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SFC WG                                                             T. Ao
Internet-Draft                                                Individual
Intended status: Standards Track                               G. Mirsky
Expires: December 6, 2019                                      ZTE Corp.
                                                                 Z. Chen
                                                           China Telecom
                                                            June 4, 2019


      Controlled Return Path for Service Function Chain (SFC) OAM
               draft-ao-sfc-oam-return-path-specified-04

Abstract

   This document defines extensions to the Service Function Chain (SFC)
   Operation, Administration and Maintenance (OAM) that enable control
   of the Echo Reply return path by specifying it as Reverse Service
   Function Path.  Enforcing the specific return path can be used to
   verify bidirectional connectivity of SFC and increase the robustness
   of SFC OAM.

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
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   This Internet-Draft will expire on December 6, 2019.

Copyright Notice

   Copyright (c) 2019 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
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   (https://trustee.ietf.org/license-info) in effect on the date of
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   carefully, as they describe your rights and restrictions with respect



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   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   the Trust Legal Provisions and are provided without warranty as
   described in the Simplified BSD License.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Conventions used in this document . . . . . . . . . . . . . .   3
     2.1.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
     2.2.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  Extension . . . . . . . . . . . . . . . . . . . . . . . . . .   3
   4.  SFC Reply Path TLV  . . . . . . . . . . . . . . . . . . . . .   4
   5.  Theory of Operation . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Bi-directional SFC Case . . . . . . . . . . . . . . . . .   5
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   5
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   6
     7.1.  SFC Return Path Type  . . . . . . . . . . . . . . . . . .   6
     7.2.  New Return Codes  . . . . . . . . . . . . . . . . . . . .   6
   8.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   6
     8.1.  Normative References  . . . . . . . . . . . . . . . . . .   6
     8.2.  Informative References  . . . . . . . . . . . . . . . . .   7
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   7

1.  Introduction

   While Service Function Chain (SFC) Echo Request, defined in
   [I-D.ietf-sfc-multi-layer-oam], always traverses the SFC it directed
   to, the corresponding Echo Reply is sent over IP network
   [I-D.ietf-sfc-multi-layer-oam].  There are scenarios when it is
   beneficial to direct the responder to use a path other than the IP
   network.  This document defines extensions to the Service Function
   Chain (SFC) Operation, Administration and Maintenance (OAM) that
   enable control of the Echo Reply return path by specifying it as
   Reply Service Function Path.  This document defines a new Type-
   Length-Value (TLV), Reply Service Function Path TLV, for Reply via
   Specified Path mode of SFC Echo Reply (Section 4).

   The Reply Service Function Path TLV can provide an efficient
   mechanism to test SFCs,such as bidirectional and hybrid SFC, as these
   were defined in Section 2.2 [RFC7665].  For example, it allows an
   operator to test both directions of the bidirectional or hybrid SFP
   with a single SFC Echo Request/Echo Reply operation.








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2.  Conventions used in this document

2.1.  Terminology

   SF - Service Function

   SFF - Service Function Forwarder

   SFC - Service Function Chain, an ordered set of some abstract SFs.

   SFP - Service Function Path

   SPI - Service Path Index

   OAM - Operation, Administration, and Maintenance

2.2.  Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
   "OPTIONAL" in this document are to be interpreted as described in BCP
   14 [RFC2119] [RFC8174] when, and only when, they appear in all
   capitals, as shown here.

3.  Extension

   Following reply modes had been defined in
   [I-D.ietf-sfc-multi-layer-oam]:

   o  Do Not Reply

   o  Reply via an IPv4/IPv6 UDP Packet

   o  Reply via Application Level Control Channel

   o  Reply via Specified Path

   The Reply via Specified Path mode is intended to enforce the use of
   the particular return path specified in the included TLV.  This mode
   may help to verify bidirectional continuity or increase the
   robustness of the monitoring of the SFC by selecting a more stable
   path.  In the case of SFC, the sender of Echo Request instructs the
   destination SFF to send Echo Reply message along the SFP specified in
   the SFC Reply Path TLV as described in Section 4.







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4.  SFC Reply Path TLV

   The SFC Reply Path TLV carries the information that sufficiently
   identifies the return SFP that the SFC Echo Reply message is expected
   to follow.  The format of SFC Reply Path TLV is shown in Figure 1.

        0                   1                   2                   3
        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |     SFC Reply Path Type       |          Length               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                 Reply Service Function Path                   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 1: SFC Reply TLV Format

   where:

   o  Reply Path TLV Type: is two octets long, indicates the TLV that
      contains information about the SFC Reply path.

   o  Length: is two octets long, MUST be equal to 4

   o  Reply Service Function Path is used to describe the return path
      that an SFC Echo Reply is requested to follow.

   The format of the Reply Service Function Path field displayed in
   Figure 2

        0                   1                   2                   3
        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Reply Service Function Path Identifier     | Service Index |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 2: Reply Service Function Path Field Format

   where:

   o  Reply Service Function Path Identifier: SFP identifier for the
      path that the SFC Echo Reply message is requested to be sent over.

   o  Service Index: used for forwarding in the reply SFP.








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5.  Theory of Operation

   [RFC7110] defined mechanism to control return path for MPLS LSP Echo
   Reply.  In case of SFC, the return path is a SFP along which SFC Echo
   Reply message MUST be transmitted.  Hence, the SFC Reply Path TLV
   included in the SFC Echo Request message MUST sufficiently identify
   the SFP that the sender of the Echo Request message expects the
   receiver to use for the corresponding SFC Echo Reply.

   When sending an Echo Request, the sender MUST set the value of Reply
   Mode field to "Reply via Specified Path", defined in
   [I-D.ietf-sfc-multi-layer-oam], and if the specified path is SFC
   path, the Request MUST include SFC Reply Path TLV.  The SFC Reply
   Path TLV includes identifier of the reverse SFP and an appropriate
   Service Index.

   Echo Reply is expected to be sent by the destination SFF of the SFP
   being tested or by the SFF at which SFC TTL expires as defined
   [RFC8300].  The processing described below equally applies in both
   cases and referred to as responding SFF.

   If the Echo Request message with SFC Reply Path TLV, received by the
   responding SFF, has Reply Mode value of "Reply via Specified Path"
   but no SFC Reply Path TLV is present, then the responding SFF MUST
   send Echo Reply with Return Code set to "Reply Path TLV is missing"
   value (TBA2).  If the responding SFF cannot find requested SFP it
   MUST send Echo Reply with Return Code set to "Reply SFP was not
   found" and include the SFC Reply Path TLV from the Echo Request
   message.

5.1.  Bi-directional SFC Case

   Ability to specify the return path to be used for Echo Reply is handy
   in bi-directional SFC.  For bi-directional SFC, since the last SFF of
   the forward SFP may not co-locate with a classifier of the reverse
   SFP,it is assumed that the last SFF doesn't know the reply path of a
   SFC.  So even for bi-directional SFC, a reverse SFP also need to be
   indicated in reply path TLV in echo request message.

6.  Security Considerations

   Security considerations discussed in [RFC8300] apply to this
   document.

   In addition, the SFC Return Path extension, defined in this document,
   can be used for potential "proxying" attacks.  For example, an echo
   request initiator may specify a return path that has a destination
   different from that of the initiator.  But usually, such attacks will



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   not happen in an SFC domain where the initiators and receivers belong
   to the same domain, as specified in [RFC7665].  Even if the attack
   occurs, in order to prevent using the SFC Return Path extension for
   proxying any possible attacks, the return path SFP SHOULD have a path
   to reach the sender of the echo request, identified in SFC Source TLV
   [I-D.ietf-sfc-multi-layer-oam].  The receiver MAY drop the echo
   request when it cannot determine whether the return path SFP has the
   route to the initiator.  That means, when sending echo request, the
   sender SHOULD choose a proper source address according to specified
   return path SFP to help the receiver to make the decision.

7.  IANA Considerations

7.1.  SFC Return Path Type

   IANA is requested to assign from its SFC Echo Request/Echo Reply TLV
   registry new type as follows:

             +-------+----------------------+---------------+
             | Value | Description          | Reference     |
             +-------+----------------------+---------------+
             | TBA1  | SFC Reply Path Type  | This document |
             +-------+----------------------+---------------+

                       Table 1: SFC Return Path Type

7.2.  New Return Codes

   IANA is requested to assign new return codes from the SFC Echo
   Request/Echo Reply Return Codes registry as following:

          +-------+----------------------------+---------------+
          | Value | Description                | Reference     |
          +-------+----------------------------+---------------+
          | TBA2  | Reply Path TLV is missing  | This document |
          | TBA3  | Reply SFP was not found    | This document |
          +-------+----------------------------+---------------+

                   Table 2: SFC Echo Reply Return Codes

8.  References

8.1.  Normative References

   [I-D.ietf-sfc-multi-layer-oam]
              Mirsky, G., Meng, W., Khasnabish, B., and C. Wang, "Active
              OAM for Service Function Chains in Networks", draft-ietf-
              sfc-multi-layer-oam-03 (work in progress), May 2019.



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   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,
              <https://www.rfc-editor.org/info/rfc2119>.

   [RFC8174]  Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
              2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
              May 2017, <https://www.rfc-editor.org/info/rfc8174>.

   [RFC8300]  Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed.,
              "Network Service Header (NSH)", RFC 8300,
              DOI 10.17487/RFC8300, January 2018,
              <https://www.rfc-editor.org/info/rfc8300>.

8.2.  Informative References

   [RFC7110]  Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord,
              "Return Path Specified Label Switched Path (LSP) Ping",
              RFC 7110, DOI 10.17487/RFC7110, January 2014,
              <https://www.rfc-editor.org/info/rfc7110>.

   [RFC7665]  Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
              Chaining (SFC) Architecture", RFC 7665,
              DOI 10.17487/RFC7665, October 2015,
              <https://www.rfc-editor.org/info/rfc7665>.

Authors' Addresses

   Ting Ao
   Individual
   No.889, BiBo Road
   Shanghai  201203
   China

   Phone: +86 17721209283
   Email: 18555817@qq.com


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

   Email: gregimirsky@gmail.com






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   Zhonghua Chen
   China Telecom
   No.1835, South PuDong Road
   Shanghai  201203
   China

   Phone: +86 18918588897
   Email: 18918588897@189.cn











































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