Re: OTListen in OS 9
Re: OTListen in OS 9
- Subject: Re: OTListen in OS 9
- From: Lyndsey Ferguson <email@hidden>
- Date: Fri, 16 May 2003 15:18:37 -0400
Hi Eric,
Thanks for you input. To clarify, each program is in fact a client and
server program. This is meant to be a cross-platform (Macintosh/Windows)
program that authenticates that it is the only program on the LAN using a
serial number. I think it would be very bad and possibly disallowed by a
LAN router to broadcast to the general internet.
I know that this can be defeated by closing those ports on each computer and
that the packets can be intercepted and modified. However, I'm using our
software's previous method as my base to expand on.
Thanks for reading ;)
Lyndsey
On 5/16/03 2:31 PM, "Eric Gundrum" <email@hidden> wrote:
>
--- At 9:15 AM -0400 5/13/03, Lyndsey Ferguson wrote:
>
> Well this is a a client/server program. The client side sends out a
>
> broadcast with a port number as the message. The matching servers on the
>
> intranet use this port number to connect to the listening endpoint on the
>
> client. The server connects to the client and gives it information. This
>
> broadcast is repeated intermittently (15mins) by the client to test for
>
> information.
>
>
Lyndsey,
>
>
I am no expert on protocol design, but your description feels to me like
>
the client really is a server because it is telling the remote what port to
>
use. A protocol like this generally will not work well across network
>
address translation (NAT) or firewalls because such a protocol requires
>
that the NAT/firewall know the internals of the protocol to correctly remap
>
the ports. If you are designing this protocol, you might want to consider
>
alternatives which are firewall-friendly.
>
>
(As an example, the original FTP protocol had this backwards. Passive FTP
>
was created to correct that and now seems to be the default for FTP.)
>
>
Your description also sounds like it has a service discovery component. The
>
IETF has a protocol for service discovery called "DNS Service Discovery"
>
(imagine that ;-) <http://www.dns-sd.org/>. I believe Mac OS X supports
>
dns-sd. You may want to explore dns-sd for ideas to help you make your
>
protocol more compatible.
>
>
Hopefully others will chime in, correct my mistakes and offer more
>
information. :-)
>
>
Regards...eric
>
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--
Lyndsey D. Ferguson
Software Engineer
Nemetschek N.A., Inc.
email@hidden
--
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