Internet DRAFT - draft-lx-msr6-rgb-segment

draft-lx-msr6-rgb-segment







Network Working Group                                             Y. Liu
Internet-Draft                                              China Mobile
Intended status: Standards Track                                  J. Xie
Expires: 25 April 2024                                           X. Geng
                                                     Huawei Technologies
                                                                 M. Chen
                                                    New H3C Technologies
                                                         23 October 2023


RGB (Replication through Global Bitstring) Segment for Multicast Source
                           Routing over IPv6
                      draft-lx-msr6-rgb-segment-05

Abstract

   This document introduces the RGB (Replication through Global
   Bitstring) Segment for Multicast Source Routing over IPv6.

Requirements Language

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
   document are to be interpreted as described in RFC 2119 [RFC2119].

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 25 April 2024.

Copyright Notice

   Copyright (c) 2023 IETF Trust and the persons identified as the
   document authors.  All rights reserved.





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   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.

Table of Contents

   1.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminologies . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  RGB Destination Options Header  . . . . . . . . . . . . . . .   4
   4.  RGB Segment . . . . . . . . . . . . . . . . . . . . . . . . .   5
     4.1.  RGB Segment Definition  . . . . . . . . . . . . . . . . .   5
     4.2.  End.RGB Behavior  . . . . . . . . . . . . . . . . . . . .   6
   5.  MSR6 BE Encapsulation . . . . . . . . . . . . . . . . . . . .   7
   6.  Packet Processing Procedure . . . . . . . . . . . . . . . . .   7
   7.  Illustration  . . . . . . . . . . . . . . . . . . . . . . . .   8
   8.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  11
     8.1.  RGB Option Type . . . . . . . . . . . . . . . . . . . . .  11
     8.2.  End.RGB Function  . . . . . . . . . . . . . . . . . . . .  11
   9.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
     9.1.  Intra Domain Deployment . . . . . . . . . . . . . . . . .  12
     9.2.  ICMP Error Processing . . . . . . . . . . . . . . . . . .  13
     9.3.  Security caused by RGB option . . . . . . . . . . . . . .  13
   10. Normative References  . . . . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   Segment Routing ([RFC8402]) leverages the mechanism of source
   routing.  An ingress node steers a packet through an ordered list of
   instructions, called "segments".  Each one of these instructions
   represents a function to be implemented at a specific location in the
   network.  A function is locally defined on the node where it is
   executed.  Network Programming combines Segment Routing functions to
   achieve a networking objective that goes beyond mere packet routing.
   [RFC8986] defines the SRv6 Network Programming concept and specifies
   the main Segment Routing behaviors and network programming functions.

   Bit Index Explicit Replication (BIER) [RFC8279] is an architecture
   that provides optimal multicast forwarding without requiring a
   protocol for explicitly building multicast distribution trees or per-
   flow state maintained by intermediate routers.  When a multicast data
   packet enters BIER forwarding domain, the ingress node encapsulates
   the packet with a bitstring, each bitposition of which presents the



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   egress nodes.  To forward the packet to a given set of egress nodes,
   the bits corresponding to those egress nodes are set in the
   bitstring.  The intermediate nodes in the BIER domain replicate and
   forward the packet based on the bitstring.The mechanism of forwarding
   a packet based on bitstring of BIER are specified in [RFC8279].

   An IPv6 based multicast source routing (MSR6) solution is defined in
   [I-D.cheng-spring-ipv6-msr-design-consideration].  Like SRv6 for
   unicast, MSR6 provides network programming capability for multicast
   service by encoding network instructions in the IPv6 packet header,
   and specifies a packet to replicate and forward based on these
   instructions.  Each instruction is implemented on one or several
   nodes in the network and identified by an MSR6 Segment Identifier.
   Similar as BIER, bitstring is used in MSR6 to represent nodes or
   links in the network to save encapsulation expense.

   MSR6 has two basic modes of forwarding: one is based on Shortest Path
   First(SPF), which is called MSR6 BE(Best Effort) mode; the other is
   based on traffic engineered, which is called MSR6 TE(Traffic
   Engineering) mode.  This document defines a new type of segment,
   Replication through Global Bitstring Segment (RGB Segment), and the
   corresponding packet processing procedures over the IPv6 data plane
   for the MSR6 BE solutions.

2.  Terminologies

   The following new terms are used throughout this document:

   MSR6 Domain: a set of nodes participating in the multicast source
   routing over IPv6;

   MSR6 Ingress Node: a node through which a multicast data packet
   enters an MSR6 domain; The MSR6 Ingress Node could be a host or a
   network device.

   MSR6 Egress Node: a node through which a multicast data packet leaves
   an MSR6 domain; The MSR6 Egress Node could be a host or a network
   device.

   MSR6 Root Node: a node which is the beginning point of a multicast
   tree for multicast service using MSR6.  It encapsulates the packet
   with an MSR6 multicast header.

   MSR6 Leaf Node: a node which is the ending point of a multicast tree
   for multicast service using MSR6.  It decapsulates the MSR6 multicast
   header in the packet.





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   MSR6 Replication Endpoint: the intermediate node of a multicast
   treefor multicast service using MSR6, which replicates packet and
   forwards the packet to the downstream nodes.  For MSR6, the
   Replication Node is called Replication Endpoint which can be
   indicated by the MSR6 Segment and replicate packets according to the
   multicast source routing informated encapsulation in the MSR6 header
   of the packet.

   MSR6 Transit Node: a node which forwards the MSR6 packet as an IPv6
   unicast packet between MSR6 replication endpoints or MSR6 replication
   endpoint and MSR6 leaf node;

3.  RGB Destination Options Header

   Multicast BE flow, relative to the concept of multicast TE flow, does
   not need to go through a planning path satisfying service
   requirements.  The path for multicast BE flow is normally provided by
   routing underlay protocol, as IGP.

   In MSR6, a set of egress nodes which the packet is supposed to be
   sent to are supposed to be indicated in the packet, in order to avoid
   maintaining multicast tree for each multicast flow.  Global bitstring
   could represent the egress nodes efficiently and such mechanism has
   been defined in BIER [RFC8279] through BIER Header [RFC8279], which
   could be reused in MSR6.

   For IPv6 data plane, a new IPv6 Destination Options Header
   ([RFC8200]) option called RGB (Replication through Global Bitstring)
   is introduced in MSR6.

   The encoding of RGB Option is showed as follows:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Next Header  |  Hdr Ext Len  |  Option Type  | Option Length |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                                                               |
       ~                      RGB Option Data                         ~
       |                                                               |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Next Header  8-bit selector.  Identifies the type of header
      immediately following the Destination Options header.

   Hdr Ext Len  8-bit unsigned integer.  Length of the Destination
      Options header in 8-octet units, not including the first 8 octets.




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   Option Type  To be allocated by IANA.  See section 6.

   Option Length  8-bit unsigned integer.  Length of the option, in
      octets, excluding the Option Type and Option Length fields.

   The encoding of RGB Option is defined as follows:

        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
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |              BIFT-id                  |   Rsv |     TTL       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |  Rsv  |  Ver  |  BSL  |              Entropy                  |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |OAM|Rsv|   DSCP    |                   Rsv                     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |                BitString  (first 32 bits)                     ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                                                               ~
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       ~                BitString  (last 32 bits)                      |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   The RGB Option Data reuses some codepoint of Non-MPLS BIER Header
   defined in [RFC8296] except the fields of Nibble, DSCP and Proto,
   which are replaced as the Reserved field.  The Reserved fields SHOULD
   be set to 0 and MUST be ignored up reception.

4.  RGB Segment


4.1.  RGB Segment Definition

   As defined in [RFC8402], segment represents instruction, topological
   or service based.In an IPv6 domain, a segment could be encoded as an
   IPv6 address.















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   In MSR6, a new type of segment is defined called RGB segment.  RGB
   segment is used to identify the Replication Endpoint and direct to
   replicatereplicate the packet using BIER forwarding mechanism defined
   in [RFC8279] according to the bitstring defined in the RGB Option.
   RGB segment follows the SID format defined in [RFC8986], consisting
   of LOC:FUNCT:ARG.  RGB segment is advertised by the RGB replication
   endpoint.  In an MSR6 domain, RGB segment is used as the destination
   address of the MSR BE packet, steering the packet to the next
   Replication Endpoint.  If there is 1 or more MSR6 transit nodes
   between two Replication Endpoints, the packet is forwarded as normal
   unicast IPv6 packet, and RGB segment is treated as unicast IPv6
   prefix to route the packet




   The segment defined in [RFC8402] can represent instruction,
   topological or service based.  In an IPv6 domain, a segment could be
   encoded as an IPv6 address.

   In the IPv6 data plane, RGB segment is a new type of segment which is
   used to identify the Replication Endpoint.  Replication Endpoint is
   able to replicate the packet using BIER forwarding mechanism
   according to the bitstring defined in the RGB Option.

   RGB segment is used as an IPv6 address, which is 128 bits and follows
   the SID format defined in [RFC8986], consisting of LOC:FUNCT:ARG.
   RGB segment is advertised by the RGB replication endpoint.

   In an MSR6 domain, RGB segment is used as the destination address of
   the MSR BE packet, when a packet is replicated to the next
   Replication Endpoint.  If there is 1 or more MSR6 transit node
   between two Replication Endpoints, the packet is forwarded as normal
   unicast IPv6 packet.

4.2.  End.RGB Behavior


   In SRv6, a packet processing behavior is executed at the SRv6 Segment
   Endpoint Node ([RFC8986]).  Similarly, in MSR6, a new type of
   behavior, End.RGB(End.  Replication through Global Bitstring), is
   defined for RGB Segment.  The pseudo-code for End.RGB is defined in
   this section.

   When an MSR6 Replication Endpoint receives a packet whose IPv6 DA
   (Destination Address) is a SID and the SID is a local End.RGB SID,
   the MSR6 Replication Endpoint does the following:




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    1. IF (There is DoH as an IPv6 Extension header and one of the options type is RGB);
    2.   Lookup BIFT(Bit Index Forwarding Table, RFC8279) based on the bitstring
           inside the RGB Option Data.
    3.   Forward the packet via the matched entry in the BIFT.
    4. ELSE IF NH=ICMPv6 or (NH=RGB Extension Header Type and NH
        of Extension Header=ICMPv6)  ;
    5.   Send to CPU.
    6. ELSE  ;Ref
    7.   Drop the packet.

   Ref: An ICMPv6 packet using End.RGB as destination address.


5.  MSR6 BE Encapsulation


   MSR6 BE encapsulation is composed of 3 parts: IPv6 header, IPv6 RGB
   option DoH and client multicast packet, which is showedas follows:

      +---------------+------------------+----------------------+
      |  IPv6 header  |  IPv6 DO Header  |  Client Multicast    |
      |               |  with RGB Option |  Packet or Upper     |
      |               |                  |  Layer Encasulations |
      | Next Hdr = 60 |   Nxt Hdr = X    |                      |
      +---------------+------------------+----------------------+
      |                                  |                      |
      |<---------MSR6 BE header--------->|<--MSR6 BE payload--->|

   In the MSR6 BE header, the RGB Segment is used as the IPv6
   Destination Address and indicates the next MSR6 Replication Endpoints
   in an MSR domain.  RGB DoH option is used as the carrier of bitstring
   information and the MSR6 Replication Endpoint uses the bitstring as
   the entry to look up BIFT(Bit Index Forwarding Table) to replicate
   and find the next MSR6 Replication Endpoints.


6.  Packet Processing Procedure

   This section defines the general process of MSR6 BE to transport a
   multicast service.  The corresponding control plane is out of scope
   of this document and could be discussed in the following work.

   MSR6 Root Node: The Ingress Node of a multicast flow.  It can be
   either a host originating the MSR6 packet, or a router encapsulating
   the customer packet in an MSR6 header.  The bitstring in the DoH is
   determined by the egress nodes the packet is supposed to be
   replicated to.  The IPv6 destination address is the RGB segment which
   is determined by the next MSR6 RGB Replication Endpoints the packet



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   is supposed to be sent to.  The downstream MSR6 Replication Endpoints
   are determined by the matched entries in BIFT according to the bier
   forwarding mechanism.

   MSR6 Replication Endpoint: Replicate the packet and forward the
   packet to the next MSR6 Replication Endpoints.  When an MSR6
   Replication Endpoint receives a packet whose IPv6 Destination Address
   is A and A is the local RGB SID for the existing MSR6 Replication
   Endpoint, process the bitstring in the RGB DoH of the packet and look
   up the corresponding BITF for the next MSR6 Replication Endpoints.
   Replicate the packet, update the bitstring and DA in each replicated
   packet based on the lookup result.The RGB processing procedure
   follows the specification in BIER architecture defined in '
   [RFC8279].

   MSR6 Transit Node: Transit the packet as a unicast IPv6 packet by
   looking up FIB until find the next MSR6 Replication Endpoint.

   MSR6 Leaf Node: The Egress Node of a multicast flow.  When an MSR6
   Replication Endpoint receives a packet whose IPv6 Destination Address
   is A and A is the local RGB segment and the one of the bits which is
   set to 1 identifies the MSR6 the egress node.  If the MSR6 egress
   node is the edge of a network domain, copy the packet and send the
   copy to the multicast flow overlay; If the MSR6 egress node is the
   host supposed to receive the packet, send the packet to the upper
   layer.

                                    MSR6-RE            MSR6-EN
           +----+           +----+              +----+
           |    |-----------|    |--------------|    |
           +----+           +----+              +----+
          MSR6-IN              |     +----+     +----+
                               +-----|    |-----|    |
                                     +----+     +----+
                                     MSR6-TN   MSR6-EN

            MSR6-IN: MSR6 Ingress Node (MSR6 Root Node)
            MSR6-TN: MSR6 Transit Node (which is not MSR6 aware)
            MSR6-RE: MSR6 Replication Endpoint
            MSR6-EN: MSR6 Egress Node (MSR6 Leaf Node)

7.  Illustration

   *  Case 1: Host originating MSR6 BE







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              +-------------+      +-------------+
              | {S=S1,D=P1} |      | {S=S1,D=C1} |
              +-------------+      +-------------+
              |[BitStr=0110]|      |[BitStr=0010]|
              +=============+      +=============+
              | Upper Layer |  >>  | Upper Layer |
              +=============+      +=============+
              |  Pay Load   |      |  Pay Load   |
              +=============+      +=============+
       [Server1]--------------[P1]-------------------[Client1]
       (MSR6-IN)           (MSR6-RE)          (MSR6-EN,BFR-id=2)
                           /
                         /   +-------------+    +-------------+
                        |    | {S=S1,D=C2} |    | {S=S1,D=C2} |
                        |    +-------------+    +-------------+
                        |    |[BitStr=0100]|    |[BitStr=0100]|
                        |    +=============+    +=============+
                        | >> | Upper Layer | >> | Upper Layer |
                         \   +=============+    +=============+
                          \  |  Pay Load   |    |   Pay Load  |
                           \ +=============+    +=============+
                              +-------------[P2]-----------[Client2]
                                         (MSR6-TN)     (MSR6-EN,BFR-id=3)

{S=Server1,D=P1}: Source address and Destination address in IPv6 header.
   [BitStr=0110]: BitString value in IPv6 Destination Options Header.
         MSR6-IN: MSR6 Ingress Node
         MSR6-TN: MSR6 Transit Node (which is not MSR6 aware)
         MSR6-RE: MSR6 Replication Endpoint
         MSR6-EN: MSR6 Egress Node

   Server1 generates the packet with an IPv6 Header.  Knowing that BFR-
   ID of Client 1 is 2 and BFR-ID of Client 2 is 3, it follows that when
   the multicast service is supposed to be transmitted to Client1 and
   Client2, the bitstring in RGB DoH of the IPv6 header is set as
   "0110".  Look up the BIFT and finds the RGB segment of next MSR6 BFR
   is P1.  The IPv6 DA is set as "P1".

   P1 receives the packet with DA as "P1", which is the local RGB
   segment.  P1 parses the DoH with RGB Option Data and looks up the
   BIFT to find the corresponding entry.  P1 replicates the packets into
   2 copies based on the look up result.  DA of one replicated packet is
   set to "C1" and the bitstring is set to "0010".  DA of the other
   replicated packet is set to "C2" and the bitstring is set to "0100".
   These 2 packets are forwarded to next hop based on the updated DA.

   P2 receives the packet and forwards it Client2 based on the DA of
   "C2".



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   Client1 receives the packet with DA as "C1".  "C1" is the local RGB
   segment and "0010" identifies Client1 itself.  The packet is sent to
   the upper layer.

   Client2 receives the packet with DA as "C2".  "C2" is the local RGB
   segment and "0100" identifies Client2 itself.  The packet is sent to
   the upper layer.

   *  Caes 2: MSR6 is used in a network domain

                     +-------------+    +-------------+
                     |{S=PE1,D=P2} |    |{S=PE1,D=PE2}|
                     +-------------+    +-------------+
                     |[BitStr=0110]|    |[BitStr=0100]|
     +==========+    +=============+    +=============+    +==========+
     |(C-MC Pkt)| >> | (C-MC Pkt)  | >> | (C-MC Pkt)  | >> |(C-MC Pkt)|
     +==========+    +=============+    +=============+    +==========+
    CE1-----------[PE1]------[P1]------[P2]-----------[PE2]---------CE2
                (MSR6-SN) (MSR6-TN) /(MSR6-RE) (MSR6-DN,BFR-id=2)
                                   /
                                  /     +-------------+
                                 |      |{S=PE1,D=PE3}|
                                 |      +-------------+
                                 |      |[BitStr=0100]|
                                  \     +=============+    +==========+
                                   \ >> | (C-MC Pkt)  | >> |(C-MC Pkt)|
                                    \   +=============+    +==========+
                                     +------[P3]------[PE3]----------CE3
                                        (MSR6-TN) (MSR6-DN,BFR-id=3)

    {S=CE1,D=P1}: Source address and Destination address in IPv6 header.
   [BitStr=0110]: BitString value in IPv6 Destination Options Header.
      (C-MC Pkt): Customer MultiCast packet.
             MSR6-IN: MSR6 Ingress Node
             MSR6-TN: MSR6 Transit Node (which is not MSR6 aware)
             MSR6-RE: MSR6 Replication Endpoint
             MSR6-EN: MSR6 Egress Node

   PE1 receives the customer multicast packet from CE1.  An MSR BE
   header is encapsulated as defined in section 3.  Knowing that BFR-ID
   of PE 1 is 2 and BFR-ID of PE 2 is 3, it follows that when the
   multicast service is supposed to be transmitted to PE2 and PE3, the
   bitstring in the RGB Options Header of DoH is set as "0110".  Look up
   the corresponding BIFT and finds the RGB segment of next MSR6 BFR is
   P2.  The IPv6 DA is set as "P2".

   P1 receives the packet and forwards it P2 based on the DA of "P2".




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   P2 receives the packet with DA as "P2", which is the local RGB
   segment.  P2 parses the DoH with RGB Option Data and looks up the
   BIFT to find the corresponding entry.P2 replicates the packets into 2
   copies based on the look up result.  DA of one replicated packet is
   set to "PE2" and the bitstring is set to "0010".  DA of the other
   replicated packet is set to "PE3" and the bitstring is set to "0100".
   These 2 packets are forwarded to next hop based on the updated DA.

   P3 receives the packet and forwards it PE3 based on the DA of "PE3".

   PE2 receives the packet with DA as "PE2".  "PE2" is the local RGB
   segment and "0010" identifies PE2 itself.  The packet is sent to the
   multicast flow overlay.

   PE3 receives the packet with DA as "PE3".  "PE3" is the local RGB
   segment and "0100" identifies PE3 itself.  The packet is sent to the
   multicast flow overlay.


8.  IANA Considerations


8.1.  RGB Option Type

   Allocation is expected from IANA for a RGB Option Type codepoint from
   the "Destination Options and Hop-by-Hop Options" sub-registry of the
   "Internet Protocol Version 6 (IPv6) Parameters" registry.

           +-----------+-----+-----+-------+-------------+------------+
           | Hex Value | act | chg |  rest | Description | Reference  |
           +-----------+-----+-----+-------+-------------+------------+
           |    TBD    |  01 |  1  |  TBD  | RGB Option  | This draft |
           +-----------+-----+-----+-------+-------------+------------+

8.2.  End.RGB Function

   Allocation is expected from IANA for an End.RGB function codepoint
   from the "SRv6 Endpoint Behaviors" sub-registry.  The value 60 is
   suggested.

           +-------+--------+--------------------------+------------+
           | Value |  Hex   |    Endpoint function     | Reference  |
           +-------+--------+--------------------------+------------+
           | TBD   |  TBD   |    End.RGB               | This draft |
           +-------+--------+--------------------------+------------+






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9.  Security Considerations

   The MSR6 domain can be a single IGP area, an anonymous system (AS)
   with multiple IGP areas, or multiple anonymous systems (ASes)
   operated by a network operator.

   It is expected that all nodes in an MSR6 domain are managed by the
   same administrative entity.  MSR6-encapsulated packets should
   generally not be accepted from untrusted interfaces or tunnels.  For
   example, an operator may wish to have a policy of accepting MSR6
   encapsulated packets only from interfaces to trusted routers, and not
   from customer-facing interfaces.

   For applications that require a MSR6 Replication Endpoint to accept a
   MSR6 encapsulated packet from an interface to a system that is not
   controlled by the network operator, the security considerations of
   [RFC8296] apply

9.1.  Intra Domain Deployment

   Generally nodes outside the MSR6 Domain are not trusted: they cannot
   directly use the End.RGB segment of the domain.  This is enforced by
   two levels of access control lists:

   1.  Any packet entering the MSR6 Domain and destined to an End.RGB
   Segment within the MSR6 Domain is dropped.  This may be realized with
   the following logic.  Other methods with equivalent outcome are
   considered compliant:

   * allocate all the End.RGB Segment from a block S/s

   * configure each external interface of each edge node of the domain
   with an inbound infrastructure access list (IACL) which drops any
   incoming packet with a destination address in S/s

   * Failure to implement this method of ingress filtering may expose
   the MSR6 Domain to BIER attacks.  The security consideration on BIER
   attacks is as described and referenced in [RFC8296].

   2.  The distributed protection in #1 is complemented with per node
   protection, dropping packets to End.RGB Segment from source addresses
   outside the MSR6 Domain.  This may be realized with the following
   logic.  Other methods with equivalent outcome are considered
   compliant:

   * assign all interface addresses from prefix A/a





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   * assign all the IPv6 addresses used as source address of MSR6
   packets from a block B/b

   * at node k, all End.RGB Segment IPv6 addresses local to k are
   assigned from prefix Sk/sk

   * configure each internal interface of each MSR6 node k in the MSR6
   Domain with an inbound IACL which drops any incoming packet with a
   destination address in Sk/sk if the source address is not in A/a or
   B/b.

   For simplicity of deployment, a configuration of IACL effective for
   all interfaces can be provided by a router.  Such IACL can be
   referred to as global IACL(GIACL) .Each MSR6 node k then simply
   configures a GIACL which drops any incoming packet with a destination
   address in Sk/sk if the source address is not in A/a or B/b for the
   intra-domain deployment mode.


9.2.  ICMP Error Processing

   The MSR6 Replication Endpoint does not send ICMP error messages to
   the source address of a MSR BE packet, but there is still chance that
   Non-MSR6 Replication Endpoint routers send ICMP error messages to
   source nodes within the MSR6 Domain.

   A large number of ICMP may be elicited and sent to a MSR6 Ingress
   router, in case when an MSR6 BE packet is filled with wrong Hop
   Limit, either error or malfeasance.  A rate-limiting of ICMP packet
   should be implemented on each MSR6 Replication Endpoint.

   The ingress node can take note of the fact that it is getting, in
   response to MSR6 BE packet, one or more ICMP error packets.  By
   default, the reception of such packet MUST be countered and logged.
   However, it is possible for such log entries to be "false positives"
   that generate a lot of "noise" in the log; therefore, implementations
   SHOULD have a knob to disable this logging.


9.3.  Security caused by RGB option

   This document introduces a new option used in IPv6 Destination
   Options Header.  An IPv6 packet with a normal IPv6 address of a
   router (e.g. loopback IPv6 address of the router) as destination
   address will possibly carry a RGB option.






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   For a router incapable of MSR6 BE, such MSR6 BE packet will not be
   processed by the procedure described in this document, but be
   processed as normal IPv6 packet with unknown option, and the existing
   security considerations for handling IPv6 options apply.  Possible
   way of handling IPv6 packets with RGB option may be send to CPU for
   slow path processing, with rate-limiting, or be discarded according
   to the local policy.

   For a router capable of MSR6 BE, such MSR6 BE packet MUST NOT be
   forwarded, but should be processed as a normal IPv6 packet with
   unknown option, or additionally and optionally be countered and
   logged if the router is capable of doing so.


10.  Normative References

   [I-D.cheng-spring-ipv6-msr-design-consideration]
              Cheng, W., Mishra, G. S., Li, Z., Wang, A., Qin, Z., and
              C. Fan, "Design Consideration of IPv6 Multicast Source
              Routing (MSR6)", Work in Progress, Internet-Draft, draft-
              cheng-spring-ipv6-msr-design-consideration-01, 25 October
              2021, <https://datatracker.ietf.org/doc/html/draft-cheng-
              spring-ipv6-msr-design-consideration-01>.

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

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
              (IPv6) Specification", STD 86, RFC 8200,
              DOI 10.17487/RFC8200, July 2017,
              <https://www.rfc-editor.org/info/rfc8200>.

   [RFC8279]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
              Explicit Replication (BIER)", RFC 8279,
              DOI 10.17487/RFC8279, November 2017,
              <https://www.rfc-editor.org/info/rfc8279>.

   [RFC8296]  Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
              Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
              for Bit Index Explicit Replication (BIER) in MPLS and Non-
              MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
              2018, <https://www.rfc-editor.org/info/rfc8296>.






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   [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/info/rfc8402>.

   [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/info/rfc8986>.

Authors' Addresses

   Yisong Liu
   China Mobile
   Email: liuyisong@chinamobile.com


   Jingrong Xie
   Huawei Technologies
   Email: xiejingrong@huawei.com


   Xuesong Geng
   Huawei Technologies
   Email: gengxuesong@huawei.com


   Mengxiao Chen
   New H3C Technologies
   Email: chen.mengxiao@h3c.com




















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