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Versions: 00 01

RTGWG Working Group                                                C. Li
Internet-Draft                                                     Z. Hu
Intended status: Standards Track                     Huawei Technologies
Expires: July 14, 2020                                  January 11, 2020


    Enhanced Topology Independent Loop-free Alternate Fast Re-route
                   draft-li-rtgwg-enhanced-ti-lfa-01

Abstract

   Topology Independent Loop-free Alternate Fast Re-route (TI-LFA) aims
   at providing protection of node and adjacency segments within the
   Segment Routing (SR) framework.  A key aspect of TI-LFA is the FRR
   path selection approach establishing protection over the expected
   post-convergence paths from the point of local repair.  However, the
   TI-LFA FRR path may skip the node even if it is specified in the SID
   list to be traveled.

   This document defines Enhanced TI-LFA(TI-LFA+) by adding a No-bypass
   indicator for segments to ensure that the FRR route will not bypass
   the specific node, such as firewall.

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
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   This Internet-Draft will expire on July 14, 2020.

Copyright Notice

   Copyright (c) 2020 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



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   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.  Terminology . . . . . . . . . . . . . . . . . . . . . . . . .   3
     2.1.  Requirements Language . . . . . . . . . . . . . . . . . .   3
   3.  Overview of Enhanced TI-LFA . . . . . . . . . . . . . . . . .   3
   4.  IGP Protocol Extensions . . . . . . . . . . . . . . . . . . .   4
     4.1.  IS-IS . . . . . . . . . . . . . . . . . . . . . . . . . .   4
     4.2.  OSPF  . . . . . . . . . . . . . . . . . . . . . . . . . .   5
   5.  IANA Considerations . . . . . . . . . . . . . . . . . . . . .   8
   6.  Security Considerations . . . . . . . . . . . . . . . . . . .   8
   7.  References  . . . . . . . . . . . . . . . . . . . . . . . . .   8
     7.1.  Normative References  . . . . . . . . . . . . . . . . . .   8
     7.2.  Informative References  . . . . . . . . . . . . . . . . .   9
   Authors' Addresses  . . . . . . . . . . . . . . . . . . . . . . .   9

1.  Introduction

   Segment Routing [RFC8402] enables to steer packets by explicitly
   encoding instructions in the data packets at the source node to
   support services like traffic engineer.  Relying on SR,
   [I-D.ietf-rtgwg-segment-routing-ti-lfa] defines Topology Independent
   Loop-free Alternate Fast Re-route (TI-LFA), a local repair mechanism
   for IGP shortest path that capable of restoring end-to-end
   connectivity in the case of a sudden directly connected failure of a
   network component.

   TI-LFA supports to establish a loop free backup path over the
   expected post-convergence paths from the point of local repair
   irrespective of the topologies used in the network, which provides a
   major improvment compared to LFA [RFC5286], and remote LFA [RFC7490]
   which cannot be applicable in some topologies [RFC6571].

   However, the TI-LFA path may skip the node that the active SID points
   to when protecting [Adjacency, Node] segment lists.  For instance,
   the node that a adjacency SID points to is a very important node and
   can not be skipped, such as a firewall node.  When the link between
   the local repair node and firewall node fails, the packets should be
   steered back to the firewall and then forwarding.  But in TI-LFA, if
   the next SID in the SID list is a node SID, the TI-LFA FRR path MAY
   bypass the node that the active segment points to.  Also, if the



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   firewall node is down, the packets should be dropped instead for fast
   reroute to bypass the node.  Bypassing nodes like firewall in FRR
   brings issues of network security and reliability.

   To enhance the security and reliability of networks, this document
   defines an Enhanced Topology Independent Loop-free Alternate Fast Re-
   route (TI-LFA+) based on TI-LFA by adding a No-bypass flag for
   segments to explicitly specify what node can not be bypassed.

2.  Terminology

   This document makes use of the terms defined in
   [I-D.ietf-rtgwg-segment-routing-ti-lfa] and [RFC8402].  The reader is
   assumed to be familiar with the terminology defined in
   [I-D.ietf-rtgwg-segment-routing-ti-lfa] and [RFC8402].

2.1.  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.

3.  Overview of Enhanced TI-LFA

   Enhanced Topology Independent Loop-free Alternate Fast Re-route (TI-
   LFA+) is an enhancement of TI-LFA to explicitly indicate whether a
   node that segment points to can not be bypassed in FRR scenarios.

   TI-LFA+ will not change the main process and algorithm of TI-LFA.
   Instead, in TI-LFA+, when generating repair SID list for a SID, the
   node should consider whether the SID endpoint can be baseed or not,
   which is explicitly encoded in IGP messages.  If the node that
   segment points to can not be bypassed, then the repair SID MUST lead
   the packets to that node.  This document defines a No-bypass flag for
   segments in IS-IS and OSPF.  Details will be discussed in section 4.

   A node should advertise two kinds of segment to meet various service
   policy requirements.

   o  Bypassing capable segment with No-bypass flag unset

   o  No-bypassing segment with No-bypass flag set.

   A controller or control plane should choose specific segment
   according to the service policy.




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4.  IGP Protocol Extensions

4.1.  IS-IS

   [I-D.ietf-isis-segment-routing-extensions] describes the necessary
   IS-IS extensions that need to be introduced for Segment
   Routing.[I-D.ietf-lsr-isis-srv6-extensions] defines the IS-IS
   extensions required to support Segment Routing over an IPv6 data
   plane.  This documment defines a No-bypass flag in flag filed of the
   following IS-IS sub-TLV/TLV.

   o  Prefix Segment Identifier sub-TLV (Prefix-SID sub-TLV)
      [I-D.ietf-isis-segment-routing-extensions]

   o  Adjacency Segment Identifier sub- TLV (Adj-SID sub-
      TLV).[I-D.ietf-isis-segment-routing-extensions]

   o  Locator entry in SRv6 Locator TLV
      [I-D.ietf-lsr-isis-srv6-extensions]

   The following figures are included here for reference and will be
   deleted in the future version.

       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     |   Algorithm   |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                        SID/Index/Label (variable)             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       0  1  2  3  4  5  6  7
      +--+--+--+--+--+--+--+--+
      |R | N| P| E| V| L|NB|  |
      +--+--+--+--+--+--+--+--+

                Figure 1. Prefix-SID sub-TLV and No-bypass Flag














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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    |     Flags     |     Weight    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                         SID/Label/Index (variable)            |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       0  1  2  3  4  5  6  7
      +--+--+--+--+--+--+--+--+
      |F | B| V| L| S|NB|  |  |
      +--+--+--+--+--+--+--+--+
                Figure 2. Adj-SID sub-TLV and No-bypass Flag

     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
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                          Metric                               |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |   Flags       |  Algorithm    |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Loc Size     | Locator (variable)...
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |  Sub-tlv-len  |         Sub-TLVs (variable) . . .             |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

       0  1  2  3  4  5  6  7
      +--+--+--+--+--+--+--+--+
      |D |NB|  |  |  |  |  |  |
      +--+--+--+--+--+--+--+--+
                Figure 3. SRv6 Locator Entry and No-bypass Flag

   If the No-bypass(NB) flag is set, means the node that the SID/Label/
   Locator points to can not be bypassed.  Oterwise, the node can be
   bypassed.

4.2.  OSPF

   [I-D.ietf-ospf-segment-routing-extensions] describes the necessary
   OSPF extensions that need to be introduced for Segment
   Routing.[I-D.li-ospf-ospfv3-srv6-extensions] defines the OSPF
   extensions required to support Segment Routing over an IPv6 data
   plane.  This documment defines a No-bypass flag in flag filed of the
   following OSPF sub-TLV/TLV.

   o  Prefix SID Sub-TLV [I-D.ietf-ospf-segment-routing-extensions]

   o  Adj-SID sub-TLV [I-D.ietf-ospf-segment-routing-extensions]



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   o  SRv6 Node SID TLV [I-D.li-ospf-ospfv3-srv6-extensions]

   o  SRv6 SID Link Attribute Sub-TLV
      [I-D.li-ospf-ospfv3-srv6-extensions]

   The following figures are included here for reference and will be
   deleted in the future version.

       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    |      MT-ID    |    Algorithm  |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                     SID/Index/Label (variable)                |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


        0  1  2  3  4  5  6  7
      +--+--+--+--+--+--+--+--+
      |  |NP|M |E |V |L |NB|  |
      +--+--+--+--+--+--+--+--+

                Figure 4. Prefix-SID sub-TLV and No-bypass Flag


       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   |   MT-ID       |  Weight       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      |                   SID/Label/Index (variable)                  |
      +---------------------------------------------------------------+


       0  1  2  3  4  5  6  7
      +--+--+--+--+--+--+--+--+
      |B | V| L| G| P|NB|  |  |
      +--+--+--+--+--+--+--+--+

                Figure 5. Adj-SID sub-TLV and No-bypass Flag







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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    | Function-Flags|           Function Code       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Reserved                    |  SID Flags    |  SID-size     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   SID (variable - 32 bit aligned) ...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Sub-TLVs (variable) . . .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


       0 1 2 3 4 5 6 7
      +--+--+--+--+--+--+--+--+
      |D |NB|  |  |  |  |  |  |
      +--+--+--+--+--+--+--+--+
                Figure 6. SRv6 Node SID TLV and No-bypass Flag

        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    | Function-Flags|           Function Code       |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   Reserved                    |  SID Flags    |  SID-size     |
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |   SID (variable - 32 bit aligned) ...
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
       |    Sub-TLVs (variable) . . .
       +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+


       0 1 2 3 4 5 6 7
      +--+--+--+--+--+--+--+--+
      |NB|  |  |  |  |  |  |  |
      +--+--+--+--+--+--+--+--+
                Figure 7. SRv6 Adj-SID TLV and No-bypass Flag

   If the No-bypass(NB) flag is set, means the node that the SID/Label/
   Locator points to can not be bypassed.  Oterwise, the node can be
   bypassed.






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5.  IANA Considerations

   TBD.

6.  Security Considerations

   TBD.

7.  References

7.1.  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>.

   [RFC5286]  Atlas, A., Ed. and A. Zinin, Ed., "Basic Specification for
              IP Fast Reroute: Loop-Free Alternates", RFC 5286,
              DOI 10.17487/RFC5286, September 2008,
              <https://www.rfc-editor.org/info/rfc5286>.

   [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>.

   [RFC7490]  Bryant, S., Filsfils, C., Previdi, S., Shand, M., and N.
              So, "Remote Loop-Free Alternate (LFA) Fast Reroute (FRR)",
              RFC 7490, DOI 10.17487/RFC7490, April 2015,
              <https://www.rfc-editor.org/info/rfc7490>.

   [RFC6571]  Filsfils, C., Ed., Francois, P., Ed., Shand, M., Decraene,
              B., Uttaro, J., Leymann, N., and M. Horneffer, "Loop-Free
              Alternate (LFA) Applicability in Service Provider (SP)
              Networks", RFC 6571, DOI 10.17487/RFC6571, June 2012,
              <https://www.rfc-editor.org/info/rfc6571>.

   [I-D.ietf-rtgwg-segment-routing-ti-lfa]
              Litkowski, S., Bashandy, A., Filsfils, C., Decraene, B.,
              Francois, P., Voyer, D., Clad, F., and P. Camarillo,
              "Topology Independent Fast Reroute using Segment Routing",
              draft-ietf-rtgwg-segment-routing-ti-lfa-01 (work in
              progress), March 2019.








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7.2.  Informative References

   [RFC4657]  Ash, J., Ed. and J. Le Roux, Ed., "Path Computation
              Element (PCE) Communication Protocol Generic
              Requirements", RFC 4657, DOI 10.17487/RFC4657, September
              2006, <https://www.rfc-editor.org/info/rfc4657>.

   [RFC8253]  Lopez, D., Gonzalez de Dios, O., Wu, Q., and D. Dhody,
              "PCEPS: Usage of TLS to Provide a Secure Transport for the
              Path Computation Element Communication Protocol (PCEP)",
              RFC 8253, DOI 10.17487/RFC8253, October 2017,
              <https://www.rfc-editor.org/info/rfc8253>.

   [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>.

   [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-07 (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-03
              (work in progress), October 2019.

Authors' Addresses








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   Cheng Li
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: chengli13@huawei.com


   Zhibo Hu
   Huawei Technologies
   Huawei Campus, No. 156 Beiqing Rd.
   Beijing  100095
   China

   Email: huzhibo@huawei.com



































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