On Thu, Aug 25, 2011 at 10:49 PM, Lloyd
Why the DNS protocol can't be extended to resolve services also? So many people must have faced this issue, and why didn't thay think in this way? Is there any technical barrier?
only well-known service names can be reliably resolved via name; DNS doesn't address this because DNS was conceived to deal with domain name-to-IP address resolution. As someone else mentioned, there is a SRV record type in DNS that was intended to function similar to what you're after, but I do not believe that the value of the SRV records were standardize or that they were even intended to be only port names. If memory recalls correctly, the idea was to be able to search for a service within a subdomain. SRV never got much widespread use for whatever reason, and its proposed functionality may be largely subsumed and overshadowed by the much better specified and much more widely-deployed zeroconf protocol, two implementations of which are Bonjour (from Apple) and Avahi (on linux). The answer to your original issue of how to get the port number for your own service is to simply embed the default port number in your code, allow the user to specify a different port from a command line/config file, and allow specification of the port by name or by number. That's pretty much how it's been done for the last 20+ years. -cj