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Encapsulating MPLS in UDP

The information below is for an old version of the document.
Document Type
This is an older version of an Internet-Draft that was ultimately published as RFC 7510.
Authors Xiaohu Xu , Nischal Sheth , Lucy Yong , Yongbing Fan
Last updated 2013-01-12
Replaces draft-xu-mpls-in-udp
RFC stream Internet Engineering Task Force (IETF)
Additional resources Mailing list discussion
Stream WG state WG Document
Associated WG milestone
Jun 2015
++ Progress draft-ietf-mpls-in-udp to publication
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IESG IESG state Became RFC 7510 (Proposed Standard)
Consensus boilerplate Unknown
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Network working group                                             X. Xu 

Internet Draft                                                   Huawei 

Category: Standard Track                                       N. Sheth         

                                                       Contrail Systems         

                                                                L. Yong 


                                                            C Pignataro 


                                                                 Y. Fan 

                                                          China Telecom  


Expires: July 2013                                     January 11, 2013 



                         Encapsulating MPLS in UDP  




   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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   time.  It is inappropriate to use Internet-Drafts as reference
   material or to cite them other than as "work in progress."

   The list of current Internet-Drafts can be accessed at 




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   The list of Internet-Draft Shadow Directories can be accessed at

   This Internet-Draft will expire on July 11, 2013. 

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
   Provisions Relating to IETF Documents
   ( in effect on the date of
   publication of this document.  Please review these documents
   carefully, as they describe your rights and restrictions with respect
   to this document.  Code Components extracted from this document must
   include Simplified BSD License text as described in Section 4.e of
   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", 


   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 


   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 much 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                   


   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 



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                certain 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 the MPLS 

                packet encapsulated in the UDP header is a MPLS one or a 

                MPLS one with upstream-assigned label. 

            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.     

            MPLS Label Stack 

                This field contains an MPLS Label Stack as defined in            


            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.  

   P routers, upon receiving these UDP encapsulated packets, could 

   balance these packets based on the hash of the five-tuple of UDP 


   Upon receiving these UDP encapsulated packets, egress PE routers 

   would decapsulate them by removing the UDP headers and then process 

   them accordingly. 



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   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] 

   [E-VPN] 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 seeable 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 

   Two distinct UDP destination port numbers indicating MPLS and MPLS 

   with upstream-assigned label respectively need to be assigned by 


8. Acknowledgements 

   Thanks to Shane Amante, Dino Farinacci, Keshava A K, Ivan Pepelnjak, 

   Eric Rosen, Andrew G. Malis, Kireeti Kompella, Marshall Eubanks, 

   Vivek Kumar, Weiguo Hao, Zhenxiao Liu and Xing Tong for their 

   valuable comments on the idea of MPLS-in-UDP encapsulation. Thanks 

   to Daniel King, Gregory Mirsky and Eric Osborne for their valuable 

   reviews on this draft. 



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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. 

   [RFC5332] Eckert, T., Rosen, E., Aggarwal, R., and Y. Rekhter, "MPLS         

             Multicast Encapsulations", RFC 5332, August 2008. 

   [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. 

   [RFC6391] Bryant, S., Filsfils, C., Drafz, U., Kompella, V., Regan,          

             J., and S. Amante, "Flow Aware Transport of Pseudowires            

             over an MPLS Packet Switched Network", RFC6391, November 


   [RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and L. 

             Yong, "The Use of Entropy Labels in MPLS Forwarding", 

             draft-ietf-mpls-entropy-label-01, work in progress, 

             October, 2011. 

   [RFC5512] Mohapatra, P. and E. Rosen, "The BGP Encapsulation                 

             Subsequent Address Family Identifier (SAFI) and the                

             BGP Tunnel Encapsulation Attribute", RFC 5512, April               


   [RFC4798] J Declerq et al., "Connecting IPv6 Islands over IPv4 MPLS 

             using IPv6 Provider Edge Routers (6PE)", RFC4798, February 




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   [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. 

   [E-VPN] Aggarwal et al., "BGP MPLS Based Ethernet VPN", draft-ietf-          

             l2vpn-evpn-00.txt, work in progress, February, 2012. 

   [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,             

             Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack             

             Encoding", RFC 3032, January 2001. 

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

             August 1980. 

   [I-D.ietf-6man-udpchecksums] Eubanks, M., Chimento, P., and M. 

             Westerlund, "UDP Checksums for Tunneled Packets",              

             draft-ietf-6man-udpchecksums-04 (work in progress),              

             September 2012. 

   [I-D.ietf-6man-udpzero] Fairhurst, G. and M. Westerlund, 

             "Applicability Statement for the use of IPv6 UDP Datagrams 

             with Zero Checksums", draft-ietf-6man-udpzero-07 (work in 

             progress), October 2012. 

Authors' Addresses 

   Xiaohu Xu 

   Huawei Technologies, 

   Beijing, China 

   Phone: +86-10-60610041 



   Nischal Sheth 

   Contrail Systems  



   Lucy Yong 

   Huawei USA 

   5340 Legacy Dr. 

   Plano TX75025 

   Phone: 469-277-5837 





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   Carlos Pignataro 

   Cisco Systems 

   7200-12 Kit Creek Road 

   Research Triangle Park, NC  27709 




   Yongbing Fan  

   China Telecom  

   Guangzhou, China.  

   Phone: +86 20 38639121  



   Zhenbin Li 

   Huawei Technologies, 

   Beijing, China 

   Phone: +86-10-60613676


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