draft-ietf-mpls-tp-gach-gal-03.txt   draft-ietf-mpls-tp-gach-gal-04.txt 
MPLS Working Group M. Bocci, Ed. MPLS Working Group M. Bocci, Ed.
Internet-Draft M. Vigoureux, Ed. Internet-Draft M. Vigoureux, Ed.
Updates: 3032, 4385, 5085 Alcatel-Lucent Updates: 3032, 4385, 5085 Alcatel-Lucent
(if approved) G. Swallow (if approved) G. Swallow
Intended status: Standards Track D. Ward Intended status: Standards Track D. Ward
Expires: October 11, 2009 S. Bryant Expires: November 1, 2009 S. Bryant
Cisco Cisco
R. Aggarwal R. Aggarwal
Juniper Networks Juniper Networks
April 9, 2009 April 30, 2009
MPLS Generic Associated Channel MPLS Generic Associated Channel
draft-ietf-mpls-tp-gach-gal-03 draft-ietf-mpls-tp-gach-gal-04
Status of this Memo Status of this Memo
This Internet-Draft is submitted to IETF in full conformance with the This Internet-Draft is submitted to IETF in full conformance with the
provisions of BCP 78 and BCP 79. provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF), its areas, and its working groups. Note that Task Force (IETF), its areas, and its working groups. Note that
other groups may also distribute working documents as Internet- other groups may also distribute working documents as Internet-
Drafts. Drafts.
skipping to change at page 1, line 38 skipping to change at page 1, line 38
and may be updated, replaced, or obsoleted by other documents at any and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress." material or to cite them other than as "work in progress."
The list of current Internet-Drafts can be accessed at The list of current Internet-Drafts can be accessed at
http://www.ietf.org/ietf/1id-abstracts.txt. http://www.ietf.org/ietf/1id-abstracts.txt.
The list of Internet-Draft Shadow Directories can be accessed at The list of Internet-Draft Shadow Directories can be accessed at
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This Internet-Draft will expire on October 11, 2009. This Internet-Draft will expire on November 1, 2009.
Copyright Notice Copyright Notice
Copyright (c) 2009 IETF Trust and the persons identified as the Copyright (c) 2009 IETF Trust and the persons identified as the
document authors. All rights reserved. document authors. All rights reserved.
This document is subject to BCP 78 and the IETF Trust's Legal This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents in effect on the date of Provisions Relating to IETF Documents in effect on the date of
publication of this document (http://trustee.ietf.org/license-info). publication of this document (http://trustee.ietf.org/license-info).
Please review these documents carefully, as they describe your rights Please review these documents carefully, as they describe your rights
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Table of Contents Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Contributing Authors . . . . . . . . . . . . . . . . . . . 5 1.1. Contributing Authors . . . . . . . . . . . . . . . . . . . 5
1.2. Objectives . . . . . . . . . . . . . . . . . . . . . . . . 5 1.2. Objectives . . . . . . . . . . . . . . . . . . . . . . . . 5
1.3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 5 1.3. Scope . . . . . . . . . . . . . . . . . . . . . . . . . . 5
1.4. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6 1.4. Terminology . . . . . . . . . . . . . . . . . . . . . . . 6
2. Generic Associated Channel Header . . . . . . . . . . . . . . 6 2. Generic Associated Channel Header . . . . . . . . . . . . . . 6
2.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . 6 2.1. Definition . . . . . . . . . . . . . . . . . . . . . . . . 6
2.2. Allocation of Channel Types . . . . . . . . . . . . . . . 7 2.2. Allocation of Channel Types . . . . . . . . . . . . . . . 7
3. ACH TLVs . . . . . . . . . . . . . . . . . . . . . . . . . . . 7 3. ACH TLVs . . . . . . . . . . . . . . . . . . . . . . . . . . . 8
3.1. ACH TLV Payload Structure . . . . . . . . . . . . . . . . 8 3.1. ACH TLV Payload Structure . . . . . . . . . . . . . . . . 8
3.2. ACH TLV Header . . . . . . . . . . . . . . . . . . . . . . 8 3.2. ACH TLV Header . . . . . . . . . . . . . . . . . . . . . . 9
3.3. ACH TLV Object . . . . . . . . . . . . . . . . . . . . . . 9 3.3. ACH TLV Object . . . . . . . . . . . . . . . . . . . . . . 9
4. Generalized Exception Mechanism . . . . . . . . . . . . . . . 9 4. Generalized Exception Mechanism . . . . . . . . . . . . . . . 10
4.1. Relationship with Existing MPLS OAM Alert Mechanisms . . . 10 4.1. Relationship with Existing MPLS OAM Alert Mechanisms . . . 10
4.2. GAL Applicability and Usage . . . . . . . . . . . . . . . 10 4.2. GAL Applicability and Usage . . . . . . . . . . . . . . . 11
4.2.1. GAL Processing . . . . . . . . . . . . . . . . . . . . 10 4.2.1. GAL Processing . . . . . . . . . . . . . . . . . . . . 11
4.3. Relationship with RFC 3429 . . . . . . . . . . . . . . . . 13 4.3. Relationship with RFC 3429 . . . . . . . . . . . . . . . . 14
5. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 14 5. Compatibility . . . . . . . . . . . . . . . . . . . . . . . . 14
6. Congestion Considerations . . . . . . . . . . . . . . . . . . 15 6. Congestion Considerations . . . . . . . . . . . . . . . . . . 15
7. Security Considerations . . . . . . . . . . . . . . . . . . . 15 7. Security Considerations . . . . . . . . . . . . . . . . . . . 15
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 15
9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 16 9. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 17
10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 16 10. References . . . . . . . . . . . . . . . . . . . . . . . . . . 17
10.1. Normative References . . . . . . . . . . . . . . . . . . . 16 10.1. Normative References . . . . . . . . . . . . . . . . . . . 17
10.2. Informative References . . . . . . . . . . . . . . . . . . 17 10.2. Informative References . . . . . . . . . . . . . . . . . . 18
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 18 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 19
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 fault detection, diagnostics, mechanisms that can be used for fault detection, diagnostics,
maintenance and other functions on a pseudowire (PW) and a Label maintenance and other functions on a pseudowire (PW) and a Label
Switched Path (LSP). These functions can be used between any two Switched Path (LSP). These functions can be used between any two
Label Edge Routers (LERs) / Label Switching Router (LSRs) or Label Edge Routers (LERs) / Label Switching Router (LSRs) or
Terminating Provider Edge routers (T-PEs) / Switching Provider Edge Terminating Provider Edge routers (T-PEs) / Switching Provider Edge
routers (S-PEs) along the path of an LSP or PW respectively [14]. routers (S-PEs) along the path of an LSP or PW respectively [11].
Some of these functions can be supported using existing tools such as Some of these functions can be supported using existing tools such as
Virtual Circuit Connectivity Verification (VCCV) [2], Bidirectional Virtual Circuit Connectivity Verification (VCCV) [2], Bidirectional
Forwarding Detection for MPLS LSPs (BFD-MPLS) [3], LSP-Ping [4], or Forwarding Detection for MPLS LSPs (BFD-MPLS) [12], LSP-Ping [13], or
BFD-VCCV [5]. However, a requirement has been indicated to augment BFD-VCCV [14]. However, a requirement has been indicated to augment
this set of maintenance functions, in particular when MPLS networks this set of maintenance functions, in particular when MPLS networks
are used for packet transport services and transport network are used for packet transport services and transport network
operations [15]. Examples of these functions include performance operations [15]. Examples of these functions include performance
monitoring, automatic protection switching, and support for monitoring, automatic protection switching, and support for
management and signaling communication channels. These tools MUST be management and signaling communication channels. These tools MUST be
applicable to, and function in essentially the same manner (from an applicable to, and function in essentially the same manner (from an
operational point of view) on MPLS PWs, MPLS LSPs and MPLS Sections. operational point of view) on MPLS PWs, MPLS LSPs and MPLS Sections.
They MUST also operate in-band on the PW or LSP such that they do not They MUST also operate in-band on the PW or LSP such that they do not
depend on Packet Switched Network (PSN) routing or on user traffic, depend on Packet Switched Network (PSN) routing or on user traffic,
and MUST also NOT depend on dynamic control plane functions. and MUST also NOT depend on dynamic control plane functions.
VCCV [2] can use an Associated Channel Header (ACH) to provide a PW- VCCV [2] can use an Associated Channel Header (ACH) to provide a PW-
associated control channel between a PW's end points, over which OAM associated control channel between a PW's end points, over which OAM
and other control messages can be exchanged. This document and other control messages can be exchanged. This document
generalizes the applicability of the ACH to enable the same generalizes the applicability of the ACH to enable the same
associated control channel mechanism to be used for Sections, LSPs associated control channel mechanism to be used for Sections, LSPs
and PWs. The associated control channel thus generalized is known as and PWs. The associated control channel thus generalized is known as
the Generic Associated Channel (G-ACh). The ACH, specified in RFC the Generic Associated Channel (G-ACh). The ACH, specified in RFC
4385 [6], may be used with additional code points to support 4385 [3], may be used with additional code points to support
additional MPLS maintenance functions on the G-ACh. additional MPLS maintenance functions on the G-ACh.
Generalizing the applicability of the ACH to LSPs and Sections also Generalizing the applicability of the ACH to LSPs and Sections also
requires a method to identify that a packet contains an ACH followed requires a method to identify that a packet contains an ACH followed
by a non-service payload. Therefore, this document also defines a by a non-service payload. Therefore, this document also defines a
label based exception mechanism that serves to inform an LSR (or LER) label based exception mechanism that serves to inform an LSR (or LER)
that a packet it receives on an LSP or Section belongs to an that a packet it receives on an LSP or Section belongs to an
associated control channel. The label used for that purpose is one associated control channel. The label used for that purpose is one
of the MPLS reserved labels and is referred to as the GAL (G-ACh of the MPLS reserved labels and is referred to as the GAL (G-ACh
Label). The GAL mechanism is defined to work together with the ACH Label). The GAL mechanism is defined to work together with the ACH
for LSPs and MPLS Sections. for LSPs and MPLS Sections.
RFC 4379 [4] and BFD-MPLS [3] define alert mechanisms that enable an RFC 4379 [13] and BFD-MPLS [12] define alert mechanisms that enable
MPLS LSR to identify and process MPLS OAM packets when these are an MPLS LSR to identify and process MPLS OAM packets when these are
encapsulated in an IP header. These alert mechanisms are based, for encapsulated in an IP header. These alert mechanisms are based, for
example, on Time To Live (TTL) expiration and/or on the use of an IP example, on Time To Live (TTL) expiration and/or on the use of an IP
destination address in the range of 127/8 or 0:0:0:0:0:FFFF: destination address in the range of 127/8 or 0:0:0:0:0:FFFF:
127.0.0.0/104, respectively for IPv4 and IPv6. These mechanisms are 127.0.0.0/104, respectively for IPv4 and IPv6. These mechanisms are
the default mechanisms for identifying MPLS OAM packets when the default mechanisms for identifying MPLS OAM packets when
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 to use these mechanisms in some MPLS applications e.g., MPLS
Transport Profile (MPLS-TP) [14], particularly when IP based Transport Profile (MPLS-TP) [11], particularly when IP based
demultiplexing cannot be used. This document defines a mechanism demultiplexing cannot be used. This document defines a mechanism
that is RECOMMENDED for identifying and encapsulating MPLS OAM and that is RECOMMENDED for identifying and encapsulating MPLS OAM and
other maintenance messages when IP based mechanisms such as those other maintenance messages when IP based mechanisms such as those
used in [4] and [3] are not available. Yet, this mechanism MAY be used in [13] and [12] are not available. Yet, this mechanism MAY be
used in addition to IP-based mechanisms. used in addition to IP-based mechanisms.
Note that, in this document, maintenance functions and packets should Note that, in this document, maintenance functions and packets should
be understood in the broad sense. That is, a set of maintenance and be understood in the broad sense. That is, a set of maintenance and
management mechanisms that include OAM, Automatic Protection management mechanisms that include OAM, Automatic Protection
Switching (APS), Signaling Communication Channel (SCC) and Management Switching (APS), Signaling Communication Channel (SCC) and Management
Communication Channel (MCC) messages. Communication Channel (MCC) messages.
Also note that the GAL and ACH are applicable to MPLS in general. Also note that the GAL and ACH are applicable to MPLS and PWs in
Their applicability to specific applications of MPLS is outside the general. This document specifies general mechanism and uses MPLS-TP
scope of this document. as an example application. The application of the GAL and ACH to
other specific MPLS uses is outside the scope of this document.
1.1. Contributing Authors 1.1. Contributing Authors
The editors gratefully acknowledge the contributions of Sami Boutros, The editors gratefully acknowledge the contributions of Sami Boutros,
Italo Busi, Marc Lasserre, Lieven Levrau and Siva Sivabalan Italo Busi, Marc Lasserre, Lieven Levrau and Siva Sivabalan
1.2. Objectives 1.2. Objectives
This document defines a mechanism that provides a solution to the This document defines a mechanism that provides a solution to the
extended maintenance needs of emerging applications for MPLS. It extended maintenance needs of emerging applications for MPLS. It
skipping to change at page 6, line 18 skipping to change at page 6, line 20
G-ACh: Generic Associated Channel G-ACh: Generic Associated Channel
GAL: G-ACh Label GAL: G-ACh Label
G-ACh packet: Any packet containing a message belonging to a protocol G-ACh packet: Any packet containing a message belonging to a protocol
that is carried on a PW, LSP or MPLS Section associated control that is carried on a PW, LSP or MPLS Section associated control
channel. Examples include maintenance protocols such as OAM channel. Examples include maintenance protocols such as OAM
functions, signaling communications or management communications. functions, signaling communications or management communications.
The terms 'Section' and 'Concatenated Segment' are defined in [16]. The terms 'Section' and 'Concatenated Segment' are defined in [16] as
follows (note that the terms 'Section' and ''Section Layer Network'
are synonymous):
Concatenated Segment: A serial-compound link connection as defined in
[17]. A concatenated segment is a contiguous part of an LSP or
multi-segment PW that comprises a set of segments and their
interconnecting nodes in sequence.
Section Layer Network: A section is a server layer (which may be
MPLS-TP or a different technology) which provides for encapsulation
and OAM of a client layer network. A section layer may provide for
aggregation of multiple MPLS-TP clients. Note that G.805 [17]
defines the section layer as one of the two layer networks in a
transmission media layer network. The other layer network is the
physical media layer network.
2. Generic Associated Channel Header 2. Generic Associated Channel Header
VCCV [2] defines three Control Channel (CC) Types that may be used to VCCV [2] defines three Control Channel (CC) Types that may be used to
exchange OAM messages through a PW: CC Type 1 uses an ACH and is exchange OAM messages through a PW: CC Type 1 uses an ACH and is
referred to as "In-band VCCV"; CC Type 2 uses the MPLS Router Alert referred to as "In-band VCCV"; CC Type 2 uses the MPLS Router Alert
Label to indicate VCCV packets and is referred to as "Out of Band 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 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 the targeted router control plane and is referred to as "MPLS PW
Label with TTL == 1". Label with TTL == 1".
2.1. Definition 2.1. Definition
The use of the ACH, previously limited to PWs, is here generalized to The use of the ACH, previously limited to PWs, is here generalized to
also apply to LSPs and to Sections. Note that for PWs, the PWE3 also apply to LSPs and to Sections. Note that for PWs, the PWE3
control word [6] MUST be present in the encapsulation of user packets control word [3] MUST be present in the encapsulation of user packets
when the ACH is used to realize the associated control channel. when the ACH is used to realize the associated control channel.
The ACH used by CC Type 1 is depicted in figure below: The ACH used by CC Type 1 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| Reserved | Channel Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: Associated Channel Header Figure 1: 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
control channel associated with a PW, an LSP or a Section. The control channel associated with a PW, an LSP or a Section. The
Version field is set to 0, as specified in RFC 4385 [6]. Bits 8 to Version field is set to 0, as specified in RFC 4385 [3]. Bits 8 to
15 of the ACH are reserved and MUST be set to 0 and ignored on 15 of the ACH are reserved and MUST be set to 0 and ignored on
reception. Bits 16 to 31 are used to encode the possible Channel reception. Bits 16 to 31 are used to encode the possible Channel
Types. Types.
Note that VCCV [2] also includes mechanisms for negotiating the Note that VCCV [2] also includes mechanisms for negotiating the
Control Channel and Connectivity Verification (i.e., OAM function) Control Channel and Connectivity Verification (i.e., OAM function)
Types between PEs. It is anticipated that similar mechanisms will be Types between PEs. It is anticipated that similar mechanisms will be
applied to LSPs. Such application will require further applied to LSPs. Such application will require further
specification. However, such specification is beyond the scope of specification. However, such specification is beyond the scope of
this document. this document.
The G-ACh MUST NOT be used to transport user traffic.
2.2. Allocation of Channel Types 2.2. Allocation of Channel Types
The Channel Type field indicates the type of message carried on the The Channel Type field indicates the type of message carried on the
associated control channel e.g., IPv4 or IPv6 if IP demultiplexing is associated control channel e.g., IPv4 or IPv6 if IP demultiplexing is
used for messages sent on the associated control channel, or OAM or used for messages sent on the associated control channel, or OAM or
other maintenance function if IP demultiplexing is not used. For other maintenance function if IP demultiplexing is not used. For
associated control channel packets where IP is not used as the associated control channel packets where IP is not used as the
multiplexer, the Channel Type indicates the specific protocol carried multiplexer, the Channel Type indicates the specific protocol carried
in the associated control channel. in the associated control channel.
Values for the Channel Type field currently used for VCCV are Values for the Channel Type field currently used for VCCV are
specified elsewhere e.g., in RFC 4446 [7] and RFC 4385 [6]. specified elsewhere e.g., in RFC 4446 [4] and RFC 4385 [3].
Additional Channel Type values and the associated maintenance Additional Channel Type values and the associated maintenance
functionality will be defined in other documents. Each document, functionality will be defined in other documents. Each document,
specifying a protocol solution relying on the ACH, MUST also specify specifying a protocol solution relying on the ACH, MUST also specify
the applicable Channel Type field value. the applicable Channel Type field value.
Note that these values are allocated from the PW Associated Channel Note that these values are allocated from the PW Associated Channel
Type registry [7], but this document modifies the existing policy to Type registry [4], but this document modifies the existing policy to
accommodate a level of experimentation. See Section 8 for further accommodate a level of experimentation. See Section 8 for further
details. details.
3. ACH TLVs 3. ACH TLVs
In some applications of the generalized associated control channel it In some applications of the generalized associated control channel it
is necessary to include one or more ACH TLVs to provide additional is necessary to include one or more ACH TLVs to provide additional
context information to the G-ACh packet. One use of these ACH TLVs context information to the G-ACh packet. One use of these ACH TLVs
might be to identify the source and/or intended destination of the might be to identify the source and/or intended destination of the
associated channel message. However, the use of this construct is associated channel message. However, the use of this construct is
skipping to change at page 9, line 39 skipping to change at page 10, line 24
Figure 4: ACH TLV Format Figure 4: ACH TLV Format
4. Generalized Exception Mechanism 4. Generalized Exception Mechanism
Generalizing the associated control channel mechanism to LSPs and Generalizing the associated control channel mechanism to LSPs and
Sections also requires a method to identify that a packet contains an Sections also requires a method to identify that a packet contains an
ACH followed by a non-service payload. This document specifies that ACH followed by a non-service payload. This document specifies that
a label is used for that purpose and calls this special label the a label is used for that purpose and calls this special label the
G-ACh Label (GAL). One of the reserved label values defined in RFC G-ACh Label (GAL). One of the reserved label values defined in RFC
3032 [8] is assigned for this purpose. The value of the label is to 3032 [5] is assigned for this purpose. The value of the label is to
be allocated by IANA; this document suggests the value 13. be allocated by IANA; this document suggests the value 13.
The GAL provides an alert based exception mechanism to: The GAL provides an alert based exception mechanism to:
o differentiate specific packets (i.e., G-ACh packets) from others, o differentiate specific packets (i.e., G-ACh packets) from others,
such as user-plane ones, such as user-plane ones,
o indicate that the ACH appears immediately after the bottom of the o indicate that the ACH appears immediately after the bottom of the
label stack. label stack.
The GAL MUST only be used where both these purposes apply. The GAL MUST only be used where both these purposes apply.
4.1. Relationship with Existing MPLS OAM Alert Mechanisms 4.1. Relationship with Existing MPLS OAM Alert Mechanisms
RFC 4379 [4] and BFD-MPLS [3] define alert mechanisms that enable an RFC 4379 [13] and BFD-MPLS [12] define alert mechanisms that enable
MPLS LSR to identify and process MPLS OAM packets when these are an MPLS LSR to identify and process MPLS OAM packets when these are
encapsulated in an IP header. These alert mechanisms are based, for encapsulated in an IP header. These alert mechanisms are based, for
example, on Time To Live (TTL) expiration and/or on the use of an IP example, on Time To Live (TTL) expiration and/or on the use of an IP
destination address in the range of 127/8 or 0:0:0:0:0:FFFF: destination address in the range of 127/8 or 0:0:0:0:0:FFFF:
127.0.0.0/104, respectively for IPv4 and IPv6. 127.0.0.0/104, respectively for IPv4 and IPv6.
These mechanisms are the default mechanisms for identifying MPLS OAM These mechanisms are the default mechanisms for identifying MPLS OAM
packets when encapsulated in an IP header although the mechanism packets when encapsulated in an IP header although the mechanism
defined in this document MAY also be used. defined in this document MAY also be used.
4.2. GAL Applicability and Usage 4.2. GAL Applicability and Usage
The GAL MUST only be used with LSPs, Concatenated Segments of LSPs, In MPLS-TP, the GAL MUST be used with packets on a G-ACh on LSPs,
and with Sections. Concatenated Segments of LSPs, and with Sections, and MUST NOT be
used with PWs. It 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, for document places no restrictions on where the GAL may appear within
example those using entropy labels [17], this document places no the label stack or its use with PWs. Where the GAL is at the bottom
restrictions on where the GAL may appear within the label stack. of the label stack (i.e. S bit set to 1) then it MUST always be
Where the GAL is at the bottom of the label stack (i.e. S bit set to followed by an ACH.
1) then it MUST always be followed by an ACH.
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, when present, the GAL MUST only user-plane packets. Furthermore, when present, the GAL MUST NOT
appear once in the label stack. appear more than once in the label stack.
A receiving LSR, LER or PE MUST NOT forward a G-ACh packet to another
node based on the GAL label.
4.2.1. GAL Processing 4.2.1. 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 (LSE) containing the GAL follows the definition and Label Stack Entry (LSE) containing the GAL follows the definition and
processing rules specified and referenced in [9]. processing rules specified and referenced in [6].
The Time-To-Live (TTL) field of the LSE that contains the GAL follows The Time-To-Live (TTL) field of the LSE that contains the GAL follows
the definition and processing rules specified in [10]. the definition and processing rules specified in [7].
4.2.1.1. MPLS Label Switched Paths and Segments 4.2.1.1. MPLS Label Switched Paths and Segments
The following figure (Figure 5) depicts two LERs (A and D) and two The following figure (Figure 5) depicts two LERs (A and D) and two
LSRs (B and C) for a given LSP which is established from A to D and LSRs (B and C) for a given LSP which is established from A to D and
switched in B and C. switched in B and C.
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
| A |-------------| B |-------------| C |-------------| D | | A |-------------| B |-------------| C |-------------| D |
+---+ +---+ +---+ +---+ +---+ +---+ +---+ +---+
skipping to change at page 13, line 48 skipping to change at page 14, line 23
See Section 4.2.1 for definition and processing rules. See Section 4.2.1 for definition and processing rules.
The G-ACh message, the ACH and the GAL SHOULD NOT be modified towards The G-ACh message, the ACH and the GAL SHOULD NOT be modified towards
the tail-end LSR (Z). Upon reception of the G-ACh packet, the tail- the tail-end LSR (Z). Upon reception of the G-ACh packet, the tail-
end LSR (Z), after having checked the GAL LSE fields, SHOULD pass the end LSR (Z), after having checked the GAL LSE fields, SHOULD pass the
whole packet to the appropriate processing entity. whole packet to the appropriate processing entity.
4.3. Relationship with RFC 3429 4.3. Relationship with RFC 3429
RFC 3429 [18] 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 [8], to the 'OAM Alert Label' that is values, defined in RFC 3032 [5], 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 [18] therefore describe the Both this document and RFC 3429 [18] therefore describe the
assignment of reserved label values for similar purposes. The assignment of reserved label values for similar purposes. The
rationale for the assignment of a new reserved label can be rationale for the assignment of a new reserved label can be
summarized as follows: summarized as follows:
o Unlike the mechanisms described and referenced in RFC 3429 [18], o Unlike the mechanisms described and referenced in RFC 3429 [18],
G-ACh messages will not reside immediately after the GAL but G-ACh messages will not reside immediately after the GAL but
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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 [18]. It is therefore not possible to modify the 'OAM RFC 3429 [18]. It is therefore not possible to modify the 'OAM
Alert Label' allocation, purpose or usage. Nevertheless, it is Alert Label' allocation, purpose or usage. Nevertheless, it is
RECOMMENDED that no further OAM extensions based on 'OAM Alert RECOMMENDED that no further OAM extensions based on 'OAM Alert
Label' (Label 14) usage be specified or developed. Label' (Label 14) usage be specified or developed.
5. Compatibility 5. Compatibility
Procedures for handling a packet received with an invalid incoming Procedures for handling a packet received with an invalid incoming
label are specified in RFC 3031[11]. label are specified in RFC 3031[8].
An LER, LSR or PE MUST discard received associated channel packets on An LER, LSR or PE MUST discard received associated channel packets on
which all of the MPLS or PW labels have been popped if any one of the which all of the MPLS or PW labels have been popped if any one of the
following conditions is true: following conditions is true:
o It is not capable of processing packets on the Channel Type o It is not capable of processing packets on the Channel Type
indicated by the ACH of the received packet. indicated by the ACH of the received packet.
o It has not, through means outside the scope of this document, o It has not, through means outside the scope of this document,
indicated to the sending LSR, LER or PE that it will process indicated to the sending LSR, LER or PE that it will process
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In addition, it MAY increment an error counter and MAY also issue a In addition, it MAY increment an error counter and MAY also issue a
system and/or SNMP notification. system and/or SNMP notification.
6. Congestion Considerations 6. Congestion Considerations
The congestion considerations detailed in RFC 5085 [2] apply. The congestion considerations detailed in RFC 5085 [2] apply.
7. Security Considerations 7. Security Considerations
The security considerations for the associated control channel are The security considerations for the associated control channel are
described in RFC 4385 [6]. Further security considerations MUST be described in RFC 4385 [3]. Further security considerations MUST be
described in the relevant associated channel type specification. described in the relevant associated channel type specification.
RFC 5085 [2] provides data plane related security considerations. RFC 5085 [2] provides data plane related security considerations.
These also apply to a G-ACh, whether the alert mechanism uses a GAL These also apply to a G-ACh, whether the alert mechanism uses a GAL
or only an ACH. or only an ACH.
8. IANA Considerations 8. IANA Considerations
This document requests that IANA allocates a label value, to the GAL, This document requests that IANA allocates a label value, to the GAL,
from the pool of reserved labels in the "Multiprotocol Label from the pool of reserved labels in the "Multiprotocol Label
Switching Architecture (MPLS) Label Values" registry, and suggests Switching Architecture (MPLS) Label Values" registry, and suggests
this value to be 13. this value to be 13.
Channel Types for the Associated Channel Header are allocated from Channel Types for the Associated Channel Header are allocated from
the IANA "PW Associated Channel Type" registry [7]. The PW the IANA "PW Associated Channel Type" registry [4]. The PW
Associated Channel Type registry is currently allocated based on the Associated Channel Type registry is currently allocated based on the
IETF consensus process, described in [12]. This allocation process IETF consensus process, described in [9]. This allocation process
was chosen based on the consensus reached in the PWE3 working group was chosen based on the consensus reached in the PWE3 working group
that pseudowire associated channel mechanisms should be reviewed by that pseudowire associated channel mechanisms should be reviewed by
the IETF and only those that are consistent with the PWE3 the IETF and only those that are consistent with the PWE3
architecture and requirements should be allocated a code point. architecture and requirements should be allocated a code point.
However, a requirement has emerged (see [15]) to allow for However, a requirement has emerged (see [15]) 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 without resorting running in an associated channel to be experimented without resorting
to the IETF standards process, by supporting experimental code to the IETF standards process, by supporting experimental code
points. This would prevent code points used for such functions from points. This would prevent code points used for such functions from
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thus protects an installed base of equipment from potential thus protects an installed base of equipment from potential
inadvertent overloading of code points. In order to support this inadvertent overloading of code points. In order to support this
requirement, this document requests that the code point allocation requirement, this document requests that the code point allocation
scheme for the PW Associated Channel Type be changed as follows: scheme for the PW Associated Channel Type be changed as follows:
0 - 32751 : IETF Consensus 0 - 32751 : IETF Consensus
32760 - 32767 : Experimental 32760 - 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 [13]. Functions using experimental G-ACh code guidelines of RFC 3692 [10]. Functions using experimental G-ACh code
points MUST be disabled by default. The Channel Type value used for points MUST be disabled by default. The Channel Type value used for
a given experimental OAM function MUST be configurable, and care MUST a given experimental OAM function MUST be configurable, and care MUST
be taken to ensure that different OAM functions that are not inter- be taken to ensure that different OAM functions that are not inter-
operable are configured to use different Channel Type values. operable are configured to use different Channel Type values.
The PW Associated Channel Type registry needs to be updated to The PW Associated Channel Type registry needs to be updated to
include a column indicating whether the ACH is followed by a ACH TLV include a column indicating whether the ACH is followed by a ACH TLV
header (Yes/No). There are two ACH Channel Type code-points header (Yes/No). There are two ACH Channel Type code-points
currently assigned and in both cases no ACH TLV header is used. Thus currently assigned and in both cases no ACH TLV header is used. Thus
the new format of the PW Channel Type registry is: the new format of the PW Channel Type registry is:
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consensus. This registry MUST record the following information. consensus. This registry MUST record the following information.
There are no initial entries. There are no initial entries.
Name Type Length Description Reference Name Type Length Description Reference
(octets) (octets)
Figure 10: ACH TLV registry Figure 10: ACH TLV registry
9. Acknowledgments 9. Acknowledgments
The authors would like to thank all members of the teams (the Joint The authors would like to thank Malcolm Betts, ITU-T Study Group 15,
Working Team, the MPLS Interoperability Design Team in IETF and the and all members of the teams (the Joint Working Team, the MPLS
MPLS-TP Ad-Hoc Team in ITU-T) involved in the definition and Interoperability Design Team in IETF and the MPLS-TP Ad-Hoc Team in
specification of MPLS Transport Profile. ITU-T) involved in the definition and specification of the MPLS
Transport Profile.
10. References 10. References
10.1. Normative References 10.1. 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
Levels", BCP 14, RFC 2119, March 1997. Levels", BCP 14, RFC 2119, March 1997.
[2] Nadeau, T. and C. Pignataro, "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.
[3] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, "BFD [3] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
For MPLS LSPs", draft-ietf-bfd-mpls-07 (work in progress),
June 2008.
[4] Kompella, K. and G. Swallow, "Detecting Multi-Protocol Label
Switched (MPLS) Data Plane Failures", RFC 4379, February 2006.
[5] Nadeau, T. and C. Pignataro, "Bidirectional Forwarding
Detection (BFD) for the Pseudowire Virtual Circuit
Connectivity Verification (VCCV)", draft-ietf-pwe3-vccv-bfd-03
(work in progress), February 2009.
[6] Bryant, S., Swallow, G., Martini, L., and D. McPherson,
"Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use "Pseudowire Emulation Edge-to-Edge (PWE3) Control Word for Use
over an MPLS PSN", RFC 4385, February 2006. over an MPLS PSN", RFC 4385, February 2006.
[7] Martini, L., "IANA Allocations for Pseudowire Edge to Edge [4] Martini, L., "IANA Allocations for Pseudowire Edge to Edge
Emulation (PWE3)", BCP 116, RFC 4446, April 2006. Emulation (PWE3)", BCP 116, RFC 4446, April 2006.
[8] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, [5] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci,
D., Li, T., and A. Conta, "MPLS Label Stack Encoding", D., Li, T., and A. Conta, "MPLS Label Stack Encoding",
RFC 3032, January 2001. RFC 3032, January 2001.
[9] Andersson, L. and R. Asati, "Multiprotocol Label Switching [6] Andersson, L. and R. Asati, "Multiprotocol Label Switching
(MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic (MPLS) Label Stack Entry: "EXP" Field Renamed to "Traffic
Class" Field", RFC 5462, February 2009. Class" Field", RFC 5462, February 2009.
[10] Agarwal, P. and B. Akyol, "Time To Live (TTL) Processing in [7] Agarwal, P. and B. Akyol, "Time To Live (TTL) Processing in
Multi-Protocol Label Switching (MPLS) Networks", RFC 3443, Multi-Protocol Label Switching (MPLS) Networks", RFC 3443,
January 2003. January 2003.
[11] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label [8] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol Label
Switching Architecture", RFC 3031, January 2001. Switching Architecture", RFC 3031, January 2001.
[12] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA [9] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 5226, May 2008. Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
[13] Narten, T., "Assigning Experimental and Testing Numbers [10] Narten, T., "Assigning Experimental and Testing Numbers
Considered Useful", BCP 82, RFC 3692, January 2004. Considered Useful", BCP 82, RFC 3692, January 2004.
10.2. Informative References 10.2. Informative References
[14] Bocci, M., Bryant, S., and L. Levrau, "A Framework for MPLS in [11] Bocci, M., Bryant, S., and L. Levrau, "A Framework for MPLS in
Transport Networks", draft-ietf-mpls-tp-framework-00 (work in Transport Networks", draft-ietf-mpls-tp-framework-00 (work in
progress), November 2008. progress), November 2008.
[12] Aggarwal, R., Kompella, K., Nadeau, T., and G. Swallow, "BFD
For MPLS LSPs", draft-ietf-bfd-mpls-07 (work in progress),
June 2008.
[13] Kompella, K. and G. Swallow, "Detecting Multi-Protocol Label
Switched (MPLS) Data Plane Failures", RFC 4379, February 2006.
[14] Nadeau, T. and C. Pignataro, "Bidirectional Forwarding
Detection (BFD) for the Pseudowire Virtual Circuit
Connectivity Verification (VCCV)", draft-ietf-pwe3-vccv-bfd-03
(work in progress), February 2009.
[15] Vigoureux, M., Ward, D., and M. Betts, "Requirements for OAM in [15] Vigoureux, M., Ward, D., and M. Betts, "Requirements for OAM in
MPLS Transport Networks", MPLS Transport Networks",
draft-ietf-mpls-tp-oam-requirements-01 (work in progress), draft-ietf-mpls-tp-oam-requirements-01 (work in progress),
March 2009. March 2009.
[16] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and [16] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and
S. Ueno, "MPLS-TP Requirements", S. Ueno, "MPLS-TP Requirements",
draft-ietf-mpls-tp-requirements-06 (work in progress), draft-ietf-mpls-tp-requirements-06 (work in progress),
April 2009. April 2009.
[17] Kompella, K. and S. Amante, "The Use of Entropy Labels in MPLS [17] International Telecommunication Union, "Generic Functional
Forwarding", draft-kompella-mpls-entropy-label-00 (work in Architecture of Transport Networks", ITU-T G.805, March 2000.
progress), July 2008.
[18] Ohta, H., "Assignment of the 'OAM Alert Label' for [18] Ohta, H., "Assignment of the 'OAM Alert Label' for
Multiprotocol Label Switching Architecture (MPLS) Operation and Multiprotocol Label Switching Architecture (MPLS) Operation and
Maintenance (OAM) Functions", RFC 3429, November 2002. Maintenance (OAM) Functions", RFC 3429, November 2002.
Authors' Addresses Authors' Addresses
Matthew Bocci (editor) Matthew Bocci (editor)
Alcatel-Lucent Alcatel-Lucent
Voyager Place, Shoppenhangers Road Voyager Place, Shoppenhangers Road
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