Internet DRAFT - draft-xu-sfc-coordinated-forwarding


Service Function Chaining                                       Qi Xu
Internet Draft                                            Huachun Zhou
Intended status: Informational                              Taixin Li
Expires: April 2017                                       Guanglei Li
                                                           Guanwen Li
                                           Beijing Jiaotong University
                                                       October 21, 2016

            A Coordinated Forwarding Method for Hierarchical SFC

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   Hierarchical SFC is a network architecture for implementing SFC the
   chain with an ordered set of service functions which could be
   deployed in multiple geographically dispersed networks. How to
   forward traffic between networks in Hierarchical SFC is what the
   draft wants to present.

   This document proposes a mapping-based forwarding method with
   coordinated orchestration by the translation of H-SFC and I-SFC to
   forward traffic between networks in Hierarchical SFC.

Table of Contents

   1. Introduction ................................................ 2
      1.1. Assumptions ............................................ 3
      1.2. Requirements Language................................... 3
   2. Terminology ................................................. 3
   3. Coordinated forwarding ...................................... 3
      3.1. Hierarchical Control Planes ............................ 4
         3.1.1. C5: Interface between SFC Control Planes .......... 5
         3.1.2. Interface between SFC Control Planes and IBN ...... 5
      3.2. Mapping-based forwarding method ........................ 5
   4. Metadata Consideration ...................................... 7
   5. Security Considerations ..................................... 8
   6. IANA Considerations ......................................... 8
   7. References .................................................. 8
      7.1. Normative References ................................... 8
      7.2. Informative References ................................. 8
   Authors'Addresses ............................................. 10

1. Introduction

   Hierarchical SFC is a network architecture for implementing SFC the
   chain with an ordered set of service functions which could be
   deployed in multiple geographically dispersed networks. Hierarchical
   SFC is described in detail in [I.D. dolson-sfc-hierarchical] and
   [], and is not repeated here.

   Because of hierarchical SFC supports service decomposition which
   means a SF chained by a SFC can be decomposed into several more
   refined SFs, a SF might be logical wherever it is deployed. So it is

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   necessary to check the availability of SFs especially those logical
   SFs in the procedure of orchestration.

   This document proposes that adding an interface in the SFC control
   plane for coordination between different SFC control planes of
   separate domains to achieve hierarchical service decompositions and
   describes a mapping-based forwarding method between multiple SFC
   domains for Hierarchical SFC in detail.

  1.1. Assumptions

   The following assumptions are made:

   o A Hierarchical SFC-enabled network has multiple level network
      domains. Each domain has their own control plane and data plane.

   o Control planes of different domain can work coordinately, but
      they are independent or non-transparent to each other. For
      example Top-Level network domain just uses logical SFs, but don't
      care how to construct a corresponding SFC for these logical SFs
      in Lower-Level network domains.

  1.2. Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   document are to be interpreted as described in RFC 2119 [RFC2119].

2. Terminology

   The reader should be familiar with the terms contained in [RFC7665],
   [I-D.ietf-sfc-control-plane], [I-D.dolson-sfc-hierarchical] and [I-].

   H-SFC: The SFC in the Top-Level network domain.

   I-SFC: The SFC in the Lower-Level network domain.

3. Coordinated forwarding

   When receiving a service request, the control plane should decide a
   SFC for it, select appropriate SF instances and make a SFP for the
   SFC. Furthermore, a classification policy which binds the flow with
   the request to a given SFC should be told to classifiers so that the
   flow can pass through relevant SFs along the SFP.

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   But in hierarchical SFC, SFs might be logical which means it can be
   decomposed to several less abstract, more refined SFs. Besides,
   logical SFs always represent SFCs in SFC-enabled sub-domains. So,
   how to guarantee the availability of logical SFs and forward SFC
   traffic among multiple SFC-enabled domains is an important problem.

   What follows in this document is going to describe how to solve
   aforementioned problem.

  3.1. Hierarchical Control Planes

   +----------------------+    C5
   |    SFC Control Plane +---->
   |                      |
       |    |    |    |
       |    |    |    v
       |    |    v    C4
       |    v    C3
       v    C2
               Figure 1: Interfaces of SFC Control Plane

   [I-D.ietf-sfc-control-plane] presents a reference architecture of
   the SFC control plane, including 4 kinds of interfaces between the
   SFC control plane and various SFC data plane elements.

   In hierarchical SFC that SFs are distributed over multiple SFC-
   enabled domains that the SFC needs to pass through, the control
   plane also should be hierarchical. As we know, each control plane is
   responsible for managing a single SFC-enabled domain. Then, each SFC
   control plane should gather and update information of local domain
   real-timely. Due to there is no fomal control hierarchy scheme, this
   document attempts to propose a simple Hierarchical Control Plane
   Scheme for Hierarchical SFC architecture.

   Figure 1 shows the interface reference points of the SFC control
   plane architecture. C1 is the interface between SFC Control Plane
   and SFC Classifier; C2 is the interface between SFC Control Plane
   and SFF; C3 is the interface between SFC Control Plane and SFC-aware
   SFs; C4 is the interface between SFC Control Plane and SFC Proxy; C5
   this document proposes is the interface between SFC Control Planes
   to provide an interface for coordination among those control planes
   of separate domains.

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   3.1.1. C5: Interface between SFC Control Planes

   As [I-D.ietf-sfc-hierarchical] said the IBN acts as an SFC-aware SF
   in the Top-Level domain (receiving SF instructions from the Top-
   Level control plane) and as a classifier in the Lower-Level domain
   (receiving classification rules from the Lower-Level control plane).

   At the Top-Level, the SFs that compose an SFC might be logical which
   means they are actually SFCs composed by more refined SFs in the
   Lower-Levels. To setup these logical SFs, it needs coordinated
   orchestration between the control planes of the Top-level and the
   Lower-Levels. During the orchestration for the logical SF of a SFC
   in the Top-Level, the control plane of the Top-Level should send an
   instruction to the control plane of the corresponding Lower-Level.
   When the latter receives this instruction that it is likely that the
   Top-level receives a service request from users, Lower-Level would
   construct or assign an I-SFC for this "service request?which is
   from the Top-Level, and make a classification rules for classifier
   in the IBN who connects the Top-Level with the Lowe-Level to match
   the received H-SFC with the corresponding I-SFC.

   3.1.2. Interface between SFC Control Planes and IBN

   Due to IBN behaves as an SF to Top-level domain, it is controlled by
   interface C3 or C4. Besides, IBN acts as a classifier and a SFF of
   end-of-chains to Lower-Level domain, it exchanges information with
   control plane of Lower-Level domain through interface C1 and C2.

  3.2. Mapping-based forwarding method

   This section shows an example of the processing of traffic
   forwarding between network domains. It is assumed that all logical
   SFs of H-SFC have been constructed by Lower-Level subdomains and
   relevant IBNs have known the classification rules.

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                                 |      SF#2     |
                                       |   |
                                       |   |
                                       |   |
   +---------+    +---------+       +--+---v--+       +---------+
   |  CF #1  +---->  SFF #1 +------->  SFF #2 +------->  SFF #3 +---->
   +---------+    +--+---^--+       +---------+       +--+---^--+
                     |   |                               |   |
                     |   |                         +-----v---+-----+
          +----------------------------+           | complex SF#3  |
          |          |   |             |           +---------------+
          |    +-----v---+-----+       |
          |    | complex SF#1  |       |
          |    +-----+------^--+       |           Top-Level
          |          |      |          |
          |          |      |          |
          |          |      |          |
          |        +----------------+  |           Lower-Level
          |        | |      |       |  |
          |        | |   +--+-----+ |  |
          |        | |   |  SFF   <----------------------------------+
          |        | |   +--------+ |  |                             |
          |        | |              |  |                             |
          |        | |              |  |                             |
          |        | |   +--------+ |  |   +--------+    +--------+  |
          |        | +--->  CF    +-------->SFF #1.1+---->SFF #1.2+--+
          |        |     +--------+ |  |   +--+--^--+    +--+--^--+
          |        +----------------+  |      |  |          |  |
          |  IBN                       |      |  |          |  |
          |                            |   +--v--+--+    +--v--+--+
          |                            |   | SF#1.1 |    | SF#1.2 |
          +----------------------------+   +--------+    +--------+
                Figure 2: An example of Hierarchical SFC

   Below is the working process:

   1. The IBN receives an H-SFC encapsulated packet from a Top-Level
      network domain.

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   2. To select an appropriate I-SFC encapsulation for the packet
      within the Lower-Level network domain, reclassification would be
      performed by classifier module of the IBN according to H-SFC
      header information and classification rules, as the example of
      figure 3. Extraordinarily, the last SI of I-SFC MUST be the IBN
      so that the flow can go back to the H-SFC through the IBN when
      the I-SFC is over.

   +--------+--------+               +----------+----------+
   |  H-SFC |  SF    |               |  I-SFC   |   SF     |
   +-----------------+ +-----------> +---------------------+
   |  8/2   |  FW    |               |  6/3     | EdgeFW   |
   +--------+--------+ +             +---------------------+
                       |             |  6/2     | AppFW    |
                       |             +---------------------+
                       |             |  6/1     | IBN      |
                       +-----------> +----------+----------+
                Figure 3: An example of Reclassification

   3. The IBN stores the entire original H-SFC header information, as
      well as the mapping relation of H-SFC and I-SFC.

   4. After reclassification, original H-SFC header of the packet would
      be replaced by the I-SFC header so that the packet could traverse
      the Lower-Level domain along the SFP of I-SFC.

   5. When the I-SFC encapsulated packets return to the IBN at the end,
      the SFF module of the IBN would parse the I-SFC header of the
      packets to check whether the I-SFC is over.

   6. For returning traffic from Lower-Level to Top-Level, IBN MUST
      look up the mapping relation to remove the I-SFC header and
      retrieve the original H-SFC header for the packets.

   7. Before the packets with the original H-SFC header return to the
      Top-level domain, IBN MUST decrement the value of SI of the H-SFC
      header. If necessary, IBN would modify or consume or produce
      metadata according to the policy of the complex SF.

4. Metadata Consideration

   Because the IBN is regarded as a Service Function to the Top-level
   domain, it should provide the ability to handle the metadata in the
   NSH header if necessary.

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   For example, it is common that checking the liveness of the service
   function of a service function path before the traffic selected by a
   Classifier traverse the network along a SFC which has been describe
   in [I-D.penno-sfc-trace-03]. Therefore the IBN must be able to add
   its identifying information at the end of the existing NSH headers
   as a Service Function.

5. Security Considerations


6. IANA Considerations


7. References

  7.1. Normative References

   [RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
             Chaining (SFC) Architecture", RFC 7665, DOI
             10.17487/RFC7665, October 2015, <http://www.rfc-

  7.2. Informative References

             Dolson, D., Homma, S., Lopez, D., Boucadair, M., D.Liu,
             and Ao, T., "Hierarchical Service Function Chaining",
             draft-dolson-sfc-hierarchical-05 (work in progress), March

             Ao, T. and W. Bo, "Hierarchical SFC for DC
             Interconnection", draft-ao-sfc-for-dc-interconnect-01(work
             in progress), October 2015.

             Komma, S., Tufail, M., Majee, S., Captari, C., and
             S.Homma, "Service Function Chaining Use Cases In Data
             Centers", draft-ietf-sfc-dc-use-cases-04 (work in
             progress), January 2016.

             Boucadair, M., Ed., "Service Function Chaining (SFC)
             Control Plane Components & Requirements", draft-ietf-sfc-
             control-plane-06 (work in progress), May 2016.

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             Szabo, R., Sonkoly, B., "A Multi-Domain Multi-Technology
             SFC Control Plane Experiment: A UNIFYed", draft-unify-sfc-
             control-plane-exp-00 (work in progress), March 2016.

   [1]       Sahhaf, Sahel, et al. "Network service chaining with
             optimized network function embedding supporting service
             decompositions." Computer Networks (2015): 492-505.

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Authors' Addresses

   Qi Xu
   Beijing Jiaotong University
   Beijing 100044 P.R. China


   Huachun Zhou
   Beijing Jiaotong University
   Beijing 100044 P.R. China


   Taixin Li
   Beijing Jiaotong University
   Beijing 100044 P.R. China


   Guanglei Li
   Beijing Jiaotong University
   Beijing 100044 P.R. China


   Guanwen Li
   Beijing Jiaotong University
   Beijing 100044 P.R. China


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