RFC 2782:A DNS RR for specifying the location of s...
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8. The Port number

Currently, the translation from service name to port number happens at the client, often using a file such as /etc/services.

Moving this information to the DNS makes it less necessary to update these files on every single computer of the net every time a new service is added, and makes it possible to move standard services out of the "root-only" port range on unix.


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