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     IETF                                                           Ping Pan
     Internet Draft                                               (Infinera)
                                                               Thomas Nadeau
                                                                         (CA)
     
     
     Expires: January 3, 2012                                October 3, 2011
     
     
     
     
         Software-Defined Network (SDN) Problem Statement and Use Cases for
                              Data Center Applications
     
     
              draft-pan-sdn-dc-problem-statement-and-use-cases-00.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.................................................................3
        3. Related Work...................................................3
        4. Problem Definition.............................................4
        5. The Role of SDN Layer..........................................6
        6. Use Cases......................................................7
           6.1. Data Center Network Interface.............................7
           6.2. Inter-data center transport..............................10
           6.3. VPN......................................................11
        7. Security Consideration........................................11
        8. IANA Considerations...........................................11
        9. Normative References..........................................11
        10. 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.
     
     3. Related Work
     
        There has been much work in this area in recent years.
     
     
     
     
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        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 server-to-client configuration, but not client-to-server
        alarms or feedback.
     
        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.
     
     
      4. 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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     5. 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.
     
     
     
     6. Use Cases
     
     6.1. 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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     6.2. 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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     6.3. 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.
     
     
     
     7. Security Consideration
     
     8. IANA Considerations
     
        This document has no actions for IANA.
     
     9. 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.
     
     
     
     
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     10. 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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