MPLS Working Group G. Swallow, Ed.
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track A. Fulignoli, Ed.
Expires: September 9, 2010 Ericsson
M. Vigoureux, Ed.
Alcatel-Lucent
March 8, 2010
MPLS Fault Management OAM
draft-ietf-mpls-tp-fault-01
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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 4
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 5
2. MPLS Fault Management Messages . . . . . . . . . . . . . . . . 5
2.1. MPLS-TP Alarm Indication Signal . . . . . . . . . . . . . 6
2.2. MPLS-TP Link Down Indication . . . . . . . . . . . . . . . 6
2.3. The Relationship of AIS to LDI . . . . . . . . . . . . . . 7
2.4. MPLS-TP Locked Report . . . . . . . . . . . . . . . . . . 7
3. MPLS Fault Management Channel . . . . . . . . . . . . . . . . 7
4. MPLS Fault Management Message Format . . . . . . . . . . . . . 8
5. Sending and Receiving Fault Management Messages . . . . . . . 9
5.1. Sending a Fault Management Message . . . . . . . . . . . . 9
5.2. Clearing a FM Indication . . . . . . . . . . . . . . . . . 10
5.3. Receiving a FM Indication . . . . . . . . . . . . . . . . 10
6. Security Considerations . . . . . . . . . . . . . . . . . . . 10
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10
8. References . . . . . . . . . . . . . . . . . . . . . . . . . . 10
8.1. Normative References . . . . . . . . . . . . . . . . . . . 10
8.2. Informative References . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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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, alarms 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 draft-ietf-mpls-tp-oam-requirements [2].
However, this mechanism is intended to be applicable to other aspects
of MPLS as well.
Three broad classes 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. Fault: the inability of a function to perform a required action.
This does not include an inability due to preventive maintenance,
lack of external resources, or planned actions (e.g.,
Administrative Locking). A fault is a persistent defect.
3. Lock: an administrative status in which it is expected that only
test traffic, if any, and OAM (dedicated to the LSP) can be
mapped on an LSP.
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 are used to
indicate the particular condition.
Corresponding to the three classes of service disruptive conditions
listed above, three messages are defined to communicate the type of
condition. These are known as:
Alarm Indication Signal (AIS)
Link Down Indication (LDI)
Locked Report (LKR)
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1.1. Terminology
ACH: Associated Channel Header
AII: Attachment Interface Identifier
ASN: Autonomous System Number
FEC: Forwarding Equivalence Class
FM: Fault Management
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 three types of service
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disruptive conditions, Alarm Indication Signal, Link Down Indication,
and Locked Report. These semantics of the individual messages are
described in subsections below. Although only one of the conditions
is named "Fault", we use the term "Fault Management" to generically
mean management of all three conditions.
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 codepoint.
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 is the condition is detected, that is before
any determination has been made as to whether the condition is fatal.
For example an AIS message may be sent during a protection switching
event and would cease being sent if the protection switch was
successful in restoring the link.
Its primary purpose is to suppress alarms in the MPLS-TP layer
network above the level at which the defect occurs. The AIS message
MAY be used to trigger recovery mechanisms. It should be noted that
such use would be subject to false positives, e.g. unnecessary
protection switching events in the client layer.
2.2. MPLS-TP Link Down Indication
The LDI message is generated in response to detecting a fatal failure
in the server layer. The LDI message MUST NOT be sent until the
defect has been determined to be fatal. For example during a
protection switching event LDI messages are not sent. However if the
protection switch was unsuccessful in restoring the link within the
expected repair time, an LDI message MUST be sent.
The receipt of an LDI message MAY be treated as the equivalent of
loss of continuity at the client layer. Like AIS it also is used to
suppress alarms.
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2.3. The Relationship of AIS to LDI
AIS and LDI are closely related functions and also 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,
AIS and LDI should be treated the same and used solely for alarm
suppression. In more general MPLS environments the CC function may
be running at a much slower rate. In this environment, LDI enables
faster switch-over upon a failure occurring along the LSP.
2.4. MPLS-TP Locked Report
The MPLS-TP Locked 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. Its purpose 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 receipt of an LKR message MAY be treated as the equivalent of
loss of continuity at the client layer. Like AIS it also is used to
suppress alarms.
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.] The FM Channel uses ACH
TLVs and MUST include the ACH TLV header. The FM ACH Channel and ACH
TLVs are 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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ACH TLV Header |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ~
~ zero or more ACH TLVs ~
~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| ~
~ 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)
The ACH TLVs may include (but are not limited to) the IF_ID,
Global-ID, ICC, and Authentication TLVs.
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 |Flgs |R| Msg Type | Refresh Timer | Total TLV Len |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TLVs |
~ ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: MPLS-TP OAM Message Format
Version
The Version Number is currently 1.
Flags
One flag, the R-Flag is defined. The other flags in this field
MUST be set to zero on transmission and ignored on receipt.
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R-flag
The R-flag is normally set to zero. A setting of one indicates
the removal of a previously sent FM condition.
Message Type
The Message Type indicates the type of condition as listed in the
table below.
Msg Type Description
-------- -----------------------------
0x0 Reserved
0x1 Alarm Indication Signal (AIS)
0x2 Link Down Indication (LDI)
0x3 Locked Report (LKR)
Refresh Timer
The maximum time between successive FM messages specified in
seconds. The range is 1 to 65535. The value 0 is not permitted.
Total TLV Length
The total TLV length is the total of all included TLVs. At this
time no TLVs are defined.
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.
The message is then prepended with an ACH TLV header. 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 twice 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.
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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 twice 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. 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. However, to ensure against such an attack the Authentication
TLV MAY be included among the ACH TLVs.
7. IANA Considerations
8. References
8.1. 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. and D. Ward, "Requirements for OAM in MPLS
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Transport Networks", draft-ietf-mpls-tp-oam-requirements-06
(work in progress), March 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] Boutros, S., Bryant, S., Sivabalan, S., Swallow, G., Ward, D.,
and V. Manral, "Definition of ACH TLV Structure",
draft-ietf-mpls-tp-ach-tlv-02 (work in progress), March 2010.
8.2. 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
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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
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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