KnowledgeBase/CII.md

@@ -494,8 +494,43 @@ def configure(cnf):
 
 ### ------------------------------------------------------
 ### [MAL]
+--------------------------------------------------------------------------
+--------------------------------------------------------------------------
+--------------------------------------------------------------------------
+### Avoid ephemeral ports [MAL]
+
+**Problem**
+
+When you leave a client running for a while (say 20 minutes) without server available, you start getting errors:
+```
+Message=Malformed message received, missing frames.
+```
+
+Starting the server does not fix the situation, and gives this error:
+```
+Errno 48 : Address already in use
+```
+
+**Solution**
+
+The solution is not to use ports from the ephemeral range. The port numbers in the ephemeral range can be found with `cat /proc/sys/net/ipv4/ip_local_port_range`. For DevEnv 3.x with CentOS 8 they are:
+ 
+| Port Range    | Usable for MAL |
+| ----          | ----           |
+| 1 -1023       | 🟠 No   |
+| 1024 - 32767  | 🟢 Yes  |
+| 32768 - 60999 | 🟠 No   |
+| 61000 - 65535 | 🟢 Yes  |
+
+With the implementation of ECII-402, the MAL library will write a warning log (and can also be configured to throw an exception) if an application runs a MAL instance on one of the ephemeral ports.
+
+**Background**
+
+(Explanation provided by M. Sekoranja)
 
+After a while of (re-)connection attempts, the client will manage to connect... to itself! Because a client will never expect client's messages, errors of malformed messages are emitted.
 
+This happens because TCP design allows for a 'simultaneous connect feature': if a client is trying to connect to local port and if the port is from the ephemeral range, it can occasionally connect to itself. The client thinks it is connected to a server, however it is actually connected to itself. Moreover, the server can not bind to its server port anymore.
 
 
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