Recommendation to Use the Ethernet Control Word
RFC 8469

Approval announcement
Draft of message to be sent after approval:

From: The IESG <>
To: IETF-Announce <>
Cc: The IESG <>,, Matthew Bocci <>,,,,,
Subject: Protocol Action: 'Use of Ethernet Control Word RECOMMENDED' to Proposed Standard (draft-ietf-pals-ethernet-cw-07.txt)

The IESG has approved the following document:
- 'Use of Ethernet Control Word RECOMMENDED'
  (draft-ietf-pals-ethernet-cw-07.txt) as Proposed Standard

This document is the product of the Pseudowire And LDP-enabled Services
Working Group.

The IESG contact persons are Alvaro Retana, Martin Vigoureux and Deborah

A URL of this Internet Draft is:

Technical Summary

The pseudowire (PW) encapsulation of Ethernet, as defined in RFC
4448, specifies that the use of the control word (CW) is optional.
In the absence of the CW an Ethernet pseudowire packet can be
misidentified as an IP packet by a label switching router (LSR).
This in turn may lead to the selection of the wrong equal-cost-multi-
path (ECMP) path for the packet, leading in turn to the misordering
of packets.  This problem has become more serious due to the
deployment of equipment with Ethernet MAC addresses that start with
 0x4 or 0x6.  The use of the Ethernet PW CW addresses this problem.
This document recommends the use of the Ethernet pseudowire control
word in all but exceptional circumstances.

This document updates RFC 4448.

Working Group Summary

The document was developed to try to resolve observed misordering of packets on 
Ethernet PWs which can occur when ECMP is applied and the packet aliases for
an IPv4 or IPv6 packet. Although this problem is already well 
understood, and a solution (the PW control word) is widely implemented and deployed. However
the CW was defined as optional in RFC4448 and so there are some cases where it is not 
implemented or not enabled by operators. There are reports that this is becoming 
an increasing problem with the IEEE allocating MAC addresses starting with 0x4 or 0x6,
and so stronger recommendations are required. 

Document Quality

No concerns about the quality of the document. It represents 
WG consensus, and it has been widely reviewed and discussed on the list over a 
number of years. 
The document does not specify any MIB changes or additions which would need 


   Who is the Document Shepherd for this document?  Matthew Bocci
   Who is the Responsible Area Director?  Deborah Brungard

RFC Editor Note

Section 4 1st paragraph/2nd sentence:

This document updates [RFC4448] to state that where both the ingress PE and the egress PE
support the Ethernet pseudowire control word, then the CW MUST be used.

This document updates [RFC4448] to state that both the ingress PE and the egress PE SHOULD
support the Ethernet pseudowire control word, and that if supported the CW MUST be used.