Operation of Anycast Services
RFC 4786

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Network Working Group                                           J. Abley
Request for Comments: 4786                                Afilias Canada
BCP: 126                                                    K. Lindqvist
Category: Best Current Practice                 Netnod Internet Exchange
                                                           December 2006

                     Operation of Anycast Services

Status of This Memo

   This document specifies an Internet Best Current Practices for the
   Internet Community, and requests discussion and suggestions for
   improvements.  Distribution of this memo is unlimited.

Copyright Notice

   Copyright (C) The IETF Trust (2006).

Abstract

   As the Internet has grown, and as systems and networked services
   within enterprises have become more pervasive, many services with
   high availability requirements have emerged.  These requirements have
   increased the demands on the reliability of the infrastructure on
   which those services rely.

   Various techniques have been employed to increase the availability of
   services deployed on the Internet.  This document presents commentary
   and recommendations for distribution of services using anycast.

Abley & Lindqvist        Best Current Practice                  [Page 1]
RFC 4786                      Anycast BCP                  December 2006

Table of Contents

   1. Introduction ....................................................3
   2. Terminology .....................................................4
   3. Anycast Service Distribution ....................................5
      3.1. General Description ........................................5
      3.2. Goals ......................................................5
   4. Design ..........................................................6
      4.1. Protocol Suitability .......................................6
      4.2. Node Placement .............................................7
      4.3. Routing Systems ............................................8
           4.3.1. Anycast within an IGP ...............................8
           4.3.2. Anycast within the Global Internet ..................9
      4.4. Routing Considerations .....................................9
           4.4.1. Signalling Service Availability .....................9
           4.4.2. Covering Prefix ....................................10
           4.4.3. Equal-Cost Paths ...................................10
           4.4.4. Route Dampening ....................................12
           4.4.5. Reverse Path Forwarding Checks .....................13
           4.4.6. Propagation Scope ..................................13
           4.4.7. Other Peoples' Networks ............................14
           4.4.8. Aggregation Risks ..................................14
      4.5. Addressing Considerations .................................15
      4.6. Data Synchronisation ......................................15
      4.7. Node Autonomy .............................................16
      4.8. Multi-Service Nodes .......................................17
           4.8.1. Multiple Covering Prefixes .........................17
           4.8.2. Pessimistic Withdrawal .............................17
           4.8.3. Intra-Node Interior Connectivity ...................18
      4.9. Node Identification by Clients ............................18
   5. Service Management .............................................19
      5.1. Monitoring ................................................19
   6. Security Considerations ........................................19
      6.1. Denial-of-Service Attack Mitigation .......................19
      6.2. Service Compromise ........................................20
      6.3. Service Hijacking .........................................20
   7. Acknowledgements ...............................................21
   8. References .....................................................21
      8.1. Normative References ......................................21
      8.2. Informative References ....................................21

Abley & Lindqvist        Best Current Practice                  [Page 2]
RFC 4786                      Anycast BCP                  December 2006

1.  Introduction

   This document is addressed to network operators who are considering
   whether to deploy or operate a distributed service using anycast.  It
   describes the best current practice for doing so, but does not
   recommend whether any particular service should or should not be
   deployed using anycast.

   To distribute a service using anycast, the service is first
   associated with a stable set of IP addresses, and reachability to
   those addresses is advertised in a routing system from multiple,
   independent service nodes.  Various techniques for anycast deployment
   of services are discussed in [RFC1546], [ISC-TN-2003-1], and