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Versions: (draft-xuclad-spring-sr-service-chaining) 00 01

SPRING                                                      F. Clad, Ed.
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                              X. Xu, Ed.
Expires: January 3, 2019                                         Alibaba
                                                             C. Filsfils
                                                     Cisco Systems, Inc.
                                                              D. Bernier
                                                             Bell Canada
                                                                   C. Li
                                                                  Huawei
                                                             B. Decraene
                                                                  Orange
                                                                   S. Ma
                                                                 Juniper
                                                           C. Yadlapalli
                                                                    AT&T
                                                           W. Henderickx
                                                                   Nokia
                                                              S. Salsano
                                        Universita di Roma "Tor Vergata"
                                                           July 02, 2018


                Service Programming with Segment Routing
             draft-xuclad-spring-sr-service-programming-00

Abstract

   This document defines data plane functionality required to implement
   service segments and achieve service programming in SR-enabled MPLS
   and IP networks, as described in the Segment Routing architecture.

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 https://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 January 3, 2019.



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Copyright Notice

   Copyright (c) 2018 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
   (https://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
   2.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   4
   3.  Classification and steering . . . . . . . . . . . . . . . . .   4
   4.  Service segments  . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  SR-aware services . . . . . . . . . . . . . . . . . . . .   5
     4.2.  SR-unaware services . . . . . . . . . . . . . . . . . . .   6
   5.  SR service policies . . . . . . . . . . . . . . . . . . . . .   7
     5.1.  SR-MPLS data plane  . . . . . . . . . . . . . . . . . . .   8
     5.2.  SRv6 data plane . . . . . . . . . . . . . . . . . . . . .  10
   6.  SR proxy behaviors  . . . . . . . . . . . . . . . . . . . . .  11
     6.1.  Static SR proxy . . . . . . . . . . . . . . . . . . . . .  14
       6.1.1.  SR-MPLS pseudocode  . . . . . . . . . . . . . . . . .  16
       6.1.2.  SRv6 pseudocode . . . . . . . . . . . . . . . . . . .  17
     6.2.  Dynamic SR proxy  . . . . . . . . . . . . . . . . . . . .  19
       6.2.1.  SR-MPLS pseudocode  . . . . . . . . . . . . . . . . .  19
       6.2.2.  SRv6 pseudocode . . . . . . . . . . . . . . . . . . .  20
     6.3.  Shared memory SR proxy  . . . . . . . . . . . . . . . . .  21
     6.4.  Masquerading SR proxy . . . . . . . . . . . . . . . . . .  21
       6.4.1.  SRv6 masquerading proxy pseudocode  . . . . . . . . .  22
       6.4.2.  Variant 1: Destination NAT  . . . . . . . . . . . . .  23
       6.4.3.  Variant 2: Caching  . . . . . . . . . . . . . . . . .  23
   7.  Metadata  . . . . . . . . . . . . . . . . . . . . . . . . . .  23
     7.1.  MPLS data plane . . . . . . . . . . . . . . . . . . . . .  23
     7.2.  IPv6 data plane . . . . . . . . . . . . . . . . . . . . .  24
       7.2.1.  SRH TLV objects . . . . . . . . . . . . . . . . . . .  24
       7.2.2.  SRH tag . . . . . . . . . . . . . . . . . . . . . . .  25
   8.  Implementation status . . . . . . . . . . . . . . . . . . . .  25
     8.1.  SR-aware services . . . . . . . . . . . . . . . . . . . .  25
     8.2.  Proxy behaviors . . . . . . . . . . . . . . . . . . . . .  25
   9.  Related works . . . . . . . . . . . . . . . . . . . . . . . .  26
   10. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  26



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   11. Security Considerations . . . . . . . . . . . . . . . . . . .  27
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  27
   13. Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  27
   14. References  . . . . . . . . . . . . . . . . . . . . . . . . .  27
     14.1.  Normative References . . . . . . . . . . . . . . . . . .  27
     14.2.  Informative References . . . . . . . . . . . . . . . . .  28
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction

   Segment Routing (SR) is an architecture based on the source routing
   paradigm that seeks the right balance between distributed
   intelligence and centralized programmability.  SR can be used with an
   MPLS or an IPv6 data plane to steer packets through an ordered list
   of instructions, called segments.  These segments may encode simple
   routing instructions for forwarding packets along a specific network
   path, but also steer them through VNFs or physical service appliances
   available in the network.

   In an SR network, each of these services, running either on a
   physical appliance or in a virtual environment, are associated with a
   segment identifier (SID).  These service SIDs are then leveraged as
   part of a SID-list to steer packets through the corresponding
   services.  Service SIDs may be combined together in a SID-list to
   achieve service programming, but also with other types of segments as
   defined in [I-D.ietf-spring-segment-routing].  SR thus provides a
   fully integrated solution for overlay, underlay and service
   programming.  Furthermore, the IPv6 instantiation of SR (SRv6)
   supports metadata transportation in the Segment Routing header
   [I-D.ietf-6man-segment-routing-header], either natively in the tag
   field or with extensions such as TLVs.

   This document describes how a service can be associated with a SID,
   including legacy services with no SR capabilities, and how these
   service SIDs are integrated within an SR policy.  The definition of
   an SR Policy and the traffic steering mechanisms are covered in
   [I-D.ietf-spring-segment-routing-policy] and hence outside the scope
   of this document.

   The definition of control plane components, such as service segment
   discovery, is outside the scope of this data plane document.  For
   reference, the option of using BGP extensions to support SR service
   programming is proposed in [I-D.dawra-idr-bgp-sr-service-chaining].








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2.  Terminology

   This document leverages the terminology proposed in
   [I-D.ietf-spring-segment-routing] and
   [I-D.ietf-spring-segment-routing-policy].  It also introduces the
   following new terms.

   Service segment: A segment associated with a service.  The service
   may either run on a physical appliance or in a virtual environment
   such as a virtual machine or container.

   SR-aware service: A service that is fully capable of processing SR
   traffic.  An SR-aware service can be directly associated with a
   service segment.

   SR-unaware service: A service that is unable to process SR traffic or
   may behave incorrectly due to presence of SR information in the
   packet headers.  An SR-unaware service can be associated with a
   service segment through an SR proxy function.

3.  Classification and steering

   Classification and steering mechanisms are defined in section 8 of
   [I-D.ietf-spring-segment-routing-policy] and are independent from the
   purpose of the SR policy.  From the perspective of a headend node
   classifying and steering traffic into an SR policy, there is no
   difference whether this policy contains IGP, BGP, peering, VPN or
   service segments, or any combination of these.

   As documented in the above reference, traffic is classified when
   entering an SR domain.  The SR policy headend may, depending on its
   capabilities, classify the packets on a per-destination basis, via
   simple FIB entries, or apply more complex policy routing rules
   requiring to look deeper into the packet.  These rules are expected
   to support basic policy routing such as 5-tuple matching.  In
   addition, the IPv6 SRH tag field defined in
   [I-D.ietf-6man-segment-routing-header] can be used to identify and
   classify packets sharing the same set of properties.  Classified
   traffic is then steered into the appropriate SR policy and forwarded
   as per the SID-list(s) of the active candidate path.

   SR traffic can be re-classified by an SR endpoint along the original
   SR policy (e.g., DPI service) or a transit node intercepting the
   traffic.  This node is the head-end of a new SR policy that is
   imposed onto the packet, either as a stack of MPLS labels or as an
   IPv6 SRH.





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4.  Service segments

   In the context of this document, the term service refers to a
   physical appliance running on dedicated hardware, a virtualized
   service inside an isolated environment such as a VM, container or
   namespace, or any process running on a compute element.  A service
   may also comprise multiple sub-components running in different
   processes or containers.  Unless otherwise stated, this document does
   not make any assumption on the type or execution environment of a
   service.

   The execution of a service can be integrated as part of an SR policy
   by assigning a segment identifier, or SID, to the service and
   including this service SID in the SR policy SID-list.  Such a service
   SID may be of local or global significance.  In the former case,
   other segments, such as prefix or adjacency segments, can be used to
   steer the traffic up to the node where the service segment is
   instantiated.  In the latter case, the service is directly reachable
   from anywhere in the routing domain.  This is realized with SR-MPLS
   by assigning a SID from the global label block
   ([I-D.ietf-spring-segment-routing-mpls]), or with SRv6 by advertising
   the SID locator in the routing protocol
   ([I-D.filsfils-spring-srv6-network-programming]).  It is up to the
   network operator to define the scope and reachability of each service
   SID.  This decision can be based on various considerations such as
   infrastructure dynamicity, available control plane or orchestration
   system capabilities.

   This document categorizes services in two types, depending on whether
   they are able to behave properly in the presence of SR information or
   not.  These are respectively named SR-aware and SR-unaware services.

4.1.  SR-aware services

   An SR-aware service can process the SR information in the packets it
   receives.  This means being able to identify the active segment as a
   local instruction and move forward in the segment list, but also that
   the service's own behavior is not hindered due to the presence of SR
   information.  For example, an SR-aware firewall filtering SRv6
   traffic based on its final destination must retrieve that information
   from the last entry in the SRH rather than the Destination Address
   field of the IPv6 header.

   An SR-aware service is associated with a locally instantiated service
   segment, which is used to steer traffic through it.

   If the service is configured to intercept all the packets passing
   through the appliance, the underlying routing system only has to



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   implement a default SR endpoint behavior (SR-MPLS node segment or
   SRv6 End function), and the corresponding SID will be used to steer
   traffic through the service.

   If the service requires the packets to be directed to a specific
   virtual interface, networking queue or process, a dedicated SR
   behavior may be required to steer the packets to the appropriate
   location.  The definition of such service-specific functions is out
   of the scope of this document.

   SR-aware services also enable advanced network programming
   functionalities such as conditional branching and jumping to
   arbitrary SIDs in the segment list.  In addition, SRv6 provides
   several ways of passing and exchanging information between services
   (e.g., SID arguments, tag field and TLVs).  An example scenario
   involving these features is described in [IFIP18], which discusses
   the implementation of an SR-aware Intrusion Detection System.

   Examples of SR-aware services are provided in section Section 8.1.

4.2.  SR-unaware services

   Any service that does not meet the above criteria for SR-awareness is
   considered as SR-unaware.

   An SR-unaware service is not able to process the SR information in
   the traffic that it receives.  It may either drop the traffic or take
   erroneous decisions due to the unrecognized routing information.  In
   order to include such services in an SR policy, it is thus required
   to remove the SR information as well as any other encapsulation
   header before the service receives the packet, or to alter it in such
   a way that the service can correctly process the packet.

   In this document, we define the concept of an SR proxy as an entity,
   separate from the service, that performs these modifications and
   handle the SR processing on behalf of a service.  The SR proxy can
   run as a separate process on the service appliance, on a virtual
   switch or router on the compute node or on a different host.

   An SR-unaware service is associated with a service segment
   instantiated on the SR proxy, which is used to steer traffic through
   the service.  Section 6 describes several SR proxy behaviors to
   handle the encapsulation headers and SR information under various
   circumstances.







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5.  SR service policies

   An SR service policy is an SR policy, as defined in
   [I-D.ietf-spring-segment-routing-policy], that includes at least one
   service.  This service is represented in the SID-list by its
   associated service SID.  In case the policy should include several
   services, the service traversal order is indicated by the relative
   position of each service SID in the SID-list.  Using the mechanisms
   described in [I-D.ietf-spring-segment-routing-policy], it is possible
   to load balance the traffic over several services, or instances of
   the same service, by associating with the SR service policy a
   weighted set of SID-lists, each containing a possible sequence of
   service SIDs to be traversed.  Similarly, several candidate paths can
   be specified for the SR service policy, each with its own set of SID-
   lists, for resiliency purposes.

   Furthermore, binding SIDs (BSIDs) can be leveraged in the context of
   service policies to reduce the number of SIDs imposed by the headend,
   provide opacity between domains and improve scalability, as described
   in [I-D.filsfils-spring-sr-policy-considerations].  For example, a
   network operator may want a policy in its core domain to include
   services that are running in one of its datacenters.  One option is
   to define an SR policy at ingress edge of the core domain that
   explicitly includes all the SIDs needed to steer the traffic through
   the core and in the DC, but that may result in a long SID-list and
   requires to update the ingress edge configuration every time the DC
   part of the policy is modified.  Alternatively, a separate policy can
   be defined at the ingress edge of the datacenter with only the SIDs
   that needs to be executed there and its BSID included in the core
   domain policy.  That BSID remains stable when the DC policy is
   modified and can even be shared among several core domain policies
   that would require the same type of processing in the DC.

   This section describes how services can be integrated within an SR-
   MPLS or SRv6 service policy.

        +------------------------------------------+
        |               SR network                 |
        |                                          |
   +----+----+          +---------+           +----+-----+
   |    H    +----------+    S    +-----------+    E     |
   |(headend)|          |(service)|           |(endpoint)|
   +----+----+          +---------+           +----+-----+
        |  =====================================>  |
        |     P1(H,E,C)                            |
        +------------------------------------------+

                        Figure 1: SR service policy



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   Figure 1 illustrates a basic SR service policy instantiated on a
   headend node H towards an endpoint E and traversing a service S.  The
   SR policy may also include additional requirements, such as traffic
   engineering or VPN.  On the head-end H, the SR policy P1 is created
   with a color C and endpoint E and associated with an SR path that can
   either be explicitly configured, dynamically computed on H or
   provisioned by a network controller.

   In its most basic form, the SR policy P1 would be resolved into the
   SID-list < SID(S), SID(E) >.  This is assuming that SID(S) and SID(E)
   are directly reachable from H and S, respectively, and that the
   forwarding path meets the policy requirement.  However, depending on
   the dataplane and the segments available in the network, additional
   SIDs may be required to enforce the SR policy.

   This model applies regardless of the SR-awareness of the service.  If
   it is SR-unaware, then S simply represents the proxy that takes care
   of transmitting the packet to the actual service.

   Traffic can then be steered into this policy using any of the
   mechanisms described in [I-D.ietf-spring-segment-routing-policy].

   The following subsections describe the specificities of each SR
   dataplane.

5.1.  SR-MPLS data plane

























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        +-----------------------------------------------+
        |                SR-MPLS network                |
        |                                               |
   +----+----+   ------>   +---------+   ------>   +----+-----+
   |    H    +-------------+    S    +-------------+    E     |
   |(headend)|             |(service)|             |(endpoint)|
   +----+----+             +---------+             +----+-----+
        |    (1)         (2)         (3)         (4)    |
        |+---------+ +---------+ +---------+ +---------+|
        ||   ...   | |  L(S)   | |   ...   | |  L(E)   ||
        |+---------+ +---------+ +---------+ +---------+|
        ||  L(S)   | |   ...   | |  L(E)   | |Inner pkt||
        |+---------+ +---------+ +---------+ +---------+|
        ||   ...   | |  L(E)   | |Inner pkt|            |
        |+---------+ +---------+ +---------+            |
        ||  L(E)   | |Inner pkt|                        |
        |+---------+ +---------+                        |
        ||Inner pkt|                                    |
        |+---------+                                    |
        +-----------------------------------------------+

                Figure 2: Packet walk in an SR-MPLS network

   In an SR-MPLS network, the SR policy SID-list is encoded as a stack
   of MPLS labels[I-D.ietf-spring-segment-routing-mpls] and pushed on
   top of the packet.

   In the example shown on Figure 2, the SR policy should steer the
   traffic from the head-end H to the endpoint E via a service S.  This
   translates into an MPLS label stack that includes at least a label
   L(S) associated to service S and a label L(E) associated to the
   endpoint E.  The label stack may also include additional intermediate
   segments if these are required for traffic engineering (e.g., to
   encode a low latency path between H and S and / or between S and E)
   or simply for reachability purposes.  Indeed, the service SID L(S)
   may be taken from the global or local SID block of node S and, in the
   latter case, one or more SIDs might be needed before L(S) in order
   for the packet to reach node S (e.g., a prefix-SID of S), where L(S)
   can be interpreted.  The same applies for the segment L(E) at the SR
   policy endpoint.

   Special consideration must be taken into account when using Local
   SIDs for service identification due to increased label stack depth
   and the associated impacts.

   When the packet arrives at S, this node determines how to process the
   packet based on the semantic locally associated to the top label
   L(S).  If S is an SR-aware service, the SID L(S) may provide



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   additional context or indication on how to process the packet (e.g.,
   payload type or a firewall SID may indicate which rule set should be
   applied onto the packet).  If S is a proxy in front of an SR-unaware
   service, L(S) indicates how and to which service attached to this
   proxy the packet should be transmitted.  At some point in the
   process, L(S) is also popped from the label stack in order to expose
   the next SID, which may be L(E) or another intermediate segment.

5.2.  SRv6 data plane

        +-----------------------------------------------+
        |                 SRv6 network                  |
        |                                               |
   +----+----+   ------>   +---------+   ------>   +----+-----+
   |    H    +-------------+    S    +-------------+    E     |
   |(headend)|             |(service)|             |(endpoint)|
   +----+----+             +---------+             +----+-----+
        |    (1)         (2)         (3)         (2)    |
        |+---------+ +---------+ +---------+ +---------+|
        ||IP6(H,..)| |IP6(H, S)| |IP6(H,..)| |IP6(H, E)||
        |+---------+ +---------+ +---------+ +---------+|
        ||SRH(E,..,| |SRH(E,..,| |SRH(E,..,| |SRH(E,..,||
        ||    S,..;| |    S,..;| |    S,..;| |    S,..;||
        ||    SL=i)| |    SL=j)| |    SL=k)| |    SL=0)||
        |+---------+ +---------+ +---------+ +---------+|
        ||Inner pkt| |Inner pkt| |Inner pkt| |Inner pkt||
        |+---------+ +---------+ +---------+ +---------+|
        +-----------------------------------------------+

                 Figure 3: Packet walk in an SRv6 network

   In an SRv6 network, the SR Policy is encoded into the packet as an
   IPv6 header possibly followed by a Segment Routing header (SRH)
   [I-D.ietf-6man-segment-routing-header].

   In the example shown on Figure 3, the SR policy should steer the
   traffic from the head-end H to the endpoint E via a service S.  This
   translates into an SRH that includes at least a segment SID(S) to the
   service, or service proxy, S and a segment SID(E) to the endpoint E.
   The SRH may also include additional intermediate segments if these
   are required for traffic engineering (e.g., the encode a low latency
   path between H and S and / or between S and E) or simply for
   reachability purposes.  Indeed, the service segment locator may or
   may not be advertised in the routing protocol and, in the latter
   case, one or more SIDs might be needed before SID(S) in order to
   bring the packet up to node S, where SID(S) can be interpreted.  The
   same applies for the segment SID(E) at the SR policy endpoint.




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   When the packet arrives at S, this node determines how to process the
   packet based on the semantic locally associated to the active segment
   SID(S).  If S is an SR-aware service, then SID(S) may provide
   additional context or indication on how to process the packet (e.g.,
   a firewall SID may indicate which rule set should be applied onto the
   packet).  If S is a proxy in front of an SR-unaware service, SID(S)
   indicates how and to which service attached to this proxy the packet
   should be transmitted.  At some point in the process, the SRv6 End
   function is also applied in order to make the next SID, which may be
   SID(E) or another intermediate segment, active.

   The "Inner pkt" on Figure 3 represents the SRv6 payload, which may be
   an encapsulated IP packet, an Ethernet frame or a transport-layer
   payload, for example.

6.  SR proxy behaviors

   This section describes several SR proxy behaviors designed to enable
   SR service programming through SR-unaware services.  A system
   implementing one of these functions may handle the SR processing on
   behalf of an SR-unaware service and allows the service to properly
   process the traffic that is steered through it.

   A service may be located at any hop in an SR policy, including the
   last segment.  However, the SR proxy behaviors defined in this
   section are dedicated to supporting SR-unaware services at
   intermediate hops in the segment list.  In case an SR-unaware service
   is at the last segment, it is sufficient to ensure that the SR
   information is ignored (IPv6 routing extension header with Segments
   Left equal to 0) or removed before the packet reaches the service
   (MPLS PHP, SRv6 End.D or PSP).

   As illustrated on Figure 4, the generic behavior of an SR proxy has
   two parts.  The first part is in charge of passing traffic from the
   network to the service.  It intercepts the SR traffic destined for
   the service via a locally instantiated service segment, modifies it
   in such a way that it appears as non-SR traffic to the service, then
   sends it out on a given interface, IFACE-OUT, connected to the
   service.  The second part receives the traffic coming back from the
   service on IFACE-IN, restores the SR information and forwards it
   according to the next segment in the list.  IFACE-OUT and IFACE-IN
   are respectively the proxy interface used for sending traffic to the
   service and the proxy interface that receives the traffic coming back
   from the service.  These can be physical interfaces or sub-interfaces
   (VLANs) and, unless otherwise stated, IFACE-OUT and IFACE-IN can
   represent the same interface.





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              +----------------------------+
              |                            |
              |           Service          |
              |                            |
              +----------------------------+
                       ^  Non SR   |
                       |  traffic  |
                       |           v
                 +-----------+----------+
              +--| IFACE OUT | IFACE IN |--+
   SR traffic |  +-----------+----------+  | SR traffic
   ---------->|          SR proxy          |---------->
              |                            |
              +----------------------------+

                        Figure 4: Generic SR proxy

   In the next subsections, the following SR proxy mechanisms are
   defined:

   o  Static proxy

   o  Dynamic proxy

   o  Shared-memory proxy

   o  Masquerading proxy

   Each mechanism has its own characteristics and constraints, which are
   summarized in the below table.  It is up to the operator to select
   the best one based on the proxy node capabilities, the service
   behavior and the traffic type.  It is also possible to use different
   proxy mechanisms within the same service policy.


















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                                           +-----+-----+-----+-----+
                                           |     |     |     |  M  |
                                           |     |     |  S  |  a  |
                                           |     |     |  h  |  s  |
                                           |     |     |  a  |  q  |
                                           |     |     |  r  |  u  |
                                           |     |  D  |  e  |  e  |
                                           |  S  |  y  |  d  |  r  |
                                           |  t  |  n  |     |  a  |
                                           |  a  |  a  |  m  |  d  |
                                           |  t  |  m  |  e  |  i  |
                                           |  i  |  i  |  m  |  n  |
                                           |  c  |  c  |  .  |  g  |
   +---------------------------------------+-----+-----+-----+-----+
   |                |       SR-MPLS        |  Y  |  Y  |  Y  |  -  |
   |                |                      |     |     |     |     |
   |   SR flavors   |    SRv6 insertion    |  P  |  P  |  P  |  Y  |
   |                |                      |     |     |     |     |
   |                |  SRv6 encapsulation  |  Y  |  Y  |  Y  |  -  |
   +----------------+----------------------+-----+-----+-----+-----+
   |     Chain agnostic configuration      |  N  |  N  |  Y  |  Y  |
   +---------------------------------------+-----+-----+-----+-----+
   |     Transparent to chain changes      |  N  |  Y  |  Y  |  Y  |
   +----------------+----------------------+-----+-----+-----+-----+
   |                |   DA modification    |  Y  |  Y  |  Y  | NAT |
   |                |                      |     |     |     |     |
   |                | Payload modification |  Y  |  Y  |  Y  |  Y  |
   |                |                      |     |     |     |     |
   |Service support |  Packet generation   |  Y  |  Y  |cache|cache|
   |                |                      |     |     |     |     |
   |                |   Packet deletion    |  Y  |  Y  |  Y  |  Y  |
   |                |                      |     |     |     |     |
   |                |  Transport endpoint  |  Y  |  Y  |cache|cache|
   +----------------+----------------------+-----+-----+-----+-----+
   |                |       Ethernet       |  Y  |  Y  |  Y  |  -  |
   |   Supported    |                      |     |     |     |     |
   |    traffic     |         IPv4         |  Y  |  Y  |  Y  |  -  |
   |                |                      |     |     |     |     |
   |                |         IPv6         |  Y  |  Y  |  Y  |  Y  |
   +----------------+----------------------+-----+-----+-----+-----+

                        Figure 5: SR proxy summary

   Note: The use of a shared memory proxy requires both the service
   (VNF) and the proxy to be running on the same node.






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6.1.  Static SR proxy

   The static proxy is an SR endpoint behavior for processing SR-MPLS or
   SRv6 encapsulated traffic on behalf of an SR-unaware service.  This
   proxy thus receives SR traffic that is formed of an MPLS label stack
   or an IPv6 header on top of an inner packet, which can be Ethernet,
   IPv4 or IPv6.

   A static SR proxy segment is associated with the following mandatory
   parameters

   o  INNER-TYPE: Inner packet type

   o  NH-ADDR: Next hop Ethernet address (only for inner type IPv4 and
      IPv6)

   o  IFACE-OUT: Local interface for sending traffic towards the service

   o  IFACE-IN: Local interface receiving the traffic coming back from
      the service

   o  CACHE: SR information to be attached on the traffic coming back
      from the service, including at least

      *  CACHE.SA: IPv6 source address (SRv6 only)

      *  CACHE.LIST: Segment list expressed as MPLS labels or IPv6
         address

   A static SR proxy segment is thus defined for a specific service,
   inner packet type and cached SR information.  It is also bound to a
   pair of directed interfaces on the proxy.  These may be both
   directions of a single interface, or opposite directions of two
   different interfaces.  The latter is recommended in case the service
   is to be used as part of a bi-directional SR SC policy.  If the proxy
   and the service both support 802.1Q, IFACE-OUT and IFACE-IN can also
   represent sub-interfaces.

   The first part of this behavior is triggered when the proxy node
   receives a packet whose active segment matches a segment associated
   with the static proxy behavior.  It removes the SR information from
   the packet then sends it on a specific interface towards the
   associated service.  This SR information corresponds to the full
   label stack for SR-MPLS or to the encapsulation IPv6 header with any
   attached extension header in the case of SRv6.

   The second part is an inbound policy attached to the proxy interface
   receiving the traffic returning from the service, IFACE-IN.  This



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   policy attaches to the incoming traffic the cached SR information
   associated with the SR proxy segment.  If the proxy segment uses the
   SR-MPLS data plane, CACHE contains a stack of labels to be pushed on
   top of the packets.  With the SRv6 data plane, CACHE is defined as a
   source address, an active segment and an optional SRH (tag, segments
   left, segment list and metadata).  The proxy encapsulates the packets
   with an IPv6 header that has the source address, the active segment
   as destination address and the SRH as a routing extension header.
   After the SR information has been attached, the packets are forwarded
   according to the active segment, which is represented by the top MPLS
   label or the IPv6 Destination Address.  An MPLS TTL or IPv6 Hop Limit
   value may also be configured in CACHE.  If it is not, the proxy
   should set these values according to the node's default setting for
   MPLS or IPv6 encapsulation.

   In this scenario, there are no restrictions on the operations that
   can be performed by the service on the stream of packets.  It may
   operate at all protocol layers, terminate transport layer
   connections, generate new packets and initiate transport layer
   connections.  This behavior may also be used to integrate an
   IPv4-only service into an SRv6 policy.  However, a static SR proxy
   segment can be used in only one service policy at a time.  As opposed
   to most other segment types, a static SR proxy segment is bound to a
   unique list of segments, which represents a directed SR SC policy.
   This is due to the cached SR information being defined in the segment
   configuration.  This limitation only prevents multiple segment lists
   from using the same static SR proxy segment at the same time, but a
   single segment list can be shared by any number of traffic flows.
   Besides, since the returning traffic from the service is re-
   classified based on the incoming interface, an interface can be used
   as receiving interface (IFACE-IN) only for a single SR proxy segment
   at a time.  In the case of a bi-directional SR SC policy, a different
   SR proxy segment and receiving interface are required for the return
   direction.

   The static proxy behavior may also be used for sending traffic
   through "bump in the wire" services that are transparent to the IP
   and Ethernet layers.  This type of processing is assumed when the
   inner traffic type is Ethernet, since the original destination
   address of the Ethernet frame is preserved when the packet is steered
   into the SR Policy and likely associated with a node downstream of
   the policy tail-end.  In case the inner type is IP (IPv4 or IPv6),
   the NH-ADDR parameter may be set to a dummy or broadcast Ethernet
   address, or simply to the address of the proxy receiving interface
   (IFACE-IN).






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6.1.1.  SR-MPLS pseudocode

6.1.1.1.  Static proxy for inner type Ethernet

   Upon receiving an MPLS packet with top label L, where L is an MPLS L2
   static proxy segment, a node N does:

   1.   Pop all labels
   2.   IF payload type is Ethernet THEN
   3.       Forward the exposed frame on IFACE-OUT
   4.   ELSE
   5.       Drop the packet

   Upon receiving on IFACE-IN an Ethernet frame with a destination
   address different than the interface address, a node N does:

   1.   Push labels in CACHE on top of the frame Ethernet header
   2.   Lookup the top label and proceed accordingly

   The receiving interface must be configured in promiscuous mode in
   order to accept those Ethernet frames.

6.1.1.2.  Static proxy for inner type IPv4

   Upon receiving an MPLS packet with top label L, where L is an MPLS
   IPv4 static proxy segment, a node N does:

   1.   Pop all labels
   2.   IF payload type is IPv4 THEN
   3.       Forward the exposed packet on IFACE-OUT towards NH-ADDR
   4.   ELSE
   5.       Drop the packet

   Upon receiving a non-link-local IPv4 packet on IFACE-IN, a node N
   does:

   1.   Decrement TTL and update checksum
   2.   Push labels in CACHE on top of the packet IPv4 header
   3.   Lookup the top label and proceed accordingly

6.1.1.3.  Static proxy for inner type IPv6

   Upon receiving an MPLS packet with top label L, where L is an MPLS
   IPv6 static proxy segment, a node N does:







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   1.   Pop all labels
   2.   IF payload type is IPv6 THEN
   3.       Forward the exposed packet on IFACE-OUT towards NH-ADDR
   4.   ELSE
   5.       Drop the packet

   Upon receiving a non-link-local IPv6 packet on IFACE-IN, a node N
   does:

   1.   Decrement Hop Limit
   2.   Push labels in CACHE on top of the packet IPv6 header
   3.   Lookup the top label and proceed accordingly

6.1.2.  SRv6 pseudocode

6.1.2.1.  Static proxy for inner type Ethernet

   Upon receiving an IPv6 packet destined for S, where S is an IPv6
   static proxy segment for Ethernet traffic, a node N does:

   1.   IF ENH == 59 THEN                                        ;; Ref1
   2.       Remove the (outer) IPv6 header and its extension headers
   3.       Forward the exposed frame on IFACE-OUT
   4.   ELSE
   5.       Drop the packet

   Ref1: 59 refers to "no next header" as defined by IANA allocation for
   Internet Protocol Numbers.

   Upon receiving on IFACE-IN an Ethernet frame with a destination
   address different than the interface address, a node N does:

   1.   Retrieve CACHE entry matching IFACE-IN and traffic type
   2.   Push SRH with CACHE.LIST on top of the Ethernet header   ;; Ref2
   3.   Push IPv6 header with
          SA = CACHE.SA
          DA = CACHE.LIST[0]                                     ;; Ref3
          Next Header = 43                                       ;; Ref4
   4.   Set outer payload length and flow label
   5.   Lookup outer DA in appropriate table and proceed accordingly

   Ref2: Unless otherwise specified, the segments in CACHE.LIST should
   be encoded in reversed order, Segment Left and Last Entry values
   should be set of the length of CACHE.LIST minus 1, and Next Header
   should be set to 59.

   Ref3: CACHE.LIST[0] represents the first IPv6 SID in CACHE.LIST.




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   Ref4: If CACHE.LIST contains a single entry, the SRH can be omitted
   and the Next Header value must be set to 59.

   The receiving interface must be configured in promiscuous mode in
   order to accept those Ethernet frames.

6.1.2.2.  Static proxy for inner type IPv4

   Upon receiving an IPv6 packet destined for S, where S is an IPv6
   static proxy segment for IPv4 traffic, a node N does:

   1.   IF ENH == 4 THEN                                         ;; Ref1
   2.       Remove the (outer) IPv6 header and its extension headers
   3.       Forward the exposed packet on IFACE-OUT towards NH-ADDR
   4.   ELSE
   5.       Drop the packet

   Ref1: 4 refers to IPv4 encapsulation as defined by IANA allocation
   for Internet Protocol Numbers.

   Upon receiving a non-link-local IPv4 packet on IFACE-IN, a node N
   does:

   1.   Decrement TTL and update checksum
   2.   IF CACHE.SRH THEN                                        ;; Ref2
   3.       Push CACHE.SRH on top of the existing IPv4 header
   4.       Set NH value of the pushed SRH to 4
   5.   Push outer IPv6 header with SA, DA and traffic class from CACHE
   6.   Set outer payload length and flow label
   7.   Set NH value to 43 if an SRH was added, or 4 otherwise
   8.   Lookup outer DA in appropriate table and proceed accordingly

   Ref2: CACHE.SRH represents the SRH defined in CACHE, if any, for the
   static SR proxy segment associated with IFACE-IN.

6.1.2.3.  Static proxy for inner type IPv6

   Upon receiving an IPv6 packet destined for S, where S is an IPv6
   static proxy segment for IPv6 traffic, a node N does:

   1.   IF ENH == 41 THEN                                        ;; Ref1
   2.       Remove the (outer) IPv6 header and its extension headers
   3.       Forward the exposed packet on IFACE-OUT towards NH-ADDR
   4.   ELSE
   5.       Drop the packet

   Ref1: 41 refers to IPv6 encapsulation as defined by IANA allocation
   for Internet Protocol Numbers.



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   Upon receiving a non-link-local IPv6 packet on IFACE-IN, a node N
   does:

   1.   Decrement Hop Limit
   2.   IF CACHE.SRH THEN                                        ;; Ref2
   3.       Push CACHE.SRH on top of the existing IPv6 header
   4.       Set NH value of the pushed SRH to 41
   5.   Push outer IPv6 header with SA, DA and traffic class from CACHE
   6.   Set outer payload length and flow label
   7.   Set NH value to 43 if an SRH was added, or 41 otherwise
   8.   Lookup outer DA in appropriate table and proceed accordingly

   Ref2: CACHE.SRH represents the SRH defined in CACHE, if any, for the
   static SR proxy segment associated with IFACE-IN.

6.2.  Dynamic SR proxy

   The dynamic proxy is an improvement over the static proxy that
   dynamically learns the SR information before removing it from the
   incoming traffic.  The same information can then be re-attached to
   the traffic returning from the service.  As opposed to the static SR
   proxy, no CACHE information needs to be configured.  Instead, the
   dynamic SR proxy relies on a local caching mechanism on the node
   instantiating this segment.

   Upon receiving a packet whose active segment matches a dynamic SR
   proxy function, the proxy node pops the top MPLS label or applies the
   SRv6 End behavior, then compares the updated SR information with the
   cache entry for the current segment.  If the cache is empty or
   different, it is updated with the new SR information.  The SR
   information is then removed and the inner packet is sent towards the
   service.

   The cache entry is not mapped to any particular packet, but instead
   to an SR SC policy identified by the receiving interface (IFACE-IN).
   Any non-link-local IP packet or non-local Ethernet frame received on
   that interface will be re-encapsulated with the cached headers as
   described in Section 6.1.  The service may thus drop, modify or
   generate new packets without affecting the proxy.

6.2.1.  SR-MPLS pseudocode

   The dynamic proxy SR-MPLS pseudocode is obtained by inserting the
   following instructions at the beginning of the static SR-MPLS
   pseudocode (Section 6.1.1).






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   1.   IF top label S bit is 0 THEN                             ;; Ref1
   2.       Pop top label
   3.       IF C(IFACE-IN) different from remaining labels THEN  ;; Ref2
   4.           Copy all remaining labels into C(IFACE-IN)       ;; Ref3
   5.   ELSE
   6.       Drop the packet

   Ref1: As mentioned at the beginning of Section 6, an SR proxy is not
   needed to include an SR-unaware service at the end of an SR policy.

   Ref2: A TTL margin can be configured for the top label stack entry to
   prevent constant cache updates when multiple equal-cost paths with
   different hop counts are used towards the SR proxy node.  In that
   case, a TTL difference smaller than the configured margin should not
   trigger a cache update (provided that the labels are the same).

   Ref3: C(IFACE-IN) represents the cache entry associated to the
   dynamic SR proxy segment.  It is identified with IFACE-IN in order to
   efficiently retrieve the right SR information when a packet arrives
   on this interface.

   In addition, the inbound policy should check that C(IFACE-IN) has
   been defined before attempting to restore the MPLS label stack and
   drop the packet otherwise.

6.2.2.  SRv6 pseudocode

   The dynamic proxy SRv6 pseudocode is obtained by inserting the
   following instructions between lines 1 and 2 of the static proxy SRv6
   pseudocode.

   1.   IF NH=SRH & SL > 0 THEN                                  ;; Ref1
   2.       Decrement SL and update the IPv6 DA with SRH[SL]
   3.       IF C(IFACE-IN) different from IPv6 encaps THEN       ;; Ref2
   4.           Copy the IPv6 encaps into C(IFACE-IN)            ;; Ref3
   5.   ELSE
   6.       Drop the packet

   Ref1: As mentioned at the beginning of Section 6, an SR proxy is not
   needed to include an SR-unaware service at the end of an SR policy.

   Ref2: "IPv6 encaps" represents the IPv6 header and any attached
   extension header.

   Ref3: C(IFACE-IN) represents the cache entry associated to the
   dynamic SR proxy segment.  It is identified with IFACE-IN in order to
   efficiently retrieve the right SR information when a packet arrives
   on this interface.



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   In addition, the inbound policy should check that C(IFACE-IN) has
   been defined before attempting to restore the IPv6 encapsulation and
   drop the packet otherwise.

6.3.  Shared memory SR proxy

   The shared memory proxy is an SR endpoint behavior for processing SR-
   MPLS or SRv6 encapsulated traffic on behalf of an SR-unaware service.
   This proxy behavior leverages a shared-memory interface with a
   virtualized service (VNF) in order to hide the SR information from an
   SR-unaware service while keeping it attached to the packet.  We
   assume in this case that the proxy and the VNF are running on the
   same compute node.  A typical scenario is an SR-capable vrouter
   running on a container host and forwarding traffic to VNFs isolated
   within their respective container.

   More details will be added in a future revision of this document.

6.4.  Masquerading SR proxy

   The masquerading proxy is an SR endpoint behavior for processing SRv6
   traffic on behalf of an SR-unaware service.  This proxy thus receives
   SR traffic that is formed of an IPv6 header and an SRH on top of an
   inner payload.  The masquerading behavior is independent from the
   inner payload type.  Hence, the inner payload can be of any type but
   it is usually expected to be a transport layer packet, such as TCP or
   UDP.

   A masquerading SR proxy segment is associated with the following
   mandatory parameters:

   o  S-ADDR: Ethernet or IPv6 address of the service

   o  IFACE-OUT: Local interface for sending traffic towards the service

   o  IFACE-IN: Local interface receiving the traffic coming back from
      the service

   A masquerading SR proxy segment is thus defined for a specific
   service and bound to a pair of directed interfaces or sub-interfaces
   on the proxy.  As opposed to the static and dynamic SR proxies, a
   masquerading segment can be present at the same time in any number of
   SR SC policies and the same interfaces can be bound to multiple
   masquerading proxy segments.  The only restriction is that a
   masquerading proxy segment cannot be the last segment in an SR SC
   policy.





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   The first part of the masquerading behavior is triggered when the
   proxy node receives an IPv6 packet whose Destination Address matches
   a masquerading proxy segment.  The proxy inspects the IPv6 extension
   headers and substitutes the Destination Address with the last segment
   in the SRH attached to the IPv6 header, which represents the final
   destination of the IPv6 packet.  The packet is then sent out towards
   the service.

   The service receives an IPv6 packet whose source and destination
   addresses are respectively the original source and final destination.
   It does not attempt to inspect the SRH, as RFC8200 specifies that
   routing extension headers are not examined or processed by transit
   nodes.  Instead, the service simply forwards the packet based on its
   current Destination Address.  In this scenario, we assume that the
   service can only inspect, drop or perform limited changes to the
   packets.  For example, Intrusion Detection Systems, Deep Packet
   Inspectors and non-NAT Firewalls are among the services that can be
   supported by a masquerading SR proxy.  Variants of the masquerading
   behavior are defined in Section 6.4.2 and Section 6.4.3 to support a
   wider range of services.

   The second part of the masquerading behavior, also called de-
   masquerading, is an inbound policy attached to the proxy interface
   receiving the traffic returning from the service, IFACE-IN.  This
   policy inspects the incoming traffic and triggers a regular SRv6
   endpoint processing (End) on any IPv6 packet that contains an SRH.
   This processing occurs before any lookup on the packet Destination
   Address is performed and it is sufficient to restore the right active
   segment as the Destination Address of the IPv6 packet.

6.4.1.  SRv6 masquerading proxy pseudocode

   Masquerading: Upon receiving a packet destined for S, where S is an
   IPv6 masquerading proxy segment, a node N processes it as follows.

   1.   IF NH=SRH & SL > 0 THEN
   2.       Update the IPv6 DA with SRH[0]
   3.       Forward the packet on IFACE-OUT
   4.   ELSE
   5.       Drop the packet

   De-masquerading: Upon receiving a non-link-local IPv6 packet on
   IFACE-IN, a node N processes it as follows.

   1.   IF NH=SRH & SL > 0 THEN
   2.       Decrement SL
   3.       Update the IPv6 DA with SRH[SL]                      ;; Ref1
   4.       Lookup DA in appropriate table and proceed accordingly



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   Ref1: This pseudocode can be augmented to support the Penultimate
   Segment Popping (PSP) endpoint flavor.  The exact pseudocode
   modification are provided in
   [I-D.filsfils-spring-srv6-network-programming].

6.4.2.  Variant 1: Destination NAT

   Services modifying the destination address in the packets they
   process, such as NATs, can be supported by a masquerading proxy with
   the following modification to the de-masquerading pseudocode.

   De-masquerading - NAT: Upon receiving a non-link-local IPv6 packet on
   IFACE-IN, a node N processes it as follows.

   1.   IF NH=SRH & SL > 0 THEN
   2.       Update SRH[0] with the IPv6 DA
   3.       Decrement SL
   4.       Update the IPv6 DA with SRH[SL]
   5.       Lookup DA in appropriate table and proceed accordingly

6.4.3.  Variant 2: Caching

   Services generating packets or acting as endpoints for transport
   connections can be supported by adding a dynamic caching mechanism
   similar to the one described in Section 6.2.

   More details will be added in a future revision of this document.

7.  Metadata

7.1.  MPLS data plane

   Metadata can be carried for SR-MPLS traffic in a Segment Routing
   header inserted between the last MPLS label and the MPLS payload.
   When used solely as a metadata container, the SRH does not carry any
   segment but only the mandatory header fields, including the tag and
   flags, and any TLVs that is required for transporting the metadata.

   Since the MPLS encapsulation has no explicit protocol identifier
   field to indicate the protocol type of the MPLS payload, how to
   indicate the presence of metadata in an MPLS packet is a potential
   issue to be addressed.  One possible solution is to add the
   indication about the presence of metadata in the semantic of the
   SIDs.  Note that only the SIDs whose behavior involves looking at the
   metadata or the MPLS payload would need to include such semantic
   (e.g., service segments).  Other segments, such as traffic
   engineering segments, are not affected by the presence of metadata.
   Another, more generic, solution is to introduce a protocol identifier



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   field within the MPLS packet as described in
   [I-D.xu-mpls-payload-protocol-identifier].

7.2.  IPv6 data plane

7.2.1.  SRH TLV objects

   The IPv6 SRH TLV objects are designed to carry all sorts of metadata.
   In particular, the NSH carrier TLV is defined as a container for NSH
   metadata.

   TLV objects can be imposed by the ingress edge router that steers the
   traffic into the SR SC policy.

   An SR-aware service may impose, modify or remove any TLV object
   attached to the first SRH, either by directly modifying the packet
   headers or via a control channel between the service and its
   forwarding plane.

   An SR-aware service that re-classifies the traffic and steers it into
   a new SR SC policy (e.g.  DPI) may attach any TLV object to the new
   SRH.

   Metadata imposition and handling will be further discussed in a
   future version of this document.

7.2.1.1.  NSH Carrier TLV

   The NSH Carrier TLV is a container used in order to carry TLVs that
   have been defined in [RFC8300].  The NSH Carrier TLV has the
   following format:

    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
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |      Type     |     Length    |     Flags     |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //            NSH Carried Object                               //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

   o  Type: to be assigned by IANA (suggested value 6).

   o  Length: the total length of the TLV.

   o  Flags: 8 bits.  No flags are defined in this document.  SHOULD be
      set to 0 on transmission and MUST be ignored on receipt.



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   o  NSH Carried Object: the content of the TLV which consists of the
      NSH data as defined in [RFC8300].

7.2.2.  SRH tag

   The SRH tag identifies a packet as part of a group or class of
   packets [I-D.ietf-6man-segment-routing-header].

   In the context of service programming, this field can be used to
   encode basic metadata in the SRH.  An example use case would be to
   leverage the SRH tag to encode a policy ID which could be leveraged
   in an SR-aware function to determine which processing policy to apply
   rather than having doing local classification or leverage alternate
   encapsulations.

8.  Implementation status

   This section is to be removed prior to publishing as an RFC.

8.1.  SR-aware services

   Specific SRv6 support has been implemented for the below open-source
   services:

   o  Iptables (1.6.2 and later)

   o  Nftables (0.8.4 and later)

   o  Snort

   In addition, any service relying on the Linux kernel, version 4.10
   and later, or FD.io VPP for packet forwarding can be considered as
   SR-aware.

8.2.  Proxy behaviors

   The static SR proxy is available for SR-MPLS and SRv6 on various
   Cisco hardware and software platforms.  Furthermore, the following
   proxies are available on open-source software.












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                                           +-------------+-------------+
                                           |     VPP     |    Linux    |
   +---+-----------------------------------+-------------+-------------+
   | M |           Static proxy            |  Available  | In progress |
   | P |                                   |             |             |
   | L |           Dynamic proxy           | In progress | In progress |
   | S |                                   |             |             |
   |   |        Shared memory proxy        | In progress | In progress |
   +---+-----------------------------------+-------------+-------------+
   |   |           Static proxy            |  Available  | In progress |
   |   |                                   |             |             |
   |   |Dynamic proxy - Inner type Ethernet| In progress | In progress |
   |   |                                   |             |             |
   |   |  Dynamic proxy - Inner type IPv4  |  Available  |  Available  |
   | S |                                   |             |             |
   | R |  Dynamic proxy - Inner type IPv6  |  Available  |  Available  |
   | v |                                   |             |             |
   | 6 |        Shared memory proxy        | In progress | In progress |
   |   |                                   |             |             |
   |   |        Masquerading proxy         |  Available  |  Available  |
   |   |                                   |             |             |
   |   | Masquerading proxy - NAT variant  | In progress | In progress |
   |   |                                   |             |             |
   |   |Masquerading proxy - Cache variant | In progress | In progress |
   +---+-----------------------------------+-------------+-------------+

             Figure 6: Open-source implementation status table

9.  Related works

   The Segment Routing solution addresses a wide problem that covers
   both topological and service policies.  The topological and service
   instructions can be either deployed in isolation or in combination.
   SR has thus a wider applicability than the architecture defined in
   [RFC7665].  Furthermore, the inherent property of SR is a stateless
   network fabric.  In SR, there is no state within the fabric to
   recognize a flow and associate it with a policy.  State is only
   present at the ingress edge of the SR domain, where the policy is
   encoded into the packets.  This is completely different from other
   proposals such as [RFC8300] and the MPLS label swapping mechanism
   described in [I-D.ietf-mpls-sfc], which rely on state configured at
   every hop of the service chain.

10.  IANA Considerations

   This I-D requests the IANA to allocate, within the "SRv6 Endpoint
   Types" sub-registry belonging to the top-level "Segment-routing with




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   IPv6 dataplane (SRv6) Parameters" registry, the following
   allocations:

   +-------------+-----+-----------------------------------+-----------+
   | Value/Range | Hex |         Endpoint function         | Reference |
   +-------------+-----+-----------------------------------+-----------+
   | TBA         | TBA |End.AN - SR-aware function (native)| [This.ID] |
   | TBA         | TBA |       End.AS - Static proxy       | [This.ID] |
   | TBA         | TBA |       End.AD - Dynamic proxy      | [This.ID] |
   | TBA         | TBA |    End.AM - Masquerading proxy    | [This.ID] |
   +-------------+-----+-----------------------------------+-----------+

                   Figure 7: SRv6 Service Endpoint Types

11.  Security Considerations

   The security requirements and mechanisms described in
   [I-D.ietf-spring-segment-routing],
   [I-D.ietf-6man-segment-routing-header] and
   [I-D.filsfils-spring-srv6-network-programming] also apply to this
   document.

   This document does not introduce any new security vulnerabilities.

12.  Acknowledgements

   The authors would like to thank Thierry Couture, Ketan Talaulikar,
   Loa Andersson, Andrew G.  Malis, Adrian Farrel, Alexander Vainshtein
   and Joel M.  Halpern for their valuable comments and suggestions on
   the document.

13.  Contributors

   P.  Camarillo (Cisco), B.  Peirens (Proximus), D.  Steinberg
   (Steinberg Consulting), A.  AbdelSalam (Gran Sasso Science
   Institute), G.  Dawra (LinkedIn), S.  Bryant (Huawei), H.  Assarpour
   (Broadcom), H.  Shah (Ciena), L.  Contreras (Telefonica I+D), J.
   Tantsura (Individual), M.  Vigoureux (Nokia) and J.  Bhattacharya
   (Cisco) substantially contributed to the content of this document.

14.  References

14.1.  Normative References








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   [I-D.filsfils-spring-srv6-network-programming]
              Filsfils, C., Li, Z., Leddy, J., daniel.voyer@bell.ca, d.,
              daniel.bernier@bell.ca, d., Steinberg, D., Raszuk, R.,
              Matsushima, S., Lebrun, D., Decraene, B., Peirens, B.,
              Salsano, S., Naik, G., Elmalky, H., Jonnalagadda, P., and
              M. Sharif, "SRv6 Network Programming", draft-filsfils-
              spring-srv6-network-programming-04 (work in progress),
              March 2018.

   [I-D.ietf-6man-segment-routing-header]
              Filsfils, C., Previdi, S., Leddy, J., Matsushima, S., and
              d. daniel.voyer@bell.ca, "IPv6 Segment Routing Header
              (SRH)", draft-ietf-6man-segment-routing-header-14 (work in
              progress), June 2018.

   [I-D.ietf-spring-segment-routing]
              Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing
              Architecture", draft-ietf-spring-segment-routing-15 (work
              in progress), January 2018.

   [I-D.ietf-spring-segment-routing-mpls]
              Bashandy, A., Filsfils, C., Previdi, S., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing with MPLS
              data plane", draft-ietf-spring-segment-routing-mpls-14
              (work in progress), June 2018.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d.,
              bogdanov@google.com, b., and P. Mattes, "Segment Routing
              Policy Architecture", draft-ietf-spring-segment-routing-
              policy-01 (work in progress), June 2018.

14.2.  Informative References

   [I-D.dawra-idr-bgp-sr-service-chaining]
              Dawra, G., Filsfils, C., daniel.bernier@bell.ca, d.,
              Uttaro, J., Decraene, B., Elmalky, H., Xu, X., Clad, F.,
              and K. Talaulikar, "BGP Control Plane Extensions for
              Segment Routing based Service Chaining", draft-dawra-idr-
              bgp-sr-service-chaining-02 (work in progress), January
              2018.

   [I-D.filsfils-spring-sr-policy-considerations]
              Filsfils, C., Talaulikar, K., Krol, P., Horneffer, M., and
              P. Mattes, "SR Policy Implementation and Deployment
              Considerations", draft-filsfils-spring-sr-policy-
              considerations-01 (work in progress), June 2018.



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   [I-D.ietf-mpls-sfc]
              Farrel, A., Bryant, S., and J. Drake, "An MPLS-Based
              Forwarding Plane for Service Function Chaining", draft-
              ietf-mpls-sfc-01 (work in progress), May 2018.

   [I-D.xu-mpls-payload-protocol-identifier]
              Xu, X., Assarpour, H., and S. Ma, "MPLS Payload Protocol
              Identifier", draft-xu-mpls-payload-protocol-identifier-04
              (work in progress), January 2018.

   [IFIP18]   Abdelsalam, A., Salsano, S., Clad, F., Camarillo, P., and
              C. Filsfils, "SEgment Routing Aware Firewall For Service
              Function Chaining scenarios", IFIP Networking conference ,
              May 2018.

   [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>.

   [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>.

Authors' Addresses

   Francois Clad (editor)
   Cisco Systems, Inc.
   France

   Email: fclad@cisco.com


   Xiaohu Xu (editor)
   Alibaba

   Email: xiaohu.xxh@alibaba-inc.com


   Clarence Filsfils
   Cisco Systems, Inc.
   Belgium

   Email: cf@cisco.com






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   Daniel Bernier
   Bell Canada
   Canada

   Email: daniel.bernier@bell.ca


   Cheng Li
   Huawei

   Email: chengli13@huawei.com


   Bruno Decraene
   Orange
   France

   Email: bruno.decraene@orange.com


   Shaowen Ma
   Juniper

   Email: mashaowen@gmail.com


   Chaitanya Yadlapalli
   AT&T
   USA

   Email: cy098d@att.com


   Wim Henderickx
   Nokia
   Belgium

   Email: wim.henderickx@nokia.com


   Stefano Salsano
   Universita di Roma "Tor Vergata"
   Italy

   Email: stefano.salsano@uniroma2.it






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