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

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Internet-Draft          Encapsulating MPLS in UDP        January 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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   ( in effect on the date of
   publication of this document.  Please review these documents
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   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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