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Versions: 00 01                                                         
Service Function Chaining                                      C. Huang
Internet Draft                                      Carleton University
Intended status: Informational                              Jiafeng Zhu
Expires: January 1, 2015                                         Huawei
                                                                 Peng He
                                                            July 1, 2014

           SFC Use Cases on Recursive Service Function Chaining

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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. This document describes some
   exemplary use cases that show the usage of recursive (e.g. nested)
   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......................................................7

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
   high volume servers, switches, and storage.  Through NFV, service
   providers can dynamically create a virtual environment for a

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   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 each
   level of service provider has 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. 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.

3. Use Case

   There are numerous use cases that recursive SFL 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

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   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.
   The two user groups have distinctive service function requirements.
   Therefore Enterprise B has to create two SFCs out of 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 the 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

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   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 access.

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

          Figure 2 : Recursive service function chain structure.

   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

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   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
   two types of relationship that can be envisioned. The first one is
   called opaque 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 ID 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 (e.g. the lower level may be a NAT
   function while the upper level may be SSL function). But the upper
   level module will be based on the output of lower level module. For
   example, traffic that has been filtered by lower level cannot be
   recovered by upper level. This is why it is called opaque.

   The other type is transparent relationship where service functions
   defined by upper level may require collaboration from lower level.
   For example, Enterprise B may inform Cloud Provider A about the SFCs
   it has created and ask Cloud Provider A to help implement flows
   belonging to different SFCs. 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 de-
   multiplexed to upper level. In this case, upper level functions
   inherit properties from lower 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
   transparent relationship.

   In both cases, the upper level and lower level represent different
   authorities. Cloud Provider A decides the mesh service chain while

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   Enterprise B decides the three linear service chains for its three
   tenants. This is key feature of recursive service function chaining.
   In practice, a tenant is more likely to retain some functions as
   opaque (e.g. encryption function) and some functions as transparent
   (e.g. LB).

   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.

   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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