Internet DRAFT - draft-chan-spring-srv6-sub-slice

draft-chan-spring-srv6-sub-slice



 
SPRING Working Group                                              Louis Chan 
INTERNET-DRAFT                                                          
Intended status: Standard Track                                   Juniper Networks 
Expires: Jan 4, 2023                                             Jul 4, 2022 
                                    
 
                                      
                             Sub-slicing for SRv6 
                     draft-chan-spring-srv6-sub-slice-00.txt 


Abstract 

   This document describes how to achieve further slicing or traffic engineering 
   interoperability between vendors without the use of SRH. 

   Slicing or traffic engineering information is encapsulated as part of the SRv6 SID. 
   Use of IP longest prefix match approach to identify the further slicing via sub-
   slice identifier. 

   The traffic engineering from one end to another end is seen as segment by segment 
   approach. This approach could solve the scalability of traffic engineering tunnels 
   required in a huge network, which order of N^2 has be considered. 

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 
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   http://datatracker.ietf.org/drafts/current/. 

   Internet-Drafts are draft documents valid for a maximum of six months and may be 
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   This Internet-Draft will expire on Jan 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 
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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. Encoding sub-slice in FUNCT:ARG................................3 
   4. Example of operation...........................................3 
   5. Solution to possible looping issue.............................4 
   6. Compatibility with SRv6 compression............................4 
   7. Interoperability consideration.................................5 
   8. Multi-level sub-slicing........................................5 
   9. Security Considerations........................................5 
   10. Others........................................................6 
   11. References....................................................6 
      11.1. Normative References.....................................6 
      11.2. Informative References...................................6 
   12. Acknowledgments...............................................6 
    
1. Introduction 

   The purpose of this document is to describe to a way to signal the desired slicing 
   or sub-slicing information with the SRv6 endpoint behavior SID.  

   The FUNCT:ARG portion of SRv6 SID is encoded with certain format to achieve such.  

   In the transit router, when the SRv6 packet is received, it is processed with IPv6 
   longest prefix match (LPM) approach, which in turn, could point the packet to 
   another tunnel, likely a SRv6-TE tunnel. The effect is similar to a binding 
   SID approach. 

   The benefits of this approach are 

   - Provide an easy interoperability method between vendors for slicing without the 
     full SRH header. This format looks legitimate to any vendors.  
   - Reduce the tunnels to be provisioned in the network based on tactical TE 
     strategy. It would give less work to controller to handle huge number of tunnels 
     in a big scale network. 
   - Provide an intrinsic backup path. Secondary path provisioning is not a 
     requirement. 

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. 
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3. Encoding sub-slice in FUNCT:ARG 

   The method is to encode the sub-slice information into the FUNCT:ARG or the 
   endpoint portion 

    
                   +------------+---------------+--------------------------+ 
                   |   Locator  |  Sub-slice ID |  Remainder for behavior  | 
                   +------------+---------------+--------------------------+ 
                                |<-        Endpoint Behavior             ->| 
    

   This format could be used in conjunction WITH or WITHOUT Flex-Algo. If it is used 
   with Flex-Algo, network slicing is expected. Therefore, the use of the term, sub-
   slice, is to allow further level of slicing within Flex-Algo. 

   The encoding of sub-slice information is right from the originator of endpoint 
   behavior. For example, the sub-slice information is encoded in END.DT4 and END.DT6 
   from the originator of the VPN. 

   No SRH is required in the first ingress PE to send out the packet. 

   Each node in transit would evaluate the IPv6 header according to longest prefix 
   match rule as normal IP processing. It will forward the packet according to locator 
   routes it learnt from routing protocol. 

   When a more specific IPv6 route with "locator + sub-slice", which is a longer 
   prefix, is programmed in the routing table, the forwarding decision would be 
   redirected to another TE tunnel. In this case, sub-slice is achieved. 

 
 

4. Example of operation 

              R1--/--C2--/--C3--/--R4        ;  "/ " means network in between 

    

   Between R1 and R4, it runs two L3VPN with END.DT4 SID. 
    
   Sub-slice TE tunnel is created between C2 and C3 for one of the VPN above. 
    
   The locator is encoded as  
   FC00:xxxx:nnnn::/48, where xxxx is the Flex-Algo portion. Here is 0200 as example 
                              nnnn is the locator portion. R1: 0001, R4: 0004 
    
   For the END.DT4 announced from R4 
    
   VPN1: FC00:0200:0004::1000 
   VPN2: FC00:0200:0004:0008::2000       ; 0008 here is a sub-slice ID 
    
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   From R1, it sends packets for both VPNs without any SRH. Below example only shows 
   the headers but not the payload. 
    
   In C2, its routing table has two entries. 
    
   a) FC00:0200:0004::0/48       - This is learnt via routing protocol 
   b) FC00:0200:0004:0008::0/64  - This entry is programmed by other means for TE 
    
   For VPN1 traffic, C2 will forward the packet using (a) route. 
    
   For VPN2 traffic, C2 will forward the traffic to another path via (b) route, and  
   attach tunnel information, like SRv6-TE. An example of additional hops programmed 
   in SRH sending out from C2 to C3 could be 
    
    FC00:0200:pppp::1            ; add SRH with nodes 
    FC00:0200:qqqq::1            ; where pppp and qqqq represent intermediate nodes 
    

   The SRv6-TE tunnel could be in the form of either insert mode or encapsulation 
   mode. C3 could received the packet with or without SRH depending on the 
   configuration.  

   C3 should remove SRH header if it is the endpoint of the tunnel. It would continue 
   to forward the packet according to FC00:0200:0004:0008::2000.  

   Between C2 and C3, sub-slice is thus achieved for VPN2 traffic. 

   It depends on C3 or subsequent routers' forwarding table programming. Another TE 
   action could be imposed based on /64 LPM interpretation. This allows easy 
   interoperability between vendors. C3 might be the border router from another vendor 
   domain. 

   If the above C2 to C3 tunnel is down, C2 would forward the packet using /48 route, 
   which is the default Flex-Algo route. Hence, backup path is readily available. 
   Secondary tunnel provisioning is therefore optional. 

    

5. Solution to possible looping issue 

   There is a possibility for routing loop in certain scenario. The options to 
   minimize the risk are 

   - Running OAM to detect the TE tunnel reachability up to the final end node. 
   - TE tunnel for sub-slice should be terminated on a trusted node, probably an ABR. 
     When the packet arrives this trusted node, either the packet is forwarded 
     properly, or discarded silently. 
   - Use of controller to detect the possibility of routing loop. Avoid or disable 
     the TE path for sub-slice when necessary. 

6. Compatibility with SRv6 compression  

   TBD for sub-slice notation. 

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   For the TE tunnel portion, it would be compatible to any SRv6 compression scheme. 
   This sub-slice would provide an interoperability between different domains which 
   run different kind of SRv6 compression mechanism. The lowest denominator is an SRv6 
   packet without SRH. 

7. Interoperability consideration 

   The benefit of this approach is to allow a clean handover of a SRv6 packet from one 
   domain to another domain.  

   With the use of Flex-Algo [FLEXALGO] in SRv6, there would be more granularity of 
   slicing information present in the header. A further example from section 4, 

        FC00:0200:0004:0008::2000      - 0200 means Flex-Algo A, sub-slice 0008  

        FC00:0300:0004:0009::2000      - 0300 means Flex-Algo B, sub-slice 0009  

    

   The two SRv6 connected domains do not require use of the same tunnel technology, 
   like plain Flex-Algo, SRv6-TE with or without compression. Each domain would have 
   enough information from the packet header to steer the traffic into specific 
   tunnel, if required. 

   On the other hand, the overhead of traffic engineering header is reduced from end 
   to end. If there is TE header overhead, it is reduced to local domain consumption 
   only. 

    

8. Multi-level sub-slicing 

   Multi-level of sub-slice is easily achievable via different prefix length. For 
   example, /48 up to the locator, /56 for first level sub-slice and /64 for second 
   level sub-slice. 

   As an example, /56 case could be used as an aggregate for a group of the endpoint 
   behavior function, and /64 are used on individual. 

   a) FC00:0200:0004::0/48        - No sub-slice 
   b) FC00:0200:0004:01xx::0/56   - 01 denotes a sub-slice  
   c) FC00:0200:0004:0103::0/64   - 0103 denotes further sub-slice. A more specific TE 
    
   With a longer prefix length, the traffic could be directed to more specific traffic 
   engineering path. The TE path could use any kind of tunnel method, like SRv6-TE 
   without header compression, or with compression.  
    

    

9. Security Considerations 

   TBD 

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10. Others 

   This proposed method also allow SRv6 traffic to tunnel through non-SRv6 domain in 
   the middle. Router C2 in the above example could initiate other kinds of tunnel, 
   which could be RSVP LSP, SR-TE LSP and etc. 

11. References 

11.1. Normative References 

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

11.2. Informative References 

   [RFC8200]  Deering, S. and R. Hinden, "Internet Protocol, Version 6 
              (IPv6) Specification", STD 86, RFC 8200, 
              DOI 10.17487/RFC8200, July 2017, 
              <https://www.rfc-editor.org/info/rfc8200>. 
       
   [RFC8754]  Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J., 
               Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header 
               (SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020, 
               <https://www.rfc-editor.org/info/rfc8754>. 
    
   [RFC8986]  Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer, 
              D., Matsushima, S., and Z. Li, "Segment Routing over IPv6 
              (SRv6) Network Programming", RFC 8986, 
              DOI 10.17487/RFC8986, February 2021, 
              <https://www.rfc-editor.org/info/rfc8986>. 
   [FLEXAGLO] S. Hegde, P. Psenak and etc, IGP Flexible Algorithm 
            <https://datatracker.ietf.org/doc/draft-ietf-lsr-flex-algo> 
             

12. Acknowledgments 

      
        The following people have contributed to this document: 
               Salih K A, Juniper Networks 
         
      
      
     Author Address 
      
     Louis Chan (editor) 
        Juniper Networks 
        2604, Cityplaza One, 1111 King's Road 
        Taikoo Shing 
        Hong Kong 
      
        Phone: +852-25876659 
        Email: louisc@juniper.net 


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