Practices for Scaling ARP and Neighbor Discovery (ND) in Large Data Centers
RFC 7342

Independent Submission                                         L. Dunbar
Request for Comments: 7342                                        Huawei
Category: Informational                                        W. Kumari
ISSN: 2070-1721                                                   Google
                                                            I. Gashinsky
                                                                   Yahoo
                                                             August 2014

           Practices for Scaling ARP and Neighbor Discovery (ND)
                           in Large Data Centers

Abstract

   This memo documents some operational practices that allow ARP and
   Neighbor Discovery (ND) to scale in data center environments.

Status of This Memo

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

   This is a contribution to the RFC Series, independently of any other
   RFC stream.  The RFC Editor has chosen to publish this document at
   its discretion and makes no statement about its value for
   implementation or deployment.  Documents approved for publication by
   the RFC Editor 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/rfc7342.

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
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   to this document.

Dunbar, et al.                Informational                     [Page 1]
RFC 7342             Scaling ARP and ND in Large DCs         August 2014

Table of Contents

   1. Introduction ....................................................2
   2. Terminology .....................................................4
   3. Common DC Network Designs .......................................4
   4. Layer 3 to Access Switches ......................................5
   5. Layer 2 Practices to Scale ARP/ND ...............................5
      5.1. Practices to Alleviate APR/ND Burden on L2/L3
           Boundary Routers ...........................................5
           5.1.1. Communicating with a Peer in a Different Subnet .....6
           5.1.2. L2/L3 Boundary Router Processing of Inbound
                  Traffic .............................................7
           5.1.3. Inter-Subnet Communications .........................8
      5.2. Static ARP/ND Entries on Switches ..........................8
      5.3. ARP/ND Proxy Approaches ....................................9
      5.4. Multicast Scaling Issues ...................................9
   6. Practices to Scale ARP/ND in Overlay Models ....................10
   7. Summary and Recommendations ....................................10
   8. Security Considerations ........................................11
   9. Acknowledgements ...............................................11
   10. References ....................................................12
      10.1. Normative References .....................................12
      10.2. Informative References ...................................13

1.  Introduction

   This memo documents some operational practices that allow ARP/ND to
   scale in data center environments.

   As described in [RFC6820], the increasing trend of rapid workload
   shifting and server virtualization in modern data centers requires
   servers to be loaded (or reloaded) with different Virtual Machines
   (VMs) or applications at different times.  Different VMs residing on
   one physical server may have different IP addresses or may even be in
   different IP subnets.

   In order to allow a physical server to be loaded with VMs in
   different subnets or allow VMs to be moved to different server racks
   without IP address reconfiguration, the networks need to enable
   multiple broadcast domains (many VLANs) on the interfaces of L2/L3
   boundary routers and Top-of-Rack (ToR) switches and allow some
   subnets to span multiple router ports.

   Note: L2/L3 boundary routers as discussed in this document are
   capable of forwarding IEEE 802.1 Ethernet frames (Layer 2) without a
   Media Access Control (MAC) header change.  When subnets span multiple
   ports of those routers, they still fall under the category of
   "single-link" subnets, specifically the multi-access link model