[Info-vax] Help to eliminate delay in establishing FTP connection (VMS V7.x on VAX with MultiNet V4.4)

[John E. Malmberg]

On 3/18/2021 11:05 PM, Tad Winters wrote:
> I'm hoping that you might give me some ideas to remediate this problem.
> 
> A long time customer, for whom I've done very little work for many
> years, has been running with their solution for a very long time.
> Within the last six weeks, they told me they were seeing delays in
> connecting to the system with FTP.  He has been using PHP for many years
> to upload some files to his VMS system to be processed by an
> application.  He added some timing in the PHP calls and what it revealed
> is a consistent 30 second delay from connecting until being logged in.
> I confirmed this with Filezilla.
> 
<snip>
> What am I missing?

Start looking at the FTP protocol and also see if you can get a network 
trace of the transaction.  Best if you can get it from both sides.

Going from my faulty memory:

By default, FTP clients connect to a server and then the server tries to 
open a second channel back to the client.

The FTP transaction probably waits for a period of time for second 
channel to connect.

This second connection is typically blocked by most firewalls.

FTP has a fallback mode to use a single channel in this case.

Generally on the FTP command or via some environment variable / 
configuration file, you can tell the ftp client to only use a single 
channel.

Also come corporations require FTP/HTTP/etc. communications through a 
proxy / load balancer.  That can cause problems when the internal 
address/network table is not set up right, but that usually just blocks 
communications instead of adding a delay.

Regards,
-John