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ARMD                                                       B. Schliesser
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Informational                                 L. Dunbar
Expires: November 29, 2011                           Huawei Technologies
                                                            May 28, 2011

                      ARMD Call for Investigation


   This document is a call for investigation into the topic of address
   resolution in massive datacenters.  It describes the intended work of
   the ARMD working group, providing both context and direction for
   investigating the issues outlined in the working group's charter.

Status of this Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on November 29, 2011.

Copyright Notice

   Copyright (c) 2011 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
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   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.

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Table of Contents

   1.  Call for Investigation  . . . . . . . . . . . . . . . . . . . . 3
     1.1.  Context . . . . . . . . . . . . . . . . . . . . . . . . . . 3
     1.2.  Questions . . . . . . . . . . . . . . . . . . . . . . . . . 4
   2.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . 5
   3.  IANA Considerations . . . . . . . . . . . . . . . . . . . . . . 5
   4.  Security Considerations . . . . . . . . . . . . . . . . . . . . 5
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . . . 5

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1.  Call for Investigation

1.1.  Context

   Modern datacenters are increasingly used to support advanced
   services, such as multi-tenant hosting, cloud, and Internet-scale
   websites.  Many of these datacenter facilities are being built to a
   much larger scale than previous generations.  As a result, datacenter
   network infrastructure is being stressed in a number of dimensions
   and traditional limits to scale are being tested.  One such aspect,
   being investigated by the ARMD working group, is the scaling of
   address resolution between the network (L3) and link (L2) layers of
   modern datacenter networks.

   In many cases, datacenter operators are responsible for provisioning
   and running everything from routers, switches, load balancers,
   firewalls, servers, and storage infrastructure.  Further, with the
   introduction of virtualization technology the capacity of these
   elements is increasing.  Each physical device attached to the network
   may now represent multiple logical instances, and may expose those
   instances through unique MAC and/or IP addresses.  For instance, with
   the introduction of Virtual Machine technology the operator can
   reduce wasted resources and achieve greater flexibility by
   instantiating multiple hosts on each physical server resource.
   Likewise virtual storage volumes, virtual routers, etc, may all exist
   in larger numbers.

   This virtualization trend contributes to both the increased scale and
   management complexity of these datacenter environments.  The
   flexibility of VM placement, including migration between different
   physical resources, has increased datacenter administrators' ability
   to instantiate VMs where the resources are, i.e. being able to
   relocate hosts from over-utilized servers to underutilized servers.
   There is a growing trend towards using resource-aware algorithms
   (e.g. evaluating energy, bandwidth, memory, CPU, etc) to determine
   placement that satisfies the processing and redundancy requirements
   of each VM while using the minimal number of physical resources.
   Fundamentally, such datacenter management tools are responsible for
   making trade-offs between different dimensions of scale, which can be
   difficult in very large and dynamic environments, and in all cases
   requires a significantly stronger understanding of platform

   In this environment, IP subnets can extend throughout multiple racks
   and/or rows in a data center, sometimes throughout multiple sites.
   There are cases, such as HPC and cloud datacenters, where the number
   of hosts in a single subnet (on a single segment) is growing.  In
   addition to the more recent VM environment, traditional organic

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   growth of physical hosts can also cause L2 segments to be extended
   throughout massive datacenters.  Availability / redundancy
   requirements, subnet size requirements (versus port density), and
   cost issues can all contribute to the growth and/or extension of

   The business demands and workloads for data centers have changed
   greatly over last 10 years, however some fundamental networking
   limitations remain unexplored.  Even though deployed networks
   generally do work, this often is because they're designed around
   known limitations (and redesigned around newly discovered limitations
   as time goes on).  There are datacenter networks that work fine until
   something changes, such as scale, at which time they're "fixed".
   Often the "fix" also introduces undesired limitations.  An example of
   this is a datacenter that moves from a flat L2 topology to a L3 core
   with multiple segregated L2 domains due to scale limitations, and
   subsequently is unable to distribute clustered servers beyond the
   boundaries of the "pod" in which a VLAN scope can be configured.

1.2.  Questions

   The initial goal of the ARMD working group is to document the
   limiting factors in address resolution scale and the problems
   associated with exceeding those limits.  Subsequently, the working
   group will identify operational solutions to these problems (to be
   promoted as Best Current Practice) or will identify gaps in existing
   solutions (for exploration in subsequent work).  Thus the ARMD
   working group is asked to consider the following questions:

   1.  What are the scaling characteristics of modern datacenter
       networks (e.g. "dimensions" of scale and their normal ranges)
       that are relevant to address resolution?

   2.  What are the operational problems related to address resolution
       in the modern datacenter environment?

   3.  What is the relationship between scaling characteristics of
       datacenter networks (question #1) and operational problems
       related to address resolution (question #2)?

   4.  What, if any, are alternative solutions to the operational
       problems of address resolution at massive scale?

   5.  What, if any, are the "gaps" in existing solutions?

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2.  Acknowledgements

   The authors would like to thank Ron Bonica for his significant
   contributions to this text.

3.  IANA Considerations

   This memo includes no request to IANA.

4.  Security Considerations

   This document does not, by itself, introduce any specific security
   considerations.  However, this document calls for further
   investigation into subject matter that may require significant
   consideration of security issues.  It is anticipated that documents
   submitted in response to this call for investigation will include
   appropriate Security Considerations text.

Authors' Addresses

   Benson Schliesser
   Cisco Systems, Inc.

   Email: bschlies@cisco.com

   Linda Dunbar
   Huawei Technologies

   Email: ldunbar@huawei.com

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