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Versions: (draft-previdi-6man-segment-routing-header) 00 01 02 03 04 05 06 07 08 09 10 11 12 13 14

Network Working Group                                   C. Filsfils, Ed.
Internet-Draft                                       Cisco Systems, Inc.
Intended status: Standards Track                              S. Previdi
Expires: December 30, 2018                                    Individual
                                                                J. Leddy
                                                                 Comcast
                                                           S. Matsushima
                                                                Softbank
                                                           D. Voyer, Ed.
                                                             Bell Canada
                                                           June 28, 2018


                   IPv6 Segment Routing Header (SRH)
               draft-ietf-6man-segment-routing-header-14

Abstract

   Segment Routing can be applied to the IPv6 data plane using a new
   type of Routing Extension Header.  This document describes the
   Segment Routing Extension Header and how it is used by Segment
   Routing capable nodes.

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.

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 December 30, 2018.




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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.  Segment Routing Extension Header  . . . . . . . . . . . . . .   4
     2.1.  SRH TLVs  . . . . . . . . . . . . . . . . . . . . . . . .   5
       2.1.1.  Padding TLVs  . . . . . . . . . . . . . . . . . . . .   6
       2.1.2.  HMAC TLV  . . . . . . . . . . . . . . . . . . . . . .   8
   3.  SR Nodes  . . . . . . . . . . . . . . . . . . . . . . . . . .   9
     3.1.  Source SR Node  . . . . . . . . . . . . . . . . . . . . .   9
     3.2.  Transit Node  . . . . . . . . . . . . . . . . . . . . . .   9
     3.3.  SR Segment Endpoint Node  . . . . . . . . . . . . . . . .   9
   4.  Packet Processing . . . . . . . . . . . . . . . . . . . . . .   9
     4.1.  Source SR Node  . . . . . . . . . . . . . . . . . . . . .   9
       4.1.1.  Reduced SRH . . . . . . . . . . . . . . . . . . . . .  10
     4.2.  Transit Node  . . . . . . . . . . . . . . . . . . . . . .  10
     4.3.  SR Segment Endpoint Node  . . . . . . . . . . . . . . . .  11
       4.3.1.  FIB Entry Is Locally Instantiated SRv6 END SID  . . .  11
       4.3.2.  FIB Entry is a Local Interface  . . . . . . . . . . .  13
       4.3.3.  FIB Entry Is A Non-Local Route  . . . . . . . . . . .  13
       4.3.4.  FIB Entry Is A No Match . . . . . . . . . . . . . . .  13
       4.3.5.  Load Balancing and ECMP . . . . . . . . . . . . . . .  13
   5.  Illustrations . . . . . . . . . . . . . . . . . . . . . . . .  14
     5.1.  Abstract Representation of an SRH . . . . . . . . . . . .  14
     5.2.  Example Topology  . . . . . . . . . . . . . . . . . . . .  15
     5.3.  Source SR Node  . . . . . . . . . . . . . . . . . . . . .  15
       5.3.1.  Intra SR Domain Packet  . . . . . . . . . . . . . . .  15
       5.3.2.  Transit Packet Through SR Domain  . . . . . . . . . .  16
     5.4.  Transit Node  . . . . . . . . . . . . . . . . . . . . . .  16
     5.5.  SR Segment Endpoint Node  . . . . . . . . . . . . . . . .  16
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .  17
     6.1.  Threat model  . . . . . . . . . . . . . . . . . . . . . .  17
       6.1.1.  Source routing threats  . . . . . . . . . . . . . . .  17
       6.1.2.  Applicability of RFC 5095 to SRH  . . . . . . . . . .  18



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       6.1.3.  Service stealing threat . . . . . . . . . . . . . . .  19
       6.1.4.  Topology disclosure . . . . . . . . . . . . . . . . .  19
       6.1.5.  ICMP Generation . . . . . . . . . . . . . . . . . . .  19
     6.2.  Security fields in SRH  . . . . . . . . . . . . . . . . .  19
       6.2.1.  Selecting a hash algorithm  . . . . . . . . . . . . .  21
       6.2.2.  Performance impact of HMAC  . . . . . . . . . . . . .  21
       6.2.3.  Pre-shared key management . . . . . . . . . . . . . .  22
     6.3.  Deployment Models . . . . . . . . . . . . . . . . . . . .  22
       6.3.1.  Nodes within the SR domain  . . . . . . . . . . . . .  22
       6.3.2.  Nodes outside of the SR domain  . . . . . . . . . . .  22
       6.3.3.  SR path exposure  . . . . . . . . . . . . . . . . . .  23
       6.3.4.  Impact of BCP-38  . . . . . . . . . . . . . . . . . .  23
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
     7.1.  Segment Routing Header Flags Register . . . . . . . . . .  24
     7.2.  Segment Routing Header TLVs Register  . . . . . . . . . .  24
   8.  Implementation Status . . . . . . . . . . . . . . . . . . . .  25
     8.1.  Linux . . . . . . . . . . . . . . . . . . . . . . . . . .  25
     8.2.  Cisco Systems . . . . . . . . . . . . . . . . . . . . . .  25
     8.3.  FD.io . . . . . . . . . . . . . . . . . . . . . . . . . .  25
     8.4.  Barefoot  . . . . . . . . . . . . . . . . . . . . . . . .  25
     8.5.  Juniper . . . . . . . . . . . . . . . . . . . . . . . . .  26
   9.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  26
   10. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  26
   11. References  . . . . . . . . . . . . . . . . . . . . . . . . .  26
     11.1.  Normative References . . . . . . . . . . . . . . . . . .  26
     11.2.  Informative References . . . . . . . . . . . . . . . . .  27
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  29

1.  Introduction

   Segment Routing can be applied to the IPv6 data plane using a new
   type of Routing Extension Header (SRH).  This document describes the
   Segment Routing Extension Header and how it is used by Segment
   Routing capable nodes.

   The Segment Routing Architecture [I-D.ietf-spring-segment-routing]
   describes Segment Routing and its instantiation in two data planes
   MPLS and IPv6.

   SR with the MPLS data plane is defined in
   [I-D.ietf-spring-segment-routing-mpls].

   SR with the IPv6 data plane is defined in
   [I-D.filsfils-spring-srv6-network-programming].

   The encoding of MPLS labels and label stacking are defined in
   [RFC3032].




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   The encoding of IPv6 segments in the Segment Routing Extension Header
   is defined in this document.

   Terminology used within this document is defined in detail in
   [I-D.ietf-spring-segment-routing].  Specifically, these terms:
   Segment Routing, SR Domain, SRv6, Segment ID (SID), SRv6 SID, Active
   Segment, and SR Policy.

2.  Segment Routing Extension Header

   Routing Headers are defined in [RFC8200].  The Segment Routing Header
   has a new Routing Type (suggested value 4) to be assigned by IANA.

   The Segment Routing Header (SRH) 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Next Header   |  Hdr Ext Len  | Routing Type  | Segments Left |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Last Entry   |     Flags     |              Tag              |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |            Segment List[0] (128 bits IPv6 address)            |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |                                                               |
                                  ...
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    |            Segment List[n] (128 bits IPv6 address)            |
    |                                                               |
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    //                                                             //
    //         Optional Type Length Value objects (variable)       //
    //                                                             //
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

   o  Next Header: Defined in [RFC8200]




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   o  Hdr Ext Len: Defined in [RFC8200]

   o  Routing Type: TBD, to be assigned by IANA (suggested value: 4).

   o  Segments Left: Defined in [RFC8200]

   o  Last Entry: contains the index (zero based), in the Segment List,
      of the last element of the Segment List.

   o  Flags: 8 bits of flags.  Following flags are defined:


          0 1 2 3 4 5 6 7
         +-+-+-+-+-+-+-+-+
         |U U U U U U U U|
         +-+-+-+-+-+-+-+-+

         U: Unused and for future use.  MUST be 0 on transmission and
         ignored on receipt.

   o  Tag: tag a packet as part of a class or group of packets, e.g.,
      packets sharing the same set of properties.  When tag is not used
      at source it MUST be set to zero on transmission.  When tag is not
      used during SRH Processing it SHOULD be ignored.  The allocation
      and use of tag is outside the scope of this document.

   o  Segment List[n]: 128 bit IPv6 addresses representing the nth
      segment in the Segment List.  The Segment List is encoded starting
      from the last segment of the SR Policy.  I.e., the first element
      of the segment list (Segment List [0]) contains the last segment
      of the SR Policy, the second element contains the penultimate
      segment of the SR Policy and so on.

   o  Type Length Value (TLV) are described in Section 2.1.

2.1.  SRH TLVs

   This section defines TLVs of the Segment Routing Header.

    0                   1
    0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-----------------------
   |     Type      |    Length     | Variable length data
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-----------------------

   Type: An 8 bit value.  Unrecognized Types MUST be ignored on receipt.





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   Length: The length of the Variable length data.  It is RECOMMENDED
   that the total length of new TLVs be multiple of 8 bytes to avoid the
   use of Padding TLVs.

   Variable length data: Length bytes of data that is specific to the
   Type.

   Type Length Value (TLV) contain OPTIONAL information that may be used
   by the node identified in the Destination Address (DA) of the packet.

   Each TLV has its own length, format and semantic.  The code-point
   allocated (by IANA) to each TLV Type defines both the format and the
   semantic of the information carried in the TLV.  Multiple TLVs may be
   encoded in the same SRH.

   TLVs may change en route at each segment.  To identify when a TLV
   type may change en route the most significant bit of the Type has the
   following significance:

      0: TLV data does not change en route

      1: TLV data does change en route

   Identifying which TLVs change en route, without having to understand
   the Type, is required for Authentication Header Integrity Check Value
   (ICV) computation.  Any TLV that changes en route is considered
   mutable for the purpose of ICV computation, the Type Length and
   Variable Length Data is ignored for the purpose of ICV Computation as
   defined in [RFC4302].

   The "Length" field of the TLV is used to skip the TLV while
   inspecting the SRH in case the node doesn't support or recognize the
   Type.  The "Length" defines the TLV length in octets, not including
   the "Type" and "Length" fields.

   The following TLVs are defined in this document:

      Padding TLV

      HMAC TLV

   Additional TLVs may be defined in the future.

2.1.1.  Padding TLVs

   There are two types of padding TLVs, pad0 and padN, the following
   applies to both:




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      Padding TLVs are used to pad the TLVs to a multiple of 8 octets.

      More than one Padding TLV MUST NOT appear in the SRH.

      The Padding TLVs are used to align the SRH total length on the 8
      octet boundary.

      When present, a single Pad0 or PadN TLV MUST appear as the last
      TLV.

      When present, a PadN TLV MUST have a length from 0 to 5 in order
      to align the SRH total length on a 8-octet boundary.

      Padding TLVs are ignored by a node processing the SRH TLV, even if
      more than one is present.

      Padding TLVs are ignored during ICV calculation.

2.1.1.1.  PAD0

     0 1 2 3 4 5 6 7
     +-+-+-+-+-+-+-+-+
     |     Type      |
     +-+-+-+-+-+-+-+-+

      Type: to be assigned by IANA (Suggested value 128)

   A single Pad0 TLV MUST be used when a single byte of padding is
   required.  If more than one byte of padding is required a Pad0 TLV
   MUST NOT be used, the PadN TLV MUST be used.

2.1.1.2.  PADN

    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     |      Padding (variable)       |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   //                    Padding (variable)                       //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      Type: to be assigned by IANA (suggested value 129).

      Length: 0 to 5

      Padding: Length octets of padding.  Padding bits have no
      semantics.  They MUST be set to 0 on transmission and ignored on
      receipt.



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   The PadN TLV MUST be used when more than one byte of padding is
   required.

2.1.2.  HMAC TLV

   HMAC TLV is OPTIONAL and contains the HMAC information.  The HMAC 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    |          RESERVED             |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                      HMAC Key ID (4 octets)                   |
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
   |                                                              //
   |                      HMAC (32 octets)                        //
   |                                                              //
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   where:

   o  Type: to be assigned by IANA (suggested value 5).

   o  Length: 38.

   o  RESERVED: 2 octets.  MUST be 0 on transmission and ignored on
      receipt.

   o  HMAC Key ID: 4 octets.

   o  HMAC: 32 octets.

   o  HMAC and HMAC Key ID usage is described in Section 6

   The Following applies to the HMAC TLV:

   o  Local policy determines when to check for an HMAC and potentially
      a requirement on where the HMAC TLV must appear (e.g. first TLV).
      This local policy is outside the scope of this document.  It may
      be based on the active segment at an SR Segment endpoint node, the
      result of an ACL that considers incoming interface, or other
      packet fields.








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3.  SR Nodes

   There are different types of nodes that may be involved in segment
   routing networks: source SR nodes originate packets with a segment in
   the destination address of the IPv6 header, transit nodes that
   forward packets destined to a remote segment, and SR segment endpoint
   nodes that process a local segment in the destination address of an
   IPv6 header.

3.1.  Source SR Node

   A Source SR Node is any node that originates an IPv6 packet with a
   segment (i.e.  SRv6 SID) in the destination address of the IPv6
   header.  The packet leaving the source SR Node may or may not contain
   an SRH.  This includes either:

      A host originating an IPv6 packet.

      An SR domain ingress router encapsulating a received packet in an
      outer IPv6 header, followed by an optional SRH.

   The mechanism through which a segment in the destination address of
   the IPv6 header and the Segment List in the SRH, is derived is
   outside the scope of this document.

3.2.  Transit Node

   A transit node is any node forwarding an IPv6 packet where the
   destination address of that packet is not locally configured as a
   segment nor a local interface.  A transit node is not required to be
   capable of processing a segment nor SRH.

3.3.  SR Segment Endpoint Node

   A SR segment endpoint node is any node receiving an IPv6 packet where
   the destination address of that packet is locally configured as a
   segment or local interface.

4.  Packet Processing

   This section describes SRv6 packet processing at the SR source,
   Transit and SR segment endpoint nodes.

4.1.  Source SR Node

   A Source node steers a packet into an SR Policy.  If the SR Policy
   results in a segment list containing a single segment, and there is




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   no need to add information to SRH flag or TLV, the DA is set to the
   single segment list entry and the SRH MAY be omitted.

   When needed, the SRH is created as follows:

      Next Header and Hdr Ext Len fields are set as specified in
      [RFC8200].

      Routing Type field is set as TBD (to be allocated by IANA,
      suggested value 4).

      The DA of the packet is set with the value of the first segment.

      The first element of the SRH Segment List is the ultimate segment.
      The second element is the penultimate segment and so on.

      The Segments Left field is set to n-1 where n is the number of
      elements in the SR Policy.

      The Last Entry field is set to n-1 where n is the number of
      elements in the SR Policy.

      HMAC TLV may be set according to Section 6.

      The packet is forwarded toward the packet's Destination Address
      (the first segment).

4.1.1.  Reduced SRH

   When a source does not require the entire SID list to be preserved in
   the SRH, a reduced SRH may be used.

   A reduced SRH does not contain the first segment of the related SR
   Policy (the first segment is the one already in the DA of the IPv6
   header), and the Last Entry field is set to n-2 where n is the number
   of elements in the SR Policy.

4.2.  Transit Node

   As specified in [RFC8200], the only node allowed to inspect the
   Routing Extension Header (and therefore the SRH), is the node
   corresponding to the DA of the packet.  Any other transit node MUST
   NOT inspect the underneath routing header and MUST forward the packet
   toward the DA according to its IPv6 routing table.

   When a SID is in the destination address of an IPv6 header of a
   packet, it's routed through an IPv6 network as an IPv6 address.
   SIDs, or the prefix(es) covering SIDs, and their reachability may be



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   distributed by means outside the scope of this document.  For
   example, [RFC5308] or [RFC5340] may be used to advertise a prefix
   covering the SIDs on a node.

4.3.  SR Segment Endpoint Node

   Without constraining the details of an implementation, the SR segment
   endpoint node creates Forwarding Information Base (FIB) entries for
   its local SIDs.

   When an SRv6-capable node receives an IPv6 packet, it performs a
   longest-prefix-match lookup on the packets destination address.  This
   lookup can return any of the following:

       A FIB entry that represents a locally instantiated SRv6 SID
       A FIB entry that represents a local interface, not locally
                                     instantiated as an SRv6 SID
       A FIB entry that represents a non-local route
       No Match

4.3.1.  FIB Entry Is Locally Instantiated SRv6 END SID

   This document, and section, defines a single SRv6 SID called END.
   Future documents may define additional SRv6 SIDs.  In which case, the
   entire content of this section will be defined in that document.

   If the FIB entry represents a locally instantiated SRv6 SID, process
   the next header of the IPv6 header as defined in section 4 of
   [RFC8200]

   The following sections describe the actions to take while processing
   next header fields.

4.3.1.1.  SRH Processing

















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   When an SRH is processed {
     If Segments Left is equal to zero {
       Proceed to process the next header in the packet, whose type
       is identified by the Next Header field in the Routing header.
     }
     Else {
       If local policy requires TLV processing {
         Perform TLV processing (see TLV Processing)
       }
       max_last_entry  =  ( Hdr Ext Len /  2 ) - 1

       If  ((Last Entry > max_last_entry) or
            (Segments Left is greater than (Last Entry+1)) {
         Send an ICMP Parameter Problem, Code 0, message to the
         Source Address, pointing to the Segments Left field, and
         discard the packet.
       }
       Else {
         Decrement Segments Left by 1.
         Copy Segment List[Segments Left] from the SRH to the
         destination address of the IPv6 header.
         If the IPv6 Hop Limit is less than or equal to 1 {
           Send an ICMP Time Exceeded -- Hop Limit Exceeded in
           Transit message to the Source Address and discard
           the packet.
         }
         Else {
           Decrement the Hop Limit by 1
           Resubmit the packet to the IPv6 module for transmission
           to the new destination.
         }
       }
     }
   }

4.3.1.1.1.  TLV Processing

   Local policy determines how TLV's are to be processed when the Active
   Segment is a local END SID.  The definition of local policy is
   outside the scope of this document.

   For illustration purpose only, two example local policies that may be
   associated with an END SID are provided below.








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   Example 1:
   For any packet received from interface I2
     Skip TLV processing

   Example 2:
   For any packet received from interface I1
     If first TLV is HMAC {
       Process the HMAC TLV
     }
     Else {
       Discard the packet
     }

4.3.1.2.  Upper-layer Header or No Next Header

     Send an ICMP destination unreachable to
     the Source Address and discard the packet.

4.3.2.  FIB Entry is a Local Interface

   If the FIB entry represents a local interface, not locally
   instantiated as an SRv6 SID, the SRH is processed as follows:

      If Segments Left is zero, the node must ignore the Routing header
      and proceed to process the next header in the packet, whose type
      is identified by the Next Header field in the Routing Header.

      If Segments Left is non-zero, the node must discard the packet and
      send an ICMP Parameter Problem, Code 0, message to the packet's
      Source Address, pointing to the unrecognized Routing Type.

4.3.3.  FIB Entry Is A Non-Local Route

   Processing is not changed by this document.

4.3.4.  FIB Entry Is A No Match

   Processing is not changed by this document.

4.3.5.  Load Balancing and ECMP

   Within an SR domain, an SR source node encapsulates a packet in an
   outer IPv6 header for transport to an endpoint.  The SR source node
   MUST impose a flow label computed based on the inner packet.  The
   computation of the flow label is as recommended in [RFC6438] for the
   sending Tunnel End Point.





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   At any transit node within an SR domain, the flow label MUST be used
   as defined in [RFC6438] to calculate the ECMP hash toward the
   destination address.  If flow label is not used, the transit node may
   hash all packets between a pair of SR Edge nodes to the same link.

   At an SR segment endpoint node, the flow label MUST be used as
   defined in [RFC6438] to calculate any ECMP hash used to forward the
   processed packet to the next segment.

5.  Illustrations

   This section provides illustrations of SRv6 packet processing at SR
   source, transit and SR segment endpoint nodes.

5.1.  Abstract Representation of an SRH

   For a node k, its IPv6 address is represented as Ak, its SRv6 SID is
   represented as Sk.

   IPv6 headers are represented as the tuple of (source, destination).
   For example, a packet with source address A1 and destination address
   A2 is represented as (A1,A2).  The payload of the packet is omitted.

   An SR Policy is a list of segments.  A list of segments is
   represented as <S1,S2,S3> where S1 is the first SID to visit, S2 is
   the second SID to visit and S3 is the last SID to visit.

   (SA,DA) (S3, S2, S1; SL) represents an IPv6 packet with:

   o  Source Address is SA, Destination Addresses is DA, and next-header
      is SRH.

   o  SRH with SID list <S1, S2, S3> with SegmentsLeft = SL.

   o  Note the difference between the <> and () symbols.  <S1, S2, S3>
      represents a SID list where the leftmost segment is the first
      segment.  Whereas, (S3, S2, S1; SL) represents the same SID list
      but encoded in the SRH Segment List format where the leftmost
      segment is the last segment.  When referring to an SR policy in a
      high-level use-case, it is simpler to use the <S1, S2, S3>
      notation.  When referring to an illustration of detailed behavior,
      the (S3, S2, S1; SL) notation is more convenient.

   At its SR Policy headend, the Segment List <S1,S2,S3> results in SRH
   (S3,S2,S1; SL=2) represented fully as:






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       Segments Left=2
       Last Entry=2
       Flags=0
       Tag=0
       Segment List[0]=S3
       Segment List[1]=S2
       Segment List[2]=S1

5.2.  Example Topology

   The following topology is used in examples below:

           + * * * * * * * * * * * * * * * * * * * * +

           *         [8]                [9]          *
                      |                  |
           *          |                  |           *
   [1]----[3]--------[5]----------------[6]---------[4]---[2]
           *          |                  |           *
                      |                  |
           *          |                  |           *
                      +--------[7]-------+
           *                                         *

           + * * * * * * *  SR Domain  * * * * * * * +

   o  3 and 4 are SR Domain edge routers

   o  5, 6, and 7 are all SR Domain routers

   o  8 and 9 are hosts within the SR Domain

   o  1 and 2 are hosts outside the SR Domain

5.3.  Source SR Node

5.3.1.  Intra SR Domain Packet

   When host 8 sends a packet to host 9 via an SR Policy <S7,A9> the
   packet is

   P1: (A8,S7)(A9,S7; SL=1)

5.3.1.1.  Reduced Variant

   When host 8 sends a packet to host 9 via an SR Policy <S7,A9> and it
   wants to use a reduced SRH, the packet is




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   P2: (A8,S7)(A9; SL=1)

5.3.2.  Transit Packet Through SR Domain

   When host 1 sends a packet to host 2, the packet is

   P3: (A1,A2)

   The SR Domain ingress router 3 receives P3 and steers it to SR Domain
   egress router 4 via an SR Policy <S7, S4>.  Router 3 encapsulates the
   received packet P3 in an outer header with an SRH.  The packet is

   P4: (A3, S7)(S4, S7; SL=1)(A1, A2)

   If the SR Policy contains only one segment (the egress router 4), the
   ingress Router 3 encapsulates P3 into an outer header (A3, S4).  The
   packet is

   P5: (A3, S4)(A1, A2)

5.3.2.1.  Reduced Variant

   The SR Domain ingress router 3 receives P3 and steers it to SR Domain
   egress router 4 via an SR Policy <S7, S4>.  If router 3 wants to use
   a reduced SRH, Router 3 encapsulates the received packet P3 in an
   outer header with a reduced SRH.  The packet is

   P6: (A3, S7)(S4; SL=1)(A1, A2)

5.4.  Transit Node

   Nodes 5 acts as transit nodes for packet P1, and sends packet

   P1: (A8,S7)(A9,S7;SL=1)

   on the interface toward node 7.

5.5.  SR Segment Endpoint Node

   Node 7 receives packet P1 and, using the logic in section 4.3.1,
   sends packet

   P7: (A8,A9)(A9,S7; SL=0)

   on the interface toward router 6.






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6.  Security Considerations

   This section analyzes the security threat model, the security issues
   and proposed solutions related to the new Segment Routing Header.

   The Segment Routing Header (SRH) is simply another type of the
   Routing Header as described in [RFC8200] and is:

   o  Added by an SR edge router when entering the segment routing
      domain or by the originating host itself.  The source host can
      even be outside the SR domain;

   o  inspected and acted upon when reaching the destination address of
      the IP header per [RFC8200].

   Per [RFC8200], routers on the path that simply forward an IPv6 packet
   (i.e. the IPv6 destination address is none of theirs) will never
   inspect and process the content of the SRH.  Routers whose FIB
   contains a locally instantiated SRv6 SID equal to the destination
   address field of the IPv6 packet MUST parse the SRH if present, and
   if supported and if the local configuration allows it, MUST act
   accordingly to the SRH content.

   As specified in [RFC8200], the default behavior of a non SR-capable
   router upon receipt of an IPv6 packet with SRH destined to an address
   of its, is to:

   o  ignore the SRH completely if the Segment Left field is 0 and
      proceed to process the next header in the IPv6 packet;

   o  discard the IPv6 packet if Segment Left field is greater than 0,
      it MAY send a Parameter Problem ICMP message back to the Source
      Address.

6.1.  Threat model

6.1.1.  Source routing threats

   Using an SRH is similar to source routing, therefore it has some
   well-known security issues as described in [RFC4942] section 2.1.1
   and [RFC5095]:

   o  amplification attacks: where a packet could be forged in such a
      way to cause looping among a set of SR-enabled routers causing
      unnecessary traffic, hence a Denial of Service (DoS) against
      bandwidth;





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   o  reflection attack: where a hacker could force an intermediate node
      to appear as the immediate attacker, hence hiding the real
      attacker from naive forensic;

   o  bypass attack: where an intermediate node could be used as a
      stepping stone (for example in a De-Militarized Zone) to attack
      another host (for example in the datacenter or any back-end
      server).

6.1.2.  Applicability of RFC 5095 to SRH

   First of all, the reader must remember this specific part of section
   1 of [RFC5095], "A side effect is that this also eliminates benign
   RH0 use-cases; however, such applications may be facilitated by
   future Routing Header specifications.".  In short, it is not
   forbidden to create new secure type of Routing Header; for example,
   [RFC6554] (RPL) also creates a new Routing Header type for a specific
   application confined in a single network.

   In the segment routing architecture described in
   [I-D.ietf-spring-segment-routing] there are basically two kinds of
   nodes (routers and hosts):

   o  nodes within the SR domain, which is within one single
      administrative domain, i.e., where all nodes are trusted anyway
      else the damage caused by those nodes could be worse than
      amplification attacks: traffic interception, man-in-the-middle
      attacks, more server DoS by dropping packets, and so on.

   o  nodes outside of the SR domain, which is outside of the
      administrative segment routing domain hence they cannot be trusted
      because there is no physical security for those nodes, i.e., they
      can be replaced by hostile nodes or can be coerced in wrong
      behaviors.

   The main use case for SR consists of the single administrative domain
   where only trusted nodes with SR enabled and configured participate
   in SR: this is the same model as in [RFC6554].  All non-trusted nodes
   do not participate as either SR processing is not enabled by default
   or because they only process SRH from nodes within their domain.

   Moreover, all SR nodes ignore SRH created by outsiders based on
   topology information (received on a peering or internal interface) or
   on presence and validity of the HMAC field.  Therefore, if
   intermediate nodes ONLY act on valid and authorized SRH (such as
   within a single administrative domain), then there is no security
   threat similar to RH-0.  Hence, the [RFC5095] attacks are not
   applicable.



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6.1.3.  Service stealing threat

   Segment routing is used for added value services, there is also a
   need to prevent non-participating nodes to use those services; this
   is called 'service stealing prevention'.

6.1.4.  Topology disclosure

   The SRH may also contains SIDs of some intermediate SR-nodes in the
   path towards the destination, this obviously reveals those addresses
   to the potentially hostile attackers if those attackers are able to
   intercept packets containing SRH.  On the other hand, if the attacker
   can do a traceroute whose probes will be forwarded along the SR
   Policy, then there is little learned by intercepting the SRH itself.

6.1.5.  ICMP Generation

   Per Section 4.4 of [RFC8200], when destination nodes (i.e. where the
   destination address is one of theirs) receive a Routing Header with
   unsupported Routing Type, the required behavior is:

   o  If Segments Left is zero, the node must ignore the Routing Header
      and proceed to process the next header in the packet.

   o  If Segments Left is non-zero, the node must discard the packet and
      send an ICMP Parameter Problem, Code 0, message to the packet's
      Source Address, pointing to the unrecognized Routing Type.

   This required behavior could be used by an attacker to force the
   generation of ICMP message by any node.  The attacker could send
   packets with SRH (with Segment Left not set to 0) destined to a node
   not supporting SRH.  Per [RFC8200], the destination node could
   generate an ICMP message, causing a local CPU utilization and if the
   source of the offending packet with SRH was spoofed could lead to a
   reflection attack without any amplification.

   It must be noted that this is a required behavior for any unsupported
   Routing Type and not limited to SRH packets.  So, it is not specific
   to SRH and the usual rate limiting for ICMP generation is required
   anyway for any IPv6 implementation and has been implemented and
   deployed for many years.

6.2.  Security fields in SRH

   This section summarizes the use of specific fields in the SRH.  They
   are based on a key-hashed message authentication code (HMAC).





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   The security-related fields in the SRH are instantiated by the HMAC
   TLV, containing:

   o  HMAC Key-id, 32 bits wide;

   o  HMAC, 256 bits wide (optional, exists only if HMAC Key-id is not
      0).

   The HMAC field is the output of the HMAC computation (per [RFC2104])
   using a pre-shared key identified by HMAC Key-id and of the text
   which consists of the concatenation of:

   o  the source IPv6 address;

   o  Last Entry field;

   o  an octet of bit flags;

   o  HMAC Key-id;

   o  all addresses in the Segment List.

   The purpose of the HMAC TLV is to verify the validity, the integrity
   and the authorization of the SRH itself.  If an outsider of the SR
   domain does not have access to a current pre-shared secret, then it
   cannot compute the right HMAC field and the first SR router on the
   path processing the SRH and configured to check the validity of the
   HMAC will simply reject the packet.

   The HMAC TLV is located at the end of the SRH simply because only the
   router on the ingress of the SR domain needs to process it, then all
   other SR nodes can ignore it (based on local policy) because they
   trust the upstream router.  This is to speed up forwarding operations
   because SR routers which do not validate the SRH do not need to parse
   the SRH until the end.

   The HMAC Key-id field allows for the simultaneous existence of
   several hash algorithms (SHA-256, SHA3-256 ... or future ones) as
   well as pre-shared keys.  The HMAC Key-id field is opaque, i.e., it
   has neither syntax nor semantic except as an index to the right
   combination of pre-shared key and hash algorithm and except that a
   value of 0 means that there is no HMAC field.  Having an HMAC Key-id
   field allows for pre-shared key roll-over when two pre-shared keys
   are supported for a while when all SR nodes converged to a fresher
   pre-shared key.  It could also allow for interoperation among
   different SR domains if allowed by local policy and assuming a
   collision-free HMAC Key Id allocation.




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   When a specific SRH is linked to a time-related service (such as
   turbo-QoS for a 1-hour period) where the DA, Segment ID (SID) are
   identical, then it is important to refresh the shared-secret
   frequently as the HMAC validity period expires only when the HMAC
   Key-id and its associated shared-secret expires.

6.2.1.  Selecting a hash algorithm

   The HMAC field in the HMAC TLV is 256 bit wide.  Therefore, the HMAC
   MUST be based on a hash function whose output is at least 256 bits.
   If the output of the hash function is 256, then this output is simply
   inserted in the HMAC field.  If the output of the hash function is
   larger than 256 bits, then the output value is truncated to 256 by
   taking the least-significant 256 bits and inserting them in the HMAC
   field.

   SRH implementations can support multiple hash functions but MUST
   implement SHA-2 [FIPS180-4] in its SHA-256 variant.

   NOTE: SHA-1 is currently used by some early implementations used for
   quick interoperations testing, the 160-bit hash value must then be
   right-hand padded with 96 bits set to 0.  The authors understand that
   this is not secure but is ok for limited tests.

6.2.2.  Performance impact of HMAC

   While adding an HMAC to each and every SR packet increases the
   security, it has a performance impact.  Nevertheless, it must be
   noted that:

   o  the HMAC field is used only when SRH is added by a device (such as
      a home set-top box) which is outside of the segment routing
      domain.  If the SRH is added by a router in the trusted segment
      routing domain, then, there is no need for an HMAC field, hence no
      performance impact.

   o  when present, the HMAC field need only be checked and validated by
      the first router of the segment routing domain, this router is
      named 'validating SR router'.

   o  this validating SR router can also have a cache of <IPv6 header +
      SRH, HMAC field value> to improve the performance.  It is not the
      same use case as in IPsec where HMAC value was unique per packet,
      in SRH, the HMAC value is unique per flow.

   o  hash functions such as SHA-2 have been optimized for security and
      performance and there are multiple implementations with good
      performance.



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   With the above points in mind, the performance impact of using HMAC
   is minimized.

6.2.3.  Pre-shared key management

   The field HMAC Key-id allows for:

   o  key roll-over: when there is a need to change the key (the hash
      pre-shared secret), then multiple pre-shared keys can be used
      simultaneously.  The validating SR router can have a table of
      <HMAC Key-id, pre-shared secret> for the currently active and
      future keys.

   o  different algorithms: by extending the previous table to <HMAC
      Key-id, hash function, pre-shared secret>, the validating SR
      router can also support several hash algorithms (see section
      Section 6.2.1)

   The pre-shared secret distribution can be done:

   o  in the configuration of the validating SR routers, either by
      static configuration or any SDN oriented approach;

   o  dynamically using a trusted key distribution such as [RFC6407]

   The intent of this document is NOT to define yet-another-key-
   distribution-protocol.

6.3.  Deployment Models

6.3.1.  Nodes within the SR domain

   SR Source Nodes within an SR Domain are trusted to generate IPv6
   packets with SRH.  SR segment endpoint nodes receiving packets on
   interface that are part of the SR Domain may process any packet
   destined to a local segment, containing an SRH.

6.3.2.  Nodes outside of the SR domain

   Nodes outside the SR Domain cannot be trusted.  SR Domain Ingress
   routers SHOULD discard packets destined to SIDs within the SR Domain
   (regardless of the presence of an SRH) to avoid attacks on the SR
   Domain.  This is accomplished via infrastructure Access Lists (iACLs)
   applied on domain ingress nodes.  However the SR Domain may be
   extended to nodes outside of it via use of the SRH HMAC.






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   Nodes outside the SR Domain may request, by some trusted means
   outside the scope of this document, a complete SRH including an HMAC
   TLV which is computed correctly for the SRH (see Section 6.2).

   SR Domain ingress routers permit traffic destined to select SIDs with
   local policy requiring HMAC TLV processing for those select SIDs,
   i.e. these SIDs provide a gateway to the SR Domain for a set of
   segment lists.

   If HMAC validation is successful, the packet is forwarded to the next
   segment.  Within the SR Domain no further HMAC check need be
   performed.  However, other segments in the SR domain MAY verify the
   HMAC TLV when the SRH is processed, dependent on local policy.

   If HMAC validation fails an ICMP error message (parameter problem)
   SHOULD be generated (but rate limited) and SHOULD be logged.

6.3.3.  SR path exposure

   The SRH contains a Segment List.  If an observer outside the SR
   Domain is able to inspect the SRH, they may use the segments in the
   Segment List to launch an attack on the SR Domain or obtain knowledge
   of the topology within the SR Domain.  When the SR Source node is
   outside the SR Domain and the packet traverses the public internet to
   the SR Domain ingress router it is likely that others will have
   access to the Segment List in the SRH.

   IPSec Encapsulating Security Payload (ESP), [RFC4303], cannot be use
   to protect the SRH as the ESP header must appear after the routing
   header (including SRH).

   Exposure of segments and TLV content to observers outside the SR
   Domain should be considered in any deployment.  There are two methods
   to limit exposure, and attacks on segments within the SR Domain from
   outside the SR Domain:

      Limit the number of segments and the TLV data exposed in SRH from
      nodes outside the SR Domain.

      Restrict which SIDs may accept traffic from outside the SR Domain
      to only those enforcing HMAC verification by using iACLs (as
      described in Section 6.3.2).

6.3.4.  Impact of BCP-38

   BCP-38 [RFC2827], also known as "Network Ingress Filtering", checks
   whether the source address of packets received on an interface is
   valid for this interface.  The use of loose source routing such as



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   SRH forces packets to follow a path which differs from the expected
   routing.  Therefore, if BCP-38 was implemented in all routers inside
   the SR domain, SR packets could be received by an interface which is
   not the expected one, and the packets could be dropped.

   As BCP-38 is only deployed at the ingress routers of an
   administrative domain, and as Packets arriving at those ingress
   routers have been forwarded using the routing information, then there
   is no reason why this ingress router should drop the SRH packet based
   on BCP-38.  Routers inside the domain commonly do not apply BCP-38;
   so, this is not a problem.

7.  IANA Considerations

   This document makes the following registrations in the Internet
   Protocol Version 6 (IPv6) Parameters "Routing Type" registry
   maintained by IANA:

   Suggested            Description             Reference
     Value
   ----------------------------------------------------------
      4         Segment Routing Header (SRH)    This document

   This document request IANA to create and maintain a new Registry:
   "Segment Routing Header TLVs"

7.1.  Segment Routing Header Flags Register

   This document requests the creation of a new IANA managed registry to
   identify SRH Flags Bits.  The registration procedure is "Expert
   Review" as defined in [RFC8126].  Suggested registry name is "Segment
   Routing Header Flags".  Flags is 8 bits, the following bits are
   defined in this document:

   Suggested      Description               Reference
     Bit
   -----------------------------------------------------
      4           HMAC                      This document

7.2.  Segment Routing Header TLVs Register

   This document requests the creation of a new IANA managed registry to
   identify SRH TLVs.  The registration procedure is "Expert Review" as
   defined in [RFC8126].  Suggested registry name is "Segment Routing
   Header TLVs".  A TLV is identified through an unsigned 8 bit
   codepoint value.  The following codepoints are defined in this
   document:




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   Suggested      Description               Reference
     Value
   -----------------------------------------------------
      5           HMAC TLV                  This document
      128         Pad0 TLV                  This document
      129         PadN TLV                  This document

8.  Implementation Status

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

8.1.  Linux

   Name: Linux Kernel v4.14

   Status: Production

   Implementation: adds SRH, performs END processing, supports HMAC TLV

   Details: https://irtf.org/anrw/2017/anrw17-final3.pdf and
   [I-D.filsfils-spring-srv6-interop]

8.2.  Cisco Systems

   Name: IOS XR and IOS XE

   Status: Pre-production

   Implementation: adds SRH, performs END processing, no TLV processing

   Details: [I-D.filsfils-spring-srv6-interop]

8.3.  FD.io

   Name: VPP/Segment Routing for IPv6

   Status: Production

   Implementation: adds SRH, performs END processing, no TLV processing

   Details: https://wiki.fd.io/view/VPP/Segment_Routing_for_IPv6 and
   [I-D.filsfils-spring-srv6-interop]

8.4.  Barefoot

   Name: Barefoot Networks Tofino NPU

   Status: Prototype



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   Implementation: performs END processing, no TLV processing

   Details: [I-D.filsfils-spring-srv6-interop]

8.5.  Juniper

   Name: Juniper Networks Trio and vTrio NPU's

   Status: Prototype & Experimental

   Implementation: SRH insertion mode, Process SID where SID is an
   interface address, no TLV processing

9.  Contributors

   Kamran Raza, Darren Dukes, Brian Field, Daniel Bernier, Ida Leung,
   Jen Linkova, Ebben Aries, Tomoya Kosugi, Eric Vyncke, David Lebrun,
   Dirk Steinberg, Robert Raszuk, Dave Barach, John Brzozowski, Pierre
   Francois, Nagendra Kumar, Mark Townsley, Christian Martin, Roberta
   Maglione, James Connolly, Aloys Augustin contributed to the content
   of this document.

10.  Acknowledgements

   The authors would like to thank Ole Troan, Bob Hinden, Ron Bonica,
   Fred Baker, Brian Carpenter, Alexandru Petrescu, Punit Kumar Jaiswal,
   and David Lebrun for their comments to this document.

11.  References

11.1.  Normative References

   [FIPS180-4]
              National Institute of Standards and Technology, "FIPS
              180-4 Secure Hash Standard (SHS)", March 2012,
              <http://csrc.nist.gov/publications/fips/fips180-4/
              fips-180-4.pdf>.

   [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.

   [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>.



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   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
              RFC 4303, DOI 10.17487/RFC4303, December 2005,
              <https://www.rfc-editor.org/info/rfc4303>.

   [RFC5095]  Abley, J., Savola, P., and G. Neville-Neil, "Deprecation
              of Type 0 Routing Headers in IPv6", RFC 5095,
              DOI 10.17487/RFC5095, December 2007,
              <https://www.rfc-editor.org/info/rfc5095>.

   [RFC6407]  Weis, B., Rowles, S., and T. Hardjono, "The Group Domain
              of Interpretation", RFC 6407, DOI 10.17487/RFC6407,
              October 2011, <https://www.rfc-editor.org/info/rfc6407>.

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

   [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>.

11.2.  Informative References

   [I-D.filsfils-spring-srv6-interop]
              Filsfils, C., Clad, F., Camarillo, P., Abdelsalam, A.,
              Salsano, S., Bonaventure, O., Horn, J., and J. Liste,
              "SRv6 interoperability report", draft-filsfils-spring-
              srv6-interop-00 (work in progress), March 2018.

   [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-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.







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   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
              Hashing for Message Authentication", RFC 2104,
              DOI 10.17487/RFC2104, February 1997,
              <https://www.rfc-editor.org/info/rfc2104>.

   [RFC2827]  Ferguson, P. and D. Senie, "Network Ingress Filtering:
              Defeating Denial of Service Attacks which employ IP Source
              Address Spoofing", BCP 38, RFC 2827, DOI 10.17487/RFC2827,
              May 2000, <https://www.rfc-editor.org/info/rfc2827>.

   [RFC3032]  Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
              Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
              Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
              <https://www.rfc-editor.org/info/rfc3032>.

   [RFC4302]  Kent, S., "IP Authentication Header", RFC 4302,
              DOI 10.17487/RFC4302, December 2005,
              <https://www.rfc-editor.org/info/rfc4302>.

   [RFC4942]  Davies, E., Krishnan, S., and P. Savola, "IPv6 Transition/
              Co-existence Security Considerations", RFC 4942,
              DOI 10.17487/RFC4942, September 2007,
              <https://www.rfc-editor.org/info/rfc4942>.

   [RFC5308]  Hopps, C., "Routing IPv6 with IS-IS", RFC 5308,
              DOI 10.17487/RFC5308, October 2008,
              <https://www.rfc-editor.org/info/rfc5308>.

   [RFC5340]  Coltun, R., Ferguson, D., Moy, J., and A. Lindem, "OSPF
              for IPv6", RFC 5340, DOI 10.17487/RFC5340, July 2008,
              <https://www.rfc-editor.org/info/rfc5340>.

   [RFC6438]  Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
              for Equal Cost Multipath Routing and Link Aggregation in
              Tunnels", RFC 6438, DOI 10.17487/RFC6438, November 2011,
              <https://www.rfc-editor.org/info/rfc6438>.

   [RFC6554]  Hui, J., Vasseur, JP., Culler, D., and V. Manral, "An IPv6
              Routing Header for Source Routes with the Routing Protocol
              for Low-Power and Lossy Networks (RPL)", RFC 6554,
              DOI 10.17487/RFC6554, March 2012,
              <https://www.rfc-editor.org/info/rfc6554>.

   [RFC8126]  Cotton, M., Leiba, B., and T. Narten, "Guidelines for
              Writing an IANA Considerations Section in RFCs", BCP 26,
              RFC 8126, DOI 10.17487/RFC8126, June 2017,
              <https://www.rfc-editor.org/info/rfc8126>.




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Authors' Addresses

   Clarence Filsfils (editor)
   Cisco Systems, Inc.
   Brussels
   BE

   Email: cfilsfil@cisco.com


   Stefano Previdi
   Individual
   Italy

   Email: stefano@previdi.net


   John Leddy
   Comcast
   4100 East Dry Creek Road
   Centennial, CO  80122
   US

   Email: John_Leddy@comcast.com


   Satoru Matsushima
   Softbank

   Email: satoru.matsushima@g.softbank.co.jp


   Daniel Voyer (editor)
   Bell Canada

   Email: daniel.voyer@bell.ca















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