Failed to receive length of a command during migration via Migrator Agent

Created:

2016-11-16 13:14:17 UTC

Modified:

2017-08-08 13:22:10 UTC

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Failed to receive length of a command during migration via Migrator Agent

Applicable to:

  • Plesk 12.5 for Windows

Symptoms

  1. The error appears during migration via Plesk Migration manager:
    Error:  Unable to download dump files to local store. Error:  The specified network name is no longer available

Following error in "%plesk_dir%"\\PMM\\msessions\\XXXX\\Migration.log :

    [2015-10-17 01:38:29.963|4396] Debug: ForeignMigratorCore.MigratorException: Unable to download dump files to local store. ---> System.ComponentModel.Win32Exception: The specified network name is no longer available
  1. Source server debug log C:\\panel_migrator\\panel-transfer-agent\\debug.log contains:

    [ERROR] Failed to receive length of a command
    [INFO] Finished connection from '1.1.1.1'

    Exception happened during processing of request from ('1.1.1.1', 58936)
    Traceback (most recent call last):
    File "C:\\panel_migrator\\panel-transfer-agent\\python\\lib\\SocketServer.py", line 593, in process_request_thread
    self.finish_request(request, client_address)
    File "C:\\panel_migrator\\panel-transfer-agent\\python\\lib\\SocketServer.py", line 334, in finish_request
    self.RequestHandlerClass(request, client_address, self)
    File "C:\\panel_migrator\\panel-transfer-agent\\python\\lib\\SocketServer.py", line 649, in __init__
    self.handle()
    File "server.py", line 235, in handle
    length = self._receive(4)
    File "server.py", line 267, in _receive
    r = self.request.recv(size - len(b))
    File "C:\\panel_migrator\\panel-transfer-agent\\python\\lib\\ssl.py", line 241, in recv
    return self.read(buflen)
    File "C:\\panel_migrator\\panel-transfer-agent\\python\\lib\\ssl.py", line 160, in read
    return self._sslobj.read(len)
    error: [Errno 10054] An existing connection was forcibly closed by the remote host
  2. All ports required for migration are opened # 213958185

  3. No firewalls or Anti-viruses are enabled

Cause

The source server sends ACK packet , but the destination doesn't receive it, as result is unable to confirm establishing the connection.

Resolution

According to the TCP 3-Way Handshake (SYN,SYN-ACK,ACK) SCHEME :

  • Host A sends a TCP SYNchronize packet to Host B
  • Host B receives A's SYN
  • Host B sends a SYNchronize-ACKnowledgement
  • Host A receives B's SYN-ACK
  • Host A sends ACKnowledge
  • Host B receives ACK.
  • TCP socket connection is ESTABLISHED.

To perform migration make sure the connectivity between source and destination servers can be established according to scheme above.

Please use following link for your reference: TCP 3-Way Handshake (SYN,SYN-ACK,ACK)

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