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

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Table of Contents

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 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.

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

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.

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


  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.

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


     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.

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.
[RFC5286] Atlas, A. and A. Zinin, "Basic Specification for IP Fast Reroute: Loop-Free Alternates", RFC 5286, DOI 10.17487/RFC5286, September 2008.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017.
[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.
[RFC6571] Filsfils, C., Francois, P., 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.
[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", Internet-Draft draft-ietf-rtgwg-segment-routing-ti-lfa-01, March 2019.

7.2. Informative References

[RFC4657] Ash, J. and J. Le Roux, "Path Computation Element (PCE) Communication Protocol Generic Requirements", RFC 4657, DOI 10.17487/RFC4657, September 2006.
[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.
[RFC8402] Filsfils, C., Previdi, S., Ginsberg, L., Decraene, B., Litkowski, S. and R. Shakir, "Segment Routing Architecture", RFC 8402, DOI 10.17487/RFC8402, July 2018.
[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", Internet-Draft draft-ietf-isis-segment-routing-extensions-25, 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", Internet-Draft draft-ietf-ospf-segment-routing-extensions-27, December 2018.
[I-D.li-ospf-ospfv3-srv6-extensions] Li, Z., Hu, Z., Cheng, D., Talaulikar, K. and P. Psenak, "OSPFv3 Extensions for SRv6", Internet-Draft draft-li-ospf-ospfv3-srv6-extensions-07, 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", Internet-Draft draft-ietf-lsr-isis-srv6-extensions-03, October 2019.

Authors' Addresses

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