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Versions: 00 01                                                         
Service Function Chaining                                      C. Huang
Internet Draft                                      Carleton University
Intended status: Informational                              Jiafeng Zhu
Expires: July 13, 2015                                           Huawei
                                                                Peng He
                                                       January 13, 2015

                    SFC Use Cases on Recursive Services

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   Section 4.e of the Trust Legal Provisions and are provided without
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   Service function chaining (SFC) provides various services that can
   be tailored to different requirements from diversified user groups,
   where each user group forms a collective client that requires
   similar service. SFC is typically deployed as a service overlay with
   its own service topology on top of existing network topology. This
   kind of virtualized structure naturally enables recursive service
   relationship where a client may become a service provider and resell
   SFC services to its own user groups. Alternatively, a client may
   also choose to ask its service provider to provide a structured
   service for its user groups. This document describes some exemplary
   use cases that show the usage of recursive (e.g. nested) or
   structured service function chaining relationship.

Table of Contents

   1. Introduction ................................................ 2
   2. Conventions used in this document ........................... 3
   3. Use Case .................................................... 3
   4. Analysis .................................................... 6
   5. IANA Considerations ......................................... 6
   6. Refernces ................................................... 8

1. Introduction

   New services such as service function chaining (SFC) are becoming
   popular with network function virtualization. Traditionally a
   service chain consists of a set of dedicated network service boxes
   such as firewall, load balancers, and application delivery
   controllers that are concatenated together to support a specific
   application. With a new service request, new devices must be
   installed and interconnected in certain order. This can be a very
   complex, time-consuming, and error-prone process, requiring careful
   planning of topology changes and network outages and incurring high
   OPEX. This situation is exacerbated when a tenant requires different
   service sequences for different traffic flows or when multiple
   tenants share the same underlying network.

   Today's SFC takes a new approach built upon network function
   virtualization (NFV). It involves the implementation of network
   functions in software that can run on a range of industry standard

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   high volume servers, switches, and storage.  Through NFV, service
   providers can dynamically create a virtual environment for a
   specific service chain and eliminate the dedicated hardware and
   complex labor work for supporting a new service function chain

   One of the great potentials NFV can enable is the capability to
   support recursive SFC service. A client of SFC service can resell
   customized SFC services to its own user groups, where the client
   becomes a service provider and its subscribed user groups become new
   clients, without adding any dedicated hardware. This kind of
   recursive (or nested) service relationship is quite common in daily
   life. Big wholesalers can sell products to smaller wholesalers and
   the smaller wholesalers then sell those products to other small
   wholesalers or directly to end users. In telecom area, the Carriers'
   Carriers concept is defined in RFC 4364[1], which comes from similar
   idea. Forming recursive business relationship has been proven to be
   a successful business model due to the flexibility and efficiency it
   provides. The same arguments can also be applied to SFC service

   A distinguished characteristic of recursive SFC service is that the
   service provider at each level can have its own administrative
   authority built over the virtual environment provided by the lower
   level, leading to a hierarchy of administrative levels. This kind of
   hierarchical structure poses both opportunities and challenges for
   service providers.

   While a service provider at each level can have its own
   administrative authority, it can also choose to delegate its
   authority to its service provider. In the simple case, all levels of
   services will be delegated to one service provider, which will in
   turn provide a structured service [2].

   In a later section, a use case will be presented to illustrate a
   specific application scenario.

2. Conventions used in this document

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC-2119.

   In this document, these words will appear with that interpretation
   only when in ALL CAPS. Lower case uses of these words are not to be
   interpreted as carrying RFC-2119 significance.

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3. Use Case

   There are numerous use cases that recursive SFC service can be
   applied to. A typical use case is described below.

   Consider a scenario where Enterprise B outsources its enterprise
   network to a datacenter operated by a cloud service provider A. This
   type of scenario has been widely considered as one of the major
   applications of cloud computing. It is believed that enterprises can
   save their costs and improve their IT services by exploring the
   elasticity and dynamic sharing nature of a datacenter environment.
   Different enterprises typically have different requirements about
   their outsourced enterprise networks in terms of topology and
   service function.

   Consider the case that Enterprise B requests its outsourced network
   to have mesh topology with each node dedicated to a special service
   function. After receiving the request from Enterprise B, Cloud
   Provider A will create all requested virtual service function nodes
   with a mesh topology out of its infrastructure. Provider A will also
   need to assign an ID which is unique in his authority to identify
   this mesh service function chain.

                        +---+     +---+     +---+   |   +-----+
                    |   +---+  |  +---+  |  +---+   |   +---+
                    |          +---------+          +---+Web|
                    |                                   +---+
                  +-+-+   +---+   +--+   +---+
                  +-+-+   +---+   +--+   +---+
                    |     +---+   +---+   +--+   +---+
                          +---+   +---+   +--+   +---+

        Figure 1 : Service function chains created by Enterprise B.

   Suppose initially Enterprise B wants to support two user groups. One
   group includes all its employees. The other group is for visitors
   only. The two user groups have distinctive service function
   requirements. Therefore Enterprise B has to create two SFCs out of

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   its outsourced enterprise network. The first service chain, designed
   for its employees, will force traffic flows to go through NAT
   (Network Address Translation), SSL (Secure Socket layer)/TLS
   (Transport Layer Security), DPI (Deep Packet Inspection) if
   necessary, ADC (Application Delivery Controller), and various
   servers as shown in Fig.1. In this SFC, NAT, TLS, and DPI provide
   strong firewall service while ADC conducts service routing and load
   balance. The second SFC, designed for guest visitors, will go
   through NAT, WOC (Web Optimization Control), LB (Load Balancer), and
   web servers as shown in Fig.1. Here NAT provides limited firewall
   function with access control. WOC and LB are designed to optimize
   server efficiency. Enterprise B will create these two service chains
   as overlays over its outsourced enterprise network. Because the
   underlying service chain has a mesh topology with all different
   service function nodes, Enterprise B can create the two service
   chains very fast with minimal efforts.

   Suppose Enterprise B later wants to add another user group for one
   of its customers, called Customer C, it can do so easily by adding
   another service chain which may include NAT, SSL/TLS, WOC, and LB as
   shown in Fig.1. Each user group is a tenant for Enterprise B.
   Therefore Enterprise B needs to assign an ID for each tenant so that
   it can differentiate traffic streams for the three different
   tenants. Each Id needs to be unique for Enterprise B. Customer C may
   be an enterprise that has many departments who want to access the
   resources available at Enterprise B's network. Customer C is given
   full control of the service chain created for it. Customer C may
   then create a service chain and an ID for each department that needs

                   +---+           +--+   +---+
                   |SSL+-----------+LB+---+Web|   SFC created by
                   +---+           +--+   +---+   Client C
                     :               :      :
                     :               :      :
           +---+   +---+   +---+   +--+   +---+
           |NAT+---+SSL+---+WOC+---+LB+---+Web|   SFC created by
           +---+   +---+   +---+   +--+   +---+   Enterprise B
             :       :       :       :      :
             :       :       :       :      :
  +---+    +---+   +---+   +---+   +--+   +---+
  |DPI|    |NAT|   |SSL|   |WOC|   |LB|   |Web| SFC created by Cloud
  +---+    +---+   +---+   +---+   +--+   +---+   Provider A
    |        |       |       |      |       |

           Figure 2 : Recursive service function chain structure.

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   The above structure clearly leads to a recursive service
   relationship as shown in Fig.2 where dot lines show mapping
   relationship and dash lines are service chains (For clearness, only
   one service chain is shown for each level.). Cloud Provider A
   provides the first level SFC that includes a customized topology and
   generic service function nodes. Enterprise B provides the second
   level SFC which includes three customized SFCs. Customer C builds
   the third level SFCs for several departments over the SFC created by
   Enterprise B. As we mentioned before, this structure bears some
   similarity to the Carriers' Carriers concept defined in RFC 4364[1].

4. Analysis

   One of the key issues introduced by the hierarchy of recursive SFC
   relationship is the relationship between different levels. There are
   three types of relationship that can be envisioned. The first one is
   called independent relationship where the lower level is agnostic of
   the SFCs created by upper levels. Therefore all the service
   functions created by an upper level will be implemented and enforced
   at the upper level SFC modules while the lower level modules are
   completely unaware. When traffic arrives at a lower level module,
   the module processes the incoming traffic based on its service
   function requirements and de-multiplexes the traffic to the right
   upper level module using the IDs it assigned. The lower level module
   does not execute the service functions of upper level. The upper
   level applies different service functions based on the IDs it
   assigned. In this case, the upper level module does not have to be
   the same type as the lower level module. Hence there could be a new
   requirement for SFP header encapsulation, e.g., SFC header
   'stacking', similar to MPLS label stacking or even Ethernet VLAN tag
   stacking. A simple example is encryption/decryption service. The
   lower level SFC contains the encryption/decryption service to
   encrypt/decrypt the packet contents after the SFC header, the upper
   level SFC(s) has to properly deal with the SFC header received from
   the lower level, e.g., SFC header stacking might be worthy of

   The other type is opaque relationship where service functions
   defined by upper level may require collaboration from lower level.
   For example, Enterprise B may inform Cloud Provider A about some
   service functions it needs and ask Cloud Provider A to help
   implement those service functions. When traffic arrives at Cloud
   Provider A, it will identify traffic flows using both the ID it
   assigned and the ID assigned by upper level as a concatenated ID and
   then apply associated service functions. The traffic stream will not
   be delivered to upper level for those requested service functions.
   In this case, upper level functions inherit properties from lower

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   level functions. They are also constrained by the functions
   available from lower level. However the upper level can create new
   properties such as new firewall rules as long as it doesn't violate
   the constraint posed by the lower level. Whenever service functions
   at lower level are changed, upper level service functions will also
   be changed. However changes made to the upper level may not apply to
   lower level. Fig.2 is an example of the opaque relationship.

   In both cases, the upper level and lower level represent different
   authorities. Cloud Provider A decides the mesh service chain while
   Enterprise B decides the three linear service chains for its three
   tenants. In reality, a tenant is more likely to retain some
   functions as transparent (e.g. encryption function) and some
   functions as opaque (e.g. LB).

   Other than the two types mentioned above, it is also possible that
   the Enterprise C delegates its administrative role to Enterprise B,
   which in turn delegates its authority to Cloud Provider A. The
   benefit of this single administrative domain approach is that
   Enterprises B and C do not need to handle the administrative work.
   However, both B and C need to disclose all information to A, forming
   a transparent relationship. With transparent relationship, Cloud
   Provider A has to implement all SFCs with a hierarchical structure
   that satisfies the roles and responsibilities distributed according
   to the organizational structure of Enterprises B and C [2]. This
   kind of structured service is likely to become one of the SFC
   deployment paradigms.

   The above discussions show some special properties unique to
   recursive service chain. It is necessary to investigate how these
   properties can be supported using existing protocols, proposed SFC
   mechanisms, various other mechanisms, or even new proposals.

5. IANA Considerations

   It is recommended that IANA assign a port in UDP and another port
   number in TCP to identify the existing of SFLs in Layer 5. The top
   level SFL of a SFL stack can use all existing port number
   assignments to identify various applications.

6. References

   [1]  E. Rosen and Y. Rekhter, "BGP/MPLS IP Virtual Private Networks
         (VPNs)," IETF RFC 4364, February, 2006.

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   [2]  R. Szabo, A. Csazzar, K. Pentikousis, M. Kind, and D. Daino,
         "Unifying Carrier and Cloud Networks: Problem Sttatement and
         Challenge," IETF draft, Oct. 2014.

         < https://tools.ietf.org/html/draft-unify-nfvrg-challenges-00>

   Authors' Addresses

   Changcheng Huang
   Department of Systems and Computer Engineering
   Carleton University
   1125 Colonel By Drive
   Ottawa, ON K1S 5B6
   Email: huang@sce.carleton.ca

   Jiafeng Zhu
   Huawei Technologies Inc
   Santa Clara, CA
   Email: Jiafeng.zhu@huawei.com

   Peng He
   Ciena Corp
   Email: phe@ciena.com

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