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Versions: (draft-beller-mpls-tp-gach-dcn) 00
01 02 03 04 05 06 RFC 5718
Networking Working Group D. Beller
Internet-Draft Alcatel-Lucent
Intended Status: Standards Track A. Farrel
Created: September 19, 2009 Old Dog Consulting
Expires: March 19, 2010
An Inband Data Communication Network For the MPLS Transport Profile
draft-ietf-mpls-tp-gach-dcn-06.txt
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Abstract
The Generic Associated Channel (G-ACh) has been defined as a
generalization of the pseudowire (PW) associated control channel to
enable the realization of a control/communication channel associated
with Multiprotocol Label Switching (MPLS) Label Switched Paths
(LSPs), MPLS PWs, MPLS LSP segments, and MPLS sections between
adjacent MPLS-capable devices.
The MPLS Transport Profile (MPLS-TP) is a profile of the MPLS
architecture that identifies elements of the MPLS toolkit that may be
combined to build a carrier grade packet transport network based on
MPLS packet switching technology.
This document describes how the G-ACh may be used to provide the
infrastructure that forms part of the Management Communication
Network (MCN) and a Signaling Communication Network (SCN).
Collectively, the MCN and SCN may be referred to as the Data
Communication Network (DCN). This document explains how MCN and SCN
messages are encapsulated, carried on the G-ACh, and demultiplexed
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for delivery to the management or signaling/routing control plane
components on an MPLS-TP node.
It should be noted that the use of the G-ACh to provide connectivity
for the DCN is intended for use only where the MPLS-TP network is not
capable of encapsulating or delivering native DCN messages.
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].
1. Introduction
The associated channel header (ACH) is specified in [RFC4385]. It is
a packet header format for use on pseudowires (PWs) in order to
identify packets used for OAM and similar functions.
The use of the ACH is generalized in [RFC5586] and can be applied on
any Multiprotocol Label Switching (MPLS) Label Switching Path (LSP).
This is referred to as the Generic Associated Channel (G-ACh) and is
intended to create a control/management communication channel
associated with the LSP that can be used to carry packets used for
OAM and similar functions (e.g., control/management plane messages).
The purpose of a packet carried on the G-ACh is indicated by the
value carried by the Channel Type field of the ACH and a registry of
values is maintained by IANA ([RFC4446] and [RFC4385]). The
ACH is referred in this document as the G-ACh header.
The MPLS transport profile (MPLS-TP) is described in [MPLS-TP] and in
[TP-REQ]. MPLS-TP is the application of MPLS to construct a packet
transport network. It constitutes a profile of MPLS that enables
operational models typical in transport networks, which includes
additional OAM, survivability and other maintenance functions not
previously supported by MPLS.
Label Switching Routers (LSRs) in MPLS networks may be operated using
management protocols or control plane protocols. Messaging in these
protocols is normally achieved using IP packets exchanged over IP-
capable interfaces. However, some nodes in MPLS-TP networks may be
constructed without support for direct IP encapsulation on their
line-side interfaces, and without access to an out-of-fiber data
communication network. In order that such nodes can communicate using
management plane or control plane protocols, channels must be
provided, and the only available mechanism is to use an MPLS label.
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The G-ACh provides a suitable mechanism for this purpose, and this
document defines processes and procedures to allow the G-ACh to be
used to build a management communication network (MCN) and a
signaling communication network (SCN) together known as the data
communication network (DCN) [G.7712].
1.1. Requirements
The requirements presented in this section are based on those
communicated to the IETF by the ITU-T.
1. A packet encapsulation mechanism must be provided to support the
transport of MCN and SCN packets over the G-ACh.
2. The G-ACh carrying the MCN and SCN packets shall support the
following application scenarios:
a. The G-ACh interconnects two adjacent MPLS-TP nodes (used when
the server layer does not provide a Management Communication
Channel (MCC) or a Signalling Communication Channel (SCC)).
b. The G-ACh is carried by an MPLS-TP tunnel that traverses
another operator's domain (carrier's carrier scenario)
3. The G-ACh shall provide two independent channels: an MCC to build
the MCN and an SCC to build the SCN. The G-ACh packet header shall
indicate whether the packet is an MCC or an SCC packet in order to
forward it to the management or control plane application for
processing. This facilitates easy demultiplexing of control and
management traffic from the DCN and enables separate or
overlapping address spaces and duplicate protocol instances in the
management and control planes.
4. The channel separation mechanism shall not preclude the use of
separate rate limiters and traffic shaping functions for each
channel (MCC and SCC) ensuring that the flows do not exceed their
assigned traffic profiles. The rate limiters and traffic shapers
are outside the scope of the MCC and SCC definitions.
5. The G-ACh that carries the MCC and SCC shall be capable of
carrying different OSI layer 3 (network layer) PDUs. These shall
include IPv4, IPv6, and OSI PDUs. The G-ACh header of the MCC/SCC
packet shall indicate which layer 3 PDU is contained in the
payload field of the packet such that the packet can be delivered
to the related layer 3 process within the management and control
plane application, respectively, for further processing.
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6. The G-ACh is not required to provide specific security mechanisms.
However, the management or control plane protocols that operate
over the MCC or SCC are required to provide adequate security
mechanisms in order not to be susceptible to security attacks.
2. Procedures
Figure 1 depicts the format of an MCC/SCC packet that is sent on the
G-ACh. The Channel Type field indicates the function of the ACH
message so, to send an MCC/SCC packet on the G-ACh, the MCC/SCC
message is prepended with an ACH with the Channel Type set to
indicate that the message is an MCC or SCC message. The ACH MUST NOT
include the ACH TLV Header [RFC5586] meaning that no ACH TLVs can be
included in the message. A two byte Protocol Identifier (PID) field
indicates the protocol type of the payload DCN message.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Reserved | Channel Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PID | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |
| MCC/SCC Message |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: G-ACh MCC/SCC Packet
o The Channel Type field determines whether the message is an MCC or
an SCC message. See Section 5 for the codepoint assignments.
o The presence of the PID field is deduced from the Channel Type
value indicating MCC or SCC. The field contains an identifier of
the payload protocol using the PPP protocol identifiers [RFC1661],
[RFC3818].
When the G-ACh sender receives an MCC message that is to be sent over
the MCC, the sender creates the G-ACh header, sets the Channel
Type field to MCC, fills in the PID to indicate the MCC layer 3 PDU
type,and prepends the MCC message with the G-ACh header. The same
procedure is applied when a control plane message is to be sent over
the SCC. In this case, the sender sets the Channel Type field to SCC.
If the G-ACh is associated with an MPLS section, the GAL is added to
the message as defined in [RFC5586]. The TTL field MUST be set to 1,
and the S-bit of the GAL MUST be set to 1.
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If the G-ACh is associated with an LSP, the GAL is added to the
packet and the LSP label is pushed on top of the GAL as defined in
[RFC5586]. The TTL field of the GAL MUST be set to 1, and the S-bit
of the GAL MUST be set to 1.
Note that packet processing for DCN packets in the G-ACh is, in
common with all G-ACh MPLS packets, subject to the normal processing
of the Traffic Class (TC) field of the MPLS header. This could be
used to enable prioritisation of different DCN packets.
The DCN channel MUST NOT be used to transport user traffic and SHALL
only be used to carry management or control plane messages.
Procedures that ensure this (such as deep packet inspection) are
outside the scope of this specification.
When a receiver has received a packet on the G-ACh with the ACH
Channel Type set to MCC or SCC, it SHALL look at the PID field. If
the PID value is known by the receiver it delivers the the MCC/SCC
message to the appropriate processing entity. If the PID value is
unknown, the receiver SHALL silently discard the received packet,
MAY increment a counter that records discarded or errored messages,
and MAY log an event.
It must be noted that according to [RFC5586] a receiver MUST NOT
forward a GAL packet based on the GAL label as is normally the case
for MPLS packets. If the GAL appears at the bottom of the label
stack, it MUST be processed as described in the previous paragraph.
Note that there is no requirement for MPLS-TP devices to support IP
or OSI forwarding in the fast (forwarding) path. Thus, if a message
is received on the MCC or SCC and is not targeted to an address of
the receiving MPLS-TP node the packet might not be forwarded in the
fast path. A node MAY apply layer 3 forwarding procedures in the slow
or fast path and MAY discard or reject the message using the layer 3
protocol if it is unable to forward it. Thus, protocols making use of
the DCN should make no assumptions about the forwarding capabilities
unless they are determined a priori or through the use of a routing
protocol. Furthermore it is important that user data (i.e., data
traffic) is not routed through the DCN as this would potentially
cause the traffic to be lost or delayed, and might significantly
congest the DCN.
2.1. Pseudowire Setup
Provider Edge nodes may wish to set up PWs using a signaling protocol
that uses remote adjacencies (such as LDP [RFC5036]). In the absence
of an IP-based control plane network, these PEs MUST first set up an
LSP tunnel across the MPLS-TP network. This tunnel can be used both
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to carry the PW once it has been set up and to provide a G-ACh based
DCN for control plane communications between the PEs.
3. Applicability
The DCN is intended to provide connectivity between management
stations and network nodes, and between pairs of network nodes, for
the purpose of exchanging management plane and control plane
messages.
Appendix A of [NM-REQ] describes how Control Channels (CCh) that are
the links in an MPLS-TP DCN can be out-of-fiber and out-of-band, in-
fiber and out-of-band, or in-band with respect to the user data
carried by the MPLS-TP network. The Appendix also explains how the
DCN can be constructed from a mix of different types of links and
how routing and forwarding can be used within the DCN to facilitate
multi-hop delivery of management and control plane messages.
The G-ACh used as described in this document allows the creation of
a "data channel associated CCh" (type 6 in Appendix A of [NM-REQ])
and an "in-band CCh" (type 7 in Appendix A of [NM-REQ]). In the
former case, the G-ACh is associated with an MPLS-TP section. In the
latter case, the G-ACh is associated with an MPLS-TP LSP or PW and
may span one or more hops in the MPLS-TP network.
There is no need to create a CCh for every LSP between a pair of
Indeed, where the nodes are physically adjacent, the G-ACh associated
with the MPLS-TP section would normally be used. Where nodes are
virtually adjacent (that is, connected by LSP tunnels), one or two of
the LSPs might be selected to provide the CCh and a back-up CCh.
4. Security Considerations
The G-ACh provides a virtual link between MPLS-TP nodes and might be
used to induce many forms of security attack. Protocols that operate
over the MCN or SCN are REQUIRED to include adequate security
mechanisms and implementations MUST allow operators to configure the
use of those mechanisms.
5. IANA Considerations
Channel Types for the Generic Associated Channel are allocated from
the IANA PW Associated Channel Type registry defined in [RFC4446] and
updated by [RFC5586].
IANA is requested to allocate two further Channel Types as follows:
xx Management Communication Channel (MCC)
yy Signaling Communication Channel (SCC)
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6. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC4385] Bryant, S., et al., "Pseudowire Emulation Edge-to-Edge
(PWE3) Control Word for Use over an MPLS PSN", RFC 4385,
February 2006.
[RFC4446] Martini, L., "IANA Allocations for Pseudowire Edge to Edge
Emulation (PWE3)", RFC 4446, April 2006 .
[RFC5586] Bocci, M., Vigoureux, M., and Bryant, S., "MPLS Generic
Associated Channel", RFC 5586, June 2009.
7. Informative References
[MPLS-TP] Bryant, S., Bocci, M., Lasserre, M., "A Framework for MPLS
in Transport Networks", draft-ietf-mpls-tp-framework, work
in progress.
[TP-REQ] B. Niven-Jenkins, Ed., D. Brungard, Ed., M. Betts, Ed.,
N. Sprecher, S. Ueno, "MPLS-TP Requirements",
draft-ietf-mpls-tp-requirements, work in progress.
[NM-REQ] Lam, H.-K., Mansfield, S., and Gray, E., "MPLS TP Network
Management Requirements", draft-ietf-mpls-tp-nm-req, work
in progress.
[G.7712] ITU-T Recommendation G.7712, "Architecture and
specification of data communication network", June 2008.
[RFC1661] Simpson, W., "The Point-to-Point Protocol (PPP)", STD 51,
RFC 1661, July 1994.
[RFC3818] Schryver, V., "IANA Considerations for the Point-to-Point
Protocol (PPP)", BCP 88, RFC 3818, June 2004.
[RFC5036] Andersson, L., Minei, I., and Thomas, B., "LDP
Specification", RFC 5036, October 2007.
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8. Acknowledgements
The editors wish to thank Pietro Grandi, Martin Vigoureux, Kam Lam,
Ben Niven-Jenkins, Francesco Fondelli, Walter Rothkegel, Shahram
Davari, Liu Guoman, and Alexander Vainshtein for their contribution
to this document, and the MEAD team for thorough review.
Study Group 15 of the ITU-T provided the basis for the requirements
text in Section 1.1.
9. Authors' Addresses
Dieter Beller
Alcatel-Lucent Germany
EMail: dieter.beller@alcatel-lucent.com
Adrian Farrel
Old Dog Consulting
EMail: adrian@olddog.co.uk
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Provisions Relating to IETF Documents in effect on the date of
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Please review these documents carefully, as they describe your rights
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