MPLS Working Group G. Swallow, Ed.
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track A. Fulignoli, Ed.
Expires: April 28, 2011 Ericsson
M. Vigoureux, Ed.
Alcatel-Lucent
S. Boutros
Cisco Systems, Inc.
D. Ward
Juniper Networks, Inc.
October 25, 2010
MPLS Fault Management OAM
draft-ietf-mpls-tp-fault-03
Abstract
This draft specifies OAM messages to indicate service disruptive
conditions for MPLS Transport Profile (MPLS-TP) Label Switched Paths
(LSPs). The notification mechanism employs a generic method for a
service disruptive condition to be communicated to a Maintenance End
Point (MEP). An MPLS Operation, Administration, and Maintenance
(OAM) channel is defined along with messages to communicate various
types of service disruptive conditions.
Status of this Memo
This Internet-Draft is submitted in full conformance with the
provisions of BCP 78 and BCP 79.
Internet-Drafts are working documents of the Internet Engineering
Task Force (IETF). Note that other groups may also distribute
working documents as Internet-Drafts. The list of current Internet-
Drafts is at http://datatracker.ietf.org/drafts/current/.
Internet-Drafts are draft documents valid for a maximum of six months
and may be updated, replaced, or obsoleted by other documents at any
time. It is inappropriate to use Internet-Drafts as reference
material or to cite them other than as "work in progress."
This Internet-Draft will expire on April 28, 2011.
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2. MPLS Fault Management Messages . . . . . . . . . . . . . . . . 4
2.1. MPLS-TP Alarm Indication Signal . . . . . . . . . . . . . 5
2.1.1. MPLS-TP Link Down Indication . . . . . . . . . . . . . 5
2.2. MPLS-TP Lock Report . . . . . . . . . . . . . . . . . . . 6
3. MPLS Fault Management Channel . . . . . . . . . . . . . . . . 6
4. MPLS Fault Management Message Format . . . . . . . . . . . . . 7
4.1. Fault Management Message TLVs . . . . . . . . . . . . . . 8
4.1.1. Interface Identifier TLV . . . . . . . . . . . . . . . 9
4.1.2. Global Identifier . . . . . . . . . . . . . . . . . . 10
4.1.3. International Carrier Code . . . . . . . . . . . . . . 10
5. Sending and Receiving Fault Management Messages . . . . . . . 10
5.1. Sending a Fault Management Message . . . . . . . . . . . . 10
5.2. Clearing a FM Indication . . . . . . . . . . . . . . . . . 11
5.3. Receiving a FM Indication . . . . . . . . . . . . . . . . 11
6. Minimum Implementation Requirements . . . . . . . . . . . . . 11
7. Security Considerations . . . . . . . . . . . . . . . . . . . 12
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 12
8.1. Pseudowire Associated Channel Type . . . . . . . . . . . . 12
8.2. MPLS Fault OAM Message Type Registry . . . . . . . . . . . 12
8.3. MPLS Fault OAM TLV Registry . . . . . . . . . . . . . . . 13
9. References . . . . . . . . . . . . . . . . . . . . . . . . . . 13
9.1. Normative References . . . . . . . . . . . . . . . . . . . 13
9.2. Informative References . . . . . . . . . . . . . . . . . . 14
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
In traditional transport networks, circuits such as T1 lines are
provisioned on multiple switches. When a disruption occurs on any
link or node along the path of such a transport circuit, OAM are
generated which may in turn suppress alarms and/or activate a backup
circuit. The MPLS Transport Profile (MPLS-TP) provides mechanisms to
emulate traditional transport circuits. Therefore a Fault Management
(FM) capability must be defined for MPLS. This capability is being
defined to meet the MPLS-TP requirements as defined in RFC 5654 [1],
and the MPLS-TP Operations, Administration and Maintenance
Requirements as defined in RFC 5860 [2]. However, this mechanism is
intended to be applicable to other aspects of MPLS as well.
Two broad classes of service disruptive conditions are identified.
1. Defect: the situation in which the density of anomalies has
reached a level where the ability to perform a required function
has been interrupted.
2. Lock: an administrative status in which it is expected that only
test traffic, if any, and OAM (dedicated to the LSP) can be sent
on an LSP.
Within the Defect class, a further category, Fault is identified. A
fault is the inability of a function to perform a required action. A
fault is a persistent defect.
This document specifies an MPLS OAM channel called an "MPLS-OAM Fault
Management (FM)" channel. A single message format and a set of
procedures are defined to communicate service disruptive conditions
from the location where they occur to the endpoints of LSPs which are
affected by those conditions. Multiple message types and flags are
used to indicate and qualify the particular condition.
Corresponding to the two classes of service disruptive conditions
listed above, two messages are defined to communicate the type of
condition. These are known as:
Alarm Indication Signal (AIS)
Lock Report (LKR)
1.1. Terminology
ACH: Associated Channel Header
ASN: Autonomous System Number
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CC: Continuity Check
FM: Fault Management
GAL: Generic Associated Channel Label
LOC: Loss of Continuity
LSP: Label Switched Path
LSR: Label Switching Router
MEP: Maintenance End Point
MIP: Maintenance Intermediate Point
MPLS: Multi-Protocol Label Switching
MPLS-TP: MPLS Transport Profile
OAM: Operations, Administration and Maintenance
P2MP: Point to Multi-Point
P2P: Point to Point
PSC: Protection State Coordination
PW: Pseudowire
TLV: Type Length Value
TTL: Time To Live
Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
document are to be interpreted as described in RFC 2119 [3].
2. MPLS Fault Management Messages
This document defines messages to indicate service disruptive
conditions. Two messages are defined, Alarm Indication Signal, and
Lock Report. These semantics of the individual messages are
described in subsections below.
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Fault Management messages are carried in-band by using the Associated
Channel Header (ACH) and Generic Associated Channel Label (GAL) as
defined in RFC5586 [4]. To facilitate recognition and delivery of
Fault Management messages, the Fault Management Channel is identified
by a unique ACH codepoint.
Fault OAM messages are generated by intermediate nodes where an LSP
is switched. When a server layer, (e.g. a link) used by the LSP
fails, the intermediate node sends Fault Management messages using
the LSP's Fault associated channel back to the endpoint of the LSP.
Strictly speaking, when a server MEP detects a service disruptive
condition, Fault Management messages are generated by the convergence
server-to-client adaptation function. The messages are sent to the
client MEPs by inserting them into the affected LSPs in the direction
opposite to the detecting MEP's peer server MEP(s). The message is
sent periodically until the condition is cleared.
2.1. MPLS-TP Alarm Indication Signal
The MPLS-TP Alarm Indication Signal (AIS) message is generated in
response to detecting defects in the server layer. The AIS message
SHOULD be sent as soon as the condition is detected, that is before
any determination has been made as to whether the condition is
persistent and therefore fatal. For example, an AIS message may be
sent during a protection switching event and would cease being sent
(or cease being forwarded by the protection switch selector) if the
protection switch was successful in restoring the link.
The primary purpose of the AIS message is to suppress alarms in the
MPLS-TP layer network above the level at which the defect occurs.
When the Link Down Indication is set, the AIS message MAY be used to
trigger recovery mechanisms.
2.1.1. MPLS-TP Link Down Indication
The LDI flag is set in response to detecting a fatal failure in the
server layer. The LDI flag MUST NOT be set until the defect has been
determined to be fatal. The LDI flag MUST be set if the defect has
been determined to be fatal. For example during a protection
switching event the LDI flag is not set. However if the protection
switch was unsuccessful in restoring the link within the expected
repair time, the LDI flag MUST be set.
The setting of the LDI flag can be predetermined based on the
protection state. If the Server Layer is protected and both the
working and protection paths are available, both the active and
standby MEPs should be programmed to send AIS with LDI clear upon
detecting a defect condition. If the Server Layer is unprotected or
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the Server Layer is protected but only the active path is available,
the active MEP should be programmed to send AIS with LDI set upon
detecting a defect condition.
The receipt of an AIS message with the LDI flag set MAY be treated as
the equivalent of loss of continuity (LOC) at the client layer. The
choice of treatment is related to the rate at which the Continuity
Check (CC) function is running. In a normal transport environment,
CC is run at a high rate in order to detect a failure within 10s of
milliseconds. In such an environment, the LDI flag may be ignored.
AIS messages with the LDI flag set SHOULD be treated the same as any
other AIS message, that is, used solely for alarm suppression.
In more general MPLS environments the CC function may be running at a
much slower rate. In this environment, the LDI flag enables faster
switch-over upon a failure occurring along the LSP.
2.2. MPLS-TP Lock Report
The MPLS-TP Lock Report (LKR) message is generated when a server
layer entity has been administratively locked to communicated that
condition to inform the client layer entities of that condition.
When an MPLS-TP LSP is administratively locked it is not available to
carry client traffic. The purpose of the LKR message is to suppress
alarms in the MPLS-TP layer network above the level at which the
defect occurs and to allow the clients to differentiate the lock
condition from a defect condition.
The primary purpose of the LKR message is to suppress alarms in the
MPLS-TP layer network above the level at which the defect occurs.
Like AIS with the LDI flag set, the receipt of an LKR message MAY be
treated as the equivalent of loss of continuity at the client layer.
3. MPLS Fault Management Channel
The MPLS Fault Management channel is identified by the ACH as defined
in RFC 5586 [4] with the Channel Type set to the MPLS Fault
Management (FM) code point = 0xHH. [HH to be assigned by IANA from
the PW Associated Channel Type registry. Note: An early codepoint
allocation has made: 0x0058 Fault OAM (TEMPORARY - expires
2011-07-16)] The FM Channel does not use ACH TLVs and MUST not
include the ACH TLV header. The FM ACH Channel is shown below.
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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 | 0xHH Fault Management Channel |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ~
~ MPLS Fault Management Message ~
~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1: ACH Indication of the MPLS-TP Fault Management Channel
The Fault Management Channel is 0xHH (to be assigned by IANA)
4. MPLS Fault Management Message Format
The format of the Fault Management message is shown below.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vers | Resvd | Msg Type | Flags | Refresh Timer |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Total TLV Len | ~
+-+-+-+-+-+-+-+-+ TLVs ~
~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: MPLS-TP OAM Message Format
Version
The Version Number is currently 1.
Reserved
This field MUST be set to zero on transmission and ignored on
receipt.
Message Type
The Message Type indicates the type of condition as listed in the
table below.
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Msg Type Description
-------- -----------------------------
0x0 Reserved
0x1 Alarm Indication Signal (AIS)
0x2 Lock Report (LKR)
Refresh Timer
The maximum time between successive FM messages specified in
seconds. The range is 1 to 20. The value 0 is not permitted.
Total TLV Length
The total TLV length is the total of all included TLVs.
Flags
Two flags are defined. The reserved flags in this field MUST be
set to zero on transmission and ignored on receipt.
+-+-+-+-+-+-+-+-+
| Reserved |L|R|
+-+-+-+-+-+-+-+-+
Figure 3: Flags
L-flag
Link Down Indication. See section Section 2.1.1 for details on
setting this bit.
R-flag
The R-flag is normally set to zero. A setting of one indicates
the removal of a previously sent FM condition.
4.1. Fault Management Message TLVs
TLVs are used in fault OAM to carry information that may not pertain
to all messages as well as to allow for extensibility. The TLVs
currently defined are the IF_ID, Global-ID, and ICC.
TLVs (Type-Length-Value tuples) have the following format:
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type | Length | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ .
| .
. Value .
. |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Fault TLV Format
Type
Encodes how the Value field is to be interpreted.
Length
Specifies the length of the Value field in octets.
Value
Octet string of Length octets that encodes information to be
interpreted as specified by the Type field.
4.1.1. Interface Identifier TLV
This TLV carries the Interface Identifier as defined in
draft-ietf-mpls-tp-identifiers [5]. The Type is 0x1. The length is
0x8.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-TP Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-TP Interface Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Interface Identifier TLV Format
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4.1.2. Global Identifier
This TLV carries the Interface Identifier as defined in
draft-ietf-mpls-tp-identifiers [5]. The Type is 0x2. The length is
0x4.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-TP Global Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Global Identifier TLV Format
4.1.3. International Carrier Code
This TLV carries the International Carrier Code. The Type is 0x3.
The length is 0x8. The value is an Octet string padded with nulls.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| International Carrier Code |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| International Carrier Code (Cont.) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: International Carrier Code
5. Sending and Receiving Fault Management Messages
5.1. Sending a Fault Management Message
Service disruptive conditions are indicated by sending FM messages.
The message type is set to the value corresponding to the condition.
The refresh timer is set to the maximum time between successive FM
messages. This value MUST not be changed on successive FM messages.
If the optional clearing procedures are not used, then the default
value is 1. Otherwise the default value is 20.
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A Global-ID TLV or an ICC TLV MAY be included. The IF_ID TLV SHOULD
be included. If the R-Flag clearing procedures are to be used, the
IF_ID TLV MUST be included.
The message is then sent. The message MUST be refreshed two more
times at an interval of one second. Further refreshes are sent
according to the value of the refresh timer. Refreshing continues
until the condition is cleared.
5.2. Clearing a FM Indication
Ceasing to send FM messages will clear the indication after 3.5 times
the Refresh Timer. To clear an indication more quickly, the
following procedure is used. The R-Flag of the FM message is set to
one. Other fields of the FM message SHOULD NOT be modified. The
message is sent immediately and then refreshed two more times at an
interval of one second.
5.3. Receiving a FM Indication
When a FM message is received, a MEP examines it to ensure that that
it is well formed. If the message type is unknown, the message is
ignored. If the R-Flag is zero, the condition corresponding to the
message type is entered. A timer is set to 3.5 times the refresh
timer. If the message is not refreshed within this period, the
condition is cleared. A message is considered a refresh if the
message type and IF_ID match an existing condition and the R-Flag is
set to zero.
If the R-Flag is set to one, the MEP checks to see if a condition
matching the message type and IF_ID exists. If it does, that
condition is cleared. Otherwise the message is ignored.
6. Minimum Implementation Requirements
At a minimum an implementation MUST support the following:
1. Sending AIS and LKR messages at a rate of 1 per second. In
particular other values of the Refresh Timer and setting the R
bit to value other than zero need not be supported.
2. Support of the sending the LDI flag.
3. Receiving AIS and LKR messages with any allowed Refresh Timer
value.
The following items are optional to implement.
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1. Support of receiving the LDI flag.
2. Support of receiving the R flag.
3. All TLVs.
7. Security Considerations
Spurious fault OAM messages form a vector for a denial of service
attack. However, since these messages are carried in a control
channel, one would have to gain access to a node providing the
service in order to effect such an attack. Since transport networks
are usually operated as a walled garden, such threats are less
likely.
8. IANA Considerations
8.1. Pseudowire Associated Channel Type
Fault OAM requires a unique Associated Channel Type which are
assigned by IANA from the Pseudowire Associated Channel Types
Registry.
Registry:
Value Description TLV Follows Reference
----------- ----------------------- ----------- ---------
0xHHHH Fault OAM No (This Document)
8.2. MPLS Fault OAM Message Type Registry
This sections details the MPLS Fault OAM TLV Registry, a new name
spaces to be managed by IANA. The Type space is divided into
assignment ranges; the following terms are used in describing the
procedures by which IANA allocates values: "Standards Action" (as
defined in RFC 5226 [6]) and "Private Use".
MPLS Fault OAM Message Types take values in the range 0-255.
Assignments in the range 0-251 are via Standards Action; values in
the range 251-255 are for Private Use, and MUST NOT be allocated.
Message Types defined in this document are:
Msg Type Description
-------- -----------------------------
0x0 Reserved
0x1 Alarm Indication Signal (AIS)
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0x2 Lock Report (LKR)
8.3. MPLS Fault OAM TLV Registry
This sections details the MPLS Fault OAM TLV Registry, a new name
spaces to be managed by IANA. The Type space is divided into
assignment ranges; the following terms are used in describing the
procedures by which IANA allocates values: "Standards Action" (as
defined in RFC 5226 [6]), "Specification Required" and "Private Use".
MPLS Fault OAM TLVs which take values in the range 0-255.
Assignments in the range 0-191 are via Standards Action; assignments
in the range 192-248 are made via "Specification Required"; values in
the range 248-255 are for Private Use, and MUST NOT be allocated.
TLVs defined in this document are:
Value TLV Name
----- -------
0 Reserved
1 Interface Identifier TLV
2 Global Identifier
3 International Carrier Code
9. References
9.1. Normative References
[1] Niven-Jenkins, B., Brungard, D., Betts, M., Sprecher, N., and S.
Ueno, "Requirements of an MPLS Transport Profile", RFC 5654,
September 2009.
[2] Vigoureux, M., Ward, D., and M. Betts, "Requirements for
Operations, Administration, and Maintenance (OAM) in MPLS
Transport Networks", RFC 5860, May 2010.
[3] Bradner, S., "Key words for use in RFCs to Indicate Requirement
Levels", BCP 14, RFC 2119, March 1997.
[4] Bocci, M., Vigoureux, M., and S. Bryant, "MPLS Generic
Associated Channel", RFC 5586, June 2009.
[5] Bocci, M., Swallow, G., and E. Gray, "MPLS-TP Identifiers",
draft-ietf-mpls-tp-identifiers-03 (work in progress),
October 2010.
[6] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
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Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
9.2. Informative References
Authors' Addresses
George Swallow (editor)
Cisco Systems, Inc.
300 Beaver Brook Road
Boxborough, Massachusetts 01719
United States
Email: swallow@cisco.com
Annamaria Fulignoli (editor)
Ericsson
Email: annamaria.fulignoli@ericsson.com
Martin Vigoureux (editor)
Alcatel-Lucent
Route de Villejust
Nozay, 91620
France
Email: martin.vigoureux@alcatel-lucent.com
Sami Boutros
Cisco Systems, Inc.
3750 Cisco Way
San Jose, California 95134
USA
Email: sboutros@cisco.com
David Ward
Juniper Networks, Inc.
Email: dward@juniper.net
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Stewart Bryant
Cisco Systems, Inc.
250, Longwater
Green Park, Reading RG2 6GB
UK
Email: stbryant@cisco.com
Siva Sivabalan
Cisco Systems, Inc.
2000 Innovation Drive
Kanata, Ontario K2K 3E8
Canada
Email: msiva@cisco.com
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