[Tfug] ftp question

[Robert J Hunter]

Erich,

The port number is a 16-bit field, so it can range from 0-65535.
Traditionally, it has been a common rule that only privileged server
processes can use port numbers less than 1024 (referred to as
privileged ports).

However, as "well-known" services increase in number, the availability
of privledged port numbers has all but vanished, and if you take a
peek at /etc/services you should see a number of services with very
large port numbers.

Still, the the most common services use ports numbered less than 1024.
Clients generally must request unprivileged port numbers from the
operating system.  Hence, if you need to run a server as a
non-superuser, you will usually have to accept connections on a port
greater than 1024.

-Rob

> ------------------------------
> 
> Message: 5
> Date: Fri, 15 Oct 2004 10:43:25 -0700
> From: ewf <erich at dakotacom.net>
> Subject: Re: [Tfug] ftp question
> To: Tucson Free Unix Group <tfug at tfug.org>
> Message-ID: <41700C3D.9030904 at dakotacom.net>
> Content-Type: text/plain; charset=us-ascii; format=flowed
> 
> Jim Secan wrote:
> 
> >I routinely download small files from a site in Colorado a couple of times
> >an hour from a collection of automated scripts.  Normally things work just
> >fine, but for some reason yesterday things broke down.  When I chased it
> >all down, my firewall was rejecting packets coming in from the target
> >machine to my machine at various high ports (59000+)
> >
>       This is a digression from the topic, but a 5-digit port number 
> makes me blink. The higest
> I've seen is 6000 which  corresponds to x11. My firewall rejects any 
> external service port number
> higher than 1023.
> 
>                                                                         
>                                                                         
>  Erich
> 
> > which broke the ftp
> >link.  I've had speculation that these packets to high ports are part of
> >the ftp process post-negotiation and that what I'm seeing is problems that
> >might be due to increased latency or message-order shuffling or some other
> >phenomenon between my firewall and the target machine.  When I did a
> >traceroute, the route was about 12 hops longer than usual and was highly
> >variable.  Today the traceroute shows what I consider to be the normal
> >routing and I'm not having problems.
> >
> >Does this make sense?
> >
> >TIA
> >Jim
> >*---------------------*-------------------------------*
> >| Jim Secan           | Northwest Research Assoc, Inc |
> >| (jim at nwra.com)      | 2455 E. Speedway, Suite 204   |
> >| (520) 319-7773      | Tucson, Arizona 85719         |
> >|    Space Weather Info: http://www.nwra-az.com/      |
> >*---------------------*-------------------------------*
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> >  
> >
> 
> 
> 
> 
> 
> ------------------------------