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Versions: 00

Network Working Group                                            H. Chen
Internet-Draft                                                 Futurewei
Intended status: Standards Track                                  M. Toy
Expires: January 7, 2020                                         Verizon
                                                                 A. Wang
                                                           China Telecom
                                                                   Z. Li
                                                            China Mobile
                                                                  L. Liu
                                                                 Fujitsu
                                                                  X. Liu
                                                          Volta Networks
                                                            July 6, 2019


                       SR Path Ingress Protection
                draft-chen-pce-sr-ingress-protection-00

Abstract

   This document describes protocol extensions and procedures for
   protecting the ingress node of a Segment Routing (SR) path.

Requirements Language

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

Status of This Memo

   This Internet-Draft is submitted in full conformance with the
   provisions of BCP 78 and BCP 79.

   Internet-Drafts are working documents of the Internet Engineering
   Task Force (IETF).  Note that other groups may also distribute
   working documents as Internet-Drafts.  The list of current Internet-
   Drafts is at https://datatracker.ietf.org/drafts/current/.

   Internet-Drafts are draft documents valid for a maximum of six months
   and may be updated, replaced, or obsoleted by other documents at any
   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   This Internet-Draft will expire on January 7, 2020.






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Copyright Notice

   Copyright (c) 2019 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  . . . . . . . . . . . . . . . . . . . . . . . .   2
   2.  Terminologies . . . . . . . . . . . . . . . . . . . . . . . .   3
   3.  SR Path Ingress Protection Example  . . . . . . . . . . . . .   3
   4.  Behavior after Ingress Failure  . . . . . . . . . . . . . . .   4
   5.  Extensions to PCE . . . . . . . . . . . . . . . . . . . . . .   5
     5.1.  Capability for SR Path Ingress Protection . . . . . . . .   5
     5.2.  SR Path Ingress Protection  . . . . . . . . . . . . . . .   6
       5.2.1.  Traffic-Description sub-TLV . . . . . . . . . . . . .   7
       5.2.2.  Primary-Ingress sub-TLV . . . . . . . . . . . . . . .  10
       5.2.3.  Service sub-TLV . . . . . . . . . . . . . . . . . . .  11
       5.2.4.  Downstream-Node sub-TLV . . . . . . . . . . . . . . .  12
   6.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  13
   7.  Security Considerations . . . . . . . . . . . . . . . . . . .  13
   8.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  13
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  13
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  13
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  14
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  15

1.  Introduction

   Fast protection of a transit node of a Segment Routing (SR) path is
   described in [I-D.bashandy-rtgwg-segment-routing-ti-lfa] and
   [I-D.hu-spring-segment-routing-proxy-forwarding].  However, these
   documents do not discuss the procedures for fast protection of the
   ingress node of an SR path.

   This document fills that void and specifies protocol extensions and
   procedures for fast protection of the ingress node of an SR path.
   Ingress node and ingress as well as fast protection and protection
   will be used exchangeably.



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2.  Terminologies

   The following terminologies are used in this document.

   SR:  Segment Routing

   SRv6:  SR for IPv6

   SRH:  Segment Routing Header

   SID:  Segment Identifier

   CE:  Customer Edge

   PE:  Provider Edge

   LFA:  Loop-Free Alternate

   TI-LFA:  Topology Independent LFA

   TE:  Traffic Engineering

   BFD:  Bidirectional Forwarding Detection

   VPN:  Virtual Private Network

   L3VPN:  Layer 3 VPN

   FIB:  Forwarding Information Base

   PLR:  Point of Local Repair

   BGP:  Border Gateway Protocol

   IGP:  Interior Gateway Protocol

   OSPF:  Open Shortest Path First

   IS-IS:  Intermediate System to Intermediate System

3.  SR Path Ingress Protection Example

   Figure 1 shows an example of protecting ingress PE1 of a SR path,
   which is from ingress PE1 to egress PE3.







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                    *******  *******
                [PE1]-----[P1]-----[PE3]
                / |        |&        | \            PE1 Ingress
               /  |        |&        |  \           CEx Customer Edge
          [CE1]   |        |&        |   [CE2]      Px  Non-Ingress
               \  |        |&        |  /           *** SR Path
                \ | &&&&&& |&        | /            &&& Backup Path
                [PE2]-----[P2]-----[PE4]

                 Figure 1: Protecting SR Path Ingress PE1

   In normal operations, CE1 sends the traffic with destination PE3 to
   ingress PE1, which imports the traffic into the SR path.

   When CE1 detects the failure of ingress PE1, it switches the traffic
   to backup ingress PE2, which imports the traffic from CE1 into a
   backup SR path.  In one option, this backup path is from the backup
   ingress PE2 to ingress PE1's next hop (or endpoint) node P1, where
   the traffic is "merged" into the SR path, and then sent to egress
   PE3.

   In another option, the backup path is from the backup ingress PE2 to
   the egress PE3.  When the traffic is imported into the backup path,
   it is sent to the egress PE3 along the path.

4.  Behavior after Ingress Failure

   After failure of the ingress of an SR path happens, there are a
   couple of different ways to detect the failure.  In each way, there
   may be some specific behavior for the traffic source (e.g., CE1) and
   the backup ingress (e.g., PE2).

   In one way, the traffic source (e.g., CE1) is responsible for fast
   detecting the failure of the ingress (e.g., PE1) of an SR path.  Fast
   detecting the failure means detecting the failure in a few or tens of
   milliseconds.  The backup ingress (e.g., PE2) is ready to import the
   traffic from the traffic source into the backup SR path installed.

   In normal operations, the source sends the traffic to the ingress of
   the SR path.  When the source detects the failure of the ingress, it
   switches the traffic to the backup ingress, which delivers the
   traffic to the egress of the SR path via the backup SR path.

   In another way, both the backup ingress and the traffic source are
   concurrently responsible for fast detecting the failure of the
   ingress of an SR path.





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   In normal operations, the source (e.g., CE1) sends the traffic to the
   ingress (e.g., PE1).  It switches the traffic to the backup ingress
   (e.g., PE2) when it detects the failure of the ingress.

   The backup ingress does not import any traffic from the source into
   the backup SR path in normal operations.  When it detects the failure
   of the ingress, it imports the traffic from the source into the
   backup SR path.

5.  Extensions to PCE

   PCC runs on each of the edge nodes of a network normally.  PCE runs
   on a server as a controller to communicate with PCCs.  PCE and PCCs
   work together to support protection for the ingress of a SR path.

5.1.  Capability for SR Path Ingress Protection

   When a PCE and a PCC establish a PCEP session between them, they
   exchange their capabilities of supporting protection for the ingress
   node of an SR path/tunnel.

   A new sub-TLV called SR_INGRESS_PROTECTION_CAPABILITY is defined.  It
   is included in the PATH_SETUP_TYPE_CAPABILITY TLV with PST = TBD1
   (suggested value 2 for backup SR path/tunnel) in the OPEN object,
   which is exchanged in Open messages when a PCC and a PCE establish a
   PCEP session between them.  Its format is illustrated below.

     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 = TBD2          |           Length=4            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           Reserved            |        Flags              |D|A|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

            Figure 2: SR_INGRESS_PROTECTION_CAPABILITY sub-TLV

   Type:  TBD2 is to be assigned by IANA.

   Length:  4.

   Reserved:  2 octets.  Must be set to zero in transmission and ignored
      on reception.

   Flags:  2 octets.  Two flags are defined.

      o  D flag: A PCC sets this flag to 1 to indicate that it is able
         to detect its adjacent node's failure quickly.



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      o  A flag: A PCE sets this flag to 1 to request a PCC to let the
         forwarding entry for the backup SR path/tunnel be Active.

   A PCC, which supports ingress protection for a SR tunnel/path, sends
   a PCE an Open message containing SR_INGRESS_PROTECTION_CAPABILITY
   sub-TLV.  This sub-TLV indicates that the PCC is capable of
   supporting the ingress protection for a SR tunnel/path.

   A PCE, which supports ingress protection for a SR tunnel/path, sends
   a PCC an Open message containing SR_INGRESS_PROTECTION_CAPABILITY
   sub-TLV.  This sub-TLV indicates that the PCE is capable of
   supporting the ingress protection for a SR tunnel/path.

   Assume that both a PCC and a PCE support SR_PCE_CAPABILITY, that is
   that each of the Open messages sent by the PCC and PCE contains PATH-
   SETUP-TYPE-CAPABILITY TLV with a PST list containing PST=1 and a SR-
   PCE-CAPABILITY sub-TLV.

   If a PCE receives an Open message without a
   SR_INGRESS_PROTECTION_CAPABILITY sub-TLV from a PCC, then the PCE
   MUST not send the PCC any request for ingress protection of a SR
   path/tunnel.

   If a PCC receives an Open message without a
   SR_INGRESS_PROTECTION_CAPABILITY sub-TLV from a PCE, then the PCC
   MUST ignore any request for ingress protection of a SR path/tunnel
   from the PCE.

   If a PCC sets D flag to zero, then the PCE SHOULD send the PCC an
   Open message with A flag set to one.  When the PCE sends the PCC a
   message for initiating a backup SR path/tunnel, the PCC SHOULD let
   the forwarding entry for the backup SR path/tunnel be Active.

5.2.  SR Path Ingress Protection

   A new sub-TLV called SR_INGRESS_PROTECTION is defined.  When a PCE
   sends a PCC a PCInitiate message for initiating a backup SR path/
   tunnel to protect the primary ingress node of a primary SR path/
   tunnel, the message contains this TLV in the RP/SRP object.  Its
   format is illustrated below.











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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 = TBD3           |        Length (variable)      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |           Reserved            |        Flags                |A|
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                                                               ~
    ~                        sub-TLVs (optional)                    ~
    ~                                                               ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                  Figure 3: SR_INGRESS_PROTECTION sub-TLV

   Type:  TBD3 is to be assigned by IANA.

   Length:  Variable.

   Reserved:  2 octets.  Must be set to zero in transmission and ignored
      on reception.

   Flags:  2 octets.  One flag is defined.

      o  A flag: A PCE sets this flag to 1 to request a PCC to let the
         forwarding entry for the backup SR path/tunnel be Active.

   Four optional sub-TLVs are defined.

5.2.1.  Traffic-Description sub-TLV

   A Traffic-Description sub-TLV describes the traffic to be imported
   into a backup SR path/tunnel.  Its format is illustrated below.

     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 = TBD4           |        Length (variable)      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~                                                               ~
    ~                        sub-TLVs (optional)                    ~
    ~                                                               ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 4: Traffic-Description sub-TLV

   Type:  TBD4 is to be assigned by IANA.

   Length:  Variable.



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   Two optional sub-TLVs are defined.  One is FEC sub-TLV and the other
   interface sub-TLV.

   A FEC sub-TLV describes the traffic to be imported into the backup SR
   path/tunnel.  It is an IP prefix with an optional virtual network ID.
   It has two formats: one for IPv4 and the other for IPv6, which are
   illustrated below.

     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 = TBD5           |        Length (variable)      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |IPv4 Prefix Len|          IPv4 Prefix                          ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~   (Optional) Virtual Network ID (2 octets)                    ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 5: IPv4 FEC sub-TLV

   Type:  TBD5 is to be assigned by IANA.

   Length:  Variable.

   IPv4 Prefix Len:  Indicates the length of the IPv4 Prefix.

   IPv4 Prefix:  IPv4 Prefix rounded to octets.

   Virtual Network ID:  2 octets.  This is optional.  It indicates the
      ID of a virtual network.

     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 = TBD6           |        Length (variable)      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |IPv6 Prefix Len|          IPv6 Prefix                          ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    ~   Optional Virtual Network ID (2 octets)                      ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                        Figure 6: IPv6 FEC sub-TLV

   Type:  TBD6 is to be assigned by IANA.

   Length:  Variable.

   IPv6 Prefix Len:  Indicates the length of the IPv6 Prefix.



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   IPv6 Prefix:  IPv6 Prefix rounded to octets.

   Virtual Network ID:  2 octets.  This is optional.  It indicates the
      ID of a virtual network.

   An Interface sub-TLV indicates the interface from which the traffic
   is received and imported into the backup SR path/tunnel.  It has
   three formats: one for interface index, the other two for IPv4 and
   IPv6 address, which are illustrated below.

     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 = TBD7           |          Length (4)           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                   Interface Index (4 octets)                  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 7: Interface Index sub-TLV

   Type:  TBD7 is to be assigned by IANA.

   Length:  4.

   Interface Index:  4 octets.  It indicates the index of an interface.

     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 = TBD8           |          Length (4)           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               Interface IPv4 Address (4 octets)               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 8: Interface IPv4 Address sub-TLV

   Type:  TBD8 is to be assigned by IANA.

   Length:  4.

   Interface IPv4 Address:  4 octets.  It represents the IPv4 address of
      an interface.









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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 = TBD9           |         Length (16)           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |               Interface IPv6 Address (16 octets)              |
    ~                                                               ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                 Figure 9: Interface IPv6 Address sub-TLV

   Type:  TBD9 is to be assigned by IANA.

   Length:  16.

   Interface IPv6 Address:  16 octets.  It represents the IPv6 address
      of an interface.

5.2.2.  Primary-Ingress sub-TLV

   A Primary-Ingress sub-TLV indicates the IP address of the primary
   ingress node of a primary SR path/tunnel.  It has two formats: one
   for primary ingress node IPv4 address and the other for primary
   ingress node IPv6 address, which are illustrated below.

     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 = TBDa           |          Length (4)           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |            Primary Ingress IPv4 Address (4 octets)            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 10: Primary Ingress IPv4 Address sub-TLV

   Type:  TBDa is to be assigned by IANA.

   Length:  4.

   Primary Ingress IPv4 Address:  4 octets.  It represents an IPv4 host
      address of the primary ingress node of a SR path/tunnel.










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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 = TBDb           |         Length (16)           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |            Primary Ingress IPv6 Address (16 octets)           |
    ~                                                               ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 11: Primary Ingress IPv6 Address sub-TLV

   Type:  TBDb is to be assigned by IANA.

   Length:  16.

   Primary Ingress IPv6 Address:  16 octets.  It represents an IPv6 host
      address of the primary ingress node of a SR path/tunnel.

5.2.3.  Service sub-TLV

   A Service sub-TLV contains a service ID or label to be added into a
   packet to be carried by a SR path/tunnel.  It has two formats: one
   for the service identified by a label and the other for the service
   identified by a service identifier (ID) of 32 or 128 bits, which are
   illustrated below.

     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 = TBDc           |          Length (4)           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        zero           |       Service Label (20 bits)         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                     Figure 12: Service Label sub-TLV

   Type:  TBDc is to be assigned by IANA.

   Length:  4.

   Service Label:  the least significant 20 bits.  It represents a label
      of 20 bits.









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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 = TBDd           |         Length (4/16)         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                        Service ID (4 or 16 octets)            |
    ~                                                               ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 13: Service ID sub-TLV

   Type:  TBDd is to be assigned by IANA.

   Length:  4 or 16.

   Service ID:  4 or 16 octets.  It represents Identifier (ID) of a
      service in 4 or 16 octets.

5.2.4.  Downstream-Node sub-TLV

   A Downstream-Node sub-TLV gives the IP address of the downstream
   endpoint node of the primary ingress along the primary SR path/
   tunnel.  It has two formats: one for downstream node IPv4 address and
   the other for downstream node IPv6 address, which are illustrated
   below.

     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 = TBDe           |          Length (4)           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |            Downstream Node IPv4 Address (4 octets)            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 14: Downstream-Node IPv4 Address sub-TLV

   Type:  TBDe is to be assigned by IANA.

   Length:  4.

   Downstream Node IPv4 Address:  4 octets.  It represents an IPv4 host
      address of the downstream endpoint node of the primary ingress
      node of a SR path/tunnel.








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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 = TBDf           |         Length (16)           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |            Downstream Node IPv6 Address (16 octets)           |
    ~                                                               ~
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

              Figure 15: Downstream-Node IPv6 Address sub-TLV

   Type:  TBDf is to be assigned by IANA.

   Length:  16.

   Downstream Node IPv6 Address:  4 octets.  It represents an IPv6 host
      address of the downstream endpoint node of the primary ingress
      node of a SR path/tunnel.

6.  IANA Considerations

   TBD

7.  Security Considerations

   TBD

8.  Acknowledgements

   TBD

9.  References

9.1.  Normative References

   [I-D.bashandy-isis-srv6-extensions]
              Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
              Z. Hu, "IS-IS Extensions to Support Routing over IPv6
              Dataplane", draft-bashandy-isis-srv6-extensions-05 (work
              in progress), March 2019.

   [I-D.hu-spring-segment-routing-proxy-forwarding]
              Hu, Z., Chen, H., Yao, J., Bowers, C., and Y. Zhu, "SR-TE
              Path Midpoint Protection", draft-hu-spring-segment-
              routing-proxy-forwarding-03 (work in progress), April
              2019.





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   [I-D.ietf-isis-segment-routing-extensions]
              Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
              Gredler, H., and B. Decraene, "IS-IS Extensions for
              Segment Routing", draft-ietf-isis-segment-routing-
              extensions-25 (work in progress), May 2019.

   [I-D.ietf-ospf-segment-routing-extensions]
              Psenak, P., Previdi, S., Filsfils, C., Gredler, H.,
              Shakir, R., Henderickx, W., and J. Tantsura, "OSPF
              Extensions for Segment Routing", draft-ietf-ospf-segment-
              routing-extensions-27 (work in progress), December 2018.

   [I-D.li-ospf-ospfv3-srv6-extensions]
              Li, Z., Hu, Z., Cheng, D., Talaulikar, K., and P. Psenak,
              "OSPFv3 Extensions for SRv6", draft-li-ospf-
              ospfv3-srv6-extensions-03 (work in progress), March 2019.

   [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>.

   [RFC7356]  Ginsberg, L., Previdi, S., and Y. Yang, "IS-IS Flooding
              Scope Link State PDUs (LSPs)", RFC 7356,
              DOI 10.17487/RFC7356, September 2014,
              <https://www.rfc-editor.org/info/rfc7356>.

9.2.  Informative References

   [I-D.bashandy-rtgwg-segment-routing-ti-lfa]
              Bashandy, A., Filsfils, C., Decraene, B., Litkowski, S.,
              Francois, P., daniel.voyer@bell.ca, d., Clad, F., and P.
              Camarillo, "Topology Independent Fast Reroute using
              Segment Routing", draft-bashandy-rtgwg-segment-routing-ti-
              lfa-05 (work in progress), October 2018.

   [I-D.hegde-spring-node-protection-for-sr-te-paths]
              Hegde, S., Bowers, C., Litkowski, S., Xu, X., and F. Xu,
              "Node Protection for SR-TE Paths", draft-hegde-spring-
              node-protection-for-sr-te-paths-05 (work in progress),
              July 2019.

   [I-D.ietf-spring-segment-routing-policy]
              Filsfils, C., Sivabalan, S., daniel.voyer@bell.ca, d.,
              bogdanov@google.com, b., and P. Mattes, "Segment Routing
              Policy Architecture", draft-ietf-spring-segment-routing-
              policy-03 (work in progress), May 2019.




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   [I-D.sivabalan-pce-binding-label-sid]
              Sivabalan, S., Filsfils, C., Tantsura, J., Hardwick, J.,
              Previdi, S., and C. Li, "Carrying Binding Label/Segment-ID
              in PCE-based Networks.", draft-sivabalan-pce-binding-
              label-sid-06 (work in progress), February 2019.

   [RFC5462]  Andersson, L. and R. Asati, "Multiprotocol Label Switching
              (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
              Class" Field", RFC 5462, DOI 10.17487/RFC5462, February
              2009, <https://www.rfc-editor.org/info/rfc5462>.

Authors' Addresses

   Huaimo Chen
   Futurewei
   Boston, MA
   USA

   Email: Huaimo.chen@futurewei.com


   Mehmet Toy
   Verizon
   USA

   Email: mehmet.toy@verizon.com


   Aijun Wang
   China Telecom
   Beiqijia Town, Changping District
   Beijing  102209
   China

   Email: wangaj.bri@chinatelecom.cn


   Zhenqiang Li
   China Mobile
   32 Xuanwumen West Ave, Xicheng District
   Beijing  100053
   China

   Email: lizhengqiang@chinamobile.com







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   Lei Liu
   Fujitsu
   USA

   Email: liulei.kddi@gmail.com


   Xufeng Liu
   Volta Networks
   McLean, VA
   USA

   Email: xufeng.liu.ietf@gmail.com






































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