Network working group                                            X. Xu
Internet Draft                                                  Huawei
Category: Standard Track                                      N. Sheth
                                                               L. Yong
                                                          C. Pignataro
                                                                Y. Fan
                                                         China Telecom

Expires: March 2014                                  September 9, 2013

                         Encapsulating MPLS in UDP



   This document specifies an additional IP-based encapsulation for
   MPLS, referred to as MPLS-in-UDP (User Datagram Protocol), which is
   applicable in some circumstances. This document only describes the
   MPLS-in-UDP encapsulation.

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
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   This Internet-Draft will expire on March 9, 2014.

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Copyright Notice

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   described in the Simplified BSD License.

Table of Contents

   1. Introduction ................................................ 3
      1.1. Existing Encapsulations ................................ 3
      1.2. Motivations for MPLS-in-UDP Encapsulation .............. 4
   2. Terminology ................................................. 4
   3. Encapsulation in UDP......................................... 4
   4. Processing Procedures ....................................... 5
   5. Congestion Considerations ................................... 6
   6. Security Considerations ..................................... 6
   7. IANA Considerations ......................................... 6
   8. Contributors ................................................ 7
   9. Acknowledgements ............................................ 7
   10. References ................................................. 7
      10.1. Normative References .................................. 7
      10.2. Informative References ................................ 8
   Authors' Addresses ............................................. 8

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1. Introduction

   This document specifies an additional IP-based encapsulation for
   MPLS, referred to as MPLS-in-UDP (User Datagram Protocol). It also
   describes the applicability of this encapsulation in presence of
   other IP-based encapsulations for MPLS.

   This encapsulation allows for two Label Switching Routers (LSR) to
   be adjacent on a Label Switched Path (LSP), while separated by an
   IP network. In order to support this encapsulation, each LSR needs
   to know the capability to decapsulate MPLS-in-UDP by the remote
   LSRs. This specification defines only the data plane encapsulation
   and does not concern itself with how the knowledge to use this
   encapsulation is conveyed.

   An applicability statement will compare situations in which using
   the MPLS-in-UDP encapsulation might be advantageous over other IP-
   based encapsulations for MPLS. One of the key considerations in
   this respect is how to achieve efficient load-balance of traffic
   over Equal Cost Multi-Path (ECMP) and/or Link Aggregation Group

1.1. Existing Encapsulations

   Currently, there are a number of IP-based encapsulations for MPLS.
   These include MPLS-in-IP, MPLS-in- GRE (Generic Routing
   Encapsulation) [RFC4023], and MPLS-in-L2TPv3 (Layer Two Tunneling
   Protocol - Version 3)[RFC4817]. In all these methods, the IP
   addresses can be varied to achieve load-balancing.

   All these IP-based encapsulations for MPLS are specified for both
   IPv4 and IPv6. In the case of IPv6-based encapsulations, the IPv6
   Flow Label can be used for ECMP and LAGs [RFC6438].

   For MPLS-in-GRE as well as MPLS-in-L2TPv3, protocol fields (the GRE
   Key and the L2TPv3 Session ID respectively) can be used as the
   load-balancing key. This method is described in [RFC5640]. For this,
   however, core routers need to understand these fields in the
   context of being used as load-balancing keys.

   In terms of MPLS-based encapsulations, load-balancing is achieved
   with the introduction of the Entropy Label [RFC6790].

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1.2. Motivations for MPLS-in-UDP Encapsulation

   Currently, many existing routers in IP networks are already capable
   of distributing IP traffic "microflows" [RFC2474] 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).

   The motivation of MPLS-in-UDP is to leverage this existing
   capability to provide load-balancing of MPLS traffic over IP

2. Terminology

   The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
   this document are to be interpreted as described in RFC-2119

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 a 16-bit entropy value that is
                generated by the ingress PE router. For example, the
                entropy value can be generated by performing hash
                calculation on certain fields in the customer packets
                (e.g., the five tuple of UDP/TCP packets).

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            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 [RFC768].

            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 also in
                IPv6 UDP encapsulation case if appropriate [RFC6935]

            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. 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
   "Common Procedures" defined in [RFC4023] which are applicable for
   MPLS-in-IP and MPLS-in-GRE encapsulation formats SHOULD be followed.

5. Congestion Considerations

   MPLS can carry a number of different protocols as payloads. When an
   MPLS/UDP flow carries IP-based traffic, the aggregate traffic is
   assumed to be TCP friendly due to the congestion control mechanisms
   used by the payload traffic. Packet loss will trigger the necessary
   reduction in offered load, and no additional congestion avoidance
   action is necessary. When an MPLS/UDP flow carries payload traffic
   that is not known to be TCP friendly and the flow runs across an
   unprovisioned path that could potentially become congested, the
   application that uses the encapsulation specified in this document
   MUST employ additional mechanisms to ensure that the offered load
   is reduced appropriately during periods of congestion.

6. Security Considerations

   Just like other IP-based encapsulations of MPLS, 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.

7. IANA Considerations

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

     Service Name : MPLS-in-UDP

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     Transport Protocol(s) : UDP

     Assignee : IESG <>

     Contact : IETF Chair <>.

     Description : Encapsulate MPLS packets in UDP tunnels.

     Reference : This document -- draft-ietf-mpls-in-udp (MPLS WG

     Port Number : To be assigned by IANA.

8. Contributors

   Zhenbin Li
   Huawei Technologies,
   Beijing, China
   Phone: +86-10-60613676

9. 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,
   Mark Szczesniak, Zhenxiao Liu and Xing Tong for their valuable
   comments andsuggestions on this document. Thanks to Daniel King,
   Gregory Mirsky and Eric Osborne for their valuable reviews on this

10. References

10.1. Normative References

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

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

   [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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10.2. Informative References

   [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.

   [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.

   [RFC2474] Nichols, K., Blake, S., Baker, F. and D. Black,
             "Definition of the Differentiated Services Field (DS
             Field) in the IPv4 and IPv6 Headers", RFC2474, December

   [RFC6438] Carpenter, B. and S. Amante, "Using the IPv6 Flow Label
             for Equal Cost Multipath Routing and Link Aggregation in
             Tunnels", RFC 6438, November 2011.

   [RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
             L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
             RFC 6790, November 2012.

Authors' Addresses

   Xiaohu Xu
   Huawei Technologies
   Beijing, China
   Phone: +86-10-60610041

   Nischal Sheth
   Juniper Networks
   1194 N. Mathilda Ave
   Sunnyvale, CA 94089

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   Lucy Yong
   Huawei USA
   5340 Legacy Dr.
   Plano TX75025
   Phone: 469-277-5837

   Carlos Pignataro
   Cisco Systems 7200-12 Kit Creek Road
   Research Triangle Park, NC 27709

   Yongbing Fan
   China Telecom
   Guangzhou, China.
   Phone: +86 20 38639121

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