diff --git a/ws2012/P2P/uebungen/4/src/peer/Node.java b/ws2012/P2P/uebungen/4/src/peer/Node.java
index aa19464f..462dc54d 100644
--- a/ws2012/P2P/uebungen/4/src/peer/Node.java
+++ b/ws2012/P2P/uebungen/4/src/peer/Node.java
@@ -3,6 +3,7 @@ package peer;
 import java.io.IOException;
 import java.net.Inet4Address;
 import java.net.Inet6Address;
+import java.net.InetAddress;
 import java.net.InetSocketAddress;
 import java.net.SocketAddress;
 import java.nio.ByteBuffer;
@@ -36,7 +37,7 @@ public class Node {
 			channel.configureBlocking(false);
 
 			buf = ByteBuffer.allocate(BUF_SIZE);
-
+			
 			this.name = channel.socket().getLocalSocketAddress().toString();
 
 			udpListen = new UDPListen();
@@ -173,6 +174,15 @@ public class Node {
 		return (this.neighbors.size() > 0);
 	}
 
+	public boolean hasNeighbor(SocketAddress adr) {
+		for (SocketAddress n : neighbors) {
+			if (n.toString().equals(adr.toString())) {
+				return true;
+			}
+		}
+		return false;
+	}
+
 	public String getName() {
 		return this.name;
 	}
@@ -214,7 +224,13 @@ public class Node {
 						case MessageType.LEAVE:
 							LOGGER.info(name + ": " + receivedFrom.toString()
 									+ " is leaving. Deleting...");
-							neighbors.remove(receivedFrom);
+							
+							// search the neighbor in the list and remove him.
+							for (int i = 0; i < neighbors.size(); i++) {
+								if (neighbors.get(i).equals(receivedFrom)) {
+									neighbors.remove(i);
+								}
+							}
 							break;
 
 						case MessageType.NEW_NEIGHBOR_IPV4:
@@ -233,8 +249,13 @@ public class Node {
 
 							int port = buf.getInt();
 
-							neighbors.add(new InetSocketAddress(new String(
-									byte_addr), port));
+							InetSocketAddress new_neighbor = new InetSocketAddress(
+									new String(byte_addr), port);
+							
+							// check, if we have the neighbor already.
+							if (!hasNeighbor(new_neighbor)) {
+								neighbors.add(new_neighbor);
+							}
 
 							// TODO: send PING to new neighbor and expect wait
 							// to
@@ -262,9 +283,13 @@ public class Node {
 							int new_port = Integer.valueOf(str_received
 									.substring(startOfPort + 1));
 
-							SocketAddress new_neighbor = new InetSocketAddress(
-									new_hostname, new_port);
-							neighbors.add(new_neighbor);
+							new_neighbor = new InetSocketAddress(new_hostname,
+									new_port);
+							
+							// check, if we have the neighbor already.
+							if (!hasNeighbor(new_neighbor)) {
+								neighbors.add(new_neighbor);
+							}
 
 							break;
 
@@ -273,7 +298,7 @@ public class Node {
 									+ " received unknown command from "
 									+ receivedFrom.toString() + ": "
 									+ new String(buf.array()));
-							
+
 						}
 					} else {
 						try {