The IESG has approved the following document: - 'IANA Assignment of DSCP Pool 3 (xxxx01) Values to require Publication of a Standards Track or Best Current Practice RFC' (draft-ietf-tsvwg-iana-dscp-registry-08.txt) as Proposed Standard This document is the product of the Transport Area Working Group. The IESG contact persons are Mirja Kühlewind and Spencer Dawkins. A URL of this Internet Draft is: https://datatracker.ietf.org/doc/draft-ietf-tsvwg-iana-dscp-registry/ Technical Summary The Transport Area WG (tsvwg) is in the process of updating the RFC 3662 specification of the Diffserv Lower Effort (LE) PHB/PDB, which provides a less than best effort or scavenger forwarding behavior. This update includes assignment of a new default Diffserv Codepoint (DSCP) to replace use of the CS1 DSCP (001000) for that purpose. The IANA registration policy for part of the IANA DSCP registry has to be changed in order to make that assignment; this draft makes that necessary IANA registration policy change. The number of possible DSCPs for the LE PHB is surprisingly limited: - The three most significant bits have to be '000' to accommodate legacy (non-Diffserv) routers whose forwarding behavior is based upon only those three bits, the former IP Precedence field - The least significant bit must be '1' in order to avoid priority inversion that could result from legacy router zeroing of the former IP Precedence field in a DSCP that is intended to provide better than best effort forwarding. That IP Precedence zeroing behavior has been observed in the Internet. This requirement excludes DSCP Pool 1 (xxxxx0) values. - DSCP values whose two least significant bits are '11' are not available because DSCP Pool 2 (xxxx11) values have been reserved for Experimental or Local Use. The only remaining DSCPs that could be assigned to the LE PHB are 000001 and 000101, both of which are in DSCP Pool 3 (xxxx01). DSCP Pool 3 was originally specified for experimental or local use with a note (in the IANA registry) indicating that they may be utilized for future Standards Action allocations as necessary. That has now become necessary for the LE PHB. The tsvwg WG's consensus is that it is better to reclassify the entire DSCP Pool 3 all at once for assignment by Standards Action rather than incrementally remove individual DSCPs from that Pool as needed, as a one-time change to the entire Pool is more likely to have consistent implementation results. The tsvwg WG intends to assign DSCP 000001 to the updated LE PHB. That assignment will be made by draft-ietf-tsvwg-le-phb, which specifies the updated LE PHB. The IANA registry policy change made by this draft is a necessary prerequisite to that assignment. Working Group Summary The Transport Area WG (tsvwg) is a collection of people with varied interests that don't individually justify their own working groups. This draft is supported by the portion of the tsvwg working group that is familiar with and interested in Diffserv. The draft has received significant review and critique from a number of Diffserv experts, including the draft shepherd. There is clear tsvwg WG consensus on the need to assign a pool 3 DSCP to the LE PHB, and that consensus is supported by Internet path measurements that indicate that zeroing of the former IP Precedence field, while rare, occurs often enough to be an important design consideration in assignment of a default DSCP to the updated LE PHB. Document Quality The shepherd has checked the IANA Considerations, which include updates to the references for the Pool 1 DSCP table (sub-registry) in addition to creating a new Pool 3 table (sub-registry). Personnel Document Shepherd: David Black Responsible AD: Spencer Dawkins
