MPLS D. Frost, Ed.
Internet-Draft S. Bryant, Ed.
Intended status: Standards Track Cisco Systems
Expires: August 28, 2010 M. Bocci, Ed.
Alcatel-Lucent
February 24, 2010
MPLS Transport Profile Data Plane Architecture
draft-ietf-mpls-tp-data-plane-00
Abstract
The Multiprotocol Label Switching (MPLS) Transport Profile (MPLS-TP)
is the set of MPLS protocol functions applicable to the construction
and operation of packet-switched transport networks. This document
specifies the subset of these functions that comprises the MPLS-TP
data plane: the architectural layer concerned with the encapsulation
and forwarding of packets within an MPLS-TP network.
This document is a product of a joint Internet Engineering Task Force
(IETF) / International Telecommunication Union Telecommunication
Standardization Sector (ITU-T) effort to include an MPLS Transport
Profile within the IETF MPLS and PWE3 architectures to support the
capabilities and functionalities of a packet transport network.
Requirements Language
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].
Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet-
Drafts.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at
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http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at
http://www.ietf.org/shadow.html.
This Internet-Draft will expire on August 28, 2010.
Copyright Notice
Copyright (c) 2010 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
Provisions Relating to IETF Documents
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described in the BSD License.
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
2. MPLS-TP Packet Encapsulation and Forwarding . . . . . . . . . 5
3. MPLS-TP Transport Entities . . . . . . . . . . . . . . . . . . 5
3.1. Label Switched Paths . . . . . . . . . . . . . . . . . . . 5
3.1.1. LSP Packet Encapsulation and Forwarding . . . . . . . 5
3.1.2. LSP Payloads . . . . . . . . . . . . . . . . . . . . . 6
3.1.3. LSP Types . . . . . . . . . . . . . . . . . . . . . . 6
3.2. Sections . . . . . . . . . . . . . . . . . . . . . . . . . 7
3.3. Pseudowires . . . . . . . . . . . . . . . . . . . . . . . 8
4. MPLS-TP Generic Associated Channel . . . . . . . . . . . . . . 8
5. Media-Specific Considerations . . . . . . . . . . . . . . . . 8
5.1. Ethernet . . . . . . . . . . . . . . . . . . . . . . . . . 8
5.1.1. Destination MAC Address Determination . . . . . . . . 8
5.2. Other Media . . . . . . . . . . . . . . . . . . . . . . . 9
6. Security Considerations . . . . . . . . . . . . . . . . . . . 9
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
The MPLS Transport Profile (MPLS-TP) [I-D.ietf-mpls-tp-framework] is
the set of protocol functions that meet the requirements [RFC5654]
for the application of MPLS to the construction and operation of
packet-switched transport networks. Packet transport networks are
defined and described in [I-D.ietf-mpls-tp-framework].
This document specifies the subset of protocol functions that
comprises the MPLS-TP data plane: the architectural layer concerned
with the encapsulation and forwarding of packets within an MPLS-TP
network.
This document is a product of a joint Internet Engineering Task Force
(IETF) / International Telecommunication Union Telecommunication
Standardization Sector (ITU-T) effort to include an MPLS Transport
Profile within the IETF MPLS and PWE3 architectures to support the
capabilities and functionalities of a packet transport network.
1.1. Scope
This document has the following purposes:
o To identify the data-plane functions within the MPLS Transport
Profile
o To indicate which of these data-plane functions an MPLS-TP
implementation is required to support
Note that the MPLS-TP functions discussed in this document are
considered OPTIONAL unless stated otherwise.
1.2. Terminology
Term Definition
------- ------------------------------------------
G-ACh Generic Associated Channel
GAL G-ACh Label
LER Label Edge Router
LSP Label Switched Path
LSR Label Switching Router
MAC Media Access Control
MPLS-TP MPLS Transport Profile
OAM Operations, Administration and Maintenance
PW Pseudowire
QoS Quality of Service
Additional definitions and terminology can be found in
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[I-D.ietf-mpls-tp-framework] and [RFC5654].
2. MPLS-TP Packet Encapsulation and Forwarding
This document defines the encapsulation and forwarding functions
applicable to packets traversing an MPLS-TP Label Switched Path
(LSP), Pseudowire (PW), or Section (see Section 3 for the definitions
of these transport entities). Encapsulation and forwarding functions
for packets outside an MPLS-TP LSP, PW, or Section, and mechanisms
for delivering packets to or from MPLS-TP LSPs, PWs, and Sections,
are outside the scope of this document.
3. MPLS-TP Transport Entities
The MPLS Transport Profile includes the following data-plane
transport entities:
o Label Switched Paths (LSPs)
o Sections
o Pseudowires (PWs)
3.1. Label Switched Paths
MPLS-TP LSPs are ordinary MPLS LSPs as defined in [RFC3031] except as
specifically noted otherwise in this document.
3.1.1. LSP Packet Encapsulation and Forwarding
Encapsulation and forwarding of packets traversing MPLS-TP LSPs MUST
follow standard MPLS packet encapsulation and forwarding as defined
in [RFC3031] and [RFC3032], except as explicitly stated otherwise in
this document.
Data-plane support for Internet Protocol (IP) packet encapsulation,
addressing, and forwarding is OPTIONAL.
Data-plane Quality of Service capabilities are included in the
MPLS-TP in the form of the MPLS Differentiated Services (DiffServ)
architecture [RFC3270]. Both E-LSP and L-LSP MPLS DiffServ modes are
included. The Traffic Class field (formerly the EXP field) of an
MPLS label follows the definition of [RFC5462] and [RFC3270] and MUST
be processed according to the rules specified in those documents.
The Pipe and Short Pipe DiffServ tunneling and TTL processing models
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described in [RFC3270] and [RFC3443] are included in the MPLS-TP.
The Uniform model is outside the scope of the MPLS-TP.
Per-platform, per-interface or other context-specific label space
[RFC5331] MAY be used for MPLS-TP LSPs. Note that the requirements
of a particular LSP type may dictate which label spaces it can use.
Per-packet Equal-Cost Multi-Path (ECMP) load-balancing is outside the
scope of the MPLS-TP.
Penultimate Hop Popping (PHP) MUST be disabled by default on MPLS-TP
LSPs.
Fragmentation procedures as specified in [RFC3032] are outside the
scope of the MPLS-TP.
3.1.2. LSP Payloads
The MPLS-TP includes support for the following LSP payload types:
o Network-layer protocol packets
o Pseudowire packets
The rules for processing LSP payloads that are network-layer protocol
packets SHALL be as specified in [RFC3032] except as specifically
noted otherwise in this document.
The rules for processing LSP payloads that are pseudowire packets
SHALL be as specified in [RFC3985] and the attendant standards
defined by the IETF Pseudowire Emulation Edge-to-Edge (PWE3) Working
Group.
Note that the payload of an MPLS-TP LSP may be a packet type that
itself contains one or more MPLS labels. This is true, for instance,
when the payload is a pseudowire or another MPLS-TP LSP. From the
data-plane perspective, however, an MPLS-TP packet is an MPLS packet
as specified in [RFC3032], and so in particular has precisely one
label stack, and one label in the stack with its S (Bottom of Stack)
bit set to 1.
3.1.3. LSP Types
The MPLS-TP includes the following LSP types:
o Point-to-point unidirectional
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o Point-to-point associated bidirectional
o Point-to-point co-routed bidirectional
o Point-to-multipoint unidirectional
Point-to-point unidirectional LSPs are supported by the basic MPLS
architecture [RFC3031] and are REQUIRED to function in the same
manner in the MPLS-TP data plane except as explicitly stated
otherwise in this document.
A point-to-point associated bidirectional LSP between LSRs A and B
consists of two unidirectional point-to-point LSPs, one from A to B
and the other from B to A, which are regarded as a pair providing a
single logical bidirectional transport path. The nodes A and B are
REQUIRED to be aware of this pairing relationship, but other nodes
need not be.
A point-to-point co-routed bidirectional LSP is a point-to-point
associated bidirectional LSP with the additional constraint that its
two unidirectional component LSPs follow the same path in the
network. This means that if one of the component LSPs follows the
path through the nodes N0, ..., Nk, originating on N0 and terminating
on Nk, then the path of the other component LSP is Nk, ..., N0, and
that at each node an ingress interface of one component LSP is an
egress interface of the other. In addition, each node along the path
is REQUIRED to be aware of the pairing relationship between the
component LSPs.
A point-to-multipoint unidirectional LSP functions in the same manner
in the data plane, with respect to basic label processing and packet-
switching operations, as a point-to-point unidirectional LSP, with
one difference: an LSR may have more than one (egress interface,
outgoing label) pair associated with the LSP, and any packet it
transmits on the LSP is transmitted out all associated egress
interfaces. Point-to-multipoint LSPs are described in [RFC4875] and
[RFC5332].
3.2. Sections
Two MPLS-TP LSRs are considered to be topologically adjacent at a
particular layer n >= 0 of the MPLS-TP LSP hierarchy if there exists
a link between them at the next lowest network layer. Such a link,
if it exists, will be either an MPLS-TP LSP (if n > 0) or a data-link
provided by the underlying server layer network (if n = 0), and is
referred to as an MPLS-TP Section at layer n of the MPLS-TP LSP
hierarchy. Thus, the links traversed by a layer n+1 MPLS-TP LSP are
layer n MPLS-TP sections.
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Note that the MPLS label stack associated with an MPLS-TP section at
layer n consists of n labels, in the absence of stack optimisation
mechanisms such as PHP. Note also that in order for two LSRs to
exchange MPLS-TP control packets over a section, an additional label,
the Generic Associated Channel Label (GAL) (see Section 4) must
appear at the bottom of the label stack.
3.3. Pseudowires
The data-plane architectures for Single-Segment Pseudowires
[RFC3985], Multisegment Pseudowires [RFC5659] and Point-to-Multipoint
Pseudowires [I-D.ietf-pwe3-p2mp-pw-requirements], and the associated
data-plane pseudowire protocol functions, as defined by the IETF
Pseudowire Emulation Edge-to-Edge (PWE3) Working Group, are included
in the MPLS-TP.
This document specifies no modifications or extensions to pseudowire
data-plane architectures or protocols.
4. MPLS-TP Generic Associated Channel
The MPLS Generic Associated Channel (G-ACh) mechanism is specified in
[RFC5586] and included in the MPLS-TP. The G-ACh provides an
auxiliary logical data channel associated with MPLS-TP Sections,
LSPs, and PWs in the data plane. The primary purpose of the G-ACh in
the context of MPLS-TP is to support control, management, and OAM
traffic associated with MPLS-TP transport entities. The G-ACh MUST
NOT be used to transport client layer network traffic in MPLS-TP
networks.
5. Media-Specific Considerations
This section discusses considerations for support of the MPLS-TP data
plane by specific underlying server layer media.
5.1. Ethernet
5.1.1. Destination MAC Address Determination
When two MPLS-TP nodes are connected by a point-to-point Ethernet
link, the question arises as to what destination Ethernet Media
Access Control (MAC) address should be specified in Ethernet frames
transmitted to the peer node over the link. The problem of
determining this address does not arise in IP/MPLS networks because
of the presence of the Ethernet Address Resolution Protocol (ARP)
[RFC0826] or IP version 6 Neighbor Discovery protocol [RFC4861],
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which allow the unicast MAC address of the peer device to be learned
dynamically.
If existing mechanisms are available in an MPLS-TP network to
determine the destination unicast MAC addresses of peer nodes - for
example if the network also happens to be an IP/MPLS network - such
mechanisms SHOULD be used. The remainder of this section discusses
the available options when this is not the case.
One possibility is for each node to be statically configured with the
MAC address of its peer. Static MAC address configuration MAY be
used in an MPLS-TP network, but can present an administrative burden
and lead to operational problems.
Another possibility is to use the Ethernet broadcast address, but
this may lead to excessive frame distribution and processing at the
Ethernet layer. Broadcast traffic may also be treated specially by
some devices and this may not be desirable for MPLS-TP data frames.
The preferred approach is therefore to use as the destination MAC
address an Ethernet multicast address reserved for MPLS-TP. The
address allocated for this purpose by the Internet Assigned Numbers
Authority (IANA) is 01-00-5E-XX-XX-XX. An MPLS-TP implementation
MUST process Ethernet frames received with this destination MAC
address by default.
[Editor's note: Decide what to say about multipoint Ethernet and
switched links. Decide if there is a need for protocol mechanisms to
support learning of the Ethernet unicast MAC addresses of MPLS-TP
peers that are not also IP peers.]
5.2. Other Media
[Editor's note: Decide whether any considerations for media other
than Ethernet need to be mentioned.]
6. Security Considerations
TBD
7. IANA Considerations
A future version of this document will detail IANA considerations for
the allocation of a standard Ethernet multicast MAC address for use
in MPLS-TP networks.
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8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, January 2001.
[RFC5654] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N.,
and S. Ueno, "Requirements of an MPLS Transport Profile",
RFC 5654, September 2009.
[RFC5586] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic
Associated Channel", RFC 5586, June 2009.
[RFC3270] Le Faucheur, F., Wu, L., Davie, B., Davari, S., Vaananen,
P., Krishnan, R., Cheval, P., and J. Heinanen, "Multi-
Protocol Label Switching (MPLS) Support of Differentiated
Services", RFC 3270, May 2002.
[RFC3443] Agarwal, P. and B. Akyol, "Time To Live (TTL) Processing
in Multi-Protocol Label Switching (MPLS) Networks",
RFC 3443, January 2003.
[RFC5462] Andersson, L. and R. Asati, "Multiprotocol Label Switching
(MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
Class" Field", RFC 5462, February 2009.
[RFC5331] Aggarwal, R., Rekhter, Y., and E. Rosen, "MPLS Upstream
Label Assignment and Context-Specific Label Space",
RFC 5331, August 2008.
[RFC4875] Aggarwal, R., Papadimitriou, D., and S. Yasukawa,
"Extensions to Resource Reservation Protocol - Traffic
Engineering (RSVP-TE) for Point-to-Multipoint TE Label
Switched Paths (LSPs)", RFC 4875, May 2007.
[RFC5332] Eckert, T., Rosen, E., Aggarwal, R., and Y. Rekhter, "MPLS
Multicast Encapsulations", RFC 5332, August 2008.
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8.2. Informative References
[I-D.ietf-mpls-tp-framework]
Bocci, M., Bryant, S., Frost, D., Levrau, L., and L.
Berger, "A Framework for MPLS in Transport Networks",
draft-ietf-mpls-tp-framework-10 (work in progress),
February 2010.
[I-D.ietf-pwe3-p2mp-pw-requirements]
Heron, G., Wang, L., Aggarwal, R., Vigoureux, M., Bocci,
M., Jin, L., JOUNAY, F., Niger, P., Kamite, Y., DeLord,
S., and L. Martini, "Requirements for Point-to-Multipoint
Pseudowire", draft-ietf-pwe3-p2mp-pw-requirements-02 (work
in progress), January 2010.
[RFC3985] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-
Edge (PWE3) Architecture", RFC 3985, March 2005.
[RFC5659] Bocci, M. and S. Bryant, "An Architecture for Multi-
Segment Pseudowire Emulation Edge-to-Edge", RFC 5659,
October 2009.
[RFC0826] Plummer, D., "Ethernet Address Resolution Protocol: Or
converting network protocol addresses to 48.bit Ethernet
address for transmission on Ethernet hardware", STD 37,
RFC 826, November 1982.
[RFC4861] Narten, T., Nordmark, E., Simpson, W., and H. Soliman,
"Neighbor Discovery for IP version 6 (IPv6)", RFC 4861,
September 2007.
Authors' Addresses
Dan Frost (editor)
Cisco Systems
Email: danfrost@cisco.com
Stewart Bryant (editor)
Cisco Systems
Email: stbryant@cisco.com
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Matthew Bocci (editor)
Alcatel-Lucent
Email: matthew.bocci@alcatel-lucent.com
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