Java Socket Constructor

L

Lasse Reichstein Nielsen

[FTP data transfer]
Because this nowadays typically causes firewall problems at
the client, a new "passive mode" FTP has been defined, in which,
instead of initiating the data session, the server requests the
client, via the command session, to initiate it, "active mode" being a
retronym for the original design. Passive mode must be requested
explicitly, since not all software supports it.

Actually, passive mode data transfer has been in the FTP protocol
almost since the beginning (RFC 542 from 1973). It is not new, and
not caused by firewalls.

It is true that the growth of private computers, possibly behind
firewalls, or just NAT routers, and using browsers as FTP clients
have cause passive FTP connections to become much more prevalent.
I don't know why they didn't just use a single session with a side
channel implemented in the data format in the first place, unless it
was simply to squeeze out the last drop of bandwidth.

Having separate data and control lines, along with both passive and
active data transfer, allow you to use two control lines to initiate a
direct transfer between two FTP servers, controlled by a third computer.
Pretty nifty, actually.

/L
 
J

John W. Kennedy

Lasse said:
[FTP data transfer]
Because this nowadays typically causes firewall problems at
the client, a new "passive mode" FTP has been defined, in which,
instead of initiating the data session, the server requests the
client, via the command session, to initiate it, "active mode" being a
retronym for the original design. Passive mode must be requested
explicitly, since not all software supports it.

Actually, passive mode data transfer has been in the FTP protocol
almost since the beginning (RFC 542 from 1973). It is not new, and
not caused by firewalls.

Thanks. I didn't know that. (I wrote my first e-mail server in the late
60s, but didn't get involved with TCP/IP until the Mosaic era.) That
makes it a good deal more disturbing, though, that there are still
servers out there that don't support passive mode.
 
A

Arne Vajhøj

Lew said:
Funny, but I could not corroborate that "information" with anything I
found on the 'net. /Au contraire/, I found plenty of corroboration that
'localhost' does indeed map to the loopback address, including in the
command 'man hosts' on Linux.

So EJP has a point - it is wise to corroborate from authoritative
sources, as I assume Arne intended to show as well.

My point was more about posting style ...

Arne
 
E

EJP

Arne said:
It is more OK to post wrong info to usenet than to put it on a web site.
It is more OK to (a) recommend RFCs, and it is also more OK (b) post to
usenet or elsewhere, making sure you punctiliously acknowledge and
correct all errors you make in the process, than it is to (c) construct
a hobby site with no well-defined review/editing/problem report process,
(d) recommend it all over the place as an authoritative source, and (e)
ignore all suggestions and comments for years on end and/or (f) take
them as personal insults.
 

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