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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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