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Versions: 00 01

LSR Working Group                                       U. Chunduri, Ed.
Internet-Draft                                                Huawei USA
Intended status: Standards Track                             J. Tantsura
Expires: September 6, 2018                                Nuage Networks
                                                                   Y. Qu
                                                     Huawei Technologies
                                                           March 5, 2018


       Usage of Non Shortest Path Forwarding (NSPF) Ids in IS-IS
                  draft-ct-isis-nspfid-for-sr-paths-00

Abstract

   This document specifies the advertisement of Non Shortest Path
   Forwarding IDentifier (NSPF ID) TLV and the computation procedures
   for the same in IS-IS protocol.  NSPF ID allows to simplify the data
   plane path description of data traffic in SR deployments.  This helps
   mitigate the MTU issues that are caused by additional SR overhead of
   the packet and allows traffic statistics.

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 RFC2119 [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 September 6, 2018.








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Copyright Notice

   Copyright (c) 2018 IETF Trust and the persons identified as the
   document authors.  All rights reserved.

   This document is subject to BCP 78 and the IETF Trust's Legal
   Provisions Relating to IETF Documents
   (https://trustee.ietf.org/license-info) in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
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   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
     1.1.  Mitigation with MSD and RLD . . . . . . . . . . . . . . .   3
     1.2.  Issues with Increased SID Depth . . . . . . . . . . . . .   3
     1.3.  Acronyms  . . . . . . . . . . . . . . . . . . . . . . . .   5
   2.  Non Shortest Path Forwarding IDentifier TLV . . . . . . . . .   5
     2.1.  Flags . . . . . . . . . . . . . . . . . . . . . . . . . .   7
     2.2.  NSPF-ID Fields  . . . . . . . . . . . . . . . . . . . . .   7
     2.3.  NSP sub-TLVs  . . . . . . . . . . . . . . . . . . . . . .   8
     2.4.  Non-NSP sub-TLVs  . . . . . . . . . . . . . . . . . . . .   9
   3.  Elements of Procedure . . . . . . . . . . . . . . . . . . . .   9
   4.  NSPF ID Data plane aspects  . . . . . . . . . . . . . . . . .  11
   5.  NSP Traffic Accounting  . . . . . . . . . . . . . . . . . . .  11
   6.  Acknowledgements  . . . . . . . . . . . . . . . . . . . . . .  11
   7.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .  12
   8.  Security Considerations . . . . . . . . . . . . . . . . . . .  12
   9.  References  . . . . . . . . . . . . . . . . . . . . . . . . .  12
     9.1.  Normative References  . . . . . . . . . . . . . . . . . .  12
     9.2.  Informative References  . . . . . . . . . . . . . . . . .  12
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .  14

1.  Introduction

   In a network implementing source routing, packets may be transported
   through the use of segment identifiers (SIDs), where a SID uniquely
   identifies a segment as defined in [I-D.ietf-spring-segment-routing].
   In SR-MPLS, a segment is encoded as a label and an ordered list of
   segments is encoded as a stack of labels.  In SRv6, a segment is
   encoded as an IPv6 address, with a new type of IPv6 routing header
   called SRH.  An ordered list of segments is encoded as an ordered
   list of IPv6 addresses in SRH [I-D.ietf-6man-segment-routing-header].




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   The segment may include one or more nodes, unidirectional adjecencies
   between two nodes or service instruction by a particular node in the
   network.  A Non Shortest Path (NSP) may be described using list of
   segments in SR.  However, this creates a problem of having a
   relatively large stack imposed on the data packet.  A path that is
   encoded with SIDs can be a loose or strict path.  In a strict path
   all the nodes/links on the path are encoded as SIDs, with the expense
   of number of total SIDs in the stack.

1.1.  Mitigation with MSD and RLD

   The number of SIDs in the stack a node can impose is referred as
   Maximum SID Depth (MSD) capability
   [I-D.ietf-isis-segment-routing-msd], which must be taken into
   consideration when computing a path to transport a data packet in a
   network implementing segment routing.  [I-D.ietf-isis-mpls-elc]
   defines Readable Label Depth (RLD) that is used by a head-end to
   insert Entropy Label pair (ELI/EL) at appropriate depth, so it could
   be read by transit nodes.  There are situations where the source
   routed path can be excessive as path represented by SR SIDs need to
   describe all the nodes and ELI/EL based on the readability of the
   nodes in that path.

   While MSD (and RLD) capabilities advertisement help mitigate the
   problem for a central entity to create the right source routed path
   per application/operator requirements; actual depth is still limited
   by the underlying hardware in the data path.

1.2.  Issues with Increased SID Depth

   Consider the following network where SR-MPLS data plane is in use and
   with same SRGB (5000-6000) on all nodes i.e., A1 to A7 and B1 to B7
   for illustration:

        SID:10   SID:20   SID:30   SID:40  SID:50 SID:300(Ax)  SID:60   SID:70
        A1-------A2-------A3-------A4-------A5===============A6----------A7
                 \               /          \   SID:310(Ay)   \          /
                  \ 10        10/            \                 \10      /10
                   \           /              \                 \      /
             SID:80 \A8-----A9/SID:90          \  40             \    /
                    /         \                 +-----+           \  /
                   /10         \10                     \           \/
        B1--------B2-----------B3----B4--------B5-------B6----------B7
        SID:110   SID:120  SID:130   SID:140   SID:150  SID:160  SID:170


                         Figure 1: SR-MPLS Network




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      Global ADJ SIDs are provisioned between A5 and A6 .All other SIDs
      shown are nodal SID indices.

      All metrics of the links are set to 1, other values as configured.

      Shortest Path from A1 to A7: A2-A3-A4-A5-A6-A7

      Shortest Path from B1 to B7: B2-B3-B4-B5-B6-B7

      SR-PATH-1: From A1 to A7 - A2-A8-B2-B3-A9-A5-Ax-A7; Pushed Label
      Stack @A1: 5070:5300:5050:5090:5130:5120:5080:5020

      SR-PATH-2: From B1 to B7 - B2-A8-A2-A4-A9-B4-B6-B7; Pushed Label
      Stack @B1: 5170:5160:5140:5090:5040:5020:5080:5120

   In the above example both SR-PATH-1 and SR-PATH-2 are represented
   with a combination of Adjacency and Node SIDs with a stack of 8
   labels each.  However, this value can be larger, if the use of
   entropy label is desired and based on the RLD capabilities of each
   node and additional labels required to insert ELI/EL at appropriate
   places.  Though above network is shown with SR-MPLS data plane,
   problem is similar if the network were a SR-IPv6 network with all
   SIDs encoded as IPv6 SIDs in SRH.

   In various SR deployments, the following issues may arise:

      Not all nodes in the path can support MSD or RLD needed to satisfy
      user/operator requirements, when the number of SIDs increased to
      describe the source routed path.  This problem gets multiplied by
      four times in SRH compared to MPLS data plane because of the SID
      size (16 bytes) in SRH.

      Even if all nodes can support the required MSD or RLD, the bigger
      label stack/depth can cause potential MTU/fragmentation issues.

      In some deployments, it is also required reducing the overhead in
      the network layer, especially for low packet size packets, where
      the actual data can be way lesser than all encapsulations and SR
      path overheads.

   Apart from the above some deployments need path accounting statistics
   for path monitoring and traffic re-optimizations.
   [I-D.hegde-spring-traffic-accounting-for-sr-paths] proposes a
   solution, however this further increases the depth of SID stack.  The
   approach could be counter productive in the environments, where SID
   depth is already causing deployment issues as listed above.





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   To mitigate the above issues, and also to facilitate forwarding plane
   a mechanism to identify the SR path with a corresponding data plane
   identifier for accounting of traffic for SR paths, this draft
   proposes a new IS-IS TLV (Section 2) to advertise the NSPs with Non
   Shortest Path Forwarding IDentifier (NSPF ID).

   This draft lays out procedure for IS-IS nodes to how to use NSPF ID
   TLV in Section 3.  With corresponding data plane, Section 3
   mechanism, reduces the SID stack in the data plane from 8 SIDs shown
   in SR-PATH-1 and SR-PATH-2 with a single NSPF ID.  This draft also
   introduce source routed paths with NSPF ID types defined for native
   IPv4 and IPv6 data planes as defined in Section 2.2.

1.3.  Acronyms

   EL       -  Entropy Label

   ELI      -  Entropy Label Indicator

   MPLS     -  Multi Protocol Label Switching

   MSD      -  Maximum SID Depth

   MTU      -  Maximum Transferrable Unit

   SID      -  Segment Identifier

   SPF      -  Shortest Path First

   SR       -  Segment Routing

   SRH      -  Segment Routing Header

   SR-MPLS  -  Segment Routing with MPLS data plane

   SRv6     -  Segment Routing with Ipv6 data plane with SRH

   SRH      -  IPv6 Segment Routing Header

   TE       -  Traffic Engineering

2.  Non Shortest Path Forwarding IDentifier TLV

   The NSPF-ID TLV has Type TBD (suggested value xxx), 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     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |           MT-ID               | Prefix Len    |  FEC Prefix   |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       //           FEC Prefix (continued, variable)                  //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       | NSPF-ID Type  | NSPF-ID Len   | NSPF-ID Flags |  NSPF-ID Algo |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       //           NSPF-ID  (continued, variable)                    //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |No.of NSP-STs  |  NSP sub-TLVs (Variable)                     //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |No.of Other-STs| Non-NSP sub-TLVs(variable)                   //
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

                       Figure 2: NSPF ID TLV Format

      Type - TBD from IS-IS top level TLV registry.

      Length - Total length of the value field in bytes (variable).

      Reserved - 1 Octet reserved bits for future use.  Reserved bits
      MUST be reset on transmission and ignored on receive.

      Flags - Flags for this TLV are described in Section 2.

      MT-ID - is the multi-topology identifier defined in [RFC5120] with
      4 most significant bits reset on transmission and ignored on
      receive.  The remaining 12-bit field contains the MT-ID.

      Prefix Len - contains the length of the prefix in bits.  Only the
      most significant octets of the Prefix are encoded.  (i.e., 1 octet
      for prefix length 1 up to 8, 2 octets for prefix length 9 to 16, 3
      octets for prefix length 17 up to 24 and 4 octets for prefix
      length 25 up to 32, ...., 16 octets for prefix length 113 up to
      128).

      FEC Prefix - represents the Forwarding Equivalence Class at the
      tail-end of the advertised NSP.  The 'FEC Prefix' corresponds to a
      routable prefix of the originating node, meaning one of the
      [RFC7794] flags MUST be set (X-Flag/R-Flag/N-Flag).  Value of this
      field can be 4 or 16 octets and encoding is similar to TLV 135 and
      TLV 236 or MT-Capable [RFC5120] IPv4 (TLV 235) and IPv6 Prefixes
      (TLV 237) respectively.




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2.1.  Flags

   Flags: 1 octet field of NSPD ID TLV has following flags defined.
   These flags mostly related to applicability of this TLV in an L1 area
   or entire IS-IS domain:

        NSPF ID Flags Format

            0 1 2 3 4 5 6 7
           +-+-+-+-+-+-+-+-+
           |S|D|A| Rsrvd   |
           +-+-+-+-+-+-+-+-+


      S - If set, the NSPF ID TLV SHOULD be flooded across the entire
      routing domain.  If the S flag is not set, the NSPF ID TLV MUST
      NOT be leaked between IS-IS levels.  This bit MUST NOT be altered
      during the TLV leaking

      D - when the NSPF ID TLV is leaked from IS-IS level-2 to level-1,
      the D bit MUST be set.  Otherwise, this bit MUST be clear.  NSPF
      ID TLVs with the D bit set MUST NOT be leaked from level-1 to
      level-2.  This is to prevent TLV looping across levels.

      A - The originator of the NSPF ID TLV MAY set the A bit in order
      to signal that the prefixes and NSPF-IDs advertised in the NSPF ID
      TLV are directly connected to their originators.  The mechanisms
      through which the originator of the NSPF ID TLV can figure out if
      a prefix is attached or not are outside the scope of this document
      (e.g.: through explicit configuration).  If the NSPF ID TLV is
      leaked to other areas/levels the A-flag MUST be cleared.

      Rsrvd - reserved bits for future use.  Reserved bits MUST be reset
      on transmission and ignored on receive.

   Flags defined above are similar to
   [I-D.ietf-isis-segment-routing-extensions] and section 2.4.1
   restrictions apply here.

2.2.  NSPF-ID Fields

   This represents the actual data plane identifier in the packet and
   could be of any data plane as defined in type field.  As with "FEC
   Prefix", NSPF-ID also need not be from the advertising node of NSPF
   ID itself.  However, both MUST belong to a same node in the network.

      NSPF-ID Type: This is a new registry (TBD IANA) for this TLV and
      the defined types are as follows.  Type: 1 - MPLS SID/Label Type:



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      2 Native IPv4 Address Type: 3 Native IPv6 Address Type 4: IPv6 SID
      in SRv6 with SRH

      NSPF-ID Len: Length of the NSPF Identifier field in octets and
      this depends on the NSPF-ID type.

      NSPF-ID Flags: 1 Octet field for NSPF-ID flags.  Some of the bits
      could be NSPF-ID type specific and each new type MUST define the
      flags applicable to the NSPF-ID type.  For NSPF-ID Type 1, the
      flags are same as Section 2.1 definition in
      [I-D.ietf-isis-segment-routing-extensions].  For NSPF-ID Type 2, 3
      and NSPF-ID Type 4 only 'R' flag is applicable.  Undefined flags
      for each NSPF-ID type MUST be considered as RESERVED.  RESERVED
      flag bits in each NSPF-ID type specific flags MUST be reset on
      transmission and ignored on receive.

      NSPF-ID Algo: 1 octet value represents the SPF algorithm

2.3.  NSP sub-TLVs

   A new sub-TLV registry is created (TBD IANA) called NSP sub-TLVs.
   These are used to describe the path in the form of set of contiguous
   sub-TLVs.  Total number of the non-NSP sub-TLVs are defined in
   1-octet field "No.of NSP-STs" just before the NSP sub-TLVs.

      Type 1: SID/Lable sub-TLV as defined in Section 2.3 of
      [I-D.ietf-isis-segment-routing-extensions].  Only Type is defined
      and Length/Value fields are per Section 2.3 of the referenced
      document.

      Type 2: Prefix SID sub-TLV as defined in Section 2.1
      of[I-D.ietf-isis-segment-routing-extensions].  Only Type is
      defined and Length/Value fields are per Section 2.1 of the
      referenced document.

      Type 3: Adjacency SID sub-TLV as defined in Section 2.2 of
      [I-D.ietf-isis-segment-routing-extensions].  Only Type is defined
      and Length/Value fields are per Section 2.2 of the referenced
      document.

      Type 4: Length 4 bytes, value is 4 bytes IPv4 address encoded
      similar to IPv4 FEC Prefix described above.

      Type 5: Length 16 bytes, value is 16 bytes IPv6 address encoded
      similar to IPv4 FEC Prefix described above.






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2.4.  Non-NSP sub-TLVs

   NSPF ID TLV also defines a new sub-TLV registry (TBD IANA) for
   defining extensible set of sub-TLVs other than describing the path
   sub-TLVs.  Total number of the path sub-TLVs to describe the path are
   defined in 1-octet field "No.of Other-STs" just before the Non-NSP
   sub-TLVs.  This field serves as a demarcation for set of NSP sub-TLVs
   and Non-NSP sub-TLVs.

      Type 1: Length 0 No value field.  Specifies a counter to count
      number of packets forwarded on this NSPF-ID.

      Type 2: Length 0 No value field.  Specifies a counter to count
      number of bytes forwarded on this NSPF-ID specified in the network
      header (e.g.  IPv4, IPv6).

      Type 3: Length 4 bytes, and Value is metric of this path
      represented through the NSPF-ID.  Different nodes can advertise
      the same NSPF-ID for the same FEC-Prefix with a different set of
      NSP sub-TLVs and the receiving node MUST consider the lowest
      metric value (TBD more, what happens when metric is same for two
      different set of NSP sub-TLVs).

3.  Elements of Procedure

   Consider the following IS-IS network to describe the operation of
   NSPF ID TLV as defined in Section 2:
























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                                           1
                                        _______
                                       /   1   \
                                   +---R2-------R3---+
                                  /    \_______/      \
                                 /         1           \
                              1 /        2              \ 1
                               /       ______            \
                              /       /      \            \
                            R1------R6       R7-----------R4
                              \  2    \______/    2       /
                               \          2              /
                              3 \                       / 3
                                 \                 3   /
                                  +----R8------R9-----R10--+
                                           3    \         /
                                               1 \       / 1
                                                  +-R11-+


                          Figure 3: IS-IS Network

   In the above diagram (Figure 3) node R1 is an ingress node, or a
   head-end node, and the node R4 may be an egress node or another head-
   end node.  The numbers shown on each of the links between nodes
   R1-R11 indicate a IS-IS metric as provisioned by the operator.  R1
   may be configured to receive TE source routed path information from a
   central entity that comprise NSP information which relates to sources
   that are attached to R1.  The NSP information includes the stack or
   list of nodes in the NSPs from the source to a destination in the
   network and the NSPF ID.  For example, the NSP information may
   include a sequential ordering of NSP Sub-TLVS as defined by NSPF-ID
   type, which specifies the actual path toward a FEC/Prefix by R4.

   The shortest path may be defined by the following sequence of nodes:
   R1-R2-R3-R4 based on the configured metrics.  The central entity MAY
   define a few NSPs from R1 to R4 that deviate from the shortest path
   based on other network characteristic requirements as requested by an
   application or service.  For example, the network characteristics or
   performance requirements may include bandwidth, jitter, latency,
   throughput, error rate, etc.  A first NSP may be identified by NSPF
   ID = 2 and may include the path of R1-R6-R7-R4 for a FEC Prefix
   advertised by R4.  A second NSP may be identified by NSPF ID = 3 and
   may include the path of R1-R8-R9-R10-R4.

   Each receiving node, determine whether an advertised NSP includes
   information regarding the receiving node.  This MAY be done, during
   the end of the SPF computation for MTID that is advertised in this



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   TLV and for the FEC/Prefix.  For example, suppose node R9 receives
   the NSP information, node R9 may ignore the first NSP identified by
   NSPF ID = 2 because this NSP does not include node R9.

   However, node R9 may determine that the second NSP identified by NSPF
   ID = 3 does include the node R9 for the FEC prefix advertised by R4.
   Therefore, node R9 updates the local forwarding database to include
   an entry for the destination address of R4 that indicates that when a
   data packet comprising a NSPF ID of 3 is received, node R9 is now
   configured to forward the data packet to node R10 instead of R11.
   This is even though the link to node R10 is associated with a higher
   cost of 3 than the link to node R11, which is associated with a cost
   of 1.

4.  NSPF ID Data plane aspects

   Data plane NSPF ID is selected by the entity (e.g., a controller)
   which selects a particular NSP in the network.  Section 2.2 defines
   various data plane identifier types and a corresponding data plane
   identifier type and identifier is selected by the entity which
   selects the NSP.  For example if NSPF-ID Type is 1, the NSP belongs
   to SR-MPLS data plane and the complete NSP stack is represented with
   a unique SR SID/Label.  And same logic applies to other NSPF-ID
   types.

5.  NSP Traffic Accounting

   As described in Section 2.4, each node described in the NSP sub-TLVs
   SHOULD provision the hardware to account the traffic statistics as
   indicated in the non-NSP sub-TLVs for the actual data traffic.  When
   NSP is withdrawn from the originating node, rest of the nodes in the
   NSP MUST remove the state in respective nodes.  This approach, thus
   is more safe and secure than any mechanism that involves creating
   state in the nodes with data traffic itself.  This is because
   creation and deletion of the traffic accounting state for NSPs happen
   through IS-IS LSP processing and IS-IS security Section 8 options are
   applicable to this TLV.

6.  Acknowledgements

   Thanks to Richard Li, Alex Clemm, Kiran Makhijani and Lin Han for
   initial discussions on this topic.

   Earlier versions of draft-ietf-isis-segment-routing-extensions have a
   mechanism to advertise EROs through Binding SID.






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7.  IANA Considerations

   This document requests the following new TLVin IANA IS-IS TLV code-
   point registry.

        TLV #   Name
        -----   --------------
        TBD     NSPF ID TLV


   This document also requests IANA to create new registries for NSPF ID
   TLV Flags field, NSPF-ID Type, NSPF-ID Flags, NSP sub-TLVs and Non-
   NSP sub-TLVs in NSPF ID TLV as described in Section 2.

8.  Security Considerations

   Security concerns for IS-IS are addressed in [RFC5304] and [RFC5310].
   Further security analysis for IS-IS protocol is done in [RFC7645].
   Advertisement of the additional information defined in this document
   introduces no new security concerns.

9.  References

9.1.  Normative References

   [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>.

9.2.  Informative References

   [I-D.hegde-spring-traffic-accounting-for-sr-paths]
              Hegde, S., "Traffic Accounting for MPLS Segment Routing
              Paths", draft-hegde-spring-traffic-accounting-for-sr-
              paths-01 (work in progress), October 2017.

   [I-D.ietf-6man-segment-routing-header]
              Previdi, S., Filsfils, C., Raza, K., Dukes, D., Leddy, J.,
              Field, B., daniel.voyer@bell.ca, d.,
              daniel.bernier@bell.ca, d., Matsushima, S., Leung, I.,
              Linkova, J., Aries, E., Kosugi, T., Vyncke, E., Lebrun,
              D., Steinberg, D., and R. Raszuk, "IPv6 Segment Routing
              Header (SRH)", draft-ietf-6man-segment-routing-header-08
              (work in progress), January 2018.






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   [I-D.ietf-isis-mpls-elc]
              Xu, X., Kini, S., Sivabalan, S., Filsfils, C., and S.
              Litkowski, "Signaling Entropy Label Capability and
              Readable Label-stack Depth Using IS-IS", draft-ietf-isis-
              mpls-elc-03 (work in progress), January 2018.

   [I-D.ietf-isis-segment-routing-extensions]
              Previdi, S., Ginsberg, L., Filsfils, C., Bashandy, A.,
              Gredler, H., Litkowski, S., Decraene, B., and J. Tantsura,
              "IS-IS Extensions for Segment Routing", draft-ietf-isis-
              segment-routing-extensions-15 (work in progress), December
              2017.

   [I-D.ietf-isis-segment-routing-msd]
              Tantsura, J., Chunduri, U., Aldrin, S., and L. Ginsberg,
              "Signaling MSD (Maximum SID Depth) using IS-IS", draft-
              ietf-isis-segment-routing-msd-09 (work in progress),
              January 2018.

   [I-D.ietf-spring-segment-routing]
              Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B.,
              Litkowski, S., and R. Shakir, "Segment Routing
              Architecture", draft-ietf-spring-segment-routing-15 (work
              in progress), January 2018.

   [RFC5120]  Przygienda, T., Shen, N., and N. Sheth, "M-ISIS: Multi
              Topology (MT) Routing in Intermediate System to
              Intermediate Systems (IS-ISs)", RFC 5120,
              DOI 10.17487/RFC5120, February 2008,
              <https://www.rfc-editor.org/info/rfc5120>.

   [RFC5304]  Li, T. and R. Atkinson, "IS-IS Cryptographic
              Authentication", RFC 5304, DOI 10.17487/RFC5304, October
              2008, <https://www.rfc-editor.org/info/rfc5304>.

   [RFC5310]  Bhatia, M., Manral, V., Li, T., Atkinson, R., White, R.,
              and M. Fanto, "IS-IS Generic Cryptographic
              Authentication", RFC 5310, DOI 10.17487/RFC5310, February
              2009, <https://www.rfc-editor.org/info/rfc5310>.

   [RFC7413]  Cheng, Y., Chu, J., Radhakrishnan, S., and A. Jain, "TCP
              Fast Open", RFC 7413, DOI 10.17487/RFC7413, December 2014,
              <https://www.rfc-editor.org/info/rfc7413>.

   [RFC7645]  Chunduri, U., Tian, A., and W. Lu, "The Keying and
              Authentication for Routing Protocol (KARP) IS-IS Security
              Analysis", RFC 7645, DOI 10.17487/RFC7645, September 2015,
              <https://www.rfc-editor.org/info/rfc7645>.



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Internet-DraUsage of Non Shortest Path Forwarding (NSPF) Ids  March 2018


   [RFC7794]  Ginsberg, L., Ed., Decraene, B., Previdi, S., Xu, X., and
              U. Chunduri, "IS-IS Prefix Attributes for Extended IPv4
              and IPv6 Reachability", RFC 7794, DOI 10.17487/RFC7794,
              March 2016, <https://www.rfc-editor.org/info/rfc7794>.

Authors' Addresses

   Uma Chunduri (editor)
   Huawei USA
   2330 Central Expressway
   Santa Clara, CA  95050
   USA

   Email: uma.chunduri@huawei.com


   Jeff Tantsura
   Nuage Networks
   755 Ravendale Drive
   Mountain View, CA  94043
   USA

   Email: jefftant.ietf@gmail.com


   Yingzhen Qu
   Huawei Technologies
   2330 Central Expressway
   Santa Clara, CA  95050
   USA

   Email: yingzhen.qu@huawei.com



















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