Architectural Considerations of IP Anycast
RFC 7094

Document Type RFC - Informational (January 2014; No errata)
Last updated 2014-01-16
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Internet Architecture Board (IAB)                           D. McPherson
Request for Comments: 7094                                Verisign, Inc.
Category: Informational                                          D. Oran
ISSN: 2070-1721                                            Cisco Systems
                                                               D. Thaler
                                                   Microsoft Corporation
                                                            E. Osterweil
                                                          Verisign, Inc.
                                                            January 2014

               Architectural Considerations of IP Anycast

Abstract

   This memo discusses architectural implications of IP anycast and
   provides some historical analysis of anycast use by various IETF
   protocols.

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 Architecture Board (IAB)
   and represents information that the IAB has deemed valuable to
   provide for permanent record.  It represents the consensus of the
   Internet Architecture Board (IAB).  Documents approved for
   publication by the IAB are not a candidate for any level of Internet
   Standard; see 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/rfc7094.

Copyright Notice

   Copyright (c) 2014 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
   (http://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.

McPherson, et al.             Informational                     [Page 1]
RFC 7094            Arch Considerations of IP Anycast       January 2014

Table of Contents

   1. Overview ........................................................2
   2. Background ......................................................3
      2.1. Anycast History ............................................3
      2.2. Anycast in IPv6 ............................................6
      2.3. DNS Anycast ................................................6
      2.4. BCP 126 on Operation of Anycast Services ...................8
   3. Principles ......................................................8
      3.1. Layering and Resiliency ....................................8
      3.2. Anycast Addresses as Destinations ..........................9
      3.3. Anycast Addresses as Sources ..............................10
      3.4. Service Discovery .........................................10
   4. Analysis .......................................................11
      4.1. Regarding Widespread Anycast Use ..........................11
      4.2. Transport Implications ....................................11
      4.3. Stateful Firewalls, Middleboxes, and Anycast ..............12
      4.4. Security Considerations ...................................12
      4.5. Deployment Considerations .................................15
   5. Conclusions ....................................................16
   6. Acknowledgements ...............................................16
   7. Informative References .........................................16
   Appendix A. IAB Members at the Time of Approval ...................21

1.  Overview

   IP anycast is a technique with a long legacy and interesting
   engineering challenges.  However, at its core, it is a relatively
   simple concept.  As described in BCP 126 [RFC4786], the general form
   of IP anycast is the practice of making a particular Service Address
   available in multiple, discrete, autonomous locations, such that
   datagrams sent are routed to one of several available locations.

   IP anycast is used for at least one critical Internet service: that
   of the Domain Name System [RFC1035] root servers.  By late 2007, at
   least 10 of the 13 root name servers were already using IP anycast
   [RSSAC29].  Use of IP anycast is growing for other applications as
   well.  It has been deployed for over a decade for DNS resolution
   services and is currently used by several DNS Top Level Domain (TLD)
   operators.  IP anycast is also used for other services in operational
   environments, including Network Time Protocol (NTP) [RFC5905]
   services.

   Anycast addresses are syntactically indistinguishable from unicast
   addresses.  Anycast addressing is equivalent to that of unicast in
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