[Xitami] Xitami FTP port.

[Brian {Hamilton Kelly}]

In message <051020041639.7881.409FB03C000836C600001EC92160376021FFCC9891909=
398@att.net>
   jglong3@att.net writes:

> The following was listed at IANA for ports 20 and 21;
>=20
>       ftp-data         20/tcp    File Transfer [Default Data]
>       ftp-data         20/udp    File Transfer [Default Data]
>       ftp              21/tcp    File Transfer [Control]
>       ftp              21/udp    File Transfer [Control]
>=20
> Please forgive me, the last time I worked with any level of protocol
> was a long time ago (circa "IBM BI-SYNC" and previous).
>=20
> It does look like port 21 is to logon with username:password control
> (authentication???) and that 20 would be the up/down load of files(???).
>=20
>=20
>         1. Is this the meaning for port 20 and 21?=20

Yes: port 21 is used for control connections (of course, the originating
FTP client can use anything it likes).  Port 20 is used, by an FTP
server, for uploaded [i.e. PUT] data; in the full protocol, downloaded
[i.e. GET] data is sent TO whichever port the client has negotiated with
a PORT command, from port 20 on the server.

>         2. If so and port 20 is used by Xitami should it=20
>            be discussed in the documentation?

Why should it?  Port 20/21 is part and parcel of FTP, which was
standardized in RFC-765 way back in June of 1980.

It's only things like firewalls and NATted routers which cause difficulty
with this standard, and it is in that area that further documentation
ought to be expected.

RFC-765 includes a rather useful bit of "ASCII Art":

                                            -------------
                                            |/---------\|
                                            ||   User  ||    --------
                                            ||Interface|<--->| User |
                                            |\----:----/|    --------
                  ----------                |     V     |
                  |/------\|  FTP Commands  |/---------\|
                  ||Server|<---------------->|   User  ||
                  ||  PI  ||   FTP Replies  ||    PI   ||
                  |\--:---/|                |\----:----/|
                  |   V    |                |     V     |
      --------    |/------\|      Data      |/---------\|    --------
      | File |<--->|Server|<---------------->|  User   |<--->| File |
      |System|    || DTP  ||   Connection   ||   DTP   ||    |System|
      --------    |\------/|                |\---------/|    --------
                  ----------                -------------

                  Server-FTP                   User-FTP

      NOTES: 1. The data connection may be used in either direction.
             2. The data connection need not exist all of the time.

                      Figure 1  Model for FTP Use

PI =3D Protocol Interpreter; DTP =3D Data Transfer Port.

--=20
   fix (vb.): 1. to paper over, obscure, hide from public view; 2. to
   work around, in a way that produces unintended consequences that are
   worse than the original problem.  Usage: "Windows ME fixes many of the
   shortcomings of Windows 98 SE".