Software-Defined Network (SDN) Problem Statement and Use Cases for Data Center Applications
draft-pan-sdn-dc-problem-statement-and-use-cases-01
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draft-pan-sdn-dc-problem-statement-and-use-cases-01
IETF Ping Pan
Internet Draft (Infinera)
Thomas Nadeau
(CA)
Expires: January 31, 2012 October 31, 2011
Software-Defined Network (SDN) Problem Statement and Use Cases for
Data Center Applications
draft-pan-sdn-dc-problem-statement-and-use-cases-01.txt
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Abstract
Service providers and enterprises are increasingly offering services
and applications from data centers. Subsequently, data centers
originate significant amount of network traffic. Without proper
network provisioning, user applications and services are subject to
congestion and delay.
In this document, we argue the necessity in providing network
information to the applications, and thereby enabling the
applications to directly provision network edge devices and relevant
applications.
Table of Contents
1. Introduction...................................................3
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2. Related Work...................................................3
3. Problem Definition.............................................4
4. The Role of SDN Layer..........................................6
5. Use Cases......................................................7
5.1. Data Center Network Interface.............................7
5.2. Inter-data center transport..............................10
5.3. VPN......................................................11
5.4. VM Mobility..............................................11
6. Security Consideration........................................12
7. IANA Considerations...........................................12
8. Normative References..........................................12
9. Acknowledgments...............................................12
1. Introduction
Service providers and enterprises are increasingly offering services
and applications from data centers. Subsequently, data centers
originate significant amount of network traffic. On contrast to end-
to-end user applications, much of the inter-data center traffic is
aggregated over a finite number of links over the backbone network.
As such, without proper network provisioning, user applications and
services are subject to congestion and delay.
Further, many web applications would require the interaction between
multiple servers in the networks. Without adequate level of
monitoring and provisioning on the network, the users may experience
unacceptable services.
In this document, we argue the necessity in providing network
information to the applications, and thereby enabling the
applications to provision the underlying network edge devices and
relevant applications directly.
Here are some of the conventions used in this document. The key
words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC-2119 [RFC2119].
2. Related Work
There has been much work in this area in recent years.
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OpenFlow [OpenFlow] has pioneered the concept of software-defined
network via FlowVisor. It has introduced a new packet forwarding
methodology to be applied on hardware or software L2 switches.
OpenFlow Version 1.0 and 1.1 have been in deployment in VM
hypervisor environment. The new versions will address issues such as
extendibility, modularity and carrier-grade. Currently, OpenFlow
does not support a mechanism to interface with network devices
through the existing IP/MPLS control-plane protocols.
NETCONF/YANG provides a XML-based solution for network device
configuration. It has been in wide-deployment. By definition, it
supports client-to-server configuration, and server-to-client
alarms or feedback (The servers are the devices/systems to be
configured; the clients are the network configuration/management
systems). NETCONF provides support for executing configuration
change transactions over multiple devices.
ALTO is a server solution designed to gather network abstraction
information and interface with applications (such as P2P) for more
efficient traffic distribution. It does not require configuring the
underlying network devices.
PCE is a client-server protocol that operates in MPLS networks that
enables the network operators to compute and potentially provision
optimal point-to-point and point-to-multipoint connections. However,
PCE does not interface with applications to optimize traffic from
user applications.
DMTF is a cloud computing standardization organization, which have
defined many virtualization management interfaces using Restful API.
However, it does not include any interface to the underlying
networks.
3. Problem Definition
Figure 1 illustrates the relationship between application and
network today, where the applications have little or fragmented
knowledge, control of or visibility of underlying networks and
resources.
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+-------------+ +-------------+ +-------------+
| Application | | Application | | Application |
| #1 | | #2 | | #3 |
+-------------+ +-------------+ +-------------+
| | |
| | |
+---------------------------------------------------+
| Physical Network |
+---------------------------------------------------+
Figure 1: Application to network relationship today
This presents a number of challenges and problems.
First, due to the lack of correlation, it becomes difficult to
provide service guarantees at network-level (in particular, delay)
to the applications. The operators may over-provision network links
to overcome to potential network congestion and packet drop within
data centers. However, such practice may become too costly in many
networking scenarios.
Second, many services require the interface and interaction with 3rd
party back-end applications that may operate from remote locations
(such as ads networks). This requires the service operators to
constantly monitor the SLA conditions with remote applications, and
adjust the network resources if necessary.
Third, many data center applications (such as VM) require massive
user data replication on different sites for performance and
redundancy purposes. Also, due to the limitation in routing and load
balancing, much user traffic may be routed between data centers. As
such, the inter-data center data transport need to be efficient,
which requires the proper interface between applications and
network.
Finally, to scale up enterprise applications on data centers, the
VM's may locate on different data centers, and mirage between data
centers depending on capacity and other constraints. This requires
the collaboration between VM applications and the underlying
networks.
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4. The Role of SDN Layer
To solve the above problem, one simple way is to introduce a
software-define network (SDN) layer (as shown in Figure 2), that is
responsible for network virtualization, programmability and
monitoring, between applications and network.
+-------------+ +-------------+ +-------------+
| Application | | Application | | Application |
| #1 | | #2 | | #3 |
+-------------+ +-------------+ +-------------+
| | |
| | |
+---------------------------------------------------+
| SDN Layer |
| (Network virtualization, programmability |
| and Monitoring) |
+---------------------------------------------------+
| | |
| | |
+---------------------------------------------------+
| Physical Network |
+---------------------------------------------------+
Figure 2: Application to network relationship today
The purpose of the SDN Layer is to enable the applications to
visualize the traffic flows at IP network layer, and manage the
mapping or binding between user traffic flows to the network
connections from the edge of the networks.
There are multiple ways in implementing the SDN Layer. There have
been multiple proprietary solutions in the area of interfacing
Virtual Machines (VM) to the underlying network interfaces. In
particular, solutions such as OpenFlow support such vision by
directly programming the underlying network interface via a new
protocol.
The implementation of SDN Layer involves the interfacing among
applications, storage and network devices, which implies that there
is a need for having a standardized interface.
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Further, we recommend of utilizing the existing technologies and
protocols to provision, manage and monitor network connections. The
focus in realizing the SDN Layer is in optimizing the application-
to-network workflow. The associated SDN protocols need to be
modular, scalable and simple in design.
5. Use Cases
5.1. Data Center Network Interface
Figure 3 illustrates the data flow in data centers.
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+--------------------+
| User Applications |
+--------------------+
|
\|/
+------------------------------------------------------+
| | Data |
| +--------------------------+ Centers |
| | Application Interface | |
| +--------------------------+ |
| | |
| \|/ |
| +-------+ |
| | Tasks | |
| +-------+ |
| / \ |
| / \ |
| +--------+ +--------+ |
| | Server | | Server | +-------+ |
| | #1 | ... | #N |<----->| SDN | |
| +--------+ +--------+ |Control| |
| | | +-------+ |
| \|/ \|/ ^ |
| +-------------------------------+ | |
| | Network Interface |<------+ |
| +-------------------------------+ |
| | |
+------------------------------------------------------+
|
\|/
+--------------------+
| User Applications |
+--------------------+
Figure 3: Data Center Traffic Flow
The data centers are designed to scale up to handle a large volume
of user requests. To handle the user requests, the application
interface would process and bundle the requests to different
servers. Depending on the application, the data may flow between the
servers or be forwarded to the users through network interface.
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Note that when the servers transmit data, they typically do not have
the knowledge on network connection bandwidth, delay and distance
information. For intra-data center communication, this can be
compensated by over-provisioning local networks. However, for
transferring data between two remotely located data centers, the
applications have no control of the data transmission.
Further, today, when setting up VM's over different servers,
extensive manual configuration may be required. For example, all the
traffic belongs to the same group/enterprise must share the same
VLAN over all involved servers. This can potentially handicap the
usability of the applications.
In this case, it would be desirable to have a standardized SDP
protocol that can be used by the applications to interface with the
networks. Through this protocol, the applications should be able to
assign VLAN values to the appropriate VM sessions over all servers,
and interface with the connected networks to balance the traffic
load if necessary.
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5.2. Inter-data center transport
+------------+
+----------------------| |-----------------------+
| +-------------| |-------------+ |
| | +-----| SDN |----+ | |
| | | | Controller | | | |
| | | +------------+ | | |
| | | | | |
| | | ^^^^^^ | | |
| | | ( ) | | |
+------+ +---+ +----+ ( ) +----+ +---+ +------
+
|Server|---|TOR|---|Core|---( Backbone )---|Core|---|TOR|---
|Server|
+------+ +---+ +----+ ( ) +----+ +---+ +------
+
( )
Data Center vvvvvv Data Center
#1 #2
Figure 4: Inter-data center transport
When transporting data between data centers, the packets will be
encapsulated into one or multiple tunnels before sending over the
Internet. Traffic engineering is typically applied at tunnel-level.
For instance, user IP packets at servers may be encapsulated first
into a VLAN tunnel, and then aggregated into MPLS LSP's at the core
node.
In this case, it would be desirable of having a SDN controller to
coordinate the aggregation procedure. The controller is responsible
for determining the mapping of the VLAN's to the MPLS LSP's.
Further, it is possible that the controller can interface with the
core node to adjust the LSP bandwidth.
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5.3. VPN
Another use case is VPN, as shown in Figure 5.
+----------+
+------+ | SDN |
|Office| +--|Controller|-------+
| A |----+ | +----------+ |
+------+ | ^^^^^^^^ | | |
+----+ ( ) +----+ +------+ +-------+
| CE |---( Backbone )---| PE |----|Switch|---|Servers|
+----+ ( ) +----+ +------+ +-------+
+------+ | vvvvvvvv
|Office| | Data Center X
| B |----+
+------+
Figure 5: VM Groups to MPLS VPN Mapping
At application level, the service providers may initiate a set of
VM's for a specific enterprise. For service guarantee, it requires
all the VM's that may be distributed on various servers and data
centers to be mapped to the same MPLS (L2)VPN.
There are multiple ways in achieving this goal. One is to utilize a
centralized SDN Controller to coordinate the mapping.
5.4. VM Mobility
VM mobility is to move one or multiple VM instances from one data
centers to another without disturbing the user existing setting and
applications. Once again, there are many ways to achieve such
objective.
Traditionally, the operators may create network tunnels between
routers/switches in the data centers, and switch VM traffic over the
tunnels. However, a more effective solution is to create a logical
controller between hypervisors to perform the VM mobility operator.
In the context of SDN, SDN controller can be used to coordinate the
hypervisors and the underlying network. It can provide the
efficiency in managing the VM's, while making the best use of the
underlying network resources.
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6. Security Consideration
TBD
7. IANA Considerations
This document has no actions for IANA.
8. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[2] Crocker, D. and Overell, P.(Editors), "Augmented BNF for
Syntax Specifications: ABNF", RFC 2234, Internet Mail
Consortium and Demon Internet Ltd., November 1997.
9. Acknowledgments
This work is based on the conversation with many people, including
Thomas Nadeau, Lydon Ong and Benson Schliesser.
Authors' Addresses
Ping Pan
Email: ppan@infinera.com
Thomas Nadeau
Email: Thomas.nadeau@ca.com
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