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Sporadic FTP error when moving files from a PC to MVS

We keep receiving FTP error code 451 when transferring files to MVS from a PC. Sometime it will work, and it's inconsistent on when it fails. Any ideas?

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This is probably the FTP server problem. What FTP server is installed on the PC side? One possible reason is from Microsoft:
When FTP clients initiate passive file transfer operations, the FTP server uses asynchronous network notification to wait for the actual client connection to a passive data socket. By default, the FTP server allows 60 passive file transfer operations to be queued simultaneously. Once the queue reaches 60, subsequent client requests receive error 451: Too many Passive Users. Client connections remain in this transient state for a short time, between issuing a file transfer command (e.g. RETR, STOR) and connecting the data channel to the passive socket. For this reason, this error can only occur in one of the following scenarios:

-- A DoS attack has issued concurrent file transfer commands without actually connecting to the data socket.
-- An extremely large number of concurrent users are transferring files in passive mode (which is possible on slow networks).

You may try to work around this problem using non-passive file transfer or changing a registry entry as described here.

This was first published in May 2005

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