Network working group X. Xu
Internet Draft Huawei
Category: Standard Track N. Sheth
Contrail Systems
L. Yong
Huawei
C Pignataro
Cisco
Y. Fan
China Telecom
Expires: May 2013 December 6, 2012
Encapsulating MPLS in UDP
draft-xu-mpls-in-udp-05
Abstract
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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Conventions used in this document
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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 ............................................... 5
6. Security Considerations ..................................... 6
7. IANA Considerations ......................................... 6
8. Acknowledgements ............................................ 6
9. References .................................................. 6
9.1. Normative References ................................... 6
9.2. Informative References ................................. 6
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
protocol).
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 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 [RFC5460] 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
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the GRE 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 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 Packet ~
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
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
certain fields in the customer packets (e.g., the five
tuple of UDP/TCP packets).
Destination Port of UDP
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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.
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
packets.
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
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.
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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
IANA.
8. Acknowledgements
Thanks to Shane Amante, Dino Farinacci, Keshava A K, Ivan Pepelnjak,
Eric Rosen, Andrew G. Malis, Kireeti Kompella, Marshall Eubanks,
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.
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.
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[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
2011
[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
2009.
[RFC4798] J Declerq et al., "Connecting IPv6 Islands over IPv4 MPLS
using IPv6 Provider Edge Routers (6PE)", RFC4798, February
2007.
[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.
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[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
Email: xuxiaohu@huawei.com
Nischal Sheth
Contrail Systems
Email: nsheth@contrailsystems.com
Lucy Yong
Huawei USA
1700 Alma Dr. Suite 500
Plano, TX 75075, US
Email: lucyyong@huawei.com
Carlos Pignataro
Cisco System
Email: cpignata@cisco.com
Yongbing Fan
China Telecom
Guangzhou, China.
Phone: +86 20 38639121
Zhenbin Li
Huawei Technologies,
Beijing, China
Phone: +86-10-60613676
Email: lizhenbin@huawei.com
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