Network working group X. Xu
Internet Draft Huawei
Category: Standard Track N. Sheth
Juniper
L. Yong
Huawei
C. Pignataro
Cisco
Y. Fan
China Telecom
Expires: March 2014 September 9, 2013
Encapsulating MPLS in UDP
draft-ietf-mpls-in-udp-03
Abstract
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
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This Internet-Draft will expire on March 9, 2014.
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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
(LAG).
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
networks.
2. Terminology
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].
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]
[RFC6936].
MPLS Label Stack
This field contains an MPLS Label Stack as defined in
[RFC3032].
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 <iesg@ietf.org>
Contact : IETF Chair <chair@ietf.org>.
Description : Encapsulate MPLS packets in UDP tunnels.
Reference : This document -- draft-ietf-mpls-in-udp (MPLS WG
document).
Port Number : To be assigned by IANA.
8. Contributors
Zhenbin Li
Huawei Technologies,
Beijing, China
Phone: +86-10-60613676
Email: lizhenbin@huawei.com
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
document.
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
1998.
[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
Email: xuxiaohu@huawei.com
Nischal Sheth
Juniper Networks
1194 N. Mathilda Ave
Sunnyvale, CA 94089
Email: nsheth@juniper.net
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Lucy Yong
Huawei USA
5340 Legacy Dr.
Plano TX75025
Phone: 469-277-5837
Email: Lucy.yong@huawei.com
Carlos Pignataro
Cisco Systems 7200-12 Kit Creek Road
Research Triangle Park, NC 27709
USA
Email: cpignata@cisco.com
Yongbing Fan
China Telecom
Guangzhou, China.
Phone: +86 20 38639121
Email: fanyb@gsta.com
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