scope:

Introduction

The Diameter Base specification, described in [RFC3588], provides a number of ways to extend Diameter, with new Diameter commands (i.e., messages used by Diameter applications) and applications as the most extensive enhancements. [RFC3588] illustrates the conditions that require the definition of a new Diameter application or a new command. Depending on the scope of the Diameter extension, IETF actions are necessary. Although defining new Diameter applications does not require IETF consensus, defining new Diameter commands requires IETF consensus per RFC 3588. This has led to questionable design decisions by other Standards Development Organizations (SDOs), which chose to define new applications on existing commands -- rather than asking for assignment of new command codes -- for the pure purpose of avoiding bringing their specifications to the IETF. In some cases, interoperability problems were an effect of poor the design caused by overloading existing commands.

This document aligns the extensibility rules for Diameter command codes with those defined for Diameter application identifiers and offers a consistent way to delegate work on Diameter to other SDOs to extend Diameter in a way that does not lead to poor design choices.

This is achieved by splitting the command code space into ranges and providing different allocation policies to them: the first range is reserved for RADIUS backward compatibility, allocation of a command code in the second number range requires IETF review, the third range is utilized by vendor-specific command codes, and finally the last range is for experimental commands. Section 4 provides more details about the command code number ranges, and the different allocation policies are described in [RFC5226].

A revision of RFC 3588 is currently in development in the IETF DIME WG [RFC3588bis]; when approved, it will obsolete RFC 3588 as well as this document. A goal of this document is to provide in advance the change in the command codes allocation policy, so that interoperability problems like the ones described above are avoided as soon as possible.