Re: OTListen in OS 9
Re: OTListen in OS 9
- Subject: Re: OTListen in OS 9
- From: Eric Gundrum <email@hidden>
- Date: Fri, 16 May 2003 11:31:01 -0700
--- 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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