Environment
Novell NetWare 6.5
NetWare FTP Server (NWFTPD.NLM)
Situation
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.
- and-
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.
Resolution
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.