LSR Working Group                                                Louis Chan 
INTERNET-DRAFT                                                   Krzysztof Szarkowicz 
Intended status: Standard Track                                  Juniper Networks 
Expires: Mar 4, 2023                                             Sep 4, 2022 
                                    
    
                 IGP extensions for Advertising Offset for Flex-Algorithm 
                         draft-chan-lsr-igp-adv-offset-01.txt 


   Abstract 

      This document describes the IGP extensions to provide predictable Adjacency-SIDs 
      per Flex-Algorithm [FLEXALGO] in segment routing. 

      We propose some methods to allow the advertisement of additional TLV in IGP so that 
      the Flex-Algorithm specific Adjacency-SIDs could be automatically derived. 

      With the proposed method, the size of advertisement on per node per link basis is 
      greatly reduced. Each participating router would derive the required labels 
      automatically. 

      Extensions for offset to derive Flex-Algorithm Prefix-SID is also included in the 
      document. 

   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 
      http://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 Mar 4, 2023. 

   Copyright Notice 

      Copyright (c) 2017 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 (http://trustee.ietf.org/license-info) in effect on the date of 
      publication of this document.  Please review these documents carefully, as they 
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      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. Conventions used in this document..............................2 
      3. ISIS extension.................................................2 
         3.1. Algorithm Offset for Adj-SID..............................3 
         3.2. Algorithm Offset for LAN based Adj-SID....................4 
         3.3. Algorithm Offset for Prefix SID...........................5 
      4. Compatibility..................................................6 
      5. OSPF extension.................................................6 
         5.1. Algorithm Offset for Adj-SID..............................7
         5.2. Algorithm Offset for LAN based Adj-SID....................8 
         5.3. Algorithm Offset for Prefix SID...........................9 
      6. Security Consideration........................................10 
      7. References....................................................10 
         7.1. Normative References.....................................10 
         7.2. Informative References...................................10 
      8. Acknowledgments...............................................11 
       
   1. Introduction 

       
      The draft proposes methods for routers to announce Flex-Algorithm specific 
      Adjacency-SID with minimal advertisement in IGP. When the other routers need a SR 
      policy (aka SR-TE) or TI-LFA path, the Flex-Algorithm specific Adjacency-SID would 
      be taken into the path label construction. 

      Hence, the top most label, either node or link related, in a SR policy stack would 
      be used to identify a certain Flex-Algo with full identification. 

       

   2. Conventions used in this document 

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

      In this document, these words will appear with that interpretation only when in ALL 
      CAPS. Lower case uses of these words are not to be interpreted as carrying 
      significance described in RFC 2119. 


   3. ISIS extension 

      With reference to RFC8667, the information could be advertised in SR-Capabilities 
      sub-TLV in Section 3. 

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   3.1. Algorithm Offset for Adj-SID 

       
       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/Label   |      Base offset/Index offset (variable)      ~           
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
       
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      ~           Flags/ Algo/ Base offset/ Index offset              ~         
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
       
      where: 
       
      Type:           TDB 
       
      Length:         variable; multiple advertisements  
       
      Flags:          1 octet field of the following flags: 
       
                            0 1 2 3 4 5 6 7 
                           +-+-+-+-+-+-+-+-+ 
                           | |B|V|L|       | 
                           +-+-+-+-+-+-+-+-+ 
       
                     where: 
       
                     B-Flag:  Backup Flag.  If set, the Adj-SID is eligible 
                              for protection (e.g., using IP Fast Reroute 
                              (IPFRR) or MPLS Fast Reroute (MPLS-FRR)) as 
                              described in [RFC8402]. 
       
       
                     V-Flag:  Value Flag.  If set, then it carries 
                              a label value. If not set, it is an index value. 
       
                     L-Flag:  Local Flag.  Always set to 1 
       
        
      Algorithm:              1 octet 
                              Flex-Algo value is between 128 and 255.                
       
      Base Offset:            3 octets 
                              Local label base for Adjacency-SIDs for given Flex- 
                              Algorithm. The derived Adjacency-SID is the sum of the base  
                              offset and the Algo 0 label 
       
      Index Offset:           4 octets 
                              If Adjacency-SID is advertised as index, this provides an  
							  
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                             offset index value. The new label is sum of (SRGB base +  
                             index + index offset) 
       
      The format of Base Offset and Index Offset is the same as RFC8667. The choice of 
      advertising Base Offset or Index Offset must match the advertisement of original 
      Adjacency-SID method from the same router. 
       
   3.2. Algorithm Offset for LAN based Adj-SID 
      
          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   | 
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
         |                  Neighbor System-ID (ID length octets)        | 
         +                               +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
         |                               | 
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
         |        SID/Label Base Offset/Index Offset (variable)          ~ 
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
         ~    Flags/ Algo/NB Sys-ID/ SID/Label/Index Offset (variable)   ~ 
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
       
      where: 
       
      Type:           TDB 
       
      Length:         variable; multiple advertisements  
       
      Flags:          1 octet field of the following flags: 
       
                            0 1 2 3 4 5 6 7 
                           +-+-+-+-+-+-+-+-+ 
                           | |B|V|L|       | 
                           +-+-+-+-+-+-+-+-+ 
       
                     where: 
       
                     B-Flag:  Backup Flag.  If set, the Adj-SID is eligible 
                              for protection (e.g., using IP Fast Reroute 
                              (IPFRR) or MPLS Fast Reroute (MPLS-FRR)) as 
                              described in [RFC8402]. 
       
                     V-Flag:  Value Flag.  If set, then it carries 
                              a label value. If not set, it is an index value. 
       
                     L-Flag:  Local Flag.  Always set to 1 
              
      Algorithm:              1 octet. Same as Section 5.1 
	  
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      Neighbor System-ID:     IS-IS System-ID of length "ID Length" as 
                              defined in [ISO10589]. 
       
      Base Offset:            3 octets. Same as Section 5.1 
       
      Index Offset:           4 octets. Same as Section 5.1 
       
       
   3.3. Algorithm Offset for Prefix SID  

      Prefix-SID for Algorithm could also be generated by adding an index offset value or 
      a base offset for label. 
       
      This advertisement is an sub-TLV in RFC8667 Section 2. 
       
      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/Label Base offset/ Index offset                    ~  
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+      
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
      ~      Flags/ Algorithm/ Base Offset/ Index offset             ~         
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
              
      Type:           TDB 
       
      Length:         variable  
       
      Flags:          1 octet field of the following flags: 
       
                            0 1 2 3 4 5 6 7 
                           +-+-+-+-+-+-+-+-+ 
                           |R|N|   |V|L|   | 
                           +-+-+-+-+-+-+-+-+ 
       
                     where: 
       
                     R-Flag:  Re-advertisement Flag.  If set, then the prefix 
                              to which this Prefix-SID is attached has been 
                              propagated by the router from either another 
                              level (i.e., from Level-1 to Level-2 or the 
                              opposite) or redistribution (e.g., from another 
                              protocol). 
       
                     N-Flag:  Node-SID Flag.  If set, then the Prefix-SID 
                              refers to the router identified by the prefix. 
                              Typically, the N-Flag is set on Prefix-SIDs that 
                              are attached to a router loopback address.  The 
							  
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                              N-Flag is set when the Prefix-SID is a Node-SID 
                              as described in [RFC8402]. 
       
       
                     V-Flag:  Value Flag.  If set, then it carries 
                              a label value. If not set, it is an index value. 
       
                     L-Flag:  Local Flag.  Always set to 0 
       
      Algorithm:              1 octet 
                              Flex-Algo value is between 128 and 255 
        
       
      Base offset:            3 octets 
                              Label base for Prefix-SIDs for given Algorithm 
                              The derived Prefix-SID is the sum of the base  
                              Offset and the Algo 0 label 
       
      Index Offset:           4 octets 
                              Index offset counting from Algo 0 
                              The new label for Prefix is sum of (SRGB base +  
                              index + index offset) 
       
      The format of Base offset and Index Offset is the same as RFC8667. The choice of 
      advertising Base Offset or Index Offset MUST match the advertisement of original 
      Prefix-SID method from the same router. 
       
   4. Compatibility 

      For nodes that do not support Algorithm Offset for Adj-SID extension, the label 
      stack could use normal Adj-SID, providing that the node still support Flex-Algo 
      Prefix SID. 

      For TI-LFA, there would be two modes of operation - loose or strict. For strict 
      mode, all Adj-SID involved in TI-LFA candidate path must be derived with offset 
      method. 

      For loose mode, Adj-SID in the TI-LFA candidate path could be a mix of Adj-SID's 
      with and without offset. This allows backward compatibility with routers which only 
      support Flex-Algo. 

       
       
       
       
       
       
       
       
   5. OSPF extension 

      The following TLVs are advertised in the Router Information Opaque LSA (defined in 
      [RFC7770]).  these TLVs are applicable to both OSPFv2 and OSPFv3. 


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   5.1. Algorithm Offset for Adj-SID 

          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       | 
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
         |   Algorithm   | 
         +---------------------------------------------------------------+ 
         |          SID/Label Offset/Index Offset (variable)             ~ 
         +---------------------------------------------------------------+ 
         ~  Flags/R/MT-ID/Algo/Weight/SID/Label/Index Offset(variable)   ~ 
         +---------------------------------------------------------------+ 
       
       
       where: 
       
            Type:    TBD 
       
            Length:  Variable 
       
            Flags:   Single-octet field containing the following flags: 
       
                   0 1 2 3 4 5 6 7 
                  +-+-+-+-+-+-+-+-+ 
                  |B|V|L|         | 
                  +-+-+-+-+-+-+-+-+ 
       
               where: 
       
                     B-Flag:  Backup Flag.  If set, the Adj-SID is eligible 
                              for protection (e.g., using IP Fast Reroute 
                              (IPFRR) or MPLS Fast Reroute (MPLS-FRR)) as 
                              described in [RFC8402]. 
       
                     V-Flag:  Value Flag.  If set, then it carries 
                              a label value. If not set, it is an index value. 
       
                     L-Flag:  Local Flag.  Always set to 1 
                
       
                 Other bits:  Reserved.  These MUST be zero when sent and are 
                              ignored when received. 
       
             MT-ID:           Multi-Topology ID (as defined in [RFC4915] 
       
            Weight:           Weight used for load-balancing purposes.  The use of the 
                              weight is defined in [RFC8402]. 
       
        
         Algorithm:           1 octets 
                              Flex-Algo value is between 128 and 255. 
							  
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       Base Offset:          3 octets 
                             Local label base for Adjacency-SIDs for given Flex- 
                             Algorithm. The derived Adjacency-SID is the sum of the base  
                             offset and the Algo 0 label 
       
      Index Offset:          4 octets 
                             If Adjacency-SID is advertised as index, this provides an  
                             offset index value. The new label is sum of (SRGB base +  
                             index + index offset) 
       
      The format of Base Offset and Index Offset is the same as RFC8665 or RFC8666. The 
      choice of advertising Base Offset or Index Offset must match the advertisement of 
      original Adjacency-SID method from the same router. 
       
       

   5.2. Algorithm Offset for LAN based Adj-SID 

          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     | 
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
         |   Algorithm   | 
         +---------------------------------------------------------------+ 
         |                        Neighbor ID                            | 
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
         |          SID/Label Offset/Index Offset (variable)             ~ 
         +---------------------------------------------------------------+ 
         ~ Flags/R/MT-ID/Weight/Algo/NHR ID/S/Lab/Index Offset(variable) ~ 
         +---------------------------------------------------------------+ 
       
       
      where: 
       
            Type:    TBD 
       
            Length:  Variable 
       
                     Flags:  Same as 5.1 
       
                  Reserved:  Same as 5.1 
       
             MT-ID:          Same as 5.1 
       
            Weight:          Same as 5.1 
       
         Algorithm:          Same as 5.1 
       
       Neighbor ID:          The Router ID of the neighbor for which the LAN 
                             Adjacency SID is advertised 

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       Base offset:          Same as 5.1   
      Index Offset:          Same as 5.1 
       
       
       
       
   5.3. Algorithm Offset for Prefix SID  

          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 Offset/Label Offset(variable)              ~ 
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
         ~     Flags/R/MT-ID/Algo/SID/Index/Label Offset(variable)       ~ 
         +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
       
       
       
         where: 
       
            Type:    TDB 
       
            Length:  Variable 
       
            Flags:   Single-octet field.  The following flags are defined: 
       
                    0  1  2  3  4  5  6  7 
                  +--+--+--+--+--+--+--+--+ 
                  |  |  |  |E |V |L |  |  | 
                  +--+--+--+--+--+--+--+--+ 
       

                     E-Flag:  Explicit Null Flag.  If set, any upstream neighbor 
                              of the Prefix-SID originator MUST replace the Prefix-SID 
                              with the Explicit NULL label (0 for IPv4) before 
                              forwarding the packet. 
       
                     V-Flag:  Value Flag.  If set, then it carries 
                              a label value. If not set, it is an index value. 
       
                     L-Flag:  Local Flag.  Always set to 0 
       
                 Other bits:  Reserved.  These MUST be zero when sent and are 
                              ignored when received. 
       
       
            MT-ID:            Multi-Topology ID (as defined in [RFC4915]) 
       
       
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         Algorithm:          1 octet 
                             Flex-Algo value is between 128 and 255 
        
       
       Base offset:          3 octets 
                             Label base for Prefix-SIDs for given Algorithm 
                             The derived Prefix-SID is the sum of the base  
                             Offset and the Algo 0 label 
       
      Index Offset:          4 octets 
                             Index offset counting from Algo 0 
                             The new label for Prefix is sum of (SRGB base +  
                             index + index offset) 
       
      The format of Base offset and Index Offset is the same as RFC8665 or RFC8666. The 
      choice of advertising Base Offset or Index Offset MUST match the advertisement of 
      original Prefix-SID method from the same router. 
       
       

       

       

   6. Security Consideration 

      TBD 

   7. References 

   7.1. Normative References 

      [RFC2119]     Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", 
                    BCP 14, RFC 2119, March 1997. 

   7.2. Informative References 

       
      [RFC8665]     Psenak, P., Ed., Previdi, S., Ed., Filfils, C., Gredler, 
                    H., Shakir, R., Henderickx, W., and J. Tantsura, "OSPF 
                    Extensions for Segment Routing", RFC 8665, 
                    DOI 10.17487/RFC8665, December 2019, 
                    <https://www.rfc-editor.org/info/rfc8665>. 
       
      [RFC8666]     Psenak, P., Ed. and S. Previdi, Ed., "OSPFv3 Extensions 
                    for Segment Routing", RFC 8666, DOI 10.17487/RFC8666, 
                    December 2019, <https://www.rfc-editor.org/info/rfc8666> 
       
      [RFC8667]     Previdi, S., Ed., Ginsberg, L., Ed., Filsfils, C., 
                    Bashandy, A., Gredler, H., and B. Decraene, "IS-IS 
                    Extensions for Segment Routing", RFC 8667, 
                    DOI 10.17487/RFC8667, December 2019, 
                    <https://www.rfc-editor.org/info/rfc8667>. 
               
           
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       [TI-LFA]     Litkowski, S., Bashandy, A., Filsfils, C., Francois, P., 
                    Decraene, B., and D. Voyer, "Topology Independent Fast 
                    Reroute using Segment Routing",  
                    <https://datatracker.ietf.org/doc/html/draft-ietf-rtgwg-segment- 
                    routing-ti-lfa> 
       
       [FLEXAGLO]   S. Hegde, P. Psenak and etc, IGP Flexible Algorithm 
                    https://datatracker.ietf.org/doc/draft-ietf-lsr-flex-algo 
       
       
       [ISO10589]   International Organization for Standardization, 
                    "Information technology -- Telecommunications and 
                    information exchange between systems -- Intermediate 
                    system to Intermediate system intra-domain routeing 
                    information exchange protocol for use in conjunction with 
                    the protocol for providing the connectionless-mode network 
                    service (ISO 8473)", ISO/IEC 10589:2002, Second Edition, 
                    November 2002. 
       
               

   8. Acknowledgments 

         
           The following people have contributed to this document: 
               Shraddha Hegde, Juniper Networks 
            
         
         
        Authors' Address 
         
        Louis Chan (Editor)  
           Juniper Networks Group (Hong Kong) Limited 
           Suites 3001-7 
           30th Floor Tower 2 
           Times Square 
           1 Matheson Street 
           Causeway Bay 
           Hong Kong 
         
           Phone: +852-25876659 
           Email: louisc@juniper.net 
         
         
        Krzysztof Grzegorz Szarkowicz 
           Juniper Networks 
           Parkring 10 
           A-1010 Wien 
           Austria 
         
           Phone: +49 89 203012127 
           Email: kszarkowicz@juniper.net 
       
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