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
draft-ietf-armd-call-for-investigation-00
Abstract
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
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This Internet-Draft will expire on November 29, 2011.
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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
capabilities.
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
segments.
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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