Address Resolution Problems in Large Data Center Networks
RFC 6820

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Internet Engineering Task Force (IETF)                         T. Narten
Request for Comments: 6820                               IBM Corporation
Category: Informational                                         M. Karir
ISSN: 2070-1721                                       Merit Network Inc.
                                                                  I. Foo
                                                     Huawei Technologies
                                                            January 2013

       Address Resolution Problems in Large Data Center Networks

Abstract

   This document examines address resolution issues related to the
   scaling of data centers with a very large number of hosts.  The scope
   of this document is relatively narrow, focusing on address resolution
   (the Address Resolution Protocol (ARP) in IPv4 and Neighbor Discovery
   (ND) in IPv6) within a data center.

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 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/rfc6820.

Narten, et al.                Informational                     [Page 1]
RFC 6820                      ARMD-Problems                 January 2013

Copyright Notice

   Copyright (c) 2013 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.  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 ....................................................3
   2. Terminology .....................................................3
   3. Background ......................................................4
   4. Address Resolution in IPv4 ......................................6
   5. Address Resolution in IPv6 ......................................7
   6. Generalized Data Center Design ..................................7
      6.1. Access Layer ...............................................8
      6.2. Aggregation Layer ..........................................8
      6.3. Core .......................................................9
      6.4. L3/L2 Topological Variations ...............................9
           6.4.1. L3 to Access Switches ...............................9
           6.4.2. L3 to Aggregation Switches ..........................9
           6.4.3. L3 in the Core Only ................................10
           6.4.4. Overlays ...........................................10
      6.5. Factors That Affect Data Center Design ....................11
           6.5.1. Traffic Patterns ...................................11
           6.5.2. Virtualization .....................................11
           6.5.3. Summary ............................................12
   7. Problem Itemization ............................................12
      7.1. ARP Processing on Routers .................................12
      7.2. IPv6 Neighbor Discovery ...................................14
      7.3. MAC Address Table Size Limitations in Switches ............15
   8. Summary ........................................................15
   9. Acknowledgments ................................................16
   10. Security Considerations .......................................16
   11. Informative References ........................................16

Narten, et al.                Informational                     [Page 2]
RFC 6820                      ARMD-Problems                 January 2013

1.  Introduction

   This document examines issues related to the scaling of large data
   centers.  Specifically, this document focuses on address resolution
   (ARP in IPv4 and Neighbor Discovery in IPv6) within the data center.
   Although strictly speaking the scope of address resolution is
   confined to a single L2 broadcast domain (i.e., ARP runs at the L2
   layer below IP), the issue is complicated by routers having many
   interfaces on which address resolution must be performed or with the