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5. Service Names

5. Service Names​

Service names are the unique key in the Service Name and Transport Protocol Port Number registry. This unique symbolic name for a service may also be used for other purposes, such as in DNS SRV records [RFC2782]. Within the registry, this unique key ensures that different services can be unambiguously distinguished, thus preventing name collisions and avoiding confusion about who is the Assignee for a particular entry.

There may be more than one service name associated with a particular transport protocol and port. There are three ways that such port number overloading can occur:

  • Overloading occurs when one service is an extension of another service, and an in-band mechanism exists for determining if the extension is present or not.
  • By historical accident, the service name "http" has two synonyms "www" and "www-http". When used in SRV records, only the service name "http" should be used.
  • As indicated in Section 10.1, overloading has been used to create replacement names that are consistent with the syntax this document prescribes for legacy names.

Service names are assigned on a "first come, first served" basis. Names should be brief and informative, avoiding words or abbreviations that are redundant in the context of the registry.

5.1. Service Name Syntax​

Valid service names are hereby normatively defined as follows:

  • MUST be at least 1 character and no more than 15 characters long
  • MUST contain only US-ASCII letters 'A' - 'Z' and 'a' - 'z', digits '0' - '9', and hyphens ('-')
  • MUST contain at least one letter ('A' - 'Z' or 'a' - 'z')
  • MUST NOT begin or end with a hyphen
  • hyphens MUST NOT be adjacent to other hyphens

The reason for requiring at least one letter is to avoid service names like "23" (could be confused with a numeric port) or "6000-6063" (could be confused with a numeric port range).

5.2. Service Name Usage in DNS SRV Records​

The DNS SRV specification [RFC2782] states that the Service Label part of the owner name of a DNS SRV record includes a "Service" element, described as "the symbolic name of the desired service".

This document clarifies that the Service Label MUST be a service name as defined herein with an underscore prepended. The service name SHOULD be registered with IANA and recorded in the Service Name and Transport Protocol Port Number registry [PORTREG].

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