Routing Bridges (RBridges): Appointed Forwarders
RFC 6439

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Internet Engineering Task Force (IETF)                        R. Perlman
Request for Comments: 6439                                    Intel Labs
Updates: 6325                                            D. Eastlake 3rd
Category: Standards Track                                          Y. Li
ISSN: 2070-1721                                      Huawei Technologies
                                                             A. Banerjee
                                                           Cisco Systems
                                                                   F. Hu
                                                         ZTE Corporation
                                                           November 2011

            Routing Bridges (RBridges): Appointed Forwarders

Abstract

   The IETF TRILL (TRansparent Interconnection of Lots of Links)
   protocol provides least cost pair-wise data forwarding without
   configuration in multi-hop networks with arbitrary topology, safe
   forwarding even during periods of temporary loops, and support for
   multipathing of both unicast and multicast traffic.  TRILL
   accomplishes this by using IS-IS (Intermediate System to Intermediate
   System) link state routing and by encapsulating traffic using a
   header that includes a hop count.  Devices that implement TRILL are
   called "RBridges" (Routing Bridges).

   TRILL supports multi-access LAN (Local Area Network) links that can
   have multiple end stations and RBridges attached.  Where multiple
   RBridges are attached to a link, native traffic to and from end
   stations on that link is handled by a subset of those RBridges called
   "Appointed Forwarders", with the intent that native traffic in each
   VLAN (Virtual LAN) be handled by at most one RBridge.  The purpose of
   this document is to improve the documentation of the Appointed
   Forwarder mechanism; thus, it updates RFC 6325.

Status of This Memo

   This is an Internet Standards Track document.

   This document is a product of the Internet Engineering Task Force
   (IETF).  It represents the consensus of the IETF community.  It has
   received public review and has been approved for publication by the
   Internet Engineering Steering Group (IESG).  Further information on
   Internet Standards is available in Section 2 of RFC 5741.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at
   http://www.rfc-editor.org/info/rfc6439.

Perlman, et al.              Standards Track                    [Page 1]
RFC 6439             RBridges: Appointed Forwarders        November 2011

Copyright Notice

   Copyright (c) 2011 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
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   publication of this document.  Please review these documents
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   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1. Introduction ....................................................2
      1.1. Terminology and Acronyms ...................................3
   2. Appointed Forwarders and Their Appointment ......................4
      2.1. Appointment Effects of DRB Elections .......................5
      2.2. Appointment and Removal by the DRB .........................5
           2.2.1. Processing Forwarder Appointments ...................6
           2.2.2. Frequency of Appointments ...........................7
           2.2.3. Appointed Forwarders Limit ..........................8
      2.3. Local Configuration Action Appointment Effects .............8
      2.4. VLAN Mapping within a Link .................................9
   3. The Inhibition Mechanism ........................................9
   4. Inhibited Appointed Forwarder Behavior .........................11
   5. Multiple Ports on the Same Link ................................12
   6. Security Considerations ........................................12
   7. Acknowledgements ...............................................13
   8. References .....................................................13
      8.1. Normative References ......................................13
      8.2. Informative References ....................................13
   Appendix. VLAN Inhibition Example .................................14

1.  Introduction

   The IETF TRILL (TRansparent Interconnection of Lots of Links)
   protocol [RFC6325] provides optimal pair-wise data frame forwarding
   without configuration in multi-hop networks with arbitrary topology,
   safe forwarding even during periods of temporary loops, and support