The Babel Routing Protocol
RFC 8966

Document Type RFC - Proposed Standard (January 2021; No errata)
Obsoletes RFC 6126, RFC 7557
Authors Juliusz Chroboczek  , David Schinazi 
Last updated 2021-01-11
Replaces draft-chroboczek-babel-rfc6126bis
Stream Internet Engineering Task Force (IETF)
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Stream WG state Submitted to IESG for Publication
Document shepherd Donald Eastlake
Shepherd write-up Show (last changed 2019-03-26)
IESG IESG state RFC 8966 (Proposed Standard)
Action Holders
Consensus Boilerplate Yes
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Responsible AD Martin Vigoureux
Send notices to Donald Eastlake <>
IANA IANA review state Version Changed - Review Needed
IANA action state RFC-Ed-Ack

Internet Engineering Task Force (IETF)                     J. Chroboczek
Request for Comments: 8966             IRIF, University of Paris-Diderot
Obsoletes: 6126, 7557                                        D. Schinazi
Category: Standards Track                                     Google LLC
ISSN: 2070-1721                                             January 2021

                       The Babel Routing Protocol


   Babel is a loop-avoiding, distance-vector routing protocol that is
   robust and efficient both in ordinary wired networks and in wireless
   mesh networks.  This document describes the Babel routing protocol
   and obsoletes RFC 6126 and RFC 7557.

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 7841.

   Information about the current status of this document, any errata,
   and how to provide feedback on it may be obtained at

Copyright Notice

   Copyright (c) 2021 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
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction
     1.1.  Features
     1.2.  Limitations
     1.3.  Specification of Requirements
   2.  Conceptual Description of the Protocol
     2.1.  Costs, Metrics, and Neighbourship
     2.2.  The Bellman-Ford Algorithm
     2.3.  Transient Loops in Bellman-Ford
     2.4.  Feasibility Conditions
     2.5.  Solving Starvation: Sequencing Routes
     2.6.  Requests
     2.7.  Multiple Routers
     2.8.  Overlapping Prefixes
   3.  Protocol Operation
     3.1.  Message Transmission and Reception
     3.2.  Data Structures
     3.3.  Acknowledgments and Acknowledgment Requests
     3.4.  Neighbour Acquisition
     3.5.  Routing Table Maintenance
     3.6.  Route Selection
     3.7.  Sending Updates
     3.8.  Explicit Requests
   4.  Protocol Encoding
     4.1.  Data Types
     4.2.  Packet Format
     4.3.  TLV Format
     4.4.  Sub-TLV Format
     4.5.  Parser State and Encoding of Updates
     4.6.  Details of Specific TLVs
     4.7.  Details of specific sub-TLVs
   5.  IANA Considerations
   6.  Security Considerations
   7.  References
     7.1.  Normative References
     7.2.  Informative References
   Appendix A.  Cost and Metric Computation
     A.1.  Maintaining Hello History
     A.2.  Cost Computation
     A.3.  Route Selection and Hysteresis
   Appendix B.  Protocol Parameters
   Appendix C.  Route Filtering
   Appendix D.  Considerations for Protocol Extensions
   Appendix E.  Stub Implementations
   Appendix F.  Compatibility with Previous Versions
   Authors' Addresses

1.  Introduction

   Babel is a loop-avoiding distance-vector routing protocol that is
   designed to be robust and efficient both in networks using prefix-
   based routing and in networks using flat routing ("mesh networks"),
   and both in relatively stable wired networks and in highly dynamic
   wireless networks.  This document describes the Babel routing
   protocol and obsoletes [RFC6126] and [RFC7557].

1.1.  Features

   The main property that makes Babel suitable for unstable networks is
   that, unlike naive distance-vector routing protocols [RIP], it
   strongly limits the frequency and duration of routing pathologies
   such as routing loops and black-holes during reconvergence.  Even
   after a mobility event is detected, a Babel network usually remains
   loop-free.  Babel then quickly reconverges to a configuration that
   preserves the loop-freedom and connectedness of the network, but is
   not necessarily optimal; in many cases, this operation requires no
   packet exchanges at all.  Babel then slowly converges, in a time on
   the scale of minutes, to an optimal configuration.  This is achieved
   by using sequenced routes, a technique pioneered by Destination-
   Sequenced Distance-Vector routing [DSDV].

   More precisely, Babel has the following properties:

   *  when every prefix is originated by at most one router, Babel never
      suffers from routing loops;

   *  when a single prefix is originated by multiple routers, Babel may
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