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

   Copyright (c) 2009 IETF Trust and the persons identified as the
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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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