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Compressed SID (C-SID) for SRv6 SFC
draft-lh-spring-srv6-sfc-csid-00

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This is an older version of an Internet-Draft whose latest revision state is "Active".
Authors Cheng Li , Hongyi Huang
Last updated 2023-02-07
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draft-lh-spring-srv6-sfc-csid-00
SPRING Working Group                                          C. Li, Ed.
Internet-Draft                                             H. Huang, Ed.
Intended status: Standards Track                                  Huawei
Expires: 12 August 2023                                  8 February 2023

                  Compressed SID (C-SID) for SRv6 SFC
                    draft-lh-spring-srv6-sfc-csid-00

Abstract

   In SRv6, an SRv6 SID is a 128-bit value.  When too many 128-bit SRv6
   SIDs are included in an SRH, the introduced overhead will affect the
   transmission efficiency of payload.  In order to address this
   problem, Compressed SID(C-SID) is proposed.  This document defines
   new behaviors for service segments with REPLACE-C-SID and NEXT-C-SID
   flavors to enable compressed SRv6 service programming.

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 12 August 2023.

Copyright Notice

   Copyright (c) 2023 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 Revised BSD License text as
   described in Section 4.e of the Trust Legal Provisions and are
   provided without warranty as described in the Revised BSD License.

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Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
     1.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
     1.2.  Terminology . . . . . . . . . . . . . . . . . . . . . . .   3
   2.  SR Proxy Behaviors  . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Static SR Proxy . . . . . . . . . . . . . . . . . . . . .   4
       2.1.1.  Static Proxy for Inner Type Ethernet  . . . . . . . .   4
       2.1.2.  Static Proxy for Inner Type IPv4  . . . . . . . . . .   5
       2.1.3.  Static Proxy for Inner Type IPv6  . . . . . . . . . .   6
     2.2.  Dynamic SR Proxy  . . . . . . . . . . . . . . . . . . . .   7
       2.2.1.  Dynamic Proxy for Inner Type Ethernet . . . . . . . .   7
       2.2.2.  Dynamic Proxy for Inner Type IPv4 . . . . . . . . . .   8
       2.2.3.  Dynamic Proxy for Inner Type IPv6 . . . . . . . . . .   9
     2.3.  Shared Memory SR Proxy  . . . . . . . . . . . . . . . . .  10
     2.4.  Masquerading SR Proxy . . . . . . . . . . . . . . . . . .  11
       2.4.1.  SRv6 Masquerading Proxy Pseudocode  . . . . . . . . .  11
       2.4.2.  Destination NAT Flavor  . . . . . . . . . . . . . . .  13
       2.4.3.  Cache Flavor  . . . . . . . . . . . . . . . . . . . .  13
   3.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   4.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   5.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     5.1.  Normative References  . . . . . . . . . . . . . . . . . .  14
     5.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Acknowledgements  . . . . . . . . . . . . . . . . . . . . . . . .  15
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   Segment Routing [RFC8402] is a source routing paradigm to support
   steering packets through a programmed path at the ingress node.
   Currently, two data planes are defined for Segment Routing: MPLS and
   IPv6.  When IPv6 data plane is used in Segment Routing, it is called
   SRv6 [RFC8754] . [RFC8754] defines a new extension header in IPv6,
   called Segment Routing Header (SRH), to support SRv6.  To support
   SRv6 network programming, [RFC8986] defines a framework to build a
   network program with topological and service segments carried in a
   Segment Routing header (SRH) [RFC8754].

   A Service Function Chain (SFC) [RFC7665] defines an ordered set of
   abstract service functions and ordering constraints that must be
   applied to packets and/or frames and/or flows.

   A service function chain can be implemented by SRv6 by using a
   sequence of SRv6 SIDs including service segments defined in
   [I-D.ietf-spring-sr-service-programming].

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   However, when too many 128-bit SRv6 SIDs are included in an SRH, the
   overhead of the SRH will affect the transmission efficiency of the
   payload.  [I-D.srcompdt-spring-compression-requirement] points out
   the problem of long SRv6 SID lists reduce payload efficiency.  To
   mitigate such overhead, [I-D.ietf-spring-srv6-srh-compression]
   defines new flavors for basic SR endpoint behaviors defined in
   [RFC8986].  Using the new flavored behavior SID, a 128-bit SRv6 SID
   can be compressed to be an 32-bit or 16-bit Compressed SID (C-SID),
   which reduces a lot of size of the SRv6 header.

   To enable SRv6 SID lists compression for service function chaining
   (SFC), this document defines new behaviors of service segments with
   flavors defined in [I-D.ietf-spring-srv6-srh-compression].

1.1.  Requirements Language

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

1.2.  Terminology

   This document leverages the terms defined in [RFC8402], [RFC8754],
   [RFC8986], [I-D.ietf-spring-srv6-srh-compression] and
   [I-D.ietf-spring-sr-service-programming].  The reader is assumed to
   be familiar with this terminology.  This document does not introduce
   any new terms.

2.  SR Proxy Behaviors

   [I-D.ietf-spring-sr-service-programming] defines several SRv6
   endpoint behaviors for service proxy segments.  A service proxy
   segment ID is represented as an 128-bit value just like other SIDs
   defined in [RFC8986].  This section defines some new behaviors of
   those service proxy segments by combining the existing service proxy
   segment behaviors with C-SID flavors, such as REPLACE-C-SID flavor
   and NEXT-C-SID flavor.

   The main difference between behaviors are the forwarding
   instructions.  Therefore, when C-SID compression mechanism applies to
   SR Proxy behaviors, the pseudo code of the new behaviors can be
   generated by updating the forwarding instructions of C-SID to SR
   proxy forwarding instructions.  The following sections define the
   details of the pseudo code of new behaviors.

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2.1.  Static SR Proxy

2.1.1.  Static Proxy for Inner Type Ethernet

2.1.1.1.  REPLACE-C-SID Flavor

   When processing an IPv6 packet that matches a FIB entry locally
   instantiated as an SRv6 static proxy SID with the REPLACE-C-SID
   flavor for Ethernet traffic, the procedure described in Section 4.2.1
   of [I-D.ietf-spring-srv6-srh-compression] is executed except for line
   S23 replaced as follows.

   S1.   If (Upper-layer header type != 143 (Ethernet)) {
   S2.     Resubmit the packet to the IPv6 module for transmission to
              the new destination.
   S3.   }
   S4.   Perform IPv6 decapsulation.
   S5.   Submit the frame to the Ethernet module for transmission via
            interface IFACE-OUT.

   The upper-layer header processing is unchanged as per Section 6.1.2.1
   of [I-D.ietf-spring-sr-service-programming].

   When processing an Ethernet frame received on the interface IFACE-IN
   and with a destination MAC address that is neither a broadcast
   address nor matches the address of IFACE-IN, as per Section 6.1.2.1
   of [I-D.ietf-spring-sr-service-programming].

2.1.1.2.  NEXT-C-SID Flavor

   When processing an IPv6 packet that matches a FIB entry locally
   instantiated as an SRv6 static proxy SID with the NEXT-C-SID flavor
   for Ethernet traffic, the procedure described in Section 4.1.1 of
   [I-D.ietf-spring-srv6-srh-compression] is executed except for line
   S08 of that and line S15 of Section 4.1 of [RFC8986] that are both
   replaced as follows.

   S1.   If (Upper-layer header type != 143 (Ethernet)) {
   S2.     Resubmit the packet to the IPv6 module for transmission to
              the new destination.
   S3.   }
   S4.   Perform IPv6 decapsulation.
   S5.   Submit the frame to the Ethernet module for transmission via
            interface IFACE-OUT.

   The upper-layer header processing is unchanged as per Section 6.1.2.1
   of [I-D.ietf-spring-sr-service-programming].

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   When processing an Ethernet frame received on the interface IFACE-IN
   and with a destination MAC address that is neither a broadcast
   address nor matches the address of IFACE-IN, as per Section 6.1.2.1
   of [I-D.ietf-spring-sr-service-programming].

2.1.2.  Static Proxy for Inner Type IPv4

2.1.2.1.  REPLACE-C-SID Flavor

   When processing an IPv6 packet that matches a FIB entry locally
   instantiated as an SRv6 static proxy SID with the REPLACE-C-SID
   flavor for IPv4 traffic, the procedure described in Section 4.2.1 of
   [I-D.ietf-spring-srv6-srh-compression] is executed except for line
   S23 replaced as follows.

   S1.   If (Upper-layer header type != 4 (IPv4)) {
   S2.     Resubmit the packet to the IPv6 module for transmission to
              the new destination.
   S3.   }
   S4.   Perform IPv6 decapsulation.
   S5.   Submit the packet to the IPv4 module for transmission on
            interface IFACE-OUT via NH-ADDR.

   The upper-layer header processing is unchanged as per Section 6.1.2.2
   of [I-D.ietf-spring-sr-service-programming].

   When processing an IPv4 packet received on the interface IFACE-IN and
   with a destination address that does not match any address of IFACE-
   IN, as per Section 6.1.2.2 of
   [I-D.ietf-spring-sr-service-programming].

2.1.2.2.  NEXT-C-SID Flavor

   When processing an IPv6 packet that matches a FIB entry locally
   instantiated as an SRv6 static proxy SID with the NEXT-C-SID flavor
   for IPv4 traffic, the procedure described in Section 4.1.1 of
   [I-D.ietf-spring-srv6-srh-compression] is executed except for line
   S08 of that and line S15 of Section 4.1 of [RFC8986] that are both
   replaced as follows.

   S1.   If (Upper-layer header type != 4 (IPv4)) {
   S2.     Resubmit the packet to the IPv6 module for transmission to
              the new destination.
   S3.   }
   S4.   Perform IPv6 decapsulation.
   S5.   Submit the packet to the IPv4 module for transmission on
            interface IFACE-OUT via NH-ADDR.

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   The upper-layer header processing is unchanged as per Section 6.1.2.2
   of [I-D.ietf-spring-sr-service-programming].

   When processing an IPv4 packet received on the interface IFACE-IN and
   with a destination address that does not match any address of IFACE-
   IN, as per Section 6.1.2.2 of
   [I-D.ietf-spring-sr-service-programming].

2.1.3.  Static Proxy for Inner Type IPv6

2.1.3.1.  REPLACE-C-SID Flavor

   When processing an IPv6 packet that matches a FIB entry locally
   instantiated as an SRv6 static proxy SID with the REPLACE-C-SID
   flavor for IPv6 traffic, the procedure described in Section 4.2.1 of
   [I-D.ietf-spring-srv6-srh-compression] is executed except for line
   S23 replaced as follows.

   S1.   If (Upper-layer header type != 41 (IPv6)) {
   S2.     Resubmit the packet to the IPv6 module for transmission to
              the new destination.
   S3.   }
   S4.   Perform IPv6 decapsulation.
   S5.   Submit the packet to the IPv6 module for transmission on
            interface IFACE-OUT via NH-ADDR.

   The upper-layer header processing is unchanged as per Section 6.1.2.3
   of [I-D.ietf-spring-sr-service-programming].

   When processing an IPv6 packet received on the interface IFACE-IN and
   with a destination address that does not match any address of IFACE-
   IN, as per Section 6.1.2.3 of
   [I-D.ietf-spring-sr-service-programming].

2.1.3.2.  NEXT-C-SID Flavor

   When processing an IPv6 packet that matches a FIB entry locally
   instantiated as an SRv6 static proxy SID with the NEXT-C-SID flavor
   for IPv6 traffic, the procedure described in Section 4.1.1 of
   [I-D.ietf-spring-srv6-srh-compression] is executed except for line
   S08 of that and line S15 of Section 4.1 of [RFC8986] that are both
   replaced as follows.

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   S1.   If (Upper-layer header type != 41 (IPv6)) {
   S2.     Resubmit the packet to the IPv6 module for transmission to
              the new destination.
   S3.   }
   S4.   Perform IPv6 decapsulation.
   S5.   Submit the packet to the IPv6 module for transmission on
            interface IFACE-OUT via NH-ADDR.

   The upper-layer header processing is unchanged as per Section 6.1.2.3
   of [I-D.ietf-spring-sr-service-programming].

   When processing an IPv6 packet received on the interface IFACE-IN and
   with a destination address that does not match any address of IFACE-
   IN, as per Section 6.1.2.3 of
   [I-D.ietf-spring-sr-service-programming].

2.2.  Dynamic SR Proxy

2.2.1.  Dynamic Proxy for Inner Type Ethernet

2.2.1.1.  REPLACE-C-SID Flavor

   When processing an IPv6 packet that matches a FIB entry locally
   instantiated as an SRv6 dynamic proxy SID with the REPLACE-C-SID
   flavor for Ethernet traffic, the procedure described in Section 4.2.1
   of [I-D.ietf-spring-srv6-srh-compression] is executed except for line
   S23 replaced as follows.

   S1.   If (Upper-layer header type != 143 (Ethernet)) {
   S2.     Resubmit the packet to the IPv6 module for transmission to
              the new destination.
   S3.   }
   S4.   Copy the IPv6 encapsulation in a CACHE entry associated with
               the interface IFACE-IN.
   S5.   Perform IPv6 decapsulation.
   S6.   Submit the frame to the Ethernet module for transmission via
            interface IFACE-OUT.

   The upper-layer header processing is unchanged as per Section 6.2.2
   of [I-D.ietf-spring-sr-service-programming].

   When processing an Ethernet frame received on the interface IFACE-IN
   and with a destination MAC address that is neither a broadcast
   address nor matches the address of IFACE-IN, as per Section 6.2.2 of
   [I-D.ietf-spring-sr-service-programming].

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2.2.1.2.  NEXT-C-SID Flavor

   When processing an IPv6 packet that matches a FIB entry locally
   instantiated as an SRv6 dynamic proxy SID with the NEXT-C-SID flavor
   for Ethernet traffic, the procedure described in Section 4.1.1 of
   [I-D.ietf-spring-srv6-srh-compression] is executed except for line
   S08 of that and line S15 of Section 4.1 of [RFC8986] that are both
   replaced as follows.

   S1.   If (Upper-layer header type != 143 (Ethernet)) {
   S2.     Resubmit the packet to the IPv6 module for transmission to
              the new destination.
   S3.   }
   S4.   Copy the IPv6 encapsulation in a CACHE entry associated with
               the interface IFACE-IN.
   S5.   Perform IPv6 decapsulation.
   S6.   Submit the frame to the Ethernet module for transmission via
            interface IFACE-OUT.

   The upper-layer header processing is unchanged as per Section 6.2.2
   of [I-D.ietf-spring-sr-service-programming].

   When processing an Ethernet frame received on the interface IFACE-IN
   and with a destination MAC address that is neither a broadcast
   address nor matches the address of IFACE-IN, as per Section 6.2.2 of
   [I-D.ietf-spring-sr-service-programming].

2.2.2.  Dynamic Proxy for Inner Type IPv4

2.2.2.1.  REPLACE-C-SID Flavor

   When processing an IPv6 packet that matches a FIB entry locally
   instantiated as an SRv6 dynamic proxy SID with the REPLACE-C-SID
   flavor for IPv4 traffic, the procedure described in Section 4.2.1 of
   [I-D.ietf-spring-srv6-srh-compression] is executed except for line
   S23 replaced as follows.

   S1.   If (Upper-layer header type != 4 (IPv4)) {
   S2.     Resubmit the packet to the IPv6 module for transmission to
              the new destination.
   S3.   }
   S4.   Copy the IPv6 encapsulation in a CACHE entry associated with
               the interface IFACE-IN.
   S5.   Perform IPv6 decapsulation.
   S6.   Submit the frame to the IPv4 module for transmission via
            interface IFACE-OUT via NH-ADDR.

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   The upper-layer header processing is unchanged as per Section 6.2.2
   of [I-D.ietf-spring-sr-service-programming].

   When processing an IPv4 packet received on the interface IFACE-IN and
   with a destination address that does not match any address of IFACE-
   IN, as per Section 6.2.2 of [I-D.ietf-spring-sr-service-programming].

2.2.2.2.  NEXT-C-SID Flavor

   When processing an IPv6 packet that matches a FIB entry locally
   instantiated as an SRv6 dynamic proxy SID with the NEXT-C-SID flavor
   for IPv4 traffic, the procedure described in Section 4.1.1 of
   [I-D.ietf-spring-srv6-srh-compression] is executed except for line
   S08 of that and line S15 of Section 4.1 of [RFC8986] that are both
   replaced as follows.

   S1. If (Upper-layer header type != 4 (IPv4)) {
   S2.   Resubmit the packet to the IPv6 module for transmission to
           the new destination.
   S3. }
   S4. Copy the IPv6 encapsulation in a CACHE entry associated with
           the interface IFACE-IN.
   S5. Perform IPv6 decapsulation.
   S6. Submit the frame to the IPv4 module for transmission via
         interface IFACE-OUT via NH-ADDR.

   The upper-layer header processing is unchanged as per Section 6.2.2
   of [I-D.ietf-spring-sr-service-programming].

   When processing an IPv4 packet received on the interface IFACE-IN and
   with a destination address that does not match any address of IFACE-
   IN, as per Section 6.2.2 of [I-D.ietf-spring-sr-service-programming].

2.2.3.  Dynamic Proxy for Inner Type IPv6

2.2.3.1.  REPLACE-C-SID Flavor

   When processing an IPv6 packet that matches a FIB entry locally
   instantiated as an SRv6 dynamic proxy SID with the REPLACE-C-SID
   flavor for IPv6 traffic, the procedure described in Section 4.2.1 of
   [I-D.ietf-spring-srv6-srh-compression] is executed except for line
   S23 replaced as follows.

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   S1. If (Upper-layer header type != 41 (IPv6)) {
   S2.   Resubmit the packet to the IPv6 module for transmission to
           the new destination.
   S3. }
   S4. Copy the IPv6 encapsulation in a CACHE entry associated with
           the interface IFACE-IN.
   S5. Perform IPv6 decapsulation.
   S6. Submit the frame to the IPv6 module for transmission via
         interface IFACE-OUT via NH-ADDR.

   The upper-layer header processing is unchanged as per Section 6.2.2
   of [I-D.ietf-spring-sr-service-programming].

   When processing an IPv6 packet received on the interface IFACE-IN and
   with a destination address that does not match any address of IFACE-
   IN, as per Section 6.2.2 of [I-D.ietf-spring-sr-service-programming].

2.2.3.2.  NEXT-C-SID Flavor

   When processing an IPv6 packet that matches a FIB entry locally
   instantiated as an SRv6 dynamic proxy SID with the NEXT-C-SID flavor
   for IPv6 traffic, the procedure described in Section 4.1.1 of
   [I-D.ietf-spring-srv6-srh-compression] is executed except for line
   S08 of that and line S15 of Section 4.1 of [RFC8986] that are both
   replaced as follows.

   S1. If (Upper-layer header type != 41 (IPv6)) {
   S2.   Resubmit the packet to the IPv6 module for transmission to
           the new destination.
   S3. }
   S4. Copy the IPv6 encapsulation in a CACHE entry associated with
           the interface IFACE-IN.
   S5. Perform IPv6 decapsulation.
   S6. Submit the frame to the IPv6 module for transmission via
         interface IFACE-OUT via NH-ADDR.

   The upper-layer header processing is unchanged as per Section 6.2.2
   of [I-D.ietf-spring-sr-service-programming].

   When processing an IPv6 packet received on the interface IFACE-IN and
   with a destination address that does not match any address of IFACE-
   IN, as per Section 6.2.2 of [I-D.ietf-spring-sr-service-programming].

2.3.  Shared Memory SR Proxy

   This document does not define new flavors for shared proxy behavior
   as it is just an SR endpoint behavior.

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2.4.  Masquerading SR Proxy

   As per [I-D.ietf-spring-sr-service-programming], when forwarding
   packets to SR-unaware SFs, masquerading SR proxy sets the destination
   address of the IPv6 header as segment list[0] which is the original
   final destination address.  When receiving the traffic returning from
   the service, de-masquerading sets the destination address as segment
   list[Segment Left].

   To be consistent with the behavior of masquerading proxy, it's
   required that any segment list containing one or more masquerading
   proxy C-SID MUST NOT apply any compression encoding to the last
   segment (segment list[0]).

   Note: The service receiving an IPv6 packet from the proxy uses the
   destination address (copied from last segment) as final destination
   and could apply certain actions based on that.  In order to process
   and forward packets correctly, it is required that the last segment
   not be compressed.

   To be consistent with the behavior of masquerading proxy, when
   processing an IPv6 packet matching a FIB entry locally instantiated
   as an SRv6 masquerading C-SID, it's required that the updated
   destination address MUST be cached in the proxy by adding a dynamic
   caching mechanism similar to the one described in Section 6.2 of
   [I-D.ietf-spring-sr-service-programming] in case that segment
   list[Segment Left] is a compressed SID.

   When processing an IPv6 packet received on the interface IFACE-IN and
   with a destination address that does not match any address of IFACE-
   IN, the destination address MUST be recovered from CACHE in case that
   segment list[Segment Left] could be a C-SID container.

2.4.1.  SRv6 Masquerading Proxy Pseudocode

2.4.1.1.  REPLACE-C-SID Flavor

   When processing an IPv6 packet that matches a FIB entry locally
   instantiated as an SRv6 masquerading proxy SID with the REPLACE-C-SID
   flavor, the procedure described in Figure 23 from Section 4.2.1 of
   [I-D.ietf-spring-srv6-srh-compression] is executed except for line
   S23 replaced as follows.

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   S1. Copy the IPv6 Destination Address in a CACHE entry associated
         with the interface IFACE-IN.
   S2. Copy Segment List[0] from the SRH to the Destination Address
         of the IPv6 header.
   S3. Submit the packet to the IPv6 module for transmission on
         interface IFACE-OUT via NH-ADDR.

   *De-masquerading*: When processing an IPv6 packet received on the
   interface IFACE-IN and with a destination address that does not match
   any address of IFACE-IN, the procedure described in Figure 24 from
   Section 6.4.1 of [I-D.ietf-spring-sr-service-programming] is executed
   except for line S10 that is replaced as follows.

   S01. Retrieve the CACHE entry associated with IFACE-IN.
   S02. If the CACHE entry is not empty {
   S03.    Destination Address of the IPv6 header is set to CACHE.
   S04. }

2.4.1.2.  NEXT-C-SID Flavor

   When processing an IPv6 packet that matches a FIB entry locally
   instantiated as an SRv6 masquerading proxy SID with the NEXT-C-SID
   flavor, the procedure described in Section 4.1.1 of
   [I-D.ietf-spring-srv6-srh-compression] is executed except for line
   S08 of that and line S15 of Section 4.1 of [RFC8986] that are both
   replaced as follows.

   S1. Copy the IPv6 Destination Address in a CACHE entry associated
         with the interface IFACE-IN.
   S2. Copy Segment List[0] from the SRH to the Destination Address
         of the IPv6 header.
   S3. Submit the packet to the IPv6 module for transmission on
         interface IFACE-OUT via NH-ADDR.

   *De-masquerading*: When processing an IPv6 packet received on the
   interface IFACE-IN and with a destination address that does not match
   any address of IFACE-IN, the procedure described in Section 6.4.1 of
   [I-D.ietf-spring-sr-service-programming] is executed except for line
   S10 that is replaced as follows.

   S01. Retrieve the CACHE entry associated with IFACE-IN.
   S02. If the CACHE entry is not empty {
   S03.    Destination Address of the IPv6 header is set to CACHE.
   S04. }

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2.4.2.  Destination NAT Flavor

2.4.2.1.  REPLACE-C-SID Flavor

   The Destination NAT flavor of the SRv6 masquerading proxy with the
   REPLACE-C-SID is executed except for line S09.1 and S10 in
   Section 6.4.2 of [I-D.ietf-spring-sr-service-programming] replaced as
   follows.

   S1. Copy the Destination Address of the IPv6 header to the
         Segment List[0] entry of the SRH.
   S2. Retrieve the CACHE entry associated with IFACE-IN.
   S3. If the CACHE entry is not empty {
   S4.    Destination Address of the IPv6 header is set to CACHE.
   S5. }

2.4.2.2.  NEXT-C-SID Flavor

   The Destination NAT flavor of the SRv6 masquerading proxy with the
   NEXT-C-SID is executed except for line S09.1 and S10 in Section 6.4.2
   of [I-D.ietf-spring-sr-service-programming] replaced as follows.

   S1. Copy the Destination Address of the IPv6 header to the
         Segment List[0] entry of the SRH.
   S2. Retrieve the CACHE entry associated with IFACE-IN.
   S3. If the CACHE entry is not empty {
   S4.    Destination Address of the IPv6 header is set to CACHE.
   S5. }

2.4.3.  Cache Flavor

   The caching flavor of the SRv6 masquerading proxy with C-SID is
   enabled as per Section 6.4.3 of
   [I-D.ietf-spring-sr-service-programming] without any modification.

3.  Security Considerations

   The security requirements and mechanisms described in [RFC8402] and
   [RFC8754] also apply to this document.

   This document does not introduce any new security considerations.

4.  IANA Considerations

   TBD

5.  References

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5.1.  Normative References

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

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

   [RFC8402]  Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
              Decraene, B., Litkowski, S., and R. Shakir, "Segment
              Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
              July 2018, <https://www.rfc-editor.org/rfc/rfc8402>.

   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
              Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
              (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
              <https://www.rfc-editor.org/rfc/rfc8754>.

   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
              D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
              (SRv6) Network Programming", RFC 8986,
              DOI 10.17487/RFC8986, February 2021,
              <https://www.rfc-editor.org/rfc/rfc8986>.

   [I-D.ietf-spring-srv6-srh-compression]
              Cheng, W., Filsfils, C., Li, Z., Decraene, B., and F.
              Clad, "Compressed SRv6 Segment List Encoding in SRH", Work
              in Progress, Internet-Draft, draft-ietf-spring-srv6-srh-
              compression-03, 11 January 2023,
              <https://datatracker.ietf.org/doc/html/draft-ietf-spring-
              srv6-srh-compression-03>.

   [I-D.ietf-spring-sr-service-programming]
              Clad, F., Xu, X., Filsfils, C., Bernier, D., Li, C.,
              Decraene, B., Ma, S., Yadlapalli, C., Henderickx, W., and
              S. Salsano, "Service Programming with Segment Routing",
              Work in Progress, Internet-Draft, draft-ietf-spring-sr-
              service-programming-06, 9 June 2022,
              <https://datatracker.ietf.org/doc/html/draft-ietf-spring-
              sr-service-programming-06>.

5.2.  Informative References

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   [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/rfc/rfc7665>.

   [I-D.srcompdt-spring-compression-requirement]
              Cheng, W., Xie, C., Bonica, R., Dukes, D., Li, C., Peng,
              S., and W. Henderickx, "Compressed SRv6 SID List
              Requirements", Work in Progress, Internet-Draft, draft-
              srcompdt-spring-compression-requirement-07, 11 July 2021,
              <https://datatracker.ietf.org/doc/html/draft-srcompdt-
              spring-compression-requirement-07>.

Acknowledgements

   TBD.

Authors' Addresses

   Cheng Li (editor)
   Huawei
   China
   Email: c.l@huawei.com

   Hongyi Huang (editor)
   Huawei
   China
   Email: hongyi.huang@huawei.com

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