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SFC WG                                                             T. Ao
Internet-Draft                                           ZTE Corporation
Intended status: Informational                                 G. Mirsky
Expires: September 14, 2017                                    ZTE Corp.
                                                          March 13, 2017


                    Analysis of the SFC scalability
                  draft-ao-sfc-scalability-analysis-02

Abstract

   SFC is an ordered set of service function, should be scalable to meet
   numerous requirements.  The scalability of SFC can be interpreted as
   ability of the SFC to accommodate one or more SFs joining the SFC ,
   or leaving the SFC without significant impact to SFC performance.

   This document presents four use cases on SFC scale-out and scale-in,
   and analysis of the requirements to support such capability.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
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   This Internet-Draft will expire on September 14, 2017.

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   include Simplified BSD License text as described in Section 4.e of
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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   2
   3.  Four Use cases for scale-out/scale-in . . . . . . . . . . . .   3
     3.1.  Join  . . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.2.  Redundancy  . . . . . . . . . . . . . . . . . . . . . . .   3
     3.3.  By-pass . . . . . . . . . . . . . . . . . . . . . . . . .   3
     3.4.  Failure or Remove . . . . . . . . . . . . . . . . . . . .   4
   4.  Data Plane Requirements . . . . . . . . . . . . . . . . . . .   4
   5.  Control Plane Requirements  . . . . . . . . . . . . . . . . .   5
     5.1.  Centralized CP  . . . . . . . . . . . . . . . . . . . . .   5
     5.2.  Distributed CP  . . . . . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   6
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
   8.  Information References  . . . . . . . . . . . . . . . . . . .   6
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   6

1.  Introduction

   Service Function Chain (SFC) is the chain with a series of ordered
   Service Functions(SF).  The SFC maybe changed because of load balance
   , failure, or other management requirement.  We call it SFC
   scalability.  The SFC being scalable means that the Service Functions
   can be added or removed from the path of this SFC.  With this
   capability, SFC is more flexible and elastic to adapt all kinds of
   requirements.

   In this document, we will present four use cases on SFC scale-out and
   scale-in, and analysis some requirements to support such capability.

2.  Terminology

   SFC(Service Function Chain): An ordered set of some abstract SFs.

   SFC Scale-out: One or more SFs are added into the path of the SFC for
   the sake of load balance, protection or other new services
   requirement.

   SFC Scale-in: One or more SFs are removed from the path of the SFC
   for the sake of the SFs are by-passed or the SFs are failed.






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3.  Four Use cases for scale-out/scale-in

   Following describe four use cases to illustrate the scalability of
   the SFC.

3.1.  Join

   This is SFC horizontal scale-out use case.  One or more new SFs must
   be added to a certain SFC for the traffic that has been classified to
   require application of new SF(s).  This case is the reverse scenario
   to the by-pass.  In this case one or more SFs that were by-passed
   need to be re-inserted into the SFC.  And the SFC itself can be
   characterized as being scaled out.

   There are two sub-cases of an SF joining the SFC.  One when both the
   SF and corresponding SFF are new to the SFC.  The second is when the
   SF attaches to an existing SFF.  In the first scenario, control plane
   needs to notify the upstream SFF to modify its next hop to point to
   the new SFF and configure the new SFF's forwarding information.  In
   the second scenario control plane needs to configure the existing
   SFF's forwarding information.  In this scenario, SFF forwards the
   packets not only according to the SFPID but also according to the
   metadata in the SFC header.

3.2.  Redundancy

   This is an example of SFC vertical scale-out use case.  One or more
   SFs are added into the SFC to meet the redundancy or load balance
   requirements.  This case is different with the Join case (section
   3.1) in that the SF is the same with one of the SF that is on the
   path of the SFC.  The new SF have the same function with the existing
   SF, and the new SF is added into the SFC to protect the existing
   corresponding SF and to load balance the existing corresponding SF.

   In this case, control plane need to notify the upstream SFF that the
   new SF joins the SFC as a redundancy SF for protection or load
   balance, and its next hop should be a protection group or ECMP group.
   For the purpose of load balance to ensure proper forwarding, the Flow
   Id field MUST be present in the NSH as expression of entropy so that
   SFF can select an SF from the group according to the Flow Id.

3.3.  By-pass

   This is a horizontal scale-in case.  In this scenario some SFs are
   not removed from the SFC but just by-passed by the traffic so that
   the packets will not be processed by these SFs.  Use cases for this
   scenario are described in [draft-ietf-sfc-long-lived-flow-use-cases]
   and [draft-kumar-sfc-offloads] . In these two drafts, the SF is



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   offloaded because it is not necessary to steer the traffic to the SFs
   to improve the forwarding performance.

   The corresponding solution is also provided in the above drafts.

3.4.  Failure or Remove

   This is a vertical SFC scale-in case.  This happens when the SFC is
   being protected or load balanced.  When SF in one SFC has failed or
   needs to be removed because it is no longer needed the ability of the
   SFC to scale-in is excercised.

   For this case the upstream SFF must be notified that its next hop
   must be changed to the next SF of the SF.

   From the cases described we can conclude that no matter if is SFC
   scale-out case or scale-in cases, there are some requirements to SFC
   control protocol.  And for some cases, there are requirements to data
   plane as well.

4.  Data Plane Requirements

   For the cases of load balancing or protection switch it is highly
   beneficial to have an entropy field in the SFC header to be used by
   the.  The entropy field can be named as Flow ID which should be in
   SFC header.

   This means that Classifier not only classifies the traffic based on
   different SFPID, but using Flow ID as well.

   According to the NSH draft in draft--ietf-sfc-nsh-12, we propose to
   extend NSH to include the entropy field.  Two options can be
   considered.  One is to use existing field, for example, some reserved
   bits.  Extended field in NSH Service Path Header is showed below as
   an example.

     0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |          Service Path Identifier (SPI)        | Service Index |
     +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
     |       Reserved                                |   Flow ID     |
     +-----------------------------------------------+---------------+

   Another is to extend a new metadata to meet the requirement.  Which
   has been described in draft draft-quinn-sfc-nsh-tlv-02 section 8.






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5.  Control Plane Requirements

   Another is to extend a new metadata to meet the requirement.  Which
   has been described in draft draft-quinn-sfc-nsh-tlv-02 section 8.

5.1.  Centralized CP

   Controller is required to:

   a) Send a message to SFF that the joined SF connected to set the
   correct SFPID and its next hop.

   b) Send register message to previous SFF with some information.  Such
   information not only includes next hop locator, but also includes an
   indicator that if the next hop is a new joined SF or the next hop is
   a new SF that added into a group.  If the indicator is a new joined
   SF, it means a new SF will join the SFC.  If the indicator is a group
   SF, it means a new SF will be added into a group for load balance or
   protection.

   c) Send de-register message to previous SFF with some information.
   Such information not only includes next hop locator, but also
   includes an indicator that if the next hop is the next SF because the
   current SF is by-passed, or the next hop is the SF that is removed
   from a group.  If the indicator is the by-passed SF, it means the
   current SF is by-passed or is leaving from the SFC.  If the indicator
   is group SF, it means the current SF will be removed into a
   protection group that is for load balance or protection.

5.2.  Distributed CP

   Distributed CP can be used in Plug-and-Play scenario.  Distributed CP
   requires:

   a) The SF that needs to join the SFC or by-pass from the SFC should
   notify the SFF it connects by a message.

   b) The SFF should send a register message to the previous SFF with
   some information.  Such information not only includes next hop
   locator, but also includes an indicator that if the next hop is a new
   joined SF or the next hop is a new SF that added into a group.  If
   the indicator is a new joined SF, it means a new SF will join the
   SFC.  If the indicator is a group SF, it means a new SF will be added
   into a group for load balance or protection.

   c) The SFF send de-register message to previous SFF with some
   information.  Such information not only includes next hop locator,
   but also includes an indicator that if the next hop is the next SF



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   because the current SF is by-passed, or the next hop is the SF that
   is removed from a group.  If the indicator is the by-passed SF, it
   means the current SF is by-passed or is leaving from the SFC.  If the
   indicator is group SF, it means the current SF will be removed into a
   protection group that is for load balance or protection.

6.  Security Considerations

   For the scalability of the SFC, security is very important to be
   considered.  Before allow the SF to join to the SFC, it is required
   to make sure the SF's security first.

7.  IANA Considerations

   TBD

8.  Information References

   [I-D.ietf-sfc-architecture]
              Halpern, J. and C. Pignataro, "Service Function Chaining
              (SFC) Architecture", draft-ietf-sfc-architecture-11 (work
              in progress), July 2015.

   [I-D.ietf-sfc-nsh]
              Quinn, P. and U. Elzur, "Network Service Header", draft-
              ietf-sfc-nsh-12 (work in progress), February 2017.

   [RFC7498]  Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for
              Service Function Chaining", RFC 7498,
              DOI 10.17487/RFC7498, April 2015,
              <http://www.rfc-editor.org/info/rfc7498>.

Authors' Addresses

   Ting Ao
   ZTE Corporation
   No.889, BiBo Road
   Shanghai  201203
   China

   Phone: +86 21 68897642
   Email: ao.ting@zte.com.cn









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   Greg Mirsky
   ZTE Corp.
   1900 McCarthy Blvd. #205
   Milpitas, CA  95035
   USA

   Email: gregimirsky@gmail.com












































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