draft-ietf-mpls-tp-gach-gal-00.txt   draft-ietf-mpls-tp-gach-gal-01.txt 
MPLS Working Group M. Vigoureux MPLS M. Bocci, Ed.
Internet Draft M. Bocci Internet-Draft M. Vigoureux, Ed.
Updates: 3032, 4385 Alcatel-Lucent Updates: 3032, 4385, 5085 Alcatel-Lucent
Intended status: Standard Track (if approved) G. Swallow
Expires: May 2009 G. Swallow Intended status: Standards Track D. Ward
D. Ward Expires: July 10, 2009 Cisco
Cisco Systems, Inc.
R. Aggarwal R. Aggarwal
Juniper Networks Juniper Networks
January 6, 2009
November 27, 2008
MPLS Generic Associated Channel MPLS Generic Associated Channel
draft-ietf-mpls-tp-gach-gal-00 draft-ietf-mpls-tp-gach-gal-01
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Abstract Abstract
This document generalises the applicability of the pseudowire This document generalises the applicability of the pseudowire
Associated Channel Header (ACH), enabling the realization of a Associated Channel Header (ACH), enabling the realization of a
control channel associated to MPLS Label Switched Paths (LSP), MPLS control channel associated to MPLS Label Switched Paths (LSP), MPLS
pseudowires (PW) and MPLS Sections. In order to identify the presence pseudowires (PW) and MPLS Sections. In order to identify the
of this G-ACH, this document also assigns of one of the reserved MPLS presence of the Generic ACH (G-ACH), this document also assigns of
label values to the 'Generic Alert Label (GAL)', to be used as a one of the reserved MPLS label values to the 'Generic Associated
label based exception mechanism. channel header Label (GAL)', to be used as a label based exception
mechanism.
Conventions used in this document Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [1]. document are to be interpreted as described in RFC 2119 [1].
Table of Contents Table of Contents
1. Introduction................................................3 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Contributing Authors....................................4 1.1. Contributing Authors . . . . . . . . . . . . . . . . . . . 5
1.2. Objectives.............................................4 1.2. Objectives . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Scope..................................................4 1.3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4. Terminology............................................5 1.4. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. Generic Associated Channel...................................5 2. Generic Associated Channel Header . . . . . . . . . . . . . . 6
2.1. Allocation of Channel Types.............................6 2.1. Allocation of Channel Types . . . . . . . . . . . . . . . 7
3. Generalised Exception Mechanism..............................6 3. Generalised Exception Mechanism . . . . . . . . . . . . . . . 7
3.1. Relationship with Existing MPLS OAM Alert Mechanisms.....6 3.1. Relationship with Existing MPLS OAM Alert Mechanisms . . . 8
3.2. GAL Applicability and Usage.............................7 3.2. GAL Applicability and Usage . . . . . . . . . . . . . . . 8
3.2.1. GAL Processing.....................................7 3.2.1. GAL Processing . . . . . . . . . . . . . . . . . . . . 8
3.2.1.1. MPLS Section..................................7 3.3. Relationship wth RFC 3429 . . . . . . . . . . . . . . . . 11
3.2.1.2. Label Switched Paths..........................8 4. Compatability . . . . . . . . . . . . . . . . . . . . . . . . 11
3.2.1.3. Tandem Connection Monitoring Entity...........9 5. Congestion Considerations . . . . . . . . . . . . . . . . . . 12
3.3. Relationship with RFC 3429.............................10 6. Security Consderations . . . . . . . . . . . . . . . . . . . . 12
4. Compatibility..............................................10 7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
5. Congestion Considerations...................................10 8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . . 13
6. Security Considerations.....................................11 9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations........................................11 9.1. Normative References . . . . . . . . . . . . . . . . . . . 13
8. Acknowledgments............................................12 9.2. Informative References . . . . . . . . . . . . . . . . . . 14
9. References.................................................12 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
9.1. Normative References...................................12
9.2. Informative References.................................13
Authors' Addresses............................................14
Contributing Authors' Addresses................................14
Intellectual Property Statement................................15
Disclaimer of Validity........................................15
1. Introduction 1. Introduction
There is a need for Operations, Administration and Maintenance (OAM) There is a need for Operations, Administration and Maintenance (OAM)
mechanisms that can be used for edge-to-edge (i.e. between mechanisms that can be used for edge-to-edge (i.e. between
originating and terminating LSRs or T-PEs) and segment fault originating and terminating LSRs or T-PEs) and segment (e.g. between
detection (e.g. between any two LSRs or T-PEs/S-PEs along the path of any two LSRs or T-PEs/S-PEs along the path of a LSP or PW [15]) fault
an LSP or PW or an MPLS section [17]), diagnostics, maintenance and detection, diagnostics, maintenance and other functions for a PW and
other functions for a Pseudowire and an LSP. Some of these functions a LSP. Some of these functions can be supported using tools such as
can be supported using tools such as VCCV [8], BFD [9], or LSP-Ping VCCV [2], BFD [3], or LSP-Ping [4]. However, a requirement has been
[6]. However, a requirement has been indicated to extend these indicated to augment the set of maintenance functions, in particular
toolsets, in particular where MPLS networks are used for packet where MPLS networks are used for packet transport services and
transport services and network operations [16]. These include network operations [16]. Examples include performance monitoring,
performance monitoring, automatic protection switching, and support automatic protection switching, and support for management and
for management and signaling communication channels. These tools must signaling communication channels. These tools must be applicable to,
be applicable to, and function in essentially the same manner (from and function in essentially the same manner (from an operational
an operational point of view) on both MPLS PWs and MPLS LSPs. They point of view) on both MPLS PWs and MPLS LSPs. They must also
must also operate in-band on the PW or LSP such that they do not operate in-band on the PW or LSP such that they do not depend on PSN
depend on PSN routing, user data traffic or ultimately on control routing, user data traffic or ultimately on PSN or other dynamic
plane functions. control plane functions.
Virtual Circuit Connectivity Verification (VCCV) can use an Virtual Circuit Connectivity Verification (VCCV) can use an
associated channel to provide a control channel between a PW's associated channel to provide a control channel between a PW's
ingress and egress points over which OAM and other control messages ingress and egress points and over which OAM and other control
can be exchanged. In this document, we propose a generic associated messages can be exchanged. In this document, we propose a generic
channel header (G-ACH) to enable the same control channel mechanism associated channel header (G-ACH) to enable the same control channel
be used for MPLS Sections, LSPs and PWs. The associated channel mechanism be used for MPLS Sections, LSPs and PWs. The associated
header (ACH) specified in RFC 4385 [11] is used with additional code channel header (ACH) specified in RFC 4385 [5] is used with
points to support additional MPLS OAM functions. additional code points to support additional MPLS maintenance
functions.
Generalizing the ACH mechanism to MPLS LSPs and MPLS Sections also Generalizing the ACH mechanism to MPLS LSPs and MPLS Sections also
requires a method to identify that a packet contains a G-ACH followed requires a method to identify that a packet contains a G-ACH followed
by a non-service payload. This document therefore also defines a by a non-service payload. This document therefore also defines a
label based exception mechanism (the Generic Alert Label, or GAL) label based exception mechanism (the Generic Associated channel
that serves to inform an LSR that a packet that it receives on an LSP header Label, or GAL) that serves to inform an LSR that a packet that
or section belongs to an associated channel. it receives on an LSP or section belongs to an associated channel.
RFC 4379 [6] and BFD for MPLS LSPs [9] have defined alert mechanisms RFC 4379 [4] and BFD for MPLS LSPs [3] have defined alert mechanisms
that enable a MPLS LSR to identify and process MPLS OAM packets when that enable a MPLS LSR to identify and process MPLS OAM packets when
the OAM packets are encapsulated in an IP header. These alert the OAM packets are encapsulated in an IP header. These alert
mechanisms are based on TTL expiration and/or use an IP destination mechanisms are based on TTL expiration and/or use an IP destination
address in the range 127/8. These mechanisms are the default address in the range 127/8. These mechanisms are the default
mechanisms for identifying MPLS OAM packets when the OAM packets are mechanisms for identifying MPLS OAM packets when the OAM packets are
encapsulated in an IP header. However it may not always be possible encapsulated in an IP header. However it may not always be possible
to use these mechanisms in some MPLS applications, (e.g. MPLS-TP to use these mechanisms in some MPLS applications, (e.g. MPLS-TP
[17]) particularly when IP based demultiplexing cannot be used. This [15]) particularly when IP based demultiplexing cannot be used. This
document proposes an OPTIONAL mechanism that is RECOMMENDED for document proposes an OPTIONAL mechanism that is RECOMMENDED for
identifying and demultiplexing MPLS OAM packets when IP based identifying and demultiplexing MPLS OAM and other maintenance
mechanisms such as [6] and [9] are not available. messages when IP based mechanisms such as those in [4] and [3] are
not available.
The G-ACH and GAL mechanisms are defined to work together. The G-ACH and GAL mechanisms are defined to work together.
Note that, in this document, OAM functions and packets should be Note that, in this document, maintenace functions and packets should
understood in the broad sense, that is, as a set of FCAPS mechanisms be understood in the broad sense, that is, as a set of FCAPS
that also include Automatic Protection Switching (APS), Signalling mechanisms that include OAM, Automatic Protection Switching (APS),
Control Channel (SCC) and Management Control Channel (MCC). Signalling Communication Channel (SCC) and Management Communication
Channel (MCC) messages.
Note that the GAL and G-ACH are applicable to MPLS in general. Their Note that the GAL and G-ACH are applicable to MPLS in general. Their
applicability to specific applications is outside the scope of this applicability to specific applications is outside the scope of this
document. For example, the applicability of the GAL and G-ACH to document. For example, the applicability of the GAL and G-ACH to
MPLS-TP is described in [17] and [18]. MPLS-TP is described in [15] and [17].
1.1. Contributing Authors 1.1. Contributing Authors
The editors gratefully acknowledge the following additional The editors gratefully acknowledge the contibution of Stewart Bryant,
contributors: Stewart Bryant, Italo Busi, Marc Lasserre, Lieven Italo Busi, Marc Lasserre, and Lieven Levrau.
Levrau, and Lou Berger.
1.2. Objectives 1.2. Objectives
This document proposes a mechanism to provide for the extended OAM This document proposes a mechanism to provide for the extended
needs of emerging applications for MPLS. It creates a generic OAM maintenance needs of emerging applications for MPLS. It creates a
identification mechanism that may be applied to all MPLS LSPs, while generic control channel identification mechanism that may be applied
maintaining compatibility with the PW associated channel header (ACH) to all MPLS LSPs, while maintaining compatibility with the PW
[11]. It also normalizes the use of the ACH for PWs in a transport associated channel header (ACH) . It also normalizes the use of the
context. ACH for PWs in a transport context.
1.3. Scope 1.3. Scope
This document defines the encapsulation header for LSP, MPLS Section This document defines the encapsulation header for LSP, MPLS Section
and PW associated channel messages. and PW associated channel messages.
It does not define how associated channel capabilities are signaled It does not define how associated channel capabilities are signaled
or negotiated between LSRs or PEs, the operation of various OAM or negotiated between LSRs or PEs, the operation of various OAM
functions, or the messages transmitted on the associated channel. functions, nor how the messages transmitted on the associated
channel.
This document does not deprecate existing MPLS and PW OAM mechanisms. This document does not deprecate existing MPLS and PW OAM mechanisms.
1.4. Terminology 1.4. Terminology
G-ACH: Generic Associated Channel Header G-ACH: Generic Associated Channel Header
GAL: Generic Alert Label GAL: Generic Associated Channel Header Label
MPLS Section: A network segment between two LSRs that are immediately
adjacent at the MPLS layer
2. Generic Associated Channel Maintenance Packet: Any packet containing a message belonging to a
maintenace protocol that is carried on a PW, LSP or MPLS Section
associated channel. Examples of such maintenance protocols include
OAM functions, signaling communications or management communications.
VCCV [8] defines three Control Channel Types that may be used to 2. Generic Associated Channel Header
multiplex OAM messages onto a PW: CC Type 1 uses an associated
channel header and is referred to as "In-band VCCV"; CC Type 2 uses
the router alert label to indicate VCCV packets and is referred to as
"Out of Band VCCV"; CC Type 3 uses the TTL to force the packet to be
processed by the targeted routers control plane and is referred to as
"MPLS PW Label with TTL == 1".
The use of the CC Type 1, currently limited to MPLS PWs, is extended VCCV [2] defines three MPLS Control Channel (CC) Types that may be
to apply to MPLS LSPs as well as to MPLS Sections. This associated used to multiplex OAM messages onto a PW: CC Type 1 uses an
channel header is called the Generic Associated Channel Header (G- associated channel header and is referred to as "In-band VCCV"; CC
ACH). Type 2 uses the MPLS Router Alert Label to indicate VCCV packets and
is referred to as "Out of Band VCCV"; CC Type 3 uses the TTL to force
the packet to be processed by the targeted router control plane and
is referred to as "MPLS PW Label with TTL == 1".
The use of the CC Type 1, currently limited to MPLS PWs, is here
extended to apply to MPLS LSPs as well as to MPLS Sections. This
associated channel header is called the Generic Associated Channel
Header (G- ACH). The PWE3 control word MUST be present in the
encapsulation of user packets when the G-ACH is used to demultiplex
the associated channel packet on a PW.
The CC Type 1 channel header is depicted in figure below: The CC Type 1 channel header is depicted in figure below:
0 1 2 3 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 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 | |0 0 0 1|Version|A| Reserved | Channel Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 : Generic Associated Channel Header Figure 1 : Generic Associated Channel Header
In the above figure, the first nibble is set to 0001b to indicate a In the above figure, the first nibble is set to 0001b to indicate a
channel associated with a PW, a LSP or a Section. The Version and channel associated with a PW, a LSP or a Section. The Version field
Reserved fields are set to 0, as specified in RFC 4385 [11]. is set to 0, as specified in RFC 4385 [5]. This draft allocates Bit
8 of the ACH to the ACH TLV bit. This bit is set to 1 to indicate
that an object defined in the ACH TLV registry immediately follows
the G-ACH, otherwise it is set to 0. Bits 8 to 14 of the G-ACH are
reserved and MUST be set to 0..
Note that VCCV also includes mechanisms for negotiating the control Note that VCCV also includes mechanisms for negotiating the Control
channel and connectivity verification (i.e. OAM functions) types Channel and Connectivity Verification (i.e. OAM functions) Types
between PEs. These mechanisms need to be extended when a Generalised between PEs. It is anticipated that similar mechanisms will be
associated channel is used for e.g. MPLS LSP OAM. This will most applied to existing MPLS LSPs. Such application will require further
likely require extensions to label distribution protocols and is specification. However, such specification is beyond the scope of
outside the scope of this document. this document.
2.1. Allocation of Channel Types 2.1. Allocation of Channel Types
Values for the Channel Type field, currently used for VCCV, are The Channel Type field indicates the type of message carried on the
specified in RFC 4446 [12]. associated channel e.g. IPv4 or IPv6 if IP demultiplexing is used
for messages on the G-ACH, or OAM or other FCAPS function if IP
demultiplexing is not used. For G-ACH packets where IP is not used
as the multiplexer, the Channel Type SHOULD indicate the specific
maintenance protocol carried in the associated channel.
The functionality of any additional channel types will be defined in Values for the Channel Type field currently used for VCCV are
another document. Each associated channel protocol solution document specified in RFC 4446 [6]. The functionality of any additional
must specify the value to use for any additional channel types. channel types will be defined in another document. Each associated
channel protocol solution document must specify the value to use for
any additional channel types.
Note that these values are allocated from the PW Associated Channel
Type registry, but this document modifies the existing policy to
accomodate a level of experimentation. See Section 7 for further
details.
3. Generalised Exception Mechanism 3. Generalised Exception Mechanism
The above mechanism enables the multiplexing of various OAM packets The above mechanism enables the multiplexing of various maintenace
onto a PW, LSP or section and provides information on the type of OAM packets onto a PW, LSP or Section and provides information on the
function being performed. In the case of a PW, the use of a control type of function being performed. In the case of a PW, the use of a
word is negotiated at the time of the PW establishment. However, in control word is negotiated or configured at the time of the PW
the case of an MPLS LSP or section, there is a need to notify an LSR establishment. A special case of the control word (the G-ACH) is
of the presence of an associated channel packet i.e. LSPs and used to identify packets belonging to a PW associated channel.
sections require a mechanism to differentiate specific packets (e.g.
OAM) from others, such as normal user-plane ones. This document Generalizing the ACH mechanism to MPLS LSPs and MPLS Sections also
proposes that a label be used and calls this special label the requires a method to identify that a packet contains a G-ACH followed
'Generic Alert Label (GAL)'. One of the reserved label values defined by a non-service payload. This document specifies that a label be
in RFC 3032 [3] is assigned for this purpose. The value of the label used and calls this special label the 'Generic Associated channel
is to be allocated by IANA; this document suggests the value 13. header Label (GAL)'. One of the reserved label values defined in RFC
3032 [7] is assigned for this purpose. The value of the label is to
be allocated by IANA; this document suggests the value 13.
The GAL provides a generalised exception mechanism to: The GAL provides a generalised exception mechanism to:
o Differentiate specific packets (e.g. OAM) from others, such as o Differentiate specific packets (e.g. those containing OAM
normal user-plane ones, messages) from others, such as normal user-plane ones,
o Indicate that the Generic Associated Channel Header (G-ACH) o Indicate that the Generic Associated Channel Header (G-ACH)
appears immediately after the bottom of the label stack. appears immediately after the bottom of the label stack.
The 'Generic Alert Label (GAL)' MUST only be used where both of these The 'Generic Associated channel header Label (GAL)' MUST only be used
purposes are applicable. where both of these purposes are applicable.
3.1. Relationship with Existing MPLS OAM Alert Mechanisms 3.1. Relationship with Existing MPLS OAM Alert Mechanisms
RFC 4379 [6] and BFD for MPLS LSPs [9] have defined alert mechanisms RFC 4379 [4] and BFD for MPLS LSPs [3] have defined alert mechanisms
that enable a MPLS LSR to identify and process MPLS OAM packets when that enable a MPLS LSR to identify and process MPLS OAM packets when
the OAM packets are encapsulated in an IP header. These alert the OAM packets are encapsulated in an IP header. These alert
mechanisms are based on TTL expiration and/or use an IP destination mechanisms are based on TTL expiration and/or use an IP destination
address in the range 127/8. address in the range 127/8.
These alert mechanisms SHOULD preferably be used in non MPLS-TP These alert mechanisms SHOULD preferably be used in non MPLS-TP
environments. The mechanism defined in this document MAY also be environments. The mechanism defined in this document MAY also be
used. used.
3.2. GAL Applicability and Usage 3.2. GAL Applicability and Usage
The 'Generic Alert Label (GAL)' MUST only be used with Label Switched The 'Generic Associated channel header Label (GAL)' MUST only be used
Paths (LSPs), with their associated Tandem Connection Monitoring with Label Switched Paths (LSPs), with their associated Tandem
Entities (see [18] for definitions of TCMEs) and with MPLS Sections. Connection Monitoring Entities (see [17] for definitions of TCMEs)
An MPLS Section is a network segment between two LSRs that are and with MPLS Sections.
immediately adjacent at the MPLS layer.
The GAL applies to both P2P and P2MP LSPs, unless otherwise stated. The GAL applies to both P2P and P2MP LSPs, unless otherwise stated.
In MPLS-TP, the GAL MUST always be at the bottom of the label stack In MPLS-TP, the GAL MUST always be at the bottom of the label stack
(i.e. S bit set to 1). However, in other MPLS environments, this (i.e. S bit set to 1). However, in other MPLS environments, this
document places no restrictions on where the GAL may appear within document places no restrictions on where the GAL may appear within
the label stack. the label stack.
The G-ACH MUST be used for PWs when OAM functions that cannot be
demultiplexed using the IP mechanisms described in section 1. The
PWE3 control word MUST be present in the encapsulation of user
packets when the G-ACH is used to demultiplex OAM on a PW.
The GAL MUST NOT appear in the label stack when transporting normal The GAL MUST NOT appear in the label stack when transporting normal
user-plane packets. Furthermore, the GAL MUST only appear once in the user-plane packets. Furthermore, the GAL MUST only appear once in
label stack for OAM packets of a given layer. the label stack for packets on the generic associated channel.
3.2.1. GAL Processing 3.2.1. GAL Processing
The Traffic Class (TC) field (formerly known as the EXP field) of the The Traffic Class (TC) field (formerly known as the EXP field) of the
label stack entry containing the GAL follows the definition and label stack entry containing the GAL follows the definition and
processing rules specified and referenced in [10]. processing rules specified and referenced in [8].
The Time-To-Live (TTL) field of the label stack entry that contains The Time-To-Live (TTL) field of the label stack entry that contains
the GAL follows the definition and processing rules specified in [4]. the GAL follows the definition and processing rules specified in [9].
3.2.1.1. MPLS Section 3.2.1.1. MPLS Section
The following figure (Figure 2) depicts two MPLS LSRs immediately The following figure (Figure 2) depicts two MPLS LSRs immediately
adjacent at the MPLS layer. adjacent at the MPLS layer.
+---+ +---+ +---+ +---+
| A |-------------| Z | | A |-------------| Z |
+---+ +---+ +---+ +---+
Figure 2 : MPLS-TP OAM over a MPLS Section Figure 2: Maintenance over an MPLS Section Associated Channel
With regards to the MPLS Section, both LERs contain Maintenance End
Points (see [18] for definitions of MEPs). With regards to the MPLS Section, both LERs are Maintenance End
Points (see [17] for definitions of MEPs).
The following figure (Figure 3) depicts the format of a labelled OAM The following figure (Figure 3) depicts the format of a labelled OAM
packet on an associated channel when used for MPLS Section OAM. packet on an associated channel when used for MPLS Section
maintenance.
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GAL | TC |S| TTL | | GAL | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Generic-ACH | | Generic-ACH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . | .
. MPLS-TP OAM packet . . Maintenance Message .
. | . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3 : Labelled MPLS-TP OAM packet for MPLS Section OAM Figure 3: Maintenance Packet Format for MPLS Section
To send an MPLS-TP OAM packet on an associated channel of the MPLS To send a MPLS-TP maintenance packet on an associated channel of the
Section, the head-end LSR (A) of the MPLS Section generates a OAM MPLS Section, the head-end LSR (A) of the MPLS Section generates a
packet with a G-ACH to which it pushes a GAL. maintenance packet with a G-ACH to which it pushes a GAL.
o The TTL field of the GAL SHOULD be set to 1. o The TTL field of the GAL SHOULD be set to 1.
o The S bit of the GAL MUST be set to 1. o The S bit of the GAL MUST be set to 1 in MPLS-TP.
The OAM packet, the G-ACH and the GAL SHOULD NOT be modified towards The maintenance packet, the G-ACH and the GAL SHOULD NOT be modified
the tail-end LSR (Z). Upon reception of the labelled packet, the towards the tail-end LSR (Z). Upon reception of the labelled packet,
tail-end LSR (Z), after having checked the GAL fields, SHOULD pass the tail-end LSR (Z), after having checked the GAL fields, SHOULD
the whole packet to the appropriate processing entity. pass the whole packet to the appropriate processing entity.
3.2.1.2. Label Switched Paths 3.2.1.2. Label Switched Paths
The following figure (Figure 4) depicts four LSRs. A LSP is The following figure (Figure 4) depicts four LSRs. A LSP is
established from A to D and switched in B and C. established from A to D and switched in B and C.
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
| A |-------------| B |-------------| C |-------------| D | | A |-------------| B |-------------| C |-------------| D |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
Figure 4 : MPLS-TP OAM over a LSP Figure 4: Maintenance over an LSP Associated Channel
LERs A and D contain Maintenance End Points (MEPs) with respect to LERs A and D are Maintenance End Points (MEPs) with respect to this
this LSP. Furthermore, LSRs B and C could also contain Maintenance LSP. Furthermore, LSRs B and C could also be Maintenance
Intermediate Points (MIPs) (see [18] for definitions of MEPs and Intermediate Points (MIPs) with respect to this LSP (see [17] for
MIPs). definitions of MEPs and MIPs).
The following figure (Figure 5) depicts the format of a labelled The following figure (Figure 5) depicts the format of a labelled
MPLS-TP OAM packet when used for LSP OAM. maintenance packet when used for a MPLS-TP LSP.
0 1 2 3 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 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| LSP Label | TC |S| TTL | | LSP Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GAL | TC |S| TTL | | GAL | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Generic-ACH | | Generic-ACH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| . | .
. MPLS-TP OAM packet . . Maintenance Message .
. | . |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5 : Labelled MPLS-TP OAM packet for LSP OAM Figure 5: Maintenance Packet Format for MPLS-TP LSP
Note that it is possible that the LSP MAY also be tunnelled in Note that it is possible that the LSP MAY also be tunnelled in
another LSP (e.g. if an MPLS Tunnel exists between B and C), and as another LSP (e.g. if a MPLS Tunnel exists between B and C), and as
such other labels MAY be present above it in the label stack. such other labels MAY be present above it in the label stack.
To send an MPLS-TP OAM packet on the LSP, the head-end LSR (A) To send a maintenance packet on the LSP associated channel, the head-
generates a MPLS-TP OAM packet with a G-ACH on which it first pushes end LSR (A) generates a OAM message with a G-ACH on which it first
a GAL followed by the LSP label. pushes a GAL followed by the LSP label.
o The TTL field of the GAL SHOULD be set to 1. o The TTL field of the GAL SHOULD be set to 1.
o The S bit of the GAL SHOULD be set to 1, in MPLS-TP. o The S bit of the GAL SHOULD be set to 1 in MPLS-TP.
The MPLS-TP OAM packet, the G-ACH or the GAL SHOULD NOT be modified The maintenance message, the G-ACH or the GAL SHOULD NOT be modified
towards the targeted destination. Upon reception of the labelled towards the targeted destination. Upon reception of the labelled
packet, the targeted destination, after having checked both the LSP packet, the targeted destination, after having checked both the LSP
label and GAL fields, SHOULD pass the whole packet to the appropriate label and GAL fields, SHOULD pass the whole packet to the appropriate
processing entity. processing entity.
3.2.1.3. Tandem Connection Monitoring Entity 3.2.1.3. Tandem Connection Monitoring Entity
Tandem Connection Monitoring will be specified in a separate Tandem Connection Monitoring will be specified in a separate
document. document.
3.3. Relationship with RFC 3429 3.3. Relationship wth RFC 3429
RFC 3429 [15] describes the assignment of one of the reserved label RFC 3429 [18] describes the assignment of one of the reserved label
values, defined in RFC 3032 [3], to the 'OAM Alert Label' that is values, defined in RFC 3032 [7], to the 'OAM Alert Label' that is
used by user-plane MPLS OAM functions for the identification of MPLS used by user-plane MPLS OAM functions for the identification of MPLS
OAM packets. The value of 14 is used for that purpose. OAM packets. The value of 14 is used for that purpose.
Both this document and RFC 3429 therefore describe the assignment of Both this document and RFC 3429 [18] therefore describe the
reserved label values for similar purposes. The rationale for the assignment of reserved label values for similar purposes. The
assignment of a new reserved label can be summarized as follows: rationale for the assignment of a new reserved label can be
summarized as follows:
o Unlike the mechanisms described and referenced in RFC 3429, MPLS- o Unlike the mechanisms described and referenced in RFC 3429 [18],
TP OAM packet payloads will not reside immediately after the GAL MPLS-TP OAM packet payloads will not reside immediately after the
but instead behind the G-ACH, which itself resides immediately GAL but instead behind the G-ACH, which itself resides immediately
after the bottom of the label stack when the GAL is present. This after the bottom of the label stack when the GAL is present. This
ensures that OAM using the generic associated channel complies ensures that OAM using the generic associated channel complies
with RFC 4928 [7]. with RFC 4928 [10].
o The set of OAM functions potentially operated in the context of o The set of maintenance functions potentially operated in the
the generic associated channel is wider than the set of OAM context of the generic associated channel is wider than the set of
functions referenced in RFC 3429. OAM functions referenced in RFC 3429 [18].
o It has been reported that there are existing implementations and o It has been reported that there are existing implementations and
running deployments using the 'OAM Alert Label' as described in running deployments using the 'OAM Alert Label' as described in
RFC 3429. It is therefore not possible to modify the 'OAM Alert RFC 3429 [18]. It is therefore not possible to modify the 'OAM
Label' allocation, purpose or usage. Nevertheless, it is Alert Label' allocation, purpose or usage. Nevertheless, it is
RECOMMENDED by this document that no further OAM extensions based RECOMMENDED by this document that no further OAM extensions based
on 'OAM Alert Label' (Label 14) usage be specified or developed. on 'OAM Alert Label' (Label 14) usage be specified or developed.
4. Compatibility 4. Compatability
An LER, LSR or PE MUST discard received G-ACH packets if it is not G- An LER, LSR or PE MUST discard received G-ACH packets if it is not G-
ACH capable, it is not capable of processing packets on the indicated ACH capable, if it is not capable of processing packets on the
G-ACH channel, or it has not, through means outside the scope of this indicated G-ACH channel, or if it has not, through means outside the
document, indicated to the sending LSR, LER or PE that it will scope of this document, indicated to the sending LSR, LER or PE that
process G-ACH packets received on the indicated channel. The LER, LSR it will process G-ACH packets received on the indicated channel. The
or PE MAY increment an error counter and MAY also optionally issue a LER, LSR or PE MAY increment an error counter and MAY also optionally
system and/or SNMP notification. issue a system and/or SNMP notification.
5. Congestion Considerations 5. Congestion Considerations
The congestion considerations detailed in RFC 5085 [8] apply. Further The congestion considerations detailed in RFC 5085 [2] apply.
generic associated channel-specific congestion considerations will be Further generic associated channel-specific congestion considerations
detailed in a future revision of this document. will be detailed in a future revision of this document.
6. Security Considerations 6. Security Consderations
The security considerations detailed in RFC 5085 [1], the MPLS The security considerations detailed in RFC 5085 [2], the MPLS
architecture [2], the PWE3 architecture [5] and the MPLS-TP framework architecture [11], the PWE3 architecture [12] and the MPLS-TP
[17]apply. framework [15] apply.
7. IANA Considerations 7. IANA Considerations
This document requests that IANA allocates a Label value, to the This document requests that IANA allocates a Label value, to the
'Generalised-ACH Label (GAL)', from the pool of reserved labels, and 'Generic Associated channel header Label (GAL)', from the pool of
suggests this value to be 13. reserved labels, and suggests this value to be 13.
Channel Types for the Generic Associated Channel are allocated from Channel Types for the Generic Associated Channel are allocated from
the IANA PW Associated Channel Type registry [12]. The PW Associated the IANA PW Associated Channel Type registry [6]. The PW Associated
Channel Type registry is currently allocated based on the IETF Channel Type registry is currently allocated based on the IETF
consensus process, described in [13]. This allocation process was consensus process, described in [13]. This allocation process was
chosen based on the consensus reached in the PWE3 working group that chosen based on the consensus reached in the PWE3 working group that
pseudowire associated channel mechanisms should be reviewed by the pseudowire associated channel mechanisms should be reviewed by the
IETF and only those that are consistent with the PWE3 architecture IETF and only those that are consistent with the PWE3 architecture
and requirements should be allocated a code point. and requirements should be allocated a code point.
However, a requirement has emerged (see [16]) to allow for However, a requirement has emerged (see [16]) to allow for
optimizations or extensions to OAM and other control protocols optimizations or extensions to OAM and other control protocols
running in an associated channel to be experimented with without running in an associated channel to be experimented with without
resorting to the IETF standards process, by supporting experimental resorting to the IETF standards process, by supporting experimental
code points [14]. This would prevent code points used for such code points. This would prevent code points used for such functions
functions from being used from the range allocated through the IETF from being used from the range allocated through the IETF standards
standards and thus protects an installed base of equipment from and thus protects an installed base of equipment from potential
potential inadvertent overloading of code points. In order to inadvertent overloading of code points. In order to support this
support this requirement, this document requests that the code-point requirement, this document requests that the code-point allocation
allocation scheme for the PW Associated Channel Type be changed as scheme for the PW Associated Channel Type be changed as follows:
follows:
0 - 32751 : IETF Consensus 0 - 32751 : IETF Consensus
32752 - 32767 : Experimental 32752 - 32767 : Experimental
Code points in the experimental range MUST be used according to the Code points in the experimental range MUST be used according to the
guidelines of RFC 3692 [14]. Experimental OAM functions MUST be guidelines of RFC 3692 [14]. Experimental OAM functions MUST be
disabled by default. The channel type value used for a given disabled by default. The channel type value used for a given
experimental OAM function MUST be configurable, and care MUST be experimental OAM function MUST be configurable, and care MUST be
taken to ensure that different OAM functions that are not taken to ensure that different OAM functions that are not
interoperable are configured to use different channel type values. interoperable are configured to use different channel type values.
8. Acknowledgments 8. Acknowledgements
The authors would like to thank all members of the teams (the Joint The authors would like to thank all members of the teams (the Joint
Working Team, the MPLS Interoperability Design Team in IETF and the Working Team, the MPLS Interoperability Design Team in IETF and the
T-MPLS Ad Hoc Group in ITU-T) involved in the definition and T-MPLS Ad Hoc Group in ITU-T) involved in the definition and
specification of MPLS Transport Profile. specification of MPLS Transport Profile.
9. References 9. References
9.1. Normative References 9.1. Normative References
[1] Bradner, S., "Key words for use in RFCs to Indicate Requirement [1] Bradner, S., "Key words for use in RFCs to Indicate Requirement
[2] Rosen, E., Viswanathan, A., Callon, R., "Multiprotocol Label Levels", BCP 14, RFC 2119, March 1997.
Switching Architecture", RFC 3031, January 2001
[3] Rosen, E., et al., "MPLS Label Stack Encoding", RFC 3032,
January 2001
[4] Agarwal, P., Akyol, B., "Time To Live (TTL) Processing in
Multi-Protocol Label Switching (MPLS) Networks", RFC 3443,
January 2003
[5] Bryant, S., Pate, P., "Pseudo Wire Emulation Edge-to-Edge
[6] Kompella, K., Swallow, G., "Detecting Multi-Protocol Label
Switched (MPLS) Data Plane Failures", RFC 4379, February 2006
[7] Swallow, G., Bryant, S., Andersson, L., "Avoiding Equal Cost
Multipath Treatment in MPLS Networks", BCP 128, RFC 4928, June
2007
[8] Nadeau, T., Pignataro, S., "Pseudowire Virtual Circuit [2] Nadeau, T. and C. Pignataro, "Pseudowire Virtual Circuit
Connectivity Verification (VCCV): A Control Channel for Connectivity Verification (VCCV): A Control Channel for
Pseudowires", RFC 5085, December 2007 Pseudowires", RFC 5085, December 2007.
[9] Aggarwal, R., Kompella, K., Swallow, G., Nadeau, T., "BFD For
[10] Andersson, L., ""EXP field" renamed to "CoS Field"", draft-
[11] Bryant, S., et al., "Pseudowire Emulation Edge-to-Edge (PWE3)
Control Word for Use over an MPLS PSN", RFC 4385, February 2006
[12] Martini, L., "IANA Allocations for Pseudowire Edge to Edge
[13] Narten, T., Alvestrand, H., " Guidelines for Writing an IANA
Considerations Section in RFCs", RFC 2434, October 1998
[14] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", RFC 3692, January 2004
9.2. Informative References
[15] Ohta, H., "Assignment of the 'OAM Alert Label' for [3] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, "BFD
Multiprotocol Label Switching Architecture (MPLS) Operation and For MPLS LSPs", draft-ietf-bfd-mpls-07 (work in progress),
Maintenance (OAM) Functions", RFC 3429, November 2002 June 2008.
[16] Vigoureux, M., Betts, M., Ward, D., "Requirements for OAM in [4] Kompella, K. and G. Swallow, "Detecting Multi-Protocol Label
MPLS Transport Networks", draft-vigoureux-mpls-tp-oam- Switched (MPLS) Data Plane Failures", RFC 4379, February 2006.
[17] Bryant, S., Bocci, M., Lasserre, M., "A Framework for MPLS in
Transport Networks", draft-ietf-mpls-tp-framework-00.txt,
November 2008
[18] Busi, I., Niven-Jenkins B., "MPLS-TP OAM Framework and [5] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
Overview", draft-busi-mpls-tp-oam-framework-00, October 2008 "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use
over an MPLS PSN", RFC 4385, February 2006.
Authors' Addresses [6] Martini, L., "IANA Allocations for Pseudowire Edge to Edge
Emulation (PWE3)", BCP 116, RFC 4446, April 2006.
Martin Vigoureux (Editor) [7] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci,
Alcatel-Lucent D., Li, T., and A. Conta, "MPLS Label Stack Encoding",
RFC 3032, January 2001.
Email: martin.vigoureux@alcatel-lucent.com [8] Andersson, L. and R. Asati, "Multi-Protocol Label Switching
(MPLS) label stack entry: "EXP" field renamed to "Traffic
Class" field", draft-ietf-mpls-cosfield-def-08 (work in
progress), December 2008.
Matthew Bocci (Editor) [9] Agarwal, P. and B. Akyol, "Time To Live (TTL) Processing in
Alcatel-Lucent Multi-Protocol Label Switching (MPLS) Networks", RFC 3443,
January 2003.
Email: matthew.bocci@alcatel-lucent.com [10] Swallow, G., Bryant, S., and L. Andersson, "Avoiding Equal Cost
Multipath Treatment in MPLS Networks", BCP 128, RFC 4928,
June 2007.
David Ward (Editor) [11] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label
Cisco Systems, Inc. Switching Architecture", RFC 3031, January 2001.
Email: dward@cisco.com [12] Bryant, S. and P. Pate, "Pseudo Wire Emulation Edge-to-Edge
(PWE3) Architecture", RFC 3985, March 2005.
George Swallow (Editor) [13] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Cisco Systems, Inc. Considerations Section in RFCs", BCP 26, RFC 2434,
October 1998.
Email: swallow@cisco.com [14] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692, January 2004.
Rahul Aggarwal (Editor) 9.2. Informative References
Juniper Networks
Email: rahul@juniper.net [15] Bocci, M., Bryant, S., and L. Levrau, "A Framework for MPLS in
Transport Networks", draft-ietf-mpls-tp-framework-00 (work in
progress), November 2008.
Contributing Authors' Addresses [16] Vigoureux, M., Ward, D., and M. Betts, "Requirements for OAM in
MPLS Transport Networks",
draft-ietf-mpls-tp-oam-requirements-00 (work in progress),
December 2008.
Stewart Bryant [17] Busi, I. and B. Niven-Jenkins, "MPLS-TP OAM Framework and
Cisco Systems, Inc. Overview", draft-busi-mpls-tp-oam-framework-00 (work in
progress), October 2008.
Email: stbryant@cisco.com [18] Ohta, H., "Assignment of the 'OAM Alert Label' for
Multiprotocol Label Switching Architecture (MPLS) Operation and
Maintenance (OAM) Functions", RFC 3429, November 2002.
Italo Busi Authors' Addresses
Alcatel-Lucent
Email: italo.busi@alcatel-lucent.it Matthew Bocci (editor)
Marc Lasserre
Alcatel-Lucent Alcatel-Lucent
Email: mlasserre@alcatel-lucent.com Email: matthew.bocci@alcatel-lucent.com
Martin Vigoureux (editor)
Lieven Levrau
Alcatel-Lucent Alcatel-Lucent
Email: llevrau@alcatel-lucent.com Email: martin.vigoureux@alcatel-lucent.com
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Disclaimer of Validity
This document and the information contained herein are provided on an George Swallow
"AS IS" basis and THE CONTRIBUTOR, THE ORGANIZATION HE/SHE REPRESENTS Cisco
OR IS SPONSORED BY (IF ANY), THE INTERNET SOCIETY, THE IETF TRUST AND
THE INTERNET ENGINEERING TASK FORCE DISCLAIM ALL WARRANTIES, EXPRESS
OR IMPLIED, INCLUDING BUT NOT LIMITED TO ANY WARRANTY THAT THE USE OF
THE INFORMATION HEREIN WILL NOT INFRINGE ANY RIGHTS OR ANY IMPLIED
WARRANTIES OF MERCHANTABILITY OR FITNESS FOR A PARTICULAR PURPOSE.
Copyright Statement Email: swallow@cisco.com
Copyright (C) The IETF Trust (2008). David Ward
Cisco
This document is subject to the rights, licenses and restrictions Email: dward@cisco.com
contained in BCP 78, and except as set forth therein, the authors
retain all their rights.
Acknowledgment Rahul Aggarwal
Juniper Networks
Funding for the RFC Editor function is currently provided by the Email: rahul@juniper.net
Internet Society.
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