Novell NetWare 6.5
NetWare FTP Server (NWFTPD.NLM)
In certain configurations, small files can be uploaded to the NetWare FTP Server, but uploads of files over 64K stall and do not complete.
LAN Traces shows that the TCP windows size (which determines whether more data can be send on a connection) reaches 0 at this point and does not open back up.
This is caused by the combination of two factors:
1. "TCP Large Window Option" has been set OFF. This is normally ON by default and should not need to be turned off. This is a NetWare SET parameter that can be set in the AUTOEXEC.NCF or at the console prompt.
2. The FTPSERV.CFG file has a parameter,"DATA_BUFF_SIZE", which defaults to 64K. If this is still at/near the default, or lower, this problem can occur.
The problem can be avoided by correcting either of the above factors. Either:
SET TCP Large Window Option=ON
- or -
DATA_BUFF_SIZE=68 (or higher) in SYS:\ETC\FTPSERV.CFG (or whatever custom FTP configuration file is in use). Remember to remove the # at the beginning of the line, if present.
Both of these changes will automatically take effect for any new connections.
NOTE: This scenario has also been reported to engineering for further investigation. It may be possible that a code change could address this, but it is anticipated that all cases can be safely corrected with one of the above configuration changes.