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Versions: (draft-kumar-sfc-offloads) 00

Service Function Chaining                                       S. Kumar
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                             J. Guichard
Expires: October 4, 2017                    Huawei Technologies Co.,Ltd.
                                                                P. Quinn
                                                     Cisco Systems, Inc.
                                                              J. Halpern
                                                                S. Majee
                                                             F5 Networks
                                                           April 2, 2017

                    Service Function Simple Offloads


   Service Function Chaining (SFC) enables services to be delivered by
   selective traffic steering through an ordered set of service
   functions.  Once classified into an SFC, the traffic for a given flow
   is steered through all the service functions of the SFC for the life
   of the traffic flow even though this is often not necessary.
   Steering traffic to service functions only while required and not
   otherwise, leads to shorter SFC forwarding paths with improved
   latencies, reduced resource consumption and better user experience.

   This document describes the rationale, techniques and necessary
   protocol extensions to achieve such optimization, with focus on one
   such technique termed "simple offloads".

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
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at http://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on October 4, 2017.

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Copyright Notice

   Copyright (c) 2017 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
   Provisions Relating to IETF Documents
   (http://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   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  . . . . . . . . . . . . . . . . . . . . . . . .   3
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   2.  Definition Of Terms . . . . . . . . . . . . . . . . . . . . .   3
   3.  Service Function Path Reduction . . . . . . . . . . . . . . .   4
     3.1.  Bypass  . . . . . . . . . . . . . . . . . . . . . . . . .   4
     3.2.  Simple Offload  . . . . . . . . . . . . . . . . . . . . .   5
       3.2.1.  Stateful SFF  . . . . . . . . . . . . . . . . . . . .   7
       3.2.2.  Packet Re-ordering  . . . . . . . . . . . . . . . . .   7
       3.2.3.  Race Conditions . . . . . . . . . . . . . . . . . . .   8
       3.2.4.  Policy Implications . . . . . . . . . . . . . . . . .   8
       3.2.5.  Capabilities Exchange . . . . . . . . . . . . . . . .   8
   4.  Methods For SFP Reduction . . . . . . . . . . . . . . . . . .   9
     4.1.  SFP In-band Offload . . . . . . . . . . . . . . . . . . .   9
       4.1.1.  Progression Of SFP Reduction  . . . . . . . . . . . .  11
     4.2.  Service Controller Offload  . . . . . . . . . . . . . . .  12
   5.  Simple Offload Data-plane Signaling . . . . . . . . . . . . .  13
     5.1.  Offload Flags Definition  . . . . . . . . . . . . . . . .  14
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  15
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  15
     7.1.  Standard Class Registry . . . . . . . . . . . . . . . . .  15
       7.1.1.  Simple Offloads TLV . . . . . . . . . . . . . . . . .  15
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  16
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  16
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  16
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  16

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1.  Introduction

   Service function chaining involves steering traffic flows through a
   set of service functions in a specific order.  Such an ordered list
   of service functions is called a Service Function Chain (SFC).  The
   actual forwarding path used to realize an SFC is called the Service
   Function Path (SFP).

   Service functions forming an SFC are hosted at different points in
   the network, often co-located with different types of service
   functions to form logical groupings.  Applying a SFC thus requires
   traffic steering by the SFC infrastructure from one service function
   to the next until all the service functions of the SFC are applied.
   Service functions know best what type of traffic they can service and
   how much traffic needs to be delivered to them to achieve complete
   delivery of service.  As a consequence any service function may
   potentially request, within its policy constraints, traffic no longer
   be delivered to it or its function be performed by the SFC
   infrastructure, if such a mechanism is available.

   While there are several possible means to achieve this, one of the
   most flexible, directly connected to functional semantics, is based
   on allowing service functions themselves to evaluate a particular
   flow and reflect the result of this evaluation back to the SFC

   This document outlines the "simple offloads" mechanism that avoids
   steering traffic to service functions on flow boundary, on request
   from the service functions, while still ensuring compliance to the
   instantiated policy that mandates the SFC.

1.1.  Requirements Language

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

2.  Definition Of Terms

   This document uses the following terms.  Additional terms are defined
   in [RFC7498], [I-D.ietf-sfc-architecture] and [I-D.ietf-sfc-nsh].

   Service Controller (SC):  The entity responsible for managing the
       service chains, including create/read/update/delete actions as
       well as programming the service forwarding state in the network -
       SFP distribution.

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   Classifier (CF):  The entity, responsible for selecting traffic as
       well as SFP, based on policy, and forwarding the selected traffic
       on the SFP after adding the necessary encapsulation.  Classifier
       is implicitly an SFF.

   Offload:  A request or a directive from the SF to alter the SFP so as
       to remove the requesting SF from the SFP while maintaining the
       effect of the removed SF on the offloaded flow.

3.  Service Function Path Reduction

   The packet forwarding path of a SFP involves the classifier, one or
   more SFFs and all the SFs that are part of the SFP.  Packets of a
   flow are forwarded along this path to each of the SFs, for the life
   of the flow, whether SFs perform the full function in treating the
   packet or reapply the cached result, from the last application of the
   function, on the residual packets of the flow.  In other words, every
   packet on the flow incurs the same latency and the end-to-end SFP
   latency remains more or less constant subject to the nature of the
   SFs involved.  If an SF can be removed from the SFP, for a specific
   flow, traffic steering to the SF is avoided for that flow; thus
   leading to a shorter SFP for the flow.  When multiple SFs in a SFP
   are removed, the SFP starts to converge towards the optimum path,
   incurring a fraction of the latency associated with traversing the

   Although SFs are removed from the SFP, the corresponding SFC is not
   changed - this is subtle but an important characteristic of this
   mechanism.  In other words, this mechanism does not alter the SFC and
   still uses the SFP associated with the SFC.

   There are two primary approaches to removing an SF from the SFP.

   o  Bypass: Mechanism that alters the SFC.  Described in this draft
      for completeness.

   o  Simple Offload: Mechanism that alters the SFP alone, does not
      affect the SFC.  This is the primary focus of this draft.

3.1.  Bypass

   Many service functions do not deliver service to certain types of
   traffic.  For instance, typical WAN optimization service functions
   are geared towards optimizing TCP traffic and add no value to non-TCP
   traffic.  Non-TCP traffic thus can bypass such a service function.
   Even in the case of TCP, a WAN optimization SF may not be able to
   service the traffic if the corresponding TCP flow is not seen by it

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   from inception.  In such a situation a WAN optimization SF can avoid
   the overhead of processing such a flow or reserving resources for it,
   if it had the ability to request such flows not be steered to it.  In
   other words such service functions need the ability to request they
   be bypassed for a specified flow from a certain time in the life of
   that flow.

   A seemingly simple alternative is to require service functions pre
   specify the traffic flow types they add value to, such as the one-
   tuple: IP protocol-type described above.  A classifier built to use
   such data exposed by SFs, may thus enable bypassing such SFs for
   specific flows by way of selecting a different SFC that does not
   contain the SF being removed.

   Although knowledge of detailed SF profiles helps SFC selection at the
   classifier starting the SFC, it leads to shortcomings.

   o  It adds to the overhead of classification at that classifier as
      all SF classification requirements have to be met by the

   o  It leads to conflicts in classification requirements between the
      classifier and the SFs.  Classification needs of different SFs in
      the same SFC may vary.  A classifier thus cannot classify traffic
      based on the classification of one of the SFs in the chain.  For
      instance, even though a flow is uninteresting to one SF on an SFC,
      it may be interesting to another SF in the same SFC.

   o  The trigger for bypassing an SF may be dynamic as opposed to the
      static classification at the classifier - it may originate at the
      SFs themselves and involve the control and policy planes.  The
      policy and control planes may react to such a trigger by
      instructing the classifier to select a different SFC for the flow,
      thereby achieving SF bypass.

3.2.  Simple Offload

   Service delivery by a class of service functions involves inspecting
   the initial portion of the traffic and determining whether traffic
   should be permitted or dropped.  In some service functions, such an
   inspection may be limited to just the five tuple, in some others it
   may involve protocol headers, and in yet others it may involve
   inspection of the byte stream or application content based on the
   policy specified.  Firewall service functions fall into such a class,
   for example.  In all such instances, servicing involves determining
   whether to permit the traffic to proceed onwards or to deny the
   traffic from proceeding onwards and drop the traffic.  In some cases,
   dropping of the traffic may be accompanied with the generation of a

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   response to the originator of traffic or to the destination or both.
   Once the service function determines the result - permit or deny (or
   drop), it simply applies the same result to the residual packets of
   the flow by caching the result in the flow state.

   In essence, the effect of service delivery is a PERMIT or a DENY
   action on the traffic of a flow.  This class of service functions can
   avoid all the overhead of processing such traffic at the SF, by
   simply requesting another entity in the SFP, to assume the function
   of performing the action determined by the service function.  Since
   PERMIT and DENY are very simple actions, other entities in the SFP
   are very likely to be able to perform them on behalf of the
   requesting SF.  A service function can thus offload simple functions
   to other entities in the SFP.

   As with PERMIT and DENY actions, there are others which are simple
   enough to be supported.  Some are listed here for illustration.

   Unidirectional Offload:  Client-Server communication, typical of HTTP
       request-response transactions, imposes higher cost on SFs in one
       direction.  Reponses often carry more bytes, sometimes orders of
       mangnitude more, as compared to requests.  SFs could avoid the
       cost of moving the bits in the response direction to which it may
       add no value, once the policy is satisfied, if the response flow
       can be offloaded.  Hence Offloads must be requestable on a
       unidirectional flow boundary.

   TCP Control Exception Offload:  Most SFs maintain flow state and
       would like to know when a flow terminates, so SFs can cleanup the
       flow state and associated resources.  Such SFs need to receive
       the TCP control packets, the ones with control flags [RFC0793]
       set, on the flow even when the flow itself is offloaded, in order
       to perform such activity.  Hence Offloads must be predicatable to
       offload all but the TCP control packets of a flow.

   Time Limited Offload:  SF policy may dictate flows be limited to
       certain period of time among other reasons to optimize SF load.
       SFs can request a flow be offloaded for a specific time duration
       after which, all traffic on that flow gets redirected to the SF
       as was done before the offload was initiated.  Hence Offloads
       must be requestable on a time limit.

   Volume Limited Offload:  As with time limited offlaods, SF policy may
       dictate flows be limited to certain volume of data.  SFs can
       request a flow be offloaded until a specified number of bytes
       traverse the flow.  Hence Offloads must be requestable on a
       volume limit.

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   Since SFF is the one steering traffic to the SFs and hence is on the
   SFP, it is a natural entity to assume the offload function.  A SF not
   interested in traffic being steered to it can simply perform a simple
   offload by indicating a PERMIT action along with an OFFLOAD request.
   The SFF responsible for steering the traffic to the SF takes note of
   the ACTION and offload request.  The OFFLOAD directive and the ACTION
   received from the requesting SF are cached against the SF for that
   flow.  Once cached, residual packets on the flow are serviced by the
   cached directive and action as if being serviced by the corresponding

3.2.1.  Stateful SFF

   SFFs are the closest SFC infrastructure entities to the service
   functions.  SFFs may be state-full and hence can cache the offload
   and action in both of the unidirectional flows of a connection.  As a
   consequence, action and offload become effective on both the flows
   simultaneously and remain so until cancelled or the flow terminates.

   SFFs may not always honor the offload requests received from SFs.
   This does not affect the correctness of the SFP in any way.  It
   implies that the SFs can expect traffic to arrive on a flow, which it
   offloaded, and hence must service them, which may involve requesting
   an offload again.  It is natural to think of an acknowledgement
   mechanism to provide offload guarantees to the SFs but such a
   mechanism just adds to the overhead while not providing significant
   benefit.  Offload serves as a best effort mechanism.

3.2.2.  Packet Re-ordering

   The simple offload mechanism creates short time-windows where packet
   re-ordering may occur.  While SFs request flows be offloaded to SFFs,
   packets may still be in flight at various points along the SFP,
   including some between the SFF and the SF.  Once the offload decision
   is received and committed into the flow entry at the SFF, any packets
   arriving after and destined to the offloading SF are treated to the
   offload decision and forwarded along (if it is a PERMIT action).
   Inflight packets to the offloading SF may arrive at the SFF after one
   or more packets are already treated to the offload decision and
   forwarded along.

   This is a transitional effect and may not occur in all cases.  For
   instance, if the decision to offload a flow by an SF is based on the
   first packet of TCP flow, a reasonable time window exists between the
   offload action being committed into the SFF and arrival of subsequent
   packet of the same flow at that SFF.  Likewise, request/response
   based protocols such as HTTP may not always be subject to the re-
   ordering effects.

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3.2.3.  Race Conditions

   The tuple that make up an end-to-end flow or connection, such as a
   five tuple TCP connection, may be reused in a very short span of time
   when very high performing end points are involved.  A very remote
   manifestation of this behavior may involve the wrong incarnation of a
   flow at the SFF receiving the flow offload request from a SF.

   Implementations of simple offloads must thus be aware of such a
   possibility and include appropriate measures to address it.  It is
   important to note that a SFF must maintain correctness and hence it
   is acceptable to not honor a simple offloads request to resolve such
   an occurrence.  After all SFs exist with right security posture to
   protect against malicious traffic.

   A simple and widely used method to serialize reuse of tuples is to
   use an incarnation number in addition to the five-tuple.  The
   steering SFF can pass an opaque cookie, which in its simplest form
   could be the incarnation number, that is preserved by the SF and
   passed along with the simple offload request.  SFF can thus correctly
   identify the right incarnation of the flow.  SYN detection at the SFF
   to take corrective action is another option.  The SFF implementations
   may employ any technique deemed appropriate.

3.2.4.  Policy Implications

   Offload mechanism may be controlled by the policy layer.  The SFs
   themselves may have a static policy to utilize the capability offered
   by the SFC infrastructure.  They could also be dynamic and controlled
   by the specific policy layer under which the SFs operate.

   Similarly, the SFC infrastructure, specifically the classifiers and
   the SFFs, may be under the SFC infrastructure control plane policy
   controlling the decision to honor offloads from an SF.  This policy
   in turn may be coarse-grain, at the SF level, and hence static.  It
   can also be fine grain and hence dynamic but it adds to the overhead
   of policy distribution.

   Policy model related to offloads is out of scope of this document.

3.2.5.  Capabilities Exchange

   Simple offloads can be exposed and negotiated a priori as a
   capability between the SFFs and the SFs or the corresponding control
   layers.  In the simplest of the implementations, this is provided by
   the SFC infrastructure and the SFs are statically configured to
   utilize them without capabilities negotiation, within the constraints
   of the SF specific policies.

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   Capabilities exchange is outside the scope of this document.

4.  Methods For SFP Reduction

   There are a number of different models that may be used to facilitate
   SFP shortening.

   The methods discussed in the following sections require signaling
   among the participant components to communicate offload and permit/
   deny actions.  The signaling may be performed in the data-plane or in
   the control plane.

   a.  Data-plane: A SFC specific communication channel is needed for
       SFs to communicate the offload request along with the SF treated
       packet.  [NSH] defines a header specifically for carrying SFP
       along with metadata and provides such a channel for use with
       offloads.  Necessary bits need to be allocated in NSH to convey
       the action as well as the offload directive.  This signaling may
       be limited to SF and SFF or may continue from one SFF to another
       SFF or the classifier.  It may also involve signaling directly
       from the SF to the classifier.

   b.  Control-plane: Messages are required between the SF and the
       service controller as well as between the SFF and the service
       controller.  Service controller messaging is out of scope of this
       document and it is assumed to be service controller specific,
       which may include open or standard interfaces.

4.1.  SFP In-band Offload

   SFs receive traffic on an overlay from the SFF.  SFs service the
   traffic and turn them back to the SFF on an overlay or forward the
   traffic on the underlay.  In the former case, along with returning
   the traffic to SFF, they can perform simple offload by signaling
   OFFLOAD and ACTION to the SFF.  SFF caches the OFFLOAD and ACTION
   while forwarding the serviced packet onwards to the next service hop
   on the SFP or dropping it as per the ACTION.  This may continue from
   one hop to the next on the SFP.  SFF can now enforce the OFFLOAD and
   ACTION on the residual packets of the flow.

   By performing such hop-by-hop offloads, SFP can be reduced from its
   original length, steering traffic to only the SFFs and the SFs that
   really need to see the traffic.

   Figure 1 to Figure 3 show an example of SF and SFF performing offload
   operations, with PERMIT action, and the effect thereafter on the SFP.

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                 SFID(1)            SFID(2)            SFID(3)
                +------+           +------+           +------+
            ....| SF1  |....   ....| SF2  |....   ....| SF3  |....
            .   +------+   .   .   +------+   .   .   +------+   .
            .      |       .   .      |       .   .      |       .
            .      |       .   .      |       .   .      |       .
            .      |       .   .      |       .   .      |       .
            .      |       .   .      |       .   .      |       .
            .      |       .   .      |       .   .      |       .
    +----+  .   +------+   .   .   +------+   .   .   +------+   .
    | CF |------| SFF1 |-----------| SFF2 |-----------| SFF3 |------ Net
    +----+  .   +------+   .   .   +------+   .   .   +------+   .
            .              .   .              .   .              .
     SFP1 ...              .....              .....              ... >

     SFC1 = {SF1, SF2, SF3}
     SFC1 -> SFP1

       SFC1 is a service function chain
       SF1, SF2 and SF3 are three service functions
       SFP1 is the servcie function path for SFC1
       CF is the classifier starting SFP1 based on policy

     Note: Network forwarders are omitted from the figure for simplicity

                  Figure 1: SFC1 with corresponding SFP1

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                 SFID(1)       f +- SFID(2)            SFID(3)
                +------+       l | +------+           +------+
            ....| SF1  |....   o | | SF2  |       ....| SF3  |....
            .   +------+   .   a | +------+       .   +------+   .
            .      |       .   d |    |           .      |       .
            .      |       .     |    |           .      |       .
            .      |       .     |    |           .      |       .
            .      |       .     v    |           .      |       .
            .      |       .          |           .      |       .
    +----+  .   +------+   .       +------+       .   +------+   .
    | CF |------| SFF1 |-----------| SFF2 |-----------|  SFF3 |----- Net
    +----+  .   +------+   .       +------+       .   +------+   .
            .              .                      .              .
     SFP1 ...              ........................              ... >

             Figure 2: SFP1 after SFID(2) performs an Offload

            O                                     O
            f                                     f
            f +- SFID(1)            SFID(2)       f +- SFID(3)
            l | +------+           +------+       l | +------+
            o | | SF1  |           | SF2  |       o | | SF3  |
            a | +------+           +------+       a | +------+
            d |    |                  |           d |    |
              |    |                  |             |    |
              |    |                  |             |    |
              v    |                  |             v    |
                   |                  |                  |
    +----+      +------+           +------+           +------+
    | CF |------| SFF1 |-----------| SFF2 |-----------| SFF3 |----- Net
    +----+      +------+           +------+           +------+
     SFP1 .......................................................... >

         Figure 3: SFP1 after SFID(1) and SFID(3) perform Offloads

4.1.1.  Progression Of SFP Reduction

   SFP reduction happens one SFF at a time: by collapsing the SFF-to-SF
   hops into the SFF or the SFC infrastructure.

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   Figure 1 to Figure 3 show one sequence of offload events that lead to
   a shorter SFP.

   Corresponding transformation of the actual forwarding path is
   captured by the states below.

   Stage-1:  Prior to any offloads, service function path SFP1
       (corresponding to SFC1) has the following actual forwarding path
       as shown in Figure 1:
       CF ->
       SFF1 -> SF1 -> SFF1 ->
       SFF2 -> SF2 -> SFF2 ->
       SFF3 -> SF3 -> SFF3 ->

   Stage-2:  After SF2 performs a simple offload, service function path
       SFP1 changes to the one represented below, as also shown in
       Figure 2:
       CF ->
       SFF1 -> SF1 -> SFF1 ->
       SFF2 ->
       SFF3 -> SF3 -> SFF3 ->

   Stage-3:  After SF1 and SF3 both perform simple offloads, service
       function path SFP1 changes to the one represented below, as also
       show in Figure 3:
       CF ->
       SFF1 ->
       SFF2 ->
       SFF3 ->

   When all the SFs in a SFP perform offloads the forwarding path is
   reduced to pass through just the SFFs.

4.2.  Service Controller Offload

   Each SF signals the service controller of the OFFLOAD and ACTION via
   control plane messaging for a specific flow.  The service controller
   then signals the appropriate SFFs to offload the requested SFs, there
   by achieving the hop-by-hop offload behavior.

   The service controller has full knowledge of all the SFs of the SFP
   offloading the flow and hence can determine the optimum SFP within
   the Service Controller and program the appropriate SFFs to achieve
   SFP optimization.

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5.  Simple Offload Data-plane Signaling

   Since Offload and action are signaled at the time of returning the
   traffic to SFF, post servicing the traffic, such signaling can be
   integrated into the SFC service header of the packet.

   Figure 4 and Figure 5 show the bits necessary to achieve the
   signaling using the SFC encapsulation as described in
   [I-D.ietf-sfc-nsh].  In particular, for NSH MD-Type1 header format,
   the offload bits are communicated via the flags field in the very
   first byte of the fixed context headers.  For NSH MD-Type2 header
   format, the offload bits are communicated via a new standard TLV -
   Simple Offload TLV.  The standard TLV is requested to be allocated
   from the TLV Class, "Standard Class", from the IANA.

   By integrating the signaling with the packets, the simple offloads
   scale with the traffic in the data plane.

       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
      |D| F |X|         Context Header 1                              |
      |B|U|T|D|R|R|R|R| Context Header 2                              |
      |                 Context Header 3                              |
      |                 Context Header 4                              |

   X : Extend flags into first byte of "Context Header 2"
   B : Bidirectional Offload
   U : Unidirectional Offload
   T : TCP-control Exception Offload
   D : Drop Offload

         Figure 4: NSH Type-1 Offload Bits shown for DC Allocation

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       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
      |     STANDARD CLASS            | SimpleOffload |0|0|0|   0x2   |
      |B|U|T|D|S|V|R|R|R|R|R|R|         Offload-data                  |

   B : Bidirectional Offload
   U : Unidirectional Offload
   T : TCP-control Exception Offload
   D : Drop Offload
   S : Time Limited Offload
   V : Volume Limited Offload

                     Figure 5: NSH Type-2 Offload Bits

5.1.  Offload Flags Definition

   Offload Control Flags:

   B, Bidirectional Offload:  SF requests both flows in the connection,
       described by the payload, be offloaded, by setting B=1.  B=0

   U, Unidirectional Offload:  SF requests only the current flow in the
       connection, described by the payload, be offloaded, by setting
       U=1.  U=0 otherwise.

   One and only one of 'B' and 'U' MUST be specified to indicate
   offload.  In the event a NSH encapsulated packet is received with
   both 'B' and 'U' offload flags set to 1, 'B' MUST take precedence.

   Offload Function Flags:

   B|U, Permit Offload:  When either B=1 or U=1, the implicit function
       is to PERMIT or allow all packets on the flow(s) to traverse
       along the SFP, unless over-ridden by other functional flags.

   D, Drop Offload:  Setting D=1, requests packets on the offloaded
       flow(s) be dropped; D MUST be set to 0 otherwise.  D=1 modifies
       the default PERMIT behavior of 'B' and 'U' flags.

   T, TCP-control Exception Offload:  Setting T=1 requests TCP control
       packets to be exempted from Offload behavior.  TCP control
       packets MUST continue to be forwarded to the SF while the rest of
       the packets must be allowed to bypass the SF contingent upon the

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       application of other offload flags.  T MUST be set to 0

   S, Time Limited Offload:  Setting S=1 requests the flow(s) to be
       offloaded for the duration specified, in seconds, in offload-data
       field.  After that duration, offload behavior must be cancelled
       and affected flow(s) MUST be redirected to the SF.  S MUST be set
       to 0 otherwise.

   V, Volume Limited Offload:  Setting V=1 requests the flow(s) to be
       offloaded until the volume of data specified, in Kilo Bytes, in
       offload-data field has traversed the flow(s).  After that volume
       of data has traversed, offload behavior must be cancelled and
       affected flow(s) MUST be redirected to the SF.  V MUST be set to
       0 otherwise.

6.  Acknowledgements

   The authors would like to thank Abhjit Patra, Nagaraj Bagepalli, Kent
   Leung, Erik Nordmark, Diego Lopez for their comments, thoughtful
   questions and suggestions, review, etc.

7.  IANA Considerations

7.1.  Standard Class Registry

   IANA is requested to allocate a "STANDARD" class from the TLV Class
   registry.  Allocation of the registry values under this class shall
   follow the "IETF Review" policy defined in RFC 5226 [RFC5226].

7.1.1.  Simple Offloads TLV

   IANA is requested to allocate TLV type with value 0x1 from the
   STANDARD TLV class registry.  The format of the "Simple Offloads" TLV
   is as defined in this draft.

    | TLV# |       Name      |      Description       |   Reference   |
    |  1   | Simple Offloads | SF Flow Offload to SFF | This document |

                     Table 1: Standard Class Registry

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8.  Security Considerations

   Security of the offload signaling mechanism is very important.  This
   document does not advocate any additional security mechanisms beyond
   the data plane and control plane signaling security mechanisms.

9.  References

9.1.  Normative References

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

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

   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
              Requirement Levels", BCP 14, RFC 2119,
              DOI 10.17487/RFC2119, March 1997,

9.2.  Informative References

   [RFC0793]  Postel, J., "Transmission Control Protocol", STD 7,
              RFC 793, DOI 10.17487/RFC0793, September 1981,

   [RFC5226]  Narten, T. and H. Alvestrand, "Guidelines for Writing an
              IANA Considerations Section in RFCs", BCP 26, RFC 5226,
              DOI 10.17487/RFC5226, May 2008,

   [RFC7498]  Quinn, P., Ed. and T. Nadeau, Ed., "Problem Statement for
              Service Function Chaining", RFC 7498,
              DOI 10.17487/RFC7498, April 2015,

Authors' Addresses

   Surendra Kumar
   Cisco Systems, Inc.

   Email: surendra.stds@gmail.com

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   Jim Guichard
   Huawei Technologies Co.,Ltd.

   Email: jguichard1966@gmail.com

   Paul Quinn
   Cisco Systems, Inc.

   Email: paulq@cisco.com

   Joel Halpern

   Email: joel.halpern@ericsson.com

   Sumandra Majee
   F5 Networks

   Email: S.Majee@F5.com

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