Using Conditional Router Advertisements for Enterprise Multihoming
RFC 8475

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Internet Engineering Task Force (IETF)                        J. Linkova
Request for Comments: 8475                                        Google
Category: Informational                                       M. Stucchi
ISSN: 2070-1721                                                 RIPE NCC
                                                            October 2018

   Using Conditional Router Advertisements for Enterprise Multihoming

Abstract

   This document discusses the most common scenarios of connecting an
   enterprise network to multiple ISPs using an address space assigned
   by an ISP and how the approach proposed in "Enterprise Multihoming
   using Provider-Assigned Addresses without Network Prefix Translation:
   Requirements and Solution" could be applied in those scenarios.  The
   problem of enterprise multihoming without address translation of any
   form has not been solved yet as it requires both the network to
   select the correct egress ISP based on the packet source address and
   hosts to select the correct source address based on the desired
   egress ISP for that traffic.  The aforementioned document proposes a
   solution to this problem by introducing a new routing functionality
   (Source Address Dependent Routing) to solve the uplink selection
   issue.  It also proposes using Router Advertisements to influence the
   host source address selection.  It focuses on solving the general
   problem and covering various complex use cases, and this document
   adopts its proposed approach to provide a solution for a limited
   number of common use cases.  In particular, the focus of this
   document is on scenarios in which an enterprise network has two
   Internet uplinks used either in primary/backup mode or simultaneously
   and hosts in that network might not yet properly support multihoming
   as described in RFC 8028.

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/rfc8475.

Linkova & Stucchi             Informational                     [Page 1]
RFC 8475                     Conditional RAs                October 2018

Copyright Notice

   Copyright (c) 2018 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
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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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   4
   2.  Common Enterprise Multihoming Scenarios . . . . . . . . . . .   4
     2.1.  Two ISP Uplinks, Primary and Backup . . . . . . . . . . .   4
     2.2.  Two ISP Uplinks, Used for Load-Balancing  . . . . . . . .   5
   3.  Conditional Router Advertisements . . . . . . . . . . . . . .   5
     3.1.  Solution Overview . . . . . . . . . . . . . . . . . . . .   5
       3.1.1.  Uplink Selection  . . . . . . . . . . . . . . . . . .   5
       3.1.2.  Source Address Selection and Conditional RAs  . . . .   5
     3.2.  Example Scenarios . . . . . . . . . . . . . . . . . . . .   8
       3.2.1.  Single Router, Primary/Backup Uplinks . . . . . . . .   8
       3.2.2.  Two Routers, Primary/Backup Uplinks . . . . . . . . .   9
       3.2.3.  Single Router, Load-Balancing between Uplinks . . . .  12
       3.2.4.  Two Routers, Load-Balancing between Uplinks . . . . .  12
       3.2.5.  Topologies with Dedicated Border Routers  . . . . . .  13
       3.2.6.  Intrasite Communication during Simultaneous Uplinks
               Outage  . . . . . . . . . . . . . . . . . . . . . . .  15
       3.2.7.  Uplink Damping  . . . . . . . . . . . . . . . . . . .  15
       3.2.8.  Routing Packets When the Corresponding Uplink Is
               Unavailable . . . . . . . . . . . . . . . . . . . . .  16
     3.3.  Solution Limitations  . . . . . . . . . . . . . . . . . .  16
       3.3.1.  Connections Preservation  . . . . . . . . . . . . . .  17