Connecting SPRING Islands over IP Networks
draft-xu-spring-islands-connection-over-ip-00

Network working group                                              X. Xu 
Internet Draft                                                    Huawei 
Category: Informational                                      S.Sivabalan        
                                                                   Cisco 
                                                                               
Expires: August 2014                                    February 8, 2014 
                                                                                
                                      
                 Connecting SPRING Islands over IP Networks  
                                      
               draft-xu-spring-islands-connection-over-ip-00 

Abstract 

   Segment Routing (SR) architecture [SR-ARCH] introduces a new MPLS 
   paradigm in which a sender of a packet is allowed to partially or 
   completely specify the route the packet takes through the network by 
   using stacked MPLS labels. The current SR architecture requires an 
   end-to-end MPLS Label Switched Path (LSP) between any two SR-enabled 
   routers (e.g., two adjacent hops of a given explicit path). In order 
   to enable SR to be deployed even when there are non-MPLS routers 
   along the path between two SR-enabled routers, it is desirable to 
   have an alternative, which allows the use of IP-based tunnels (e.g., 
   GRE tunnels) to connect two SR-enabled routers. This document 
   describes a mechanism for such usage. 

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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   material or to cite them other than as "work in progress." 

   This Internet-Draft will expire on August 8, 2014. 

    

                                           

 
 
 
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Copyright Notice 

   Copyright (c) 2013 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   
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   described in the Simplified BSD License. 

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]. 

Table of Contents 

    
   1. Introduction ................................................ 3 
   2. Terminology ................................................. 3 
   3. Packet Forwarding Process ................................... 3 
   4. Security Considerations ..................................... 4 
   5. IANA Considerations ......................................... 4 
   6. Acknowledgements ............................................ 4 
   7. References .................................................. 4 
      7.1. Normative References ................................... 4 
      7.2. Informative References  ................................ 4 
   Authors' Addresses ............................................. 4 

 
 
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1. Introduction 

   Segment Routing (SR) architecture [SR-ARCH] introduces a new MPLS 
   paradigm in which a sender of a packet is allowed to partially or 
   completely specify the route the packet takes through the network by 
   using stacked MPLS labels. In other words, this new paradigm could 
   support source routing by using the MPLS label stack where each MPLS 
   label represents a given hop that the packet must go through. Here 
   the MPLS label could be either locally significant or globally 
   significant.  

   The current SR architecture requires an end-to-end MPLS Label 
   Switched Path (LSP) between any two SR-enabled routers (e.g., any two 
   adjacent hops of a given explicit path). This means that SR cannot be 
   implemented if there is a part of the path between those two SR-
   enabled routers that does not support MPLS. 

   In order to enable SR to be deployed even when there are non-MPLS 
   routers along the path between two SR-enabled routers, it is 
   desirable to have an alternative, which allows the use of IP-based 
   tunnels (e.g., GRE tunnels) to connect two SR-enabled routers which 
   are specified as adjacent hops of a given explicit path. The tunnel 
   destination address would be the address of next-hop SR-enabled 
   router along the explicit path, and this would cause the packet to be 
   delivered to the next explicit hop. In this procedure, the ingress 
   and egress of IP-based tunnel themselves must support SR features 
   including the MPLS forwarding capability, whereas the transit routers 
   along the path between them don't need to support MPLS and SR. 

   The above mechanism is beneficial for incrementally deployment of the 
   SR technology, especially in the case where only a few specific 
   routers (e.g., service function nodes) in addition to Provider Edge 
   (PE) routers are actually required to be specified as explicit hops 
   of the loose explicit path.  

2. Terminology 

   This memo makes use of the terms defined in [RFC1195] and [SR-ARCH].  

3. Packet Forwarding Process 

   Assume a SR-enabled router X prepares to forward a MPLS packet to the 
   next node segment Y which is identified by the top label of the MPLS 
   packet, if the next-hop router Z which is physically adjacent to X is 
   a non-SR router, X would pop the top label (if required) and then 
   encapsulate the remaining MPLS packet into an IP-based tunnel(e.g., 

 
 
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   GRE) where the tunnel destination is an IP address of Y and the 
   tunnel source is an IP address of X. The IP encapsulated packet would 
   be forwarded according to the IP forwarding table. 

   Upon receipt of that IP encapsulated packet, Y would decapsulate it 
   and then process the decapsulated MPLS packet accordingly. 

   As for which tunnel encapsulation type should be used by X, it can be 
   manually specified on X or dynamically learnt from Y's advertisement 
   of its tunnel encapsulation capability. How to advertise tunnel 
   encapsulation capability is outside of the scope of this document. 

4. Security Considerations 

   TBD. 

5. IANA Considerations 

   No action is required for IANA.  

6. Acknowledgements 

   Thanks to. 

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. 

   [SR-ARCH] Filsfils, C., Previdi, S., Bashandy, A., Decraene, B.,             
             Litkowski, S., Horneffer, M., Milojevic, I., Shakir, R.,           
             Ytti, S., Henderickx, W., Tantsura, J., and E. Crabbe,             
             "Segment Routing Architecture", draft-filsfils-rtgwg-
             segment-routing-00 (work in progress), June 2013. 

7.2. Informative References 

   [RFC4023] Worster, T., Rekhter, Y., and E. Rosen, "Encapsulating MPLS 
             in IP or GRE", RFC4023, March 2005. 

Authors' Addresses 

   Xiaohu Xu 
   Huawei Technologies, 
   Beijing, China 

 
 
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   Phone: +86-10-60610041 
   Email: xuxiaohu@huawei.com 
    
   Siva Sivabalan 
   Cisco Systems 
    
   Email: msiva@cisco.com