.join(",")
   let req = &"{ipAddress}|{myPorts}|{peerInfo.ip}|{peerPorts}"
   let pResp = await punchdConn.sendRequest("tcp-syni-connect", req, progressCb)
   result = pResp.sock
 
+proc initServerConnection(serverHostname: string, serverPort: Port,
+                          myPort: Port, probePorts: bool):
+                          Future[ServerConnection] {.async.} =
+  if probePorts:
+    for i in 0 .. 1:
+      let sock = newAsyncSocket()
+      sock.setSockOpt(OptReuseAddr, true)
+      sock.bindAddr(myPort)
+      await sock.connect(serverHostname, serverPort)
+      let line = await sock.recvLine(maxLength = 400)
+      let endpoint = parseMessage[NotifyEndpoint](line)
+      result.probedPorts.add(endpoint.port)
+      sock.close()
+  result.sock = await asyncnet.dial(serverHostname, serverPort)
+  let line = await result.sock.recvLine(maxLength = 400)
+  result.probedIp = parseMessage[NotifyEndpoint](line).ip
+  result.outMessages = newTable[string, Future[string]]()
+  result.peerNotifications = newFutureStream[string]("initServerConnection")
+
 proc runApp(serverHostname: string, serverPort: Port, peerId: string,
             otherPeerId: string = "") {.async.} =
-  # TODO: determine endpoint in another proc
   randomize() # initialize random number generator
   var punchdConn = PunchdConnection()
   punchdConn.sock = newAsyncSocket(AF_UNIX, SOCK_STREAM, IPPROTO_IP)
   punchdConn.outMessages = newTable[string, OutgoingPunchdMessage]()
   punchdConn.inConnections = newFutureStream[AsyncSocket]("runApp")
   await punchdConn.sock.connectUnix("/tmp/punchd.socket")
-  var serverConn = ServerConnection()
-  serverConn.sock = await asyncnet.dial(serverHostname, serverPort, IPPROTO_TCP)
-  serverConn.outMessages = newTable[string, Future[string]]()
-  serverConn.peerNotifications = newFutureStream[string]("runApp")
-  let resp = await serverConn.sock.recvLine(maxLength = 400)
-  let endpoint = parseMessage[NotifyEndpoint](resp)
-  echo &"rendezvous server says I am {endpoint.ip}:{endpoint.port.int}"
   asyncCheck handlePunchdMessages(punchdConn)
-  asyncCheck handleServerMessages(serverConn)
-  asyncCheck handlePeerNotifications(serverConn, punchdConn, peerId)
   if otherPeerId.len == 0:
     # register and wait for connections
-    let req = &"{peerId}|{endpoint.ip}|{endpoint.port.int},{endpoint.port.int},{endpoint.port.int}"
+    let serverConn = await initServerConnection(serverHostname, serverPort,
+                                                Port(4321), true)
+    asyncCheck handleServerMessages(serverConn)
+    asyncCheck handlePeerNotifications(serverConn, punchdConn, peerId)
+    let myPorts = (@[Port(4321)] & serverConn.probedPorts).join(",")
+    let req = &"{peerId}|{serverConn.probedIp}|{myPorts}"
+    echo "registering: ", req
     discard await serverConn.sendRequest("register", req)
-    echo "registered"
     while true:
       let (hasSock, sock) = await punchdConn.inConnections.read
       if not hasSock:
@@ -193,8 +209,11 @@ proc runApp(serverHostname: string, serverPort: Port, peerId: string,
 
   else:
     # initiate a new connection
-    let sock = await punchHole(punchdConn, serverConn, endpoint.ip, peerId,
-                               otherPeerId)
+    let serverConn = await initServerConnection(serverHostname, serverPort,
+                                                Port(1234), true)
+    asyncCheck handleServerMessages(serverConn)
+    let sock = await punchHole(punchdConn, serverConn, serverConn.probedIp,
+                               peerId, otherPeerId)
     await sock.send("ping")
     let msg = await sock.recv(1000)
     echo "received message: ", msg