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Network Working Group                                              Z. Li
Internet-Draft                                                     Z. Hu
Intended status: Standards Track                                D. Cheng
Expires: May 7, 2020                                 Huawei Technologies
                                                           K. Talaulikar
                                                               P. Psenak
                                                           Cisco Systems
                                                        November 4, 2019

                       OSPFv3 Extensions for SRv6
                draft-li-ospf-ospfv3-srv6-extensions-07

Abstract

   Segment Routing (SR) allows for a flexible definition of end-to-end
   paths by encoding paths as sequences of topological sub-paths, called
   "segments".  Segment routing architecture can be implemented over an
   MPLS data plane as well as an IPv6 data plane.  This draft describes
   the OSPFv3 extensions required to support Segment Routing over an
   IPv6 data plane (SRv6).

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 May 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.  SRv6-Capabilities TLV . . . . . . . . . . . . . . . . . . . .   3
   3.  Advertisement of Supported Algorithms . . . . . . . . . . . .   5
   4.  Advertisement of SRH Operation Limits . . . . . . . . . . . .   5
   5.  Advertisement of SRv6 Locator and End SIDs  . . . . . . . . .   5
   6.  SRv6 Locator LSA  . . . . . . . . . . . . . . . . . . . . . .   6
     6.1.  SRv6 Locator TLV  . . . . . . . . . . . . . . . . . . . .   8
   7.  Advertisment of SRv6 End SIDs . . . . . . . . . . . . . . . .  10
   8.  Advertisment of SRv6 SIDs Associated with Adjacencies . . . .  11
     8.1.  SRv6 End.X SID Sub-TLV  . . . . . . . . . . . . . . . . .  12
     8.2.  SRv6 LAN End.X SID Sub-TLV  . . . . . . . . . . . . . . .  14
   9.  SRv6 SID Structure sub-TLV  . . . . . . . . . . . . . . . . .  15
   10. Security Considerations . . . . . . . . . . . . . . . . . . .  16
   11. IANA Considerations . . . . . . . . . . . . . . . . . . . . .  16
     11.1.  OSPF Router Information TLVs . . . . . . . . . . . . . .  17
     11.2.  OSPFv3 LSA Function Codes  . . . . . . . . . . . . . . .  17
     11.3.  OSPFv3 Extended-LSA sub-TLVs . . . . . . . . . . . . . .  17
     11.4.  OSPFv3 Locator LSA TLVs  . . . . . . . . . . . . . . . .  17
     11.5.  OSPFv3 Locator LSA sub-TLVs  . . . . . . . . . . . . . .  18
   12. Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  18
   13. References  . . . . . . . . . . . . . . . . . . . . . . . . .  19
     13.1.  Normative References . . . . . . . . . . . . . . . . . .  19
     13.2.  Informative References . . . . . . . . . . . . . . . . .  20
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  21

1.  Introduction

   Segment Routing (SR) architecture [RFC8402] specifies how a node can
   steer a packet through an ordered list of instructions, called
   segments.  These segments are identified through Segment Identifiers
   (SIDs).

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   Segment Routing can be instantiated on the IPv6 data plane through
   the use of the Segment Routing Header (SRH) defined in
   [I-D.ietf-6man-segment-routing-header].  SRv6 refers to this SR
   instantiation on the IPv6 dataplane.  The network programming
   paradigm for SRv6 is specified in
   [I-D.ietf-spring-srv6-network-programming] which describes several
   well-known functions that can be bound to SRv6 SIDs.

   This document specifies extensions to OSPFv3 in order to support SRv6
   as defined in [I-D.ietf-spring-srv6-network-programming] by signaling
   the SRv6 capabilities of the node and certain SRv6 SIDs with their
   endpoint behaviors (e.g.  End, End.X, etc.) that are instantiated on
   the SRv6 capable router.

   At a high level, the extensions to OSPFv3 comprise of the following:

   1.  SRv6 Capabilities TLV to advertise the support for SRv6 features
       and SRH operations supported by the router

   2.  SRv6 Locator TLV to advertise the SRv6 Locator - a form of
       summary address for the algorithm specific SIDs associated with
       the router

   3.  TLVs and sub-TLVs to advertise the SRv6 SIDs instantiated on the
       router along with their endpoint behaviors

2.  SRv6-Capabilities TLV

   When Segment Routing (SR) is instantiated using the IPv6 data plane
   (SRv6), the list of segments is expressed using the segment routing
   header (SRH) as defined in [I-D.ietf-6man-segment-routing-header].

   A router that supports SRv6 MUST be able to process the SRH as
   described in [I-D.ietf-6man-segment-routing-header], as well as apply
   endpoint behaviors as described in
   [I-D.ietf-spring-srv6-network-programming].

   The SRv6 Capabilities TLV is designed for an OSPFv3 router to
   advertise its SRv6 support along with its related capabilities for
   SRv6 functionality.  This is a new optional top level TLV of OSPFv3
   Router Information LSA [RFC7770] which MUST be advertised by a SRv6
   enabled router.

   This TLV SHOULD be advertised only once in the OSPFv3 Router
   Information LSA.  When multiple SRv6 Capabilities TLVs are received
   from a given router, the receiver MUST use the first occurrence of
   the TLV in the OSPFV3 Router Information Opaque LSA.  If the SRv6
   Capabilities TLV appears in multiple OSPFv3 Router Information Opaque

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   LSAs that have different flooding scopes, the TLV in the OSPFv3
   Router Information Opaque LSA with the area-scoped flooding scope
   MUST be used.  If the SRv6 Capabilities TLV appears in multiple
   OSPFv3 Router Information Opaque LSAs that have the same flooding
   scope, the TLV in the OSPFv3 Router Information Opaque LSA with the
   numerically smallest Instance ID MUST be used and subsequent
   instances of the TLV MUST be ignored.

   The OSPFv3 Router Information Opaque LSA can be advertised at any of
   the defined opaque flooding scopes (link, area, or Autonomous System
   (AS)).  For the purpose of SRv6 Capabilities TLV advertisement, area-
   scoped flooding is REQUIRED.

   The format of OSPFv3-SRv6-Capabilities TLV is shown 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            |          Length               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |             Flags             |            Reserved           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Sub-TLVs...
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:

   o  Type: 16 bit field.  TBD

   o  Length: 16 bit field.  Length of Capability TLV + length of Sub-
      TLVs

   o  Reserved : 16 bit field.  SHOULD be set to 0 and MUST be ignored
      by receiver.

   o  Flags: 16 bit field.  The following flags are defined:

             0                   1
             0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
            | |O|                           |
            +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

      where:

      *  O-flag: If set, then router is capable of supporting SRH O-bit,
         as specified in [I-D.ali-spring-srv6-oam].

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   The SRv6 Capabilities TLV may contain optional sub-TLVs.  No sub-TLVs
   are currently defined.

3.  Advertisement of Supported Algorithms

   SRv6 enabled OSPFv3 router advertises its algorithm support using the
   SR Algorithm TLV defined in
   [I-D.ietf-ospf-segment-routing-extensions] as described in
   [I-D.ietf-ospf-ospfv3-segment-routing-extensions].

4.  Advertisement of SRH Operation Limits

   A SRv6 enabled router may have different capabilities and limits when
   it comes to SRH processing and this needs to be advertised to other
   routers in the SRv6 domain.

   [RFC8476] defines the means to advertise node/link specific values
   for Maximum SID Depths (MSD) of various types.  Node MSDs are
   advertised using the Node MSD TLV in the OSPFv3 Router Information
   LSA [RFC7770] while Link MSDs are advertised using the Link MSD sub-
   TLV of the E-Router-LSA TLV [RFC8362].  The format of the MSD types
   for OSPFv3 is defined in [RFC8476].

   The MSD types for SRv6 that are defined in
   [I-D.ietf-lsr-isis-srv6-extensions] for IS-IS are also used by
   OSPFv3.  These MSD Types are allocated under the IGP MSD Types
   registry maintained by IANA that are shared by IS-IS and OSPF.

5.  Advertisement of SRv6 Locator and End SIDs

   An SRv6 Segment Identifier (SID) is 128 bits and represented as
   LOC:FUNCT as described in [I-D.ietf-spring-srv6-network-programming].

   A node is provisioned with algorithm specific locators for each
   algorithm supported by that node.  Each locator is a covering prefix
   for all SIDs provisioned on that node which have the matching
   algorithm.

   Locators MUST be advertised in the SRv6 Locator LSA (see Section 6).
   Forwarding entries for the locators advertised in the SRv6 Locator
   LSA MUST be installed in the forwarding plane of receiving SRv6
   capable routers when the associated algorithm is supported by the
   receiving node.  Locators can be of different route types similar to
   existing OSPF LSA route types - Intra-Area, Inter-Area, External and
   NSSA.  The computation of locator reachability and their
   advertisement are similar to how normal OSPF prefix reachability LSAs
   are processed as part of the SPF computation.

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   Locators are routable and MAY also be advertised via Prefix LSAs of
   different types - Inter-Area Prefix LSA, AS-External LSA, NSSA LSA or
   Intra-Area Prefix LSA (or their equivalent extended LSAs [RFC8362]).
   Locators associated with Flexible Algorithms SHOULD NOT be advertised
   via Prefix LSAs.  Locators associated with algorithm 0 (for all
   supported topologies) SHOULD be advertised in Prefix LSAs so that
   legacy routers (i.e., routers which do NOT support SRv6) will install
   a forwarding entry for algorithm 0 SRv6 traffic.

   In cases where a locator advertisement is received in both in a
   Prefix LSA and an SRv6 Locator LSA, the Prefix LSA advertisement MUST
   be preferred when installing entries in the forwarding plane.  This
   is to prevent inconsistent forwarding entries on SRv6 capable/SRv6
   incapable routers.

   SRv6 SIDs are advertised as sub-TLVs in the SRv6 Locator TLV except
   for SRv6 End.X SIDs/LAN End.X SIDs which are associated with a
   specific Neighbor/Link and are therefore advertised as sub-TLVs of E-
   Router-Link TLV.

   SRv6 SIDs are not directly routable and MUST NOT be installed in the
   forwarding plane.  Reachability to SRv6 SIDs depends upon the
   existence of a covering locator.  Adherence to the rules defined in
   this section will assure that SRv6 SIDs associated with a supported
   algorithm will be forwarded correctly, while SRv6 SIDs associated
   with an unsupported algorithm will be dropped.  NOTE: The drop
   behavior depends on the absence of a default/summary route covering a
   given locator.

6.  SRv6 Locator LSA

   The SRv6 Locator LSA has a function code of TBD while the S1/S2 bits
   are dependent on the desired flooding scope for the LSA.  The
   flooding scope of the SRv6 Locator LSA depends on the scope of the
   advertised SRv6 Locator and is under the control of the advertising
   router.  The U bit will be set indicating that the LSA should be
   flooded even if it is not understood.

   Multiple SRv6 Locator LSAs can be advertised by an OSPFv3 router and
   they are distinguished by their Link State IDs (which are chosen
   arbitrarily by the originating router).

   The format of SRv6 Locator LSA is shown 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
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |            LS age             |1|S12|   Function Code         |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       Link State ID                           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       Advertising Router                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                       LS sequence number                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |        LS checksum            |            Length             |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                                                               |
    +-                            TLVs                             -+
    |                             ...                               |

                        Figure 1: SRv6 Locator LSA

   The format of the TLVs within the body of the SRv6 Locator LSA is the
   same as the format used by [RFC3630].  The variable TLV section
   consists of one or more nested TLV tuples.  Nested TLVs are also
   referred to as sub- TLVs.  The format of each TLV is:

     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            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                            Value                              |
                                   o
                                   o
                                   o
    |                                                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 2: SRv6 Locator LSA TLV Format

   The Length field defines the length of the value portion in octets
   (thus, a TLV with no value portion would have a length of 0).  The
   TLV is padded to 4-octet alignment; padding is not included in the
   Length field (so a 3-octet value would have a length of 3, but the
   total size of the TLV would be 8 octets).  Nested TLVs are also
   32-bit aligned.  For example, a 1-byte value would have the Length
   field set to 1, and 3 octets of padding would be added to the end of
   the value portion of the TLV.  The padding is composed of zeros.

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6.1.  SRv6 Locator TLV

   The SRv6 Locator TLV is a top-level TLV of the SRv6 Locator LSA that
   is used to advertise a SRv6 Locator, its attributes and SIDs
   associated with it.  Multiple SRv6 Locator TLVs MAY be advertised in
   each SRv6 Locator LSA.  However, since the S12 bits define the
   flooding scope, the LSA flooding scope MUST satisfy the application-
   specific requirements for all the locators included in a single SRv6
   Locator LSA.

   When multiple SRv6 Locator TLVs are received from a given router in a
   SRv6 Locator LSA for the same Locator, the receiver MUST use the
   first occurrence of the TLV in the LSA.  If the SRv6 Locator TLV for
   the same Locator appears in multiple SRv6 Locator LSAs that have
   different flooding scopes, the TLV in the SRv6 Locator LSA with the
   area-scoped flooding scope MUST be used.  If the SRv6 Locator TLV for
   the same Locator appears in multiple SRv6 Locator LSAs that have the
   same flooding scope, the TLV in the SRv6 Locator LSA with the
   numerically smallest Link-State ID MUST be used and subsequent
   instances of the TLV MUST be ignored.

   The format of SRv6 Locator TLV is shown 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             |             Length            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |  Route Type   |  Algorithm    | Locator Length|    Flags      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                             Metric                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Locator (128 bits) ...                                      |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Locator cont ...                                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Locator cont ...                                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Locator cont ...                                            |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |                      Sub-TLVs (variable)                      |
    +-                                                             -+
    |                             ...                               |

                        Figure 3: SRv6 Locator TLV

   Where:

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      Type: 16 bit field.  The value is 1 for this type.

      Length: 16 bit field.  The total length of the value portion of
      the TLV including sub-TLVs.

      Route Type : 8 bit field.  The type of the locator route.
      Supported types are the ones listed below and other other types
      MUST be ignored by the receiver.

     1 - Intra-Area
     2 - Inter-Area
     3 - AS External
     4 - NSSA External

                                 Figure 4

      Algorithm: 8 bit field.  Associated algorithm.  Algorithm values
      are defined in the IGP Algorithm Type registry.

      Locator Length: 8 bit field.  Carries the length of the Locator
      prefix as number of bits (1-128).

      Flags: 8 bit field.  The following flags are defined

          0 1 2 3 4 5 6 7
         +-+-+-+-+-+-+-+-+
         |N|A| Reserved  |
         +-+-+-+-+-+-+-+-+

                                 Figure 5

      *  N flag : When the locator uniquely identifies a node in the
         network (i.e. it is provisioned on one and only one node), the
         N bit MUST be set.  Otherwise, this bit MUST be clear.

      *  A bit : When the Locator is configured as anycast, the A bit
         SHOULD be set.  Otherwise, this bit MUST be clear.

      *  Other flags are not defined and SHOULD be set to 0 and MUST be
         ignored on receipt.

      Metric : 32 bit field.  The metric value associated with the
      locator.

      Locator : 16 octets.  This field encodes the advertised SRv6
      Locator.

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      Sub-TLVs : Used to advertise sub-TLVs that provide additional
      attributes for the given SRv6 Locator and SRv6 SIDs associated
      with it.

7.  Advertisment of SRv6 End SIDs

   SRv6 End SID sub-TLV is a new sub-TLV of SRv6 Locator TLV in the SRv6
   Locator LSA (defined in Section 6).  It is used to advertise the SRv6
   SIDs belonging to the node along with their associated functions.
   SIDs associated with adjacencies are advertised as described in
   Section 8.  Every SRv6 enabled OSPFv3 router SHOULD advertise at
   least one SRv6 SID associated with an END behavior for its node as
   specified in [I-D.ietf-spring-srv6-network-programming].

   SRv6 End SIDs inherit the algorithm from the parent locator.  The
   SRv6 End SID MUST be a subnet of the associated Locator.  SRv6 End
   SIDs which are NOT a subnet of the associated locator MUST be
   ignored.

   The router MAY advertise multiple instances of the SRv6 End SID sub-
   TLV within the SRv6 Locator TLV - one for each of the SRv6 SIDs to be
   advertised.  When multiple SRv6 End SID sub-TLVs are received in the
   SRv6 Locator TLV from a given router for the same SRv6 SID value, the
   receiver MUST use the first occurrence of the sub-TLV in the SRv6
   Locator TLV.

   The format of SRv6 End SID sub-TLV is shown 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            |          Length               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |     Flags     |   Reserved    |       Endpoint Behavior ID    |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID (128 bits) ...                                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Sub-Sub-TLVs (variable) . . .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                      Figure 6: SRv6 End SID sub-TLV

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   Where:

      Type: 16 bit field.  Value is 1 for this type.

      Length: 16 bit field.  The total length of the value portion of
      the sub-TLV including sub-sub-TLVs.

      Reserved : 8 bit field.  Should be set to 0 and MUST be ignored on
      receipt.

      Flags: 8 bit field which define the flags associated with the SID.
      No flags are currently defined and SHOULD be set to 0 and MUST be
      ignored on receipt.

      Endpoint Behavior ID: 16 bit field.  The endpoint behavior code
      point for this SRv6 SID as defined in
      [I-D.ietf-spring-srv6-network-programming].

      SID : 16 octets.  This field encodes the advertised SRv6 SID.

      Sub-Sub-TLVs : Used to advertise sub-sub-TLVs that provide
      additional attributes for the given SRv6 SID.

8.  Advertisment of SRv6 SIDs Associated with Adjacencies

   The SRv6 endpoint behaviors are defined in
   [I-D.ietf-spring-srv6-network-programming] include certain behaviors
   which are specific to links or adjacencies.  The most basic of this
   which is critical for link state routing protocols like OSPFv3 is the
   End.X behavior that is an instruction to forward to a specific
   neighbor on a specific link.  These SRv6 SIDs along with others that
   are defined in [I-D.ietf-spring-srv6-network-programming] which are
   specific to links or adjacencies need to be advertised by OSPFv3 so
   that this information is available with all routers in the area to
   influence the packet path via these SRv6 SIDs over the specific
   adjacencies.

   The advertising of SRv6 SIDs and their behaviors that are specific to
   a particular neighbor are done via two different optional sub-TLVs of
   the E-Router-Link TLV defined in [RFC8362] as follows:

   o  SRv6 End.X SID Sub-TLV: for OSPFv3 adjacency over point-to-point
      or point-to-multipoint links and the adjacency to the Designated
      Router (DR) over broadcast and non-broadcast-multi-access (NBMA)
      links.

   o  SRv6 LAN End.X SID Sub-TLV: for OSPFv3 adjacency on broadcast and
      NBMA links to the Backup DR and DR-Other neighbors.  This sub-TLV

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      includes the OSPFv3 router-id of the neighbor and thus allows for
      multiple instances of this TLV for each neighbor to be explicitly
      advertised under the E-Router-Link TLV for the same link.

   Every SRv6 enabled OSPFv3 router SHOULD instantiate at least one
   End.X function with a unique SRv6 SID corresponding to each of its
   neighbor.  A router MAY instantiate more than one SRv6 SID for the
   End.X function for a single neighbor.  The same SRv6 SID MAY be
   advertised for the End.X function corresponding to more than one
   neighbor.  Thus multiple instances of the SRv6 End.X SID and SRv6 LAN
   End.X SID sub-TLVs MAY be advertised within the E-Router-Link TLV for
   a single link.

   All End.X SIDs MUST be a subnet of a Locator with matching algorithm
   which is advertised by the same node in an SRv6 Locator TLV.  End.X
   SIDs which do not meet this requirement MUST be ignored.

8.1.  SRv6 End.X SID Sub-TLV

   The format of the SRv6 End.X SID sub-TLV is shown 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            |          Length               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      Endpoint Behaviour ID    |     Flags     |   Reserved1   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Algorithm   |    Weight     |           Reserved2           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID (128 bits) ...                                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    Sub-TLVs (variable) . . .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where:

      Type is TBD

      Length: 16 bit field.  The total length of the value portion of
      the TLV.

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      Endpoint Behaviour ID: 16 bit field.  The code point for the
      endpoint behavior for this SRv6 SID as defined in
      [I-D.ietf-spring-srv6-network-programming].

      Flags: 8 bit field with the following definition:

    0 1 2 3 4 5 6 7
   +-+-+-+-+-+-+-+-+
   |B|S|P|   Rsvd  |
   +-+-+-+-+-+-+-+-+

      *  B-Flag: Backup Flag.  If set, the SID refers to a path that is
         eligible for protection.

      *  S-Flag: Set Flag.  When set, the S-Flag indicates that the
         End.X SID refers to a set of adjacencies (and therefore MAY be
         assigned to other adjacencies as well).

      *  P-Flag: Persistent Flag: If set, the SID is persistently
         allocated, i.e., the SID value remains consistent across router
         restart and session/interface flap.

      *  Rsvd bits: Reserved for future use and MUST be zero when
         originated and ignored when received.

      Reserved1 : 8 bit field.  Should be set to 0 and MUST be ignored
      on receipt.

      Algorithm : 8 bit field.  Associated algorithm.  Algorithm values
      are defined in the IGP Algorithm Type registry.

      Weight: 8 bit field whose value represents the weight of the End.X
      SID for the purpose of load balancing.  The use of the weight is
      defined in [RFC8402].

      Reserved2 : 16 bit field.  Should be set to 0 and MUST be ignored
      on receipt.

      SID: 16 octets.  This field encodes the advertised SRv6 SID.

      Sub-TLVs : Used to advertise sub-TLVs that provide additional
      attributes for the given SRv6 End.X SID.

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8.2.  SRv6 LAN End.X SID Sub-TLV

   The format of the SRv6 LAN End.X SID sub-TLV is as shown 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            |          Length               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |      Endpoint Behaviour       |     Flags     |   Reserved1   |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   Algorithm   |    Weight     |           Reserved2           |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    OSPFv3 Router-ID of neighbor                               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID (128 bits) ...                                          |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |   SID cont ...                                                |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    | Sub-TLVs (variable) . . .
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

   Where

   o  Type: TBD

   o  Length: 16 bit value.  Variable

   o  Endpoint Behaviour: 16 bit field.  The code point for the endpoint
      behavior for this SRv6 SID as defined in
      [I-D.ietf-spring-srv6-network-programming].

   o  SID Flags: 8 bit field which define the flags associated with the
      SID.  No flags are currently defined and SHOULD be set to 0 and
      MUST be ignored on receipt.

   o  Flags: 8 bit field with the following definition:

    0 1 2 3 4 5 6 7
   +-+-+-+-+-+-+-+-+
   |B|S|P|   Rsvd  |
   +-+-+-+-+-+-+-+-+

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      *  B-Flag: Backup Flag.  If set, the SID refers to a path that is
         eligible for protection.

      *  S-Flag: Set Flag.  When set, the S-Flag indicates that the
         End.X SID refers to a set of adjacencies (and therefore MAY be
         assigned to other adjacencies as well).

      *  P-Flag: Persistent Flag: If set, the SID is persistently
         allocated, i.e., the SID value remains consistent across router
         restart and session/interface flap.

      *  Rsvd bits: Reserved for future use and MUST be zero when
         originated and ignored when received.

   o  Reserved1 : 8 bit field.  Should be set to 0 and MUST be ignored
      on receipt.

   o  Algorithm : 8 bit field.  Associated algorithm.  Algorithm values
      are defined in the IGP Algorithm Type registry.

   o  Weight: 8 bit field whose value represents the weight of the End.X
      SID for the purpose of load balancing.  The use of the weight is
      defined in [RFC8402].

   o  Reserved2 : 16 bit field.  Should be set to 0 and MUST be ignored
      on receipt.

   o  Neighbor ID : 4 octets of OSPFv3 Router-id of the neighbor

   o  SID: 16 octets.  This field encodes the advertised SRv6 SID.

   o  Sub-TLVs : Used to advertise sub-TLVs that provide additional
      attributes for the given SRv6 SID.

9.  SRv6 SID Structure sub-TLV

   SRv6 SID Structure sub-TLV is used to advertise the length of each
   individual part of the SRv6 SID as defined in
   [I-D.ietf-spring-srv6-network-programming].  It is used as an
   optional sub-sub-TLV of the following:

   o  SRv6 End SID sub-TLV (refer Section 7)

   o  SRv6 End.X SID sub-TLV (refer Section 8.1)

   o  SRv6 LAN End.X SID sub-TLV (refer Section 8.2)

   The sub-TLV 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               |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
    |    LB Length  |  LN Length    | Fun. Length   |  Arg. Length  |
    +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                   Figure 7: SRv6 SID Structure sub-TLV

   Where:

      Type: 2 octet field with value TBD, see Section 11.

      Length: 2 octet field with the value 4.

      LB Length: 1 octet field.  SRv6 SID Locator Block length in bits.

      LN Length: 1 octet field.  SRv6 SID Locator Node length in bits.

      Function Length: 1 octet field.  SRv6 SID Function length in bits.

      Argument Length: 1 octet field.  SRv6 SID Argument length in bits.

10.  Security Considerations

   Existing security extensions as described in [RFC5340] and [RFC8362]
   apply to these SRv6 extensions.  While OSPFv3 is under a single
   administrative domain, there can be deployments where potential
   attackers have access to one or more networks in the OSPFv3 routing
   domain.  In these deployments, stronger authentication mechanisms
   such as those specified in [RFC4552] SHOULD be used.

   Implementations MUST assure that malformed TLV and Sub-TLV defined in
   this document are detected and do not provide a vulnerability for
   attackers to crash the OSPFv3 router or routing process.  Reception
   of malformed TLV or Sub-TLV SHOULD be counted and/or logged for
   further analysis.  Logging of malformed TLVs and Sub-TLVs SHOULD be
   rate-limited to prevent a Denial of Service (DoS) attack (distributed
   or otherwise) from overloading the OSPFv3 control plane.

11.  IANA Considerations

   This document specifies updates to multiple OSPF and OSPFv3 related
   IANA registries as follows.

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11.1.  OSPF Router Information TLVs

   This document proposes the following new code point in the "OSPF
   Router Information (RI) TLVs" registry under the "OSPF Parameters"
   registry for the new TLVs:

      Type TBD (suggested 17): SRv6-Capabilities TLV: Refer to
      Section 2.

11.2.  OSPFv3 LSA Function Codes

   This document proposes the following new code point in the "OSPFv3
   LSA Function Codes" registry under the "OSPFv3 Parameters" registry
   for the new SRv6 Locator LSA:

   o  Type TBD (suggested 42): SRv6 Locator LSA: Refer to Section 6.

11.3.  OSPFv3 Extended-LSA sub-TLVs

   This document proposes the following new code points in the "OSPFv3
   Extended-LSA Sub-TLVs" registry under the "OSPFv3 Parameters"
   registry for the new sub-TLVs:

   o  Type TBD (suggested 10): SRv6 SID Structure Sub-TLV : Refer to
      Section 9.

   o  Type TBD (suggested 11): SRv6 End.X SID Sub-TLV : Refer to
      Section 8.1.

   o  Type TBD (suggested 12): SRv6 LAN End.X SID Sub-TLV : Refer to
      Section 8.2.

11.4.  OSPFv3 Locator LSA TLVs

   This document proposes setting up of a new "OSPFv3 Locator LSA TLVs"
   registry that defines top-level TLVs for the OSPFv3 SRv6 Locator LSA
   to be added under the "OSPFv3 Parameters" registry.  The initial
   code-points assignment is as below:

   o  Type 0: Reserved.

   o  Type 1: SRv6 Locator TLV : Refer to Section 6.1.

   Types in the range 2-32767 are allocated via IETF Review or IESG
   Approval [RFC8126].

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   Types in the range 32768-33023 are Reserved for Experimental Use;
   these will not be registered with IANA and MUST NOT be mentioned by
   RFCs.

   Types in the range 33024-45055 are to be assigned on a First Come
   First Served (FCFS) basis.

   Types in the range 45056-65535 are not to be assigned at this time.
   Before any assignments can be made in the 33024-65535 range, there
   MUST be an IETF specification that specifies IANA Considerations that
   cover the range being assigned.

11.5.  OSPFv3 Locator LSA sub-TLVs

   This document proposes setting up of a new "OSPFv3 Locator LSA Sub-
   TLVs" registry that defines sub-TLVs at any level of nesting for the
   SRv6 Locator TLVs to be added under the "OSPFv3 Parameters" registry.
   The initial code-points assignment is as below:

   o  Type 0: Reserved.

   o  Type 1: SRv6 End SID sub-TLV : Refer to Section 7.

   o  Type 10: SRv6 SID Structure Sub-TLV : Refer to Section 9.

   Types in the range 2-9 and 11-32767 are allocated via IETF Review or
   IESG Approval [RFC8126].

   Types in the range 32768-33023 are Reserved for Experimental Use;
   these will not be registered with IANA and MUST NOT be mentioned by
   RFCs.

   Types in the range 33024-45055 are to be assigned on a First Come
   First Served (FCFS) basis.

   Types in the range 45056-65535 are not to be assigned at this time.
   Before any assignments can be made in the 33024-65535 range, there
   MUST be an IETF specification that specifies IANA Considerations that
   cover the range being assigned.

12.  Acknowledgements

   The authors would like to thank Chenzichao for their review and
   comments on this document.

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13.  References

13.1.  Normative References

   [I-D.ali-spring-srv6-oam]
              Ali, Z., Filsfils, C., Kumar, N., Pignataro, C.,
              faiqbal@cisco.com, f., Gandhi, R., Leddy, J., Matsushima,
              S., Raszuk, R., daniel.voyer@bell.ca, d., Dawra, G.,
              Peirens, B., Chen, M., and G. Naik, "Operations,
              Administration, and Maintenance (OAM) in Segment Routing
              Networks with IPv6 Data plane (SRv6)", draft-ali-spring-
              srv6-oam-02 (work in progress), October 2018.

   [I-D.ietf-6man-segment-routing-header]
              Filsfils, C., Dukes, D., Previdi, S., Leddy, J.,
              Matsushima, S., and d. daniel.voyer@bell.ca, "IPv6 Segment
              Routing Header (SRH)", draft-ietf-6man-segment-routing-
              header-22 (work in progress), November 2019.

   [I-D.ietf-lsr-isis-srv6-extensions]
              Psenak, P., Filsfils, C., Bashandy, A., Decraene, B., and
              Z. Hu, "IS-IS Extension to Support Segment Routing over
              IPv6 Dataplane", draft-ietf-lsr-isis-srv6-extensions-02
              (work in progress), July 2019.

   [I-D.ietf-ospf-ospfv3-segment-routing-extensions]
              Psenak, P. and S. Previdi, "OSPFv3 Extensions for Segment
              Routing", draft-ietf-ospf-ospfv3-segment-routing-
              extensions-23 (work in progress), January 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.ietf-spring-srv6-network-programming]
              Filsfils, C., Camarillo, P., Leddy, J.,
              daniel.voyer@bell.ca, d., Matsushima, S., and Z. Li, "SRv6
              Network Programming", draft-ietf-spring-srv6-network-
              programming-01 (work in progress), July 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>.

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   [RFC4552]  Gupta, M. and N. Melam, "Authentication/Confidentiality
              for OSPFv3", RFC 4552, DOI 10.17487/RFC4552, June 2006,
              <https://www.rfc-editor.org/info/rfc4552>.

   [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>.

   [RFC7770]  Lindem, A., Ed., Shen, N., Vasseur, JP., Aggarwal, R., and
              S. Shaffer, "Extensions to OSPF for Advertising Optional
              Router Capabilities", RFC 7770, DOI 10.17487/RFC7770,
              February 2016, <https://www.rfc-editor.org/info/rfc7770>.

   [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>.

   [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>.

   [RFC8362]  Lindem, A., Roy, A., Goethals, D., Reddy Vallem, V., and
              F. Baker, "OSPFv3 Link State Advertisement (LSA)
              Extensibility", RFC 8362, DOI 10.17487/RFC8362, April
              2018, <https://www.rfc-editor.org/info/rfc8362>.

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

   [RFC8476]  Tantsura, J., Chunduri, U., Aldrin, S., and P. Psenak,
              "Signaling Maximum SID Depth (MSD) Using OSPF", RFC 8476,
              DOI 10.17487/RFC8476, December 2018,
              <https://www.rfc-editor.org/info/rfc8476>.

13.2.  Informative References

   [RFC3630]  Katz, D., Kompella, K., and D. Yeung, "Traffic Engineering
              (TE) Extensions to OSPF Version 2", RFC 3630,
              DOI 10.17487/RFC3630, September 2003,
              <https://www.rfc-editor.org/info/rfc3630>.

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Authors' Addresses

   Zhenbin Li
   Huawei Technologies

   Email: lizhenbin@huawei.com

   Zhibo Hu
   Huawei Technologies

   Email: huzhibo@huawei.com

   Dean Cheng
   Huawei Technologies

   Email: dean.cheng@huawei.com

   Ketan Talaulikar
   Cisco Systems
   India

   Email: ketant@cisco.com

   Peter Psenak
   Cisco Systems
   Slovakia

   Email: ppsenak@cisco.com

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