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+Network Working Group                                    S. Previdi, Ed.
+Internet-Draft                                               C. Filsfils
+Intended status: Standards Track                     Cisco Systems, Inc.
+Expires: August 5, 2017                                         B. Field
+                                                                 Comcast
+                                                                I. Leung
+                                                   Rogers Communications
+                                                              J. Linkova
+                                                                  Google
+                                                                E. Aries
+                                                                Facebook
+                                                               T. Kosugi
+                                                                     NTT
+                                                               E. Vyncke
+                                                     Cisco Systems, Inc.
+                                                               D. Lebrun
+                                        Universite Catholique de Louvain
+                                                        February 1, 2017
+
+
+                   IPv6 Segment Routing Header (SRH)
+               draft-ietf-6man-segment-routing-header-05
+
+Abstract
+
+   Segment Routing (SR) allows a node to steer a packet through a
+   controlled set of instructions, called segments, by prepending an SR
+   header to the packet.  A segment can represent any instruction,
+   topological or service-based.  SR allows to enforce a flow through
+   any path (topological, or application/service based) while
+   maintaining per-flow state only at the ingress node to the SR domain.
+
+   Segment Routing can be applied to the IPv6 data plane with the
+   addition of a new type of Routing Extension Header.  This draft
+   describes the Segment Routing Extension Header Type and how it is
+   used by SR capable nodes.
+
+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.
+
+
+
+
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+Internet-Draft      IPv6 Segment Routing Header (SRH)      February 2017
+
+
+   Internet-Drafts are working documents of the Internet Engineering
+   Task Force (IETF).  Note that other groups may also distribute
+   working documents as Internet-Drafts.  The list of current Internet-
+   Drafts is at http://datatracker.ietf.org/drafts/current/.
+
+   Internet-Drafts are draft documents valid for a maximum of six months
+   and may be updated, replaced, or obsoleted by other documents at any
+   time.  It is inappropriate to use Internet-Drafts as reference
+   material or to cite them other than as "work in progress."
+
+   This Internet-Draft will expire on August 5, 2017.
+
+Copyright Notice
+
+   Copyright (c) 2017 IETF Trust and the persons identified as the
+   document authors.  All rights reserved.
+
+   This document is subject to BCP 78 and the IETF Trust's Legal
+   Provisions Relating to IETF Documents
+   (http://trustee.ietf.org/license-info) in effect on the date of
+   publication of this document.  Please review these documents
+   carefully, as they describe your rights and restrictions with respect
+   to this document.  Code Components extracted from this document must
+   include Simplified BSD License text as described in Section 4.e of
+   the Trust Legal Provisions and are provided without warranty as
+   described in the Simplified BSD License.
+
+Table of Contents
+
+   1.  Segment Routing Documents . . . . . . . . . . . . . . . . . .   3
+   2.  Introduction  . . . . . . . . . . . . . . . . . . . . . . . .   3
+     2.1.  Data Planes supporting Segment Routing  . . . . . . . . .   4
+     2.2.  Segment Routing (SR) Domain . . . . . . . . . . . . . . .   4
+       2.2.1.  SR Domain in a Service Provider Network . . . . . . .   5
+       2.2.2.  SR Domain in a Overlay Network  . . . . . . . . . . .   6
+   3.  Segment Routing Extension Header (SRH)  . . . . . . . . . . .   7
+     3.1.  SRH TLVs  . . . . . . . . . . . . . . . . . . . . . . . .   9
+       3.1.1.  Ingress Node TLV  . . . . . . . . . . . . . . . . . .  10
+       3.1.2.  Egress Node TLV . . . . . . . . . . . . . . . . . . .  11
+       3.1.3.  Opaque Container TLV  . . . . . . . . . . . . . . . .  11
+       3.1.4.  Padding TLV . . . . . . . . . . . . . . . . . . . . .  12
+       3.1.5.  HMAC TLV  . . . . . . . . . . . . . . . . . . . . . .  13
+     3.2.  SRH and RFC2460 behavior  . . . . . . . . . . . . . . . .  14
+   4.  SRH Procedures  . . . . . . . . . . . . . . . . . . . . . . .  14
+     4.1.  Source SR Node  . . . . . . . . . . . . . . . . . . . . .  14
+     4.2.  Transit Node  . . . . . . . . . . . . . . . . . . . . . .  15
+     4.3.  SR Segment Endpoint Node  . . . . . . . . . . . . . . . .  16
+   5.  Security Considerations . . . . . . . . . . . . . . . . . . .  16
+
+
+
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+
+     5.1.  Threat model  . . . . . . . . . . . . . . . . . . . . . .  17
+       5.1.1.  Source routing threats  . . . . . . . . . . . . . . .  17
+       5.1.2.  Applicability of RFC 5095 to SRH  . . . . . . . . . .  17
+       5.1.3.  Service stealing threat . . . . . . . . . . . . . . .  18
+       5.1.4.  Topology disclosure . . . . . . . . . . . . . . . . .  18
+       5.1.5.  ICMP Generation . . . . . . . . . . . . . . . . . . .  18
+     5.2.  Security fields in SRH  . . . . . . . . . . . . . . . . .  19
+       5.2.1.  Selecting a hash algorithm  . . . . . . . . . . . . .  20
+       5.2.2.  Performance impact of HMAC  . . . . . . . . . . . . .  21
+       5.2.3.  Pre-shared key management . . . . . . . . . . . . . .  21
+     5.3.  Deployment Models . . . . . . . . . . . . . . . . . . . .  22
+       5.3.1.  Nodes within the SR domain  . . . . . . . . . . . . .  22
+       5.3.2.  Nodes outside of the SR domain  . . . . . . . . . . .  22
+       5.3.3.  SR path exposure  . . . . . . . . . . . . . . . . . .  23
+       5.3.4.  Impact of BCP-38  . . . . . . . . . . . . . . . . . .  23
+   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  24
+   7.  Manageability Considerations  . . . . . . . . . . . . . . . .  24
+   8.  Contributors  . . . . . . . . . . . . . . . . . . . . . . . .  24
+   9.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  24
+   10. References  . . . . . . . . . . . . . . . . . . . . . . . . .  25
+     10.1.  Normative References . . . . . . . . . . . . . . . . . .  25
+     10.2.  Informative References . . . . . . . . . . . . . . . . .  25
+   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  27
+
+1.  Segment Routing Documents
+
+   Segment Routing terminology is defined in
+   [I-D.ietf-spring-segment-routing].
+
+   Segment Routing use cases are described in [RFC7855] and
+   [I-D.ietf-spring-ipv6-use-cases].
+
+   Segment Routing protocol extensions are defined in
+   [I-D.ietf-isis-segment-routing-extensions], and
+   [I-D.ietf-ospf-ospfv3-segment-routing-extensions].
+
+2.  Introduction
+
+   Segment Routing (SR), defined in [I-D.ietf-spring-segment-routing],
+   allows a node to steer a packet through a controlled set of
+   instructions, called segments, by prepending an SR header to the
+   packet.  A segment can represent any instruction, topological or
+   service-based.  SR allows to enforce a flow through any path
+   (topological or service/application based) while maintaining per-flow
+   state only at the ingress node to the SR domain.  Segments can be
+   derived from different components: IGP, BGP, Services, Contexts,
+   Locators, etc.  The list of segment forming the path is called the
+   Segment List and is encoded in the packet header.
+
+
+
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+
+   SR allows the use of strict and loose source based routing paradigms
+   without requiring any additional signaling protocols in the
+   infrastructure hence delivering an excellent scalability property.
+
+   The source based routing model described in
+   [I-D.ietf-spring-segment-routing] is inherited from the ones proposed
+   by [RFC1940] and [RFC2460].  The source based routing model offers
+   the support for explicit routing capability.
+
+2.1.  Data Planes supporting Segment Routing
+
+   Segment Routing (SR), can be instantiated over MPLS
+   ([I-D.ietf-spring-segment-routing-mpls]) and IPv6.  This document
+   defines its instantiation over the IPv6 data-plane based on the use-
+   cases defined in [I-D.ietf-spring-ipv6-use-cases].
+
+   This document defines a new type of Routing Header (originally
+   defined in [RFC2460]) called the Segment Routing Header (SRH) in
+   order to convey the Segment List in the packet header as defined in
+   [I-D.ietf-spring-segment-routing].  Mechanisms through which segment
+   are known and advertised are outside the scope of this document.
+
+   A segment is materialized by an IPv6 address.  A segment identifies a
+   topological instruction or a service instruction.  A segment can be
+   either:
+
+   o  global: a global segment represents an instruction supported by
+      all nodes in the SR domain and it is instantiated through an IPv6
+      address globally known in the SR domain.
+
+   o  local: a local segment represents an instruction supported only by
+      the node who originates it and it is instantiated through an IPv6
+      address that is known only by the local node.
+
+2.2.  Segment Routing (SR) Domain
+
+   We define the concept of the Segment Routing Domain (SR Domain) as
+   the set of nodes participating into the source based routing model.
+   These nodes may be connected to the same physical infrastructure
+   (e.g.: a Service Provider's network) as well as nodes remotely
+   connected to each other (e.g.: an enterprise VPN or an overlay).
+
+   A non-exhaustive list of examples of SR Domains is:
+
+   o  The network of an operator, service provider, content provider,
+      enterprise including nodes, links and Autonomous Systems.
+
+
+
+
+
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+   o  A set of nodes connected as an overlay over one or more transit
+      providers.  The overlay nodes exchange SR-enabled traffic with
+      segments belonging solely to the overlay routers (the SR domain).
+      None of the segments in the SR-enabled packets exchanged by the
+      overlay belong to the transit networks
+
+   The source based routing model through its instantiation of the
+   Segment Routing Header (SRH) defined in this document equally applies
+   to all the above examples.
+
+   It is assumed in this document that the SRH is added to the packet by
+   its source, consistently with the source routing model defined in
+   [RFC2460].  For example:
+
+   o  At the node originating the packet (host, server).
+
+   o  At the ingress node of an SR domain where the ingress node
+      receives an IPv6 packet and encapsulates it into an outer IPv6
+      header followed by a Segment Routing header.
+
+2.2.1.  SR Domain in a Service Provider Network
+
+   The following figure illustrates an SR domain consisting of an
+   operator's network infrastructure.
+
+     (-------------------------- Operator 1 -----------------------)
+     (                                                             )
+     (  (-----AS 1-----)  (-------AS 2-------)  (----AS 3-------)  )
+     (  (              )  (                  )  (               )  )
+ A1--(--(--11---13--14-)--(-21---22---23--24-)--(-31---32---34--)--)--Z1
+     (  ( /|\  /|\  /| )  ( |\  /|\  /|\  /| )  ( |\  /|\  /| \ )  )
+ A2--(--(/ | \/ | \/ | )  ( | \/ | \/ | \/ | )  ( | \/ | \/ |  \)--)--Z2
+     (  (  | /\ | /\ | )  ( | /\ | /\ | /\ | )  ( | /\ | /\ |   )  )
+     (  (  |/  \|/  \| )  ( |/  \|/  \|/  \| )  ( |/  \|/  \|   )  )
+ A3--(--(--15---17--18-)--(-25---26---27--28-)--(-35---36---38--)--)--Z3
+     (  (              )  (                  )  (               )  )
+     (  (--------------)  (------------------)  (---------------)  )
+     (                                                             )
+     (-------------------------------------------------------------)
+
+                   Figure 1: Service Provider SR Domain
+
+   Figure 1 describes an operator network including several ASes and
+   delivering connectivity between endpoints.  In this scenario, Segment
+   Routing is used within the operator networks and across the ASes
+   boundaries (all being under the control of the same operator).  In
+   this case segment routing can be used in order to address use cases
+   such as end-to-end traffic engineering, fast re-route, egress peer
+
+
+
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+
+   engineering, data-center traffic engineering as described in
+   [RFC7855], [I-D.ietf-spring-ipv6-use-cases] and
+   [I-D.ietf-spring-resiliency-use-cases].
+
+   Typically, an IPv6 packet received at ingress (i.e.: from outside the
+   SR domain), is classified according to network operator policies and
+   such classification results into an outer header with an SRH applied
+   to the incoming packet.  The SRH contains the list of segment
+   representing the path the packet must take inside the SR domain.
+   Thus, the SA of the packet is the ingress node, the DA (due to SRH
+   procedures described in Section 4) is set as the first segment of the
+   path and the last segment of the path is the egress node of the SR
+   domain.
+
+   The path may include intra-AS as well as inter-AS segments.  It has
+   to be noted that all nodes within the SR domain are under control of
+   the same administration.  When the packet reaches the egress point of
+   the SR domain, the outer header and its SRH are removed so that the
+   destination of the packet is unaware of the SR domain the packet has
+   traversed.
+
+   The outer header with the SRH is no different from any other
+   tunneling encapsulation mechanism and allows a network operator to
+   implement traffic engineering mechanisms so to efficiently steer
+   traffic across his infrastructure.
+
+2.2.2.  SR Domain in a Overlay Network
+
+   The following figure illustrates an SR domain consisting of an
+   overlay network over multiple operator's networks.
+
+       (--Operator 1---)  (-----Operator 2-----)  (--Operator 3---)
+       (               )  (                    )  (               )
+   A1--(--11---13--14--)--(--21---22---23--24--)--(-31---32---34--)--C1
+       ( /|\  /|\  /|  )  (  |\  /|\  /|\  /|  )  ( |\  /|\  /| \ )
+   A2--(/ | \/ | \/ |  )  (  | \/ | \/ | \/ |  )  ( | \/ | \/ |  \)--C2
+       (  | /\ | /\ |  )  (  | /\ | /\ | /\ |  )  ( | /\ | /\ |   )
+       (  |/  \|/  \|  )  (  |/  \|/  \|/  \|  )  ( |/  \|/  \|   )
+   A3--(--15---17--18--)--(--25---26---27--28--)--(-35---36---38--)--C3
+       (               )  (  |    |         |  )  (               )
+       (---------------)  (--|----|---------|--)  (---------------)
+                             |    |         |
+                             B1   B2        B3
+
+                        Figure 2: Overlay SR Domain
+
+
+
+
+
+
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+
+   Figure 2 describes an overlay consisting of nodes connected to three
+   different network operators and forming a single overlay network
+   where Segment routing packets are exchanged.
+
+   The overlay consists of nodes A1, A2, A3, B1, B2, B3, C1, C2 and C3.
+   These nodes are connected to their respective network operator and
+   form an overlay network.
+
+   Each node may originate packets with an SRH which contains, in the
+   segment list of the SRH or in the DA, segments identifying other
+   overlay nodes.  This implies that packets with an SRH may traverse
+   operator's networks but, obviously, these SRHs cannot contain an
+   address/segment of the transit operators 1, 2 and 3.  The SRH
+   originated by the overlay can only contain address/segment under the
+   administration of the overlay (e.g. address/segments supported by A1,
+   A2, A3, B1, B2, B3, C1,C2 or C3).
+
+   In this model, the operator network nodes are transit nodes and,
+   according to [RFC2460], MUST NOT inspect the routing extension header
+   since they are not the DA of the packet.
+
+   It is a common practice in operators networks to filter out, at
+   ingress, any packet whose DA is the address of an internal node and
+   it is also possible that an operator would filter out any packet
+   destined to an internal address and having an extension header in it.
+
+   This common practice does not impact the SR-enabled traffic between
+   the overlay nodes as the intermediate transit networks never see a
+   destination address belonging to their infrastructure.  These SR-
+   enabled overlay packets will thus never be filtered by the transit
+   operators.
+
+   In all cases, transit packets (i.e.: packets whose DA is outside the
+   domain of the operator's network) will be forwarded accordingly
+   without introducing any security concern in the operator's network.
+   This is similar to tunneled packets.
+
+3.  Segment Routing Extension Header (SRH)
+
+   A new type of the Routing Header (originally defined in [RFC2460]) is
+   defined: the Segment Routing Header (SRH) which has a new Routing
+   Type, (suggested value 4) to be assigned by IANA.
+
+   The Segment Routing Header (SRH) is defined as follows:
+
+
+
+
+
+
+
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+     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 |
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    | First Segment |     Flags     |           RESERVED            |
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    |                                                               |
+    |            Segment List[0] (128 bits IPv6 address)            |
+    |                                                               |
+    |                                                               |
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    |                                                               |
+    |                                                               |
+                                  ...
+    |                                                               |
+    |                                                               |
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    |                                                               |
+    |            Segment List[n] (128 bits IPv6 address)            |
+    |                                                               |
+    |                                                               |
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+    //                                                             //
+    //         Optional Type Length Value objects (variable)       //
+    //                                                             //
+    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   where:
+
+   o  Next Header: 8-bit selector.  Identifies the type of header
+      immediately following the SRH.
+
+   o  Hdr Ext Len: 8-bit unsigned integer, is the length of the SRH
+      header in 8-octet units, not including the first 8 octets.
+
+   o  Routing Type: TBD, to be assigned by IANA (suggested value: 4).
+
+   o  Segments Left.  Defined in [RFC2460], it contains the index, in
+      the Segment List, of the next segment to inspect.  Segments Left
+      is decremented at each segment.
+
+   o  First Segment: contains the index, in the Segment List, of the
+      first segment of the path which is in fact the last element of the
+      Segment List.
+
+   o  Flags: 8 bits of flags.  Following flags are defined:
+
+
+
+
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+
+          0 1 2 3 4 5 6 7
+         +-+-+-+-+-+-+-+-+
+         |U|P|O|A|H|  U  |
+         +-+-+-+-+-+-+-+-+
+
+         U: Unused and for future use.  SHOULD be unset on transmission
+         and MUST be ignored on receipt.
+
+         P-flag: Protected flag.  Set when the packet has been rerouted
+         through FRR mechanism by an SR endpoint node.
+
+         O-flag: OAM flag.  When set, it indicates that this packet is
+         an operations and management (OAM) packet.
+
+         A-flag: Alert flag.  If present, it means important Type Length
+         Value (TLV) objects are present.  See Section 3.1 for details
+         on TLVs objects.
+
+         H-flag: HMAC flag.  If set, the HMAC TLV is present and is
+         encoded as the last TLV of the SRH.  In other words, the last
+         36 octets of the SRH represent the HMAC information.  See
+         Section 3.1.5 for details on the HMAC TLV.
+
+   o  RESERVED: SHOULD be unset on transmission and MUST be ignored on
+      receipt.
+
+   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 path.  I.e., the first element of the
+      segment list (Segment List [0]) contains the last segment of the
+      path while the last segment of the Segment List (Segment List[n])
+      contains the first segment of the path.  The index contained in
+      "Segments Left" identifies the current active segment.
+
+   o  Type Length Value (TLV) are described in Section 3.1.
+
+3.1.  SRH TLVs
+
+   This section defines TLVs of the Segment Routing Header.
+
+   Type Length Value (TLV) contain optional information that may be used
+   by the node identified in the DA of the packet.  It has to be noted
+   that the information carried in the TLVs is not intended to be used
+   by the routing layer.  Typically, TLVs carry information that is
+   consumed by other components (e.g.: OAM) than the routing function.
+
+   Each TLV has its own length, format and semantic.  The code-point
+   allocated (by IANA) to each TLV defines both the format and the
+
+
+
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+   semantic of the information carried in the TLV.  Multiple TLVs may be
+   encoded in the same SRH.
+
+   The "Length" field of the TLV is primarily used to skip the TLV while
+   inspecting the SRH in case the node doesn't support or recognize the
+   TLV codepoint.  The "Length" defines the TLV length in octets and not
+   including the "Type" and "Length" fields.
+
+   The primary scope of TLVs is to give the receiver of the packet
+   information related to the source routed path (e.g.: where the packet
+   entered in the SR domain and where it is expected to exit).
+
+   Additional TLVs may be defined in the future.
+
+3.1.1.  Ingress Node TLV
+
+   The Ingress Node TLV is optional and identifies the node this packet
+   traversed when entered the SR domain.  The Ingress Node TLV has
+   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    |     Flags     |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                                                               |
+   |                 Ingress Node (16 octets)                      |
+   |                                                               |
+   |                                                               |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   where:
+
+   o  Type: to be assigned by IANA (suggested value 1).
+
+   o  Length: 18.
+
+   o  RESERVED: 8 bits.  SHOULD be unset on transmission and MUST be
+      ignored on receipt.
+
+   o  Flags: 8 bits.  No flags are defined in this document.
+
+   o  Ingress Node: 128 bits.  Defines the node where the packet is
+      expected to enter the SR domain.  In the encapsulation case
+      described in Section 2.2.1, this information corresponds to the SA
+      of the encapsulating header.
+
+
+
+
+
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+
+
+3.1.2.  Egress Node TLV
+
+   The Egress Node TLV is optional and identifies the node this packet
+   is expected to traverse when exiting the SR domain.  The Egress Node
+   TLV has 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    |     Flags     |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                                                               |
+   |                  Egress Node (16 octets)                      |
+   |                                                               |
+   |                                                               |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   where:
+
+   o  Type: to be assigned by IANA (suggested value 2).
+
+   o  Length: 18.
+
+   o  RESERVED: 8 bits.  SHOULD be unset on transmission and MUST be
+      ignored on receipt.
+
+   o  Flags: 8 bits.  No flags are defined in this document.
+
+   o  Egress Node: 128 bits.  Defines the node where the packet is
+      expected to exit the SR domain.  In the encapsulation case
+      described in Section 2.2.1, this information corresponds to the
+      last segment of the SRH in the encapsulating header.
+
+3.1.3.  Opaque Container TLV
+
+   The Opaque Container TLV is optional and has the following format:
+
+
+
+
+
+
+
+
+
+
+
+
+
+
+
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+
+    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    |     Flags     |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   |                                                               |
+   |             Opaque Container (16 octets)                      |
+   |                                                               |
+   |                                                               |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   where:
+
+   o  Type: to be assigned by IANA (suggested value 3).
+
+   o  Length: 18.
+
+   o  RESERVED: 8 bits.  SHOULD be unset on transmission and MUST be
+      ignored on receipt.
+
+   o  Flags: 8 bits.  No flags are defined in this document.
+
+   o  Opaque Container: 128 bits of opaque data not relevant for the
+      routing layer.  Typically, this information is consumed by a non-
+      routing component of the node receiving the packet (i.e.: the node
+      in the DA).
+
+3.1.4.  Padding TLV
+
+   The Padding TLV is optional and with the purpose of aligning the SRH
+   on a 8 octet boundary.  The Padding 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     |      Padding (variable)       |
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+   //                    Padding (variable)                       //
+   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
+
+   where:
+
+   o  Type: to be assigned by IANA (suggested value 4).
+
+   o  Length: 1 to 7
+
+
+
+
+
+
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+
+
+   o  Padding: from 1 to 7 octets of padding.  Padding bits have no
+      semantic.  They SHOULD be set to 0 on transmission and MUST be
+      ignored on receipt.
+
+   The following applies to the Padding TLV:
+
+   o  Padding TLV is optional and MAY only appear once in the SRH.  If
+      present, it MUST have a length between 1 and 7 octets.
+
+   o  The Padding TLV is used in order to align the SRH total length on
+      the 8 octet boundary.
+
+   o  When present, the Padding TLV MUST appear as the last TLV before
+      the HMAC TLV (if HMAC TLV is present).
+
+   o  When present, the Padding TLV MUST have a length from 1 to 7 in
+      order to align the SRH total lenght on a 8-octet boundary.
+
+   o  When a router inspecting the SRH encounters the Padding TLV, it
+      MUST assume that no other TLV (other than the HMAC) follow the
+      Padding TLV.
+
+3.1.5.  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.  SHOULD be unset on transmission and MUST be
+      ignored on receipt.
+
+
+
+
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+
+
+   o  HMAC Key ID: 4 octets.
+
+   o  HMAC: 32 octets.
+
+   o  HMAC and HMAC Key ID usage is described in Section 5
+
+   The Following applies to the HMAC TLV:
+
+   o  When present, the HMAC TLV MUST be encoded as the last TLV of the
+      SRH.
+
+   o  If the HMAC TLV is present, the SRH H-Flag (Figure 4) MUST be set.
+
+   o  When the H-flag is set in the SRH, the router inspecting the SRH
+      MUST find the HMAC TLV in the last 38 octets of the SRH.
+
+3.2.  SRH and RFC2460 behavior
+
+   The SRH being a new type of the Routing Header, it also has the same
+   properties:
+
+      SHOULD only appear once in the packet.
+
+      Only the router whose address is in the DA field of the packet
+      header MUST inspect the SRH.
+
+   Therefore, Segment Routing in IPv6 networks implies that the segment
+   identifier (i.e.: the IPv6 address of the segment) is moved into the
+   DA of the packet.
+
+   The DA of the packet changes at each segment termination/completion
+   and therefore the final DA of the packet MUST be encoded as the last
+   segment of the path.
+
+4.  SRH Procedures
+
+   In this section we describe the different procedures on the SRH.
+
+4.1.  Source SR Node
+
+   A Source SR Node can be any node originating an IPv6 packet with its
+   IPv6 and Segment Routing Headers.  This include either:
+
+      A host originating an IPv6 packet.
+
+      An SR domain ingress router encapsulating a received IPv6 packet
+      into an outer IPv6 header followed by an SRH.
+
+
+
+
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+
+   The mechanism through which a Segment List is derived is outside of
+   the scope of this document.  As an example, the Segment List may be
+   obtained through:
+
+      Local path computation.
+
+      Local configuration.
+
+      Interaction with a centralized controller delivering the path.
+
+      Any other mechanism.
+
+   The following are the steps of the creation of the SRH:
+
+      Next Header and Hdr Ext Len fields are set according to [RFC2460].
+
+      Routing Type field is set as TBD (to be allocated by IANA,
+      suggested value 4).
+
+      The Segment List is built with the FIRST segment of the path
+      encoded in the LAST element of the Segment List.  Subsequent
+      segments are encoded on top of the first segment.  Finally, the
+      LAST segment of the path is encoded in the FIRST element of the
+      Segment List.  In other words, the Segment List is encoded in the
+      reverse order of the path.
+
+      The final DA of the packet is encoded as the last segment of the
+      path (encoded in the first element of the Segment List).
+
+      The DA of the packet is set with the value of the first segment
+      (found in the last element of the segment list).
+
+      The Segments Left field is set to n-1 where n is the number of
+      elements in the Segment List.
+
+      The First Segment field is set to n-1 where n is the number of
+      elements in the Segment List.
+
+      The packet is sent out towards the first segment (i.e.:
+      represented in the packet DA).
+
+      HMAC TLV may be set according to Section 5.
+
+4.2.  Transit Node
+
+   According to [RFC2460], the only node who is 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
+
+
+
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+
+   NOT inspect the underneath routing header and MUST forward the packet
+   towards the DA and according to the IPv6 routing table.
+
+   In the example case described in Section 2.2.2, when SR capable nodes
+   are connected through an overlay spanning multiple third-party
+   infrastructure, it is safe to send SRH packets (i.e.: packet having a
+   Segment Routing Header) between each other overlay/SR-capable nodes
+   as long as the segment list does not include any of the transit
+   provider nodes.  In addition, as a generic security measure, any
+   service provider will block any packet destined to one of its
+   internal routers, especially if these packets have an extended header
+   in it.
+
+4.3.  SR Segment Endpoint Node
+
+   The SR segment endpoint node is the node whose address is in the DA.
+   The segment endpoint node inspects the SRH and does:
+
+   1.   IF DA = myself (segment endpoint)
+   2.      IF Segments Left > 0 THEN
+              decrement Segments Left
+              update DA with Segment List[Segments Left]
+   3.      ELSE continue IPv6 processing of the packet
+                End of processing.
+   4.   Forward the packet out
+
+5.  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 RFC 2460 [RFC2460] 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 RFC 2460 [RFC2460].
+
+   Per RFC2460 [RFC2460], 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
+   one interface IPv6 address equals the destination address field of
+   the IPv6 packet MUST parse the SRH and, if supported and if the local
+   configuration allows it, MUST act accordingly to the SRH content.
+
+
+
+
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+
+   According to RFC2460 [RFC2460], 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.
+
+5.1.  Threat model
+
+5.1.1.  Source routing threats
+
+   Using an SRH is similar to source routing, therefore it has some
+   well-known security issues as described in RFC4942 [RFC4942] section
+   2.1.1 and RFC5095 [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;
+
+   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).
+
+5.1.2.  Applicability of RFC 5095 to SRH
+
+   First of all, the reader must remember this specific part of section
+   1 of RFC5095 [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,
+   RFC 6554 (RPL) [RFC6554] 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):
+
+
+
+
+
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+
+   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 [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 RFC 5095 [RFC5095] attacks are
+   not applicable.
+
+5.1.3.  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'.
+
+5.1.4.  Topology disclosure
+
+   The SRH may also contains IPv6 addresses 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 path, then there is little learned by
+   intercepting the SRH itself.
+
+5.1.5.  ICMP Generation
+
+   Per section 4.4 of RFC2460 [RFC2460], 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:
+
+
+
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+
+   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 set to 0) destined to a node not
+   supporting SRH.  Per RFC2460 [RFC2460], 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.
+
+5.2.  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).
+
+   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 RFC 2104
+   [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  First Segment field;
+
+   o  an octet of bit flags;
+
+   o  HMAC Key-id;
+
+   o  all addresses in the Segment List.
+
+
+
+
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+
+   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.
+
+   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.
+
+5.2.1.  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
+
+
+
+
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+
+   right-hand padded with 96 bits set to 0.  The authors understand that
+   this is not secure but is ok for limited tests.
+
+5.2.2.  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-up 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 MUST only be checked and validated by
+      the first router of the segment routing domain, this router is
+      named 'validating SR router'.  Downstream routers may not inspect
+      the HMAC field.
+
+   o  this validating 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  Last point, hash functions such as SHA-2 have been optimized for
+      security and performance and there are multiple implementations
+      with good performance.
+
+   With the above points in mind, the performance impact of using HMAC
+   is minimized.
+
+5.2.3.  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 routing 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 router
+      can also support simultaneously several hash algorithms (see
+      section Section 5.2.1)
+
+   The pre-shared secret distribution can be done:
+
+
+
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+
+   o  in the configuration of the validating 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.
+
+5.3.  Deployment Models
+
+5.3.1.  Nodes within the SR domain
+
+   An SR domain is defined as a set of interconnected routers where all
+   routers at the perimeter are configured to add and act on SRH.  Some
+   routers inside the SR domain can also act on SRH or simply forward
+   IPv6 packets.
+
+   The routers inside an SR domain can be trusted to generate SRH and to
+   process SRH received on interfaces that are part of the SR domain.
+   These nodes MUST drop all SRH packets received on an interface that
+   is not part of the SR domain and containing an SRH whose HMAC field
+   cannot be validated by local policies.  This includes obviously
+   packet with an SRH generated by a non-cooperative SR domain.
+
+   If the validation fails, then these packets MUST be dropped, ICMP
+   error messages (parameter problem) SHOULD be generated (but rate
+   limited) and SHOULD be logged.
+
+5.3.2.  Nodes outside of the SR domain
+
+   Nodes outside of the SR domain cannot be trusted for physical
+   security; hence, they need to request by some trusted means (outside
+   of the scope of this document) a complete SRH for each new connection
+   (i.e. new destination address).  The received SRH MUST include an
+   HMAC TLV which is computed correctly (see Section 5.2).
+
+   When an outside node sends a packet with an SRH and towards an SR
+   domain ingress node, the packet MUST contain the HMAC TLV (with a
+   Key-id and HMAC fields) and the the destination address MUST be an
+   address of an SR domain ingress node .
+
+   The ingress SR router, i.e., the router with an interface address
+   equals to the destination address, MUST verify the HMAC TLV.
+
+   If the validation is successful, then the packet is simply forwarded
+   as usual for an SR packet.  As long as the packet travels within the
+   SR domain, no further HMAC check needs to be done.  Subsequent
+
+
+
+
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+
+
+   routers in the SR domain MAY verify the HMAC TLV when they process
+   the SRH (i.e. when they are the destination).
+
+   If the validation fails, then this packet MUST be dropped, an ICMP
+   error message (parameter problem) SHOULD be generated (but rate
+   limited) and SHOULD be logged.
+
+5.3.3.  SR path exposure
+
+   As the intermediate SR nodes addresses appears in the SRH, if this
+   SRH is visible to an outsider then he/she could reuse this knowledge
+   to launch an attack on the intermediate SR nodes or get some insider
+   knowledge on the topology.  This is especially applicable when the
+   path between the source node and the first SR domain ingress router
+   is on the public Internet.
+
+   The first remark is to state that 'security by obscurity' is never
+   enough; in other words, the security policy of the SR domain MUST
+   assume that the internal topology and addressing is known by the
+   attacker.  A simple traceroute will also give the same information
+   (with even more information as all intermediate nodes between SID
+   will also be exposed).  IPsec Encapsulating Security Payload
+   [RFC4303] cannot be use to protect the SRH as per RFC4303 the ESP
+   header must appear after any routing header (including SRH).
+
+   To prevent a user to leverage the gained knowledge by intercepting
+   SRH, it it recommended to apply an infrastructure Access Control List
+   (iACL) at the edge of the SR domain.  This iACL will drop all packets
+   from outside the SR-domain whose destination is any address of any
+   router inside the domain.  This security policy should be tuned for
+   local operations.
+
+5.3.4.  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
+   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, then SR packets could be received by an interface
+   which is not expected one and the packets could be dropped.
+
+   As an SR domain is usually a subset of one administrative domain, and
+   as BCP-38 is only deployed at the ingress routers of this
+   administrative domain and as packets arriving at those ingress
+   routers have been normally forwarded using the normal routing
+   information, then there is no reason why this ingress router should
+
+
+
+
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+
+   drop the SRH packet based on BCP-38.  Routers inside the domain
+   commonly do not apply BCP-38; so, this is not a problem.
+
+6.  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
+
+   In addition, this document request IANA to create and maintain a new
+   Registry: "Segment Routing Header Type-Value Objects".  The following
+   code-points are requested from the registry:
+
+   Registry: Segment Routing Header Type-Value Objects
+
+   Suggested         Description            Reference
+     Value
+   -----------------------------------------------------
+      1         Ingress Node TLV          This document
+      2         Egress Node  TLV          This document
+      3         Opaque Container TLV      This document
+      4         Padding TLV               This document
+      5         HMAC TLV                  This document
+
+7.  Manageability Considerations
+
+   TBD
+
+8.  Contributors
+
+   Dave Barach, John Leddy, John Brzozowski, Pierre Francois, Nagendra
+   Kumar, Mark Townsley, Christian Martin, Roberta Maglione, James
+   Connolly, Aloys Augustin contributed to the content of this document.
+
+9.  Acknowledgements
+
+   The authors would like to thank Ole Troan, Bob Hinden, Fred Baker,
+   Brian Carpenter, Alexandru Petrescu and Punit Kumar Jaiswal for their
+   comments to this document.
+
+
+
+
+
+
+
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+
+10.  References
+
+10.1.  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>.
+
+   [RFC2119]  Bradner, S., "Key words for use in RFCs to Indicate
+              Requirement Levels", BCP 14, RFC 2119,
+              DOI 10.17487/RFC2119, March 1997,
+              <http://www.rfc-editor.org/info/rfc2119>.
+
+   [RFC2460]  Deering, S. and R. Hinden, "Internet Protocol, Version 6
+              (IPv6) Specification", RFC 2460, DOI 10.17487/RFC2460,
+              December 1998, <http://www.rfc-editor.org/info/rfc2460>.
+
+   [RFC4303]  Kent, S., "IP Encapsulating Security Payload (ESP)",
+              RFC 4303, DOI 10.17487/RFC4303, December 2005,
+              <http://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,
+              <http://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, <http://www.rfc-editor.org/info/rfc6407>.
+
+10.2.  Informative References
+
+   [I-D.ietf-isis-segment-routing-extensions]
+              Previdi, S., Filsfils, C., Bashandy, A., Gredler, H.,
+              Litkowski, S., Decraene, B., and j. jefftant@gmail.com,
+              "IS-IS Extensions for Segment Routing", draft-ietf-isis-
+              segment-routing-extensions-09 (work in progress), October
+              2016.
+
+   [I-D.ietf-ospf-ospfv3-segment-routing-extensions]
+              Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
+              Shakir, R., Henderickx, W., and J. Tantsura, "OSPFv3
+              Extensions for Segment Routing", draft-ietf-ospf-ospfv3-
+              segment-routing-extensions-07 (work in progress), October
+              2016.
+
+
+
+
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+
+
+   [I-D.ietf-spring-ipv6-use-cases]
+              Brzozowski, J., Leddy, J., Townsley, W., Filsfils, C., and
+              R. Maglione, "IPv6 SPRING Use Cases", draft-ietf-spring-
+              ipv6-use-cases-08 (work in progress), January 2017.
+
+   [I-D.ietf-spring-resiliency-use-cases]
+              Filsfils, C., Previdi, S., Decraene, B., and R. Shakir,
+              "Resiliency use cases in SPRING networks", draft-ietf-
+              spring-resiliency-use-cases-08 (work in progress), October
+              2016.
+
+   [I-D.ietf-spring-segment-routing]
+              Filsfils, C., Previdi, S., Decraene, B., Litkowski, S.,
+              and R. Shakir, "Segment Routing Architecture", draft-ietf-
+              spring-segment-routing-10 (work in progress), November
+              2016.
+
+   [I-D.ietf-spring-segment-routing-mpls]
+              Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,
+              Litkowski, S., Horneffer, M., Shakir, R.,
+              jefftant@gmail.com, j., and E. Crabbe, "Segment Routing
+              with MPLS data plane", draft-ietf-spring-segment-routing-
+              mpls-06 (work in progress), January 2017.
+
+   [RFC1940]  Estrin, D., Li, T., Rekhter, Y., Varadhan, K., and D.
+              Zappala, "Source Demand Routing: Packet Format and
+              Forwarding Specification (Version 1)", RFC 1940,
+              DOI 10.17487/RFC1940, May 1996,
+              <http://www.rfc-editor.org/info/rfc1940>.
+
+   [RFC2104]  Krawczyk, H., Bellare, M., and R. Canetti, "HMAC: Keyed-
+              Hashing for Message Authentication", RFC 2104,
+              DOI 10.17487/RFC2104, February 1997,
+              <http://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, <http://www.rfc-editor.org/info/rfc2827>.
+
+   [RFC4942]  Davies, E., Krishnan, S., and P. Savola, "IPv6 Transition/
+              Co-existence Security Considerations", RFC 4942,
+              DOI 10.17487/RFC4942, September 2007,
+              <http://www.rfc-editor.org/info/rfc4942>.
+
+
+
+
+
+
+
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+
+
+   [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,
+              <http://www.rfc-editor.org/info/rfc6554>.
+
+   [RFC7855]  Previdi, S., Ed., Filsfils, C., Ed., Decraene, B.,
+              Litkowski, S., Horneffer, M., and R. Shakir, "Source
+              Packet Routing in Networking (SPRING) Problem Statement
+              and Requirements", RFC 7855, DOI 10.17487/RFC7855, May
+              2016, <http://www.rfc-editor.org/info/rfc7855>.
+
+Authors' Addresses
+
+   Stefano Previdi (editor)
+   Cisco Systems, Inc.
+   Via Del Serafico, 200
+   Rome  00142
+   Italy
+
+   Email: sprevidi@cisco.com
+
+
+   Clarence Filsfils
+   Cisco Systems, Inc.
+   Brussels
+   BE
+
+   Email: cfilsfil@cisco.com
+
+
+   Brian Field
+   Comcast
+   4100 East Dry Creek Road
+   Centennial, CO  80122
+   US
+
+   Email: Brian_Field@cable.comcast.com
+
+
+   Ida Leung
+   Rogers Communications
+   8200 Dixie Road
+   Brampton, ON  L6T 0C1
+   CA
+
+   Email: Ida.Leung@rci.rogers.com
+
+
+
+
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+
+
+   Jen Linkova
+   Google
+   1600 Amphitheatre Parkway
+   Mountain View, CA 94043
+   US
+
+   Email: furry@google.com
+
+
+   Ebben Aries
+   Facebook
+   US
+
+   Email: exa@fb.com
+
+
+   Tomoya Kosugi
+   NTT
+   3-9-11, Midori-Cho Musashino-Shi,
+   Tokyo  180-8585
+   JP
+
+   Email: kosugi.tomoya@lab.ntt.co.jp
+
+
+   Eric Vyncke
+   Cisco Systems, Inc.
+   De Kleetlaann 6A
+   Diegem  1831
+   Belgium
+
+   Email: evyncke@cisco.com
+
+
+   David Lebrun
+   Universite Catholique de Louvain
+   Place Ste Barbe, 2
+   Louvain-la-Neuve, 1348
+   Belgium
+
+   Email: david.lebrun@uclouvain.be
+
+
+
+
+
+
+
+
+
+
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