Encapsulating MPLS in UDP
draft-ietf-mpls-in-udp-02

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Document Type Active Internet-Draft (mpls WG)
Last updated 2013-06-08
Replaces draft-xu-mpls-in-udp
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Network working group                                             X. Xu 
Internet Draft                                                   Huawei 
Category: Standard Track                                       N. Sheth         
                                                                Juniper         
                                                                L. Yong 
                                                                 Huawei 
                                                           C. Pignataro 
                                                                  Cisco 
                                                                 Y. Fan 
                                                          China Telecom  
                                                                               
Expires: December 2013                                     June 9, 2013 
                                                                                
                                      
                         Encapsulating MPLS in UDP  
                                      
                         draft-ietf-mpls-in-udp-02 

Abstract 

   Existing technologies to encapsulate Multi-Protocol Label Switching 
   (MPLS) over IP are not adequate for efficient load balancing of MPLS 
   application traffic, such as MPLS-based Layer2 Virtual Private 
   Network (L2VPN) or Layer3 Virtual Private Network (L3VPN) traffic 
   across IP networks. This document specifies additional IP-based 
   encapsulation technology, referred to as MPLS-in-User Datagram 
   Protocol (UDP), which can facilitate the load balancing of MPLS 
   application traffic across IP networks.  

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   
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   This Internet-Draft will expire on December 9, 2013. 

 
 
 
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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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   the Trust Legal Provisions and are provided without warranty as 
   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 
      1.1. Existing Technologies .................................. 3 
      1.2. Motivations for MPLS-in-UDP Encapsulation .............. 4 
   2. Terminology ................................................. 4 
   3. Encapsulation in UDP ........................................ 4 
   4. Processing Procedures ....................................... 5 
   5. Applicability ............................................... 6 
   6. Security Considerations ..................................... 6 
   7. IANA Considerations ......................................... 6 
   8. Acknowledgements ............................................ 6 
   9. References .................................................. 7 
      9.1. Normative References ................................... 7 
      9.2. Informative References ................................. 7 
   Authors' Addresses ............................................. 8 

 
 
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1. Introduction 

   To fully utilize the bandwidth available in IP networks and/or 
   facilitate recovery from a link or node failure, load balancing of 
   traffic over Equal Cost Multi-Path (ECMP) and/or Link Aggregation 
   Group (LAG) across IP networks is widely used. In effect, most 
   existing core routers in IP networks are already capable of 
   distributing IP traffic flows over ECMP paths and/or LAG based on the 
   hash of the five-tuple of User Datagram Protocol (UDP)[RFC768] and 
   Transmission Control Protocol (TCP) packets (i.e., source IP address, 
   destination IP address, source port, destination port, and protocol). 

   In practice, there are some scenarios for Multi-Protocol Label 
   Switching (MPLS) applications (e.g., MPLS-based Layer2 Virtual 
   Private Network (L2VPN) or Layer3 Virtual Private Network (L3VPN)) 
   where the MPLS application traffic needs to be transported through 
   IP-based tunnels, rather than MPLS tunnels. For example, MPLS-based 
   L2VPN or L3VPN technologies may be used for interconnecting 
   geographically dispersed enterprise data centers or branch offices 
   across IP Wide Area Networks (WAN) where enterprise own router 
   devices are deployed as L2VPN or L3VPN Provider Edge (PE) routers. In 
   this case, efficient load balancing of the MPLS application traffic 
   across IP networks is very desirable.  

1.1. Existing Technologies 

   With existing IP-based encapsulation methods for MPLS applications, 
   such as MPLS-in-IP and MPLS-in-Generic Routing Encapsulation (GRE) 
   [RFC4023] or even MPLS-in-Layer Two Tunneling Protocol - Version 3 
   (L2TPv3)[RFC4817], distinct customer traffic flows between a given PE 
   router pair would be encapsulated with the same IP-based tunnel 
   headers prior to traversing the core of the IP WAN. Since the 
   encapsulated traffic is neither TCP nor UDP traffic, for many 
   existing core routers which could only perform hash calculation on 
   fields in the IP headers of those tunnels (i.e., source IP address, 
   destination IP address), it would be hard to achieve a fine-grained 
   load balancing of these traffic flows across the network core due to 
   the lack of adequate entropy information.  

   [RFC5640] describes a method for improving the load balancing 
   efficiency in a network carrying Softwire Mesh service over L2TPv3 
   and GRE encapsulation. However, this method requires core routers to 
   be capable of performing hash calculation on the "load-balancing" 
   field contained in the tunnel encapsulation headers (i.e., the 
   Session ID field in the L2TPv3 header or the Key field in the GRE 

 
 
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   header), which means a non-trivial change to the date plane of many 
   existing core routers.  

1.2. Motivations for MPLS-in-UDP Encapsulation 

   On basis of the fact that most existing core routers (i.e., P routers 
   in the context of MPLS-based L2VPN or L3VPN) are already capable of 
   balancing IP traffic flows over the IP networks based on the hash of 
   the five-tuple of UDP packets, it would be advantageous to use MPLS-
   in-UDP encapsulation instead of MPLS-in-GRE or MPLS-in-L2TPv3 in the 
   environments where the load balancing of MPLS application traffic 
   across IP networks is much desired but the load balancing mechanisms 
   defined in [RFC5640] have not yet been widely supported by most 
   existing core routers. In this way, the default load balancing 
   capability of most existing core routers as mentioned above can be 
   utilized directly without requiring any change to them.  

2. Terminology 

   This memo makes use of the terms defined in [RFC4364] and [RFC4664].  

3. Encapsulation in UDP 

   MPLS-in-UDP encapsulation format is shown as follows: 

   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  
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |    Source Port = Entropy      |       Dest Port = MPLS        | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |           UDP Length          |        UDP Checksum           | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 
   |                                                               | 
   ~                       MPLS Label Stack                        ~ 
   |                                                               | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+            
   |                                                               | 
   ~                         Message Body                          ~ 
   |                                                               | 
   +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ 

            Source Port of UDP 

                This field contains an entropy value that is generated by 
                the ingress PE router. For example, the entropy value can 
                be generated by performing hash calculation on certain 

 
 
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                fields in the customer packets (e.g., the five tuple of 
                UDP/TCP packets).         

            Destination Port of UDP 

                This field is set to a value (TBD) indicating that the 
                UDP tunnel payload is a MPLS packet. As for whether the 
                top label in the MPLS label stack is downstream-assigned 
                or upstream-assigned, it SHOULD be determined based on  
                the tunnel destination IP address. That is to say, if the 
                destination IP address is a multicast address, the top 
                label SHOULD be upstream-assigned, otherwise if the 
                destination IP address is a unicast address, it SHOULD be 
                downstream-assigned. 

            UDP Length 

                The usage of this field is in accordance with the current 
                UDP specification. 

            UDP Checksum  

                The usage of this field is in accordance with the current 
                UDP specification. To simplify the operation on egress PE 
                routers, this field is RECOMMENDED to be set to zero in 
                IPv4 UDP encapsulation case, and even in IPv6 UDP 
                encapsulation case if appropriate[RFC6935][RFC6936].  

            MPLS Label Stack 

                This field contains an MPLS Label Stack as defined in            
                [RFC3032]. 

            Message Body 

                This field contains one MPLS message body. 

4. Processing Procedures   

   This MPLS-in-UDP encapsulation causes MPLS packets to be forwarded 
   through "UDP tunnels". When performing MPLS-in-UDP encapsulation by 
   an ingress PE router, the entropy value would be generated by the 
   ingress PE router and then be filled in the Source Port field of the 
   UDP header. As such, P routers, upon receiving these UDP encapsulated 
   packets, could balance these packets based on the hash of the five-
   tuple of UDP packets.  

 
 
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   Upon receiving these UDP encapsulated packets, egress PE routers 
   would decapsulate them by removing the UDP headers and then process 
   them accordingly. 

   As for other common processing procedures associated with tunneling 
   encapsulation technologies including but not limited to Maximum 
   Transmission Unit (MTU) and preventing fragmentation and reassembly, 
   Time to Live (TTL) and differentiated services, the corresponding 
   procedures defined in [RFC4023] which are applicable for MPLS-in-IP 
   and MPLS-in-GRE encapsulation formats SHOULD be followed. 

5. Applicability 

   Besides the MPLS-based L3VPN [RFC4364] and L2VPN [RFC4761, RFC4762] 
   applications, MPLS-in-UDP encapsulation could apply to other MPLS 
   applications including but not limited to 6PE [RFC4798] and PWE3 
   services. 

6. Security Considerations 

   Just like MPLS-in-GRE and MPLS-in-IP encapsulation formats, the MPLS-
   in-UDP encapsulation format defined in this document by itself cannot 
   ensure the integrity and privacy of data packets being transported 
   through the MPLS-in-UDP tunnels and cannot enable the tunnel 
   decapsulators to authenticate the tunnel encapsulator. In the case 
   where any of the above security issues is concerned, the MPLS-in-UDP 
   tunnels SHOULD be secured with IPsec in transport mode. In this way, 
   the UDP header would not be visible to P routers anymore. As a result, 
   the meaning of adopting MPLS-in-UDP encapsulation format as an 
   alternative to MPLS-in-GRE and MPLS-in-IP encapsulation formats is 
   lost. Hence, MPLS-in-UDP encapsulation format SHOULD be used only in 
   the scenarios where all the security issues as mentioned above are 
   not significant concerns. For example, in a data center environment, 
   the whole network including P routers and PE routers are under the 
   control of a single administrative entity and therefore there is no 
   need to worry about the above security issues. 

7. IANA Considerations 

   One UDP destination port number indicating MPLS needs to be allocated 
   by IANA. 

8. Acknowledgements 

   Thanks to Shane Amante, Dino Farinacci, Keshava A K, Ivan Pepelnjak, 
   Eric Rosen, Andrew G. Malis, Kireeti Kompella, Marshall Eubanks, 
   George Swallow, Loa Andersson, Ross Callon, Vivek Kumar, Weiguo Hao, 

 
 
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   Zhenxiao Liu and Xing Tong for their valuable comments and 
   suggestions on this document. Thanks to Daniel King, Gregory Mirsky 
   and Eric Osborne for their valuable reviews on this document. 

9. References 

9.1. Normative References 

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

9.2. Informative References 

   [RFC4364] Rosen, E and Y. Rekhter, "BGP/MPLS IP Virtual Private              
             Networks (VPNs)", RFC 4364, February 2006. 

   [RFC4664] Andersson, L. and Rosen, E. (Editors),"Framework for Layer         
             2 Virtual Private Networks (L2VPNs)", RFC 4664, Sept 2006. 

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

   [RFC4817] M. Townsley, C. Pignataro, S. Wainner, T. Seely and J. 
             Young, "Encapsulation of MPLS over Layer 2 Tunneling 
             Protocol Version 3, March 2007. 

   [RFC5640] Filsfils, C., Mohapatra, P., and C. Pignataro, "Load-
             Balancing for Mesh Softwires", RFC 5640, August 2009. 

   [RFC5332] Eckert, T., Rosen, E., Aggarwal, R., and Y. Rekhter, "MPLS         
             Multicast Encapsulations", RFC 5332, August 2008. 

   [RFC4798] J Declerq et al., "Connecting IPv6 Islands over IPv4 MPLS 
             using IPv6 Provider Edge Routers (6PE)", RFC4798, February 
             2007. 

   [RFC4761] Kompella, K. and Y. Rekhter, "Virtual Private LAN Service 
             (VPLS) Using BGP for Auto-Discovery and Signaling", RFC 
             4761, January 2007.  

   [RFC4762] Lasserre, M. and V. Kompella, "Virtual Private LAN Service         
             (VPLS) Using Label Distribution Protocol (LDP) Signaling",         
             RFC 4762, January 2007. 

   [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,             
             Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack             
             Encoding", RFC 3032, January 2001. 

 
 
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   [RFC768]  Postel, J., "User Datagram Protocol", STD 6, RFC 768,              
             August 1980. 

   [RFC6935] Eubanks, M., Chimento, P., and M. Westerlund, "UDP 
             Checksums for Tunneled Packets", RFC6935,              
             Feburary 2013. 

   [RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement 
             for the use of IPv6 UDP Datagrams with Zero Checksums", 
             RFC6936, Feburary 2013. 

   [IP-in-UDP] Xu, etc, "Encapsulating IP in UDP", draft-xu-softwire-ip-
             in-udp-01 (work in progress), February 2013. 

Authors' Addresses 

   Xiaohu Xu 
   Huawei Technologies 
   Beijing, China 
   Phone: +86-10-60610041 
   Email: xuxiaohu@huawei.com 
    
   Nischal Sheth 
   Juniper Networks 
   1194 N. Mathilda Ave 
   Sunnyvale, CA 94089 
   Email: nsheth@juniper.net 
    
   Lucy Yong 
   Huawei USA 
   5340 Legacy Dr. 
   Plano TX75025 
   Phone: 469-277-5837 
   Email: Lucy.yong@huawei.com 
    
   Carlos Pignataro 
   Cisco Systems 
   7200-12 Kit Creek Road 
   Research Triangle Park, NC 27709 
   USA 
   EMail: cpignata@cisco.com 
    
   Yongbing Fan  
   China Telecom  
   Guangzhou, China.  
   Phone: +86 20 38639121  
   Email: fanyb@gsta.com  

 
 
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   Zhenbin Li 
   Huawei Technologies,
   Beijing, China 
   Phone: +86-10-60613676
   Email: lizhenbin@huawei.com 

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