Enterprise Multihoming using Provider-Assigned IPv6 Addresses without Network Prefix Translation: Requirements and Solutions
RFC 8678

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Internet Engineering Task Force (IETF)                          F. Baker
Request for Comments: 8678                                              
Category: Informational                                        C. Bowers
ISSN: 2070-1721                                         Juniper Networks
                                                              J. Linkova
                                                                  Google
                                                           December 2019

 Enterprise Multihoming Using Provider-Assigned IPv6 Addresses without
         Network Prefix Translation: Requirements and Solutions

Abstract

   Connecting an enterprise site to multiple ISPs over IPv6 using
   provider-assigned addresses is difficult without the use of some form
   of Network Address Translation (NAT).  Much has been written on this
   topic over the last 10 to 15 years, but it still remains a problem
   without a clearly defined or widely implemented solution.  Any
   multihoming solution without NAT requires hosts at the site to have
   addresses from each ISP and to select the egress ISP by selecting a
   source address for outgoing packets.  It also requires routers at the
   site to take into account those source addresses when forwarding
   packets out towards the ISPs.

   This document examines currently available mechanisms for providing a
   solution to this problem for a broad range of enterprise topologies.
   It covers the behavior of routers to forward traffic by taking into
   account source address, and it covers the behavior of hosts to select
   appropriate default source addresses.  It also covers any possible
   role that routers might play in providing information to hosts to
   help them select appropriate source addresses.  In the process of
   exploring potential solutions, this document also makes explicit
   requirements for how the solution would be expected to behave from
   the perspective of an enterprise site network administrator.

Status of This Memo

   This document is not an Internet Standards Track specification; it is
   published for informational purposes.

   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).  Not all documents
   approved by the IESG are candidates for any level of Internet
   Standard; see 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
   https://www.rfc-editor.org/info/rfc8678.

Copyright Notice

   Copyright (c) 2019 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
   (https://trustee.ietf.org/license-info) 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
   2.  Requirements Language
   3.  Terminology
   4.  Enterprise Multihoming Use Cases
     4.1.  Simple ISP Connectivity with Connected SERs
     4.2.  Simple ISP Connectivity Where SERs Are Not Directly
           Connected
     4.3.  Enterprise Network Operator Expectations
     4.4.  More Complex ISP Connectivity
     4.5.  ISPs and Provider-Assigned Prefixes
     4.6.  Simplified Topologies
   5.  Generating Source-Prefix-Scoped Forwarding Tables
   6.  Mechanisms for Hosts To Choose Good Default Source Addresses in
           a Multihomed Site
     6.1.  Default Source Address Selection Algorithm on Hosts
     6.2.  Selecting Default Source Address When Both Uplinks Are
           Working
       6.2.1.  Distributing Default Address Selection Policy
               Table with DHCPv6
       6.2.2.  Controlling Default Source Address Selection with
               Router Advertisements
       6.2.3.  Controlling Default Source Address Selection with
               ICMPv6
       6.2.4.  Summary of Methods for Controlling Default Source
               Address Selection to Implement Routing Policy
     6.3.  Selecting Default Source Address When One Uplink Has Failed
       6.3.1.  Controlling Default Source Address Selection with
               DHCPv6
       6.3.2.  Controlling Default Source Address Selection with
               Router Advertisements
       6.3.3.  Controlling Default Source Address Selection with
               ICMPv6
       6.3.4.  Summary of Methods for Controlling Default Source
               Address Selection on the Failure of an Uplink