Internet DRAFT - draft-xu-mpls-in-udp


Network working group                                             X. Xu 
Internet Draft                                                   Huawei 
Category: Standard Track                                       N. Sheth         
                                                       Contrail Systems         
                                                                L. Yong 
                                                            C Pignataro 
                                                                 Y. Fan 
                                                          China Telecom  
Expires: May 2013                                     December 10, 2012 
                         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 

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Copyright Notice 

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   document authors.  All rights reserved. 

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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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