MPLS Working Group G. Swallow, Ed.
Internet-Draft Cisco Systems, Inc.
Intended status: Standards Track A. Fulignoli, Ed.
Expires: January 12, 2012 Ericsson
M. Vigoureux, Ed.
Alcatel-Lucent
S. Boutros
Cisco Systems, Inc.
D. Ward
Juniper Networks, Inc.
July 11, 2011
MPLS Fault Management OAM
draft-ietf-mpls-tp-fault-05
Abstract
This draft specifies OAM messages to indicate service disruptive
conditions for MPLS based Transport Network 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
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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 January 12, 2012.
Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 4
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. MPLS Fault Management Messages . . . . . . . . . . . . . . . . 4
2.1. MPLS Alarm Indication Signal . . . . . . . . . . . . . . . 5
2.1.1. MPLS Link Down Indication . . . . . . . . . . . . . . 5
2.2. MPLS Lock Report . . . . . . . . . . . . . . . . . . . . . 6
2.3. Propagation of MPLS Fault Messages . . . . . . . . . . . . 6
3. MPLS Fault Management Channel . . . . . . . . . . . . . . . . 7
4. MPLS Fault Management Message Format . . . . . . . . . . . . . 7
4.1. Fault Management Message TLVs . . . . . . . . . . . . . . 9
4.1.1. Interface Identifier TLV . . . . . . . . . . . . . . . 9
4.1.2. Global Identifier . . . . . . . . . . . . . . . . . . 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. Normative References . . . . . . . . . . . . . . . . . . . . . 13
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 14
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1. Introduction
In traditional transport networks, circuits such as T1 lines are
typically provisioned on multiple switches. When an event that
causes disruption occurs on any link or node along the path of such a
transport circuit, OAM indications are generated which may in turn
suppress alarms and/or activate a backup circuit. The MPLS based
Transport Network provides mechanisms equivalent to 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)
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1.1. Terminology
ACH: Associated Channel Header
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 Entity Group End Point
MPLS: Multi-Protocol Label Switching
MPLS-TP: MPLS Transport Profile
MS-PW: Multi-Segment Pseudowire
OAM: Operations, Administration and Maintenance
PHP: Penultimate Hop Pop
PW: Pseudowire
S-PE: PW Switching Provider Edge
TLV: Type, Length, Value
1.2. 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. Fault OAM messages are applicable to
Bidirectional Co-Routed LSPs and to Multi-Segment Pseudowires
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(MS-PW). As MS-PWs are bidirectional LSPs, for simplicity we use the
term bidir-LSP to mean both of these. Applicability to other types
of LSPs is beyond the scope of this document.
Fault Management messages are carried in-band of the LSP or MS-PW by
using the Associated Channel Header (ACH). For Bidirectional Co-
Routed LSPs the ACH is identified by the 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 a bidir-
LSP is switched and bound to specific server layers based upon static
configuration or signaling. When a server (sub-)layer, (e.g. a link
or bidirectional LSP) used by the bidir-LSP fails, the intermediate
node sends Fault Management messages, using the bidir-LSP's Fault
associated channel, downstream to the endpoint of the bidir-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 bidir-LSPs in the
direction downstream of the fault location. The message is sent
periodically until the condition is cleared.
2.1. MPLS Alarm Indication Signal
The MPLS Alarm Indication Signal (AIS) message is generated in
response to detecting defects in the server (sub-)layer. The AIS
message SHOULD be sent as soon as the condition is detected. 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
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 Link Down Indication
The Link Down Indication (LDI) is communicated by setting the L-flag
to 1. The L-flag is set in the AIS message in response to detecting
a fault in the server layer. The L-flag MUST NOT be set until the
defect has been determined to be a fault. The L-flag MUST be set if
the defect has been determined to be a fault. For example during a
protection switching event the L-flag is not set. However if the
protection switch was unsuccessful in restoring the link within the
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expected repair time, the L-flag MUST be set.
The setting of the L-flag can be predetermined based on the
protection state. For example, if a server layer is protected and
both the working and protection paths are available, both the active
and standby server MEPs should be programmed to send AIS with the
L-flag clear upon detecting a defect condition. If the server layer
is unprotected or the server layer is protected but only the active
path is available, the active server MEP should be programmed to send
AIS with the L-flag set upon detecting a defect condition.
The receipt of an AIS message with the L-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 L-flag MAY be ignored and
the AIS message 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 Link Down Indication
enables faster switch-over upon a failure occurring along the bidir-
LSP.
2.2. MPLS Lock Report
The MPLS Lock Report (LKR) message is generated when a server
(sub-)layer entity has been administratively locked. Its purpose is
to communicate the locked condition to the client layer entities.
When a bidir-LSP is administratively locked it is not available to
carry client traffic. The purpose of the LKR message is to suppress
alarms in the layer network above the level at which the
administrative lock occurs and to allow the clients to differentiate
the lock condition from a defect condition. While the primary
purpose of the LKR message is to suppress alarms, similar to AIS with
the LDI (L-flag set), the receipt of an LKR message MAY be treated as
the equivalent of loss of continuity at the client layer.
2.3. Propagation of MPLS Fault Messages
If the CC function is disabled, a MEP SHOULD generate AIS messages
toward any client when when in either the AIS or LCK indication is
raised. Note that the L-flag is not automatically propagated, i.e.
the rules of Section 2.1.1 apply, that is the L-flag is not set until
a fault has been declared.
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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.
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 Fault Management Channel
The first three fields are defined in RFC 5586 [4].
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 Fault OAM Message Format
Version
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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.
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. The L-flag only has significance in the
AIS message. For the LKR message the L-flag MUST be set to
zero and ignored on receipt. See Section 2.1.1 for details on
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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 Management messages 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, and the
Global_ID.
TLVs (Type-Length-Value tuples) have the following format:
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
The Interface Identifier (IF_ID) TLV carries the IF_ID as defined in
draft-ietf-mpls-tp-identifiers [5]. The Type is 0x1. The length is
0x8.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-TP Node Identifier |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MPLS-TP Interface Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Interface Identifier TLV Format
4.1.2. Global Identifier
The Global Identifier (Global_ID) TLV carries the Global_ID 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
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
reporting the same incident. If the optional clearing procedures are
not used, then the default value is 1 second. Otherwise the default
value is 20 seconds.
A Global_ID MAY be included. If the R-flag clearing procedures are
to be used, the IF_ID TLV MUST be included. Otherwise, the IF_ID TLV
MAY be included.
The message is then sent. Assuming the condition persists, the
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message MUST be retransmitted two more times at an interval of one
second. Further retransmissions are made according to the value of
the refresh timer. Retransmissions continue 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 retransmitted 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 it is
well formed. If the message type is reserved or unknown, the message
is ignored.
If the R-flag is set to zero, the MEP checks to see if a condition
matching the message type and IF_ID exists. If it does not, the
condition to the message type is entered. An expiration-timer is set
to 3.5 times the refresh timer. If the message type and IF_ID match
an existing condition, message is considered a refresh and the
expiration-timer is reset.
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.
If the expiration-time expires, the condition is cleared.
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.
2. Support of setting the L-flag to indicated a fault.
3. Receiving AIS and LKR messages with any allowed Refresh Timer
value.
The following items are optional to implement.
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1. Sending AIS and LKR message with other values of the Refresh
Timer other than 1 second.
2. Support of receiving the L-flag.
3. Support of setting the R-flag to a value other than zero.
4. Support of receiving the R-flag.
5. 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, except of one case discussed below, 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. If external MPLS traffic is
mapped to a bidirectional LSP via PHP forwarding operation, it is
possible to insert a GAL label followed by a fault OAM message. In
such a situation an operator SHOULD filter any frames with the GAL
label at the top of the label stack.
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.
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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)
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
9. 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.
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[5] Bocci, M., Swallow, G., and E. Gray, "MPLS-TP Identifiers",
draft-ietf-mpls-tp-identifiers-06 (work in progress), June 2011.
[6] Narten, T. and H. Alvestrand, "Guidelines for Writing an IANA
Considerations Section in RFCs", BCP 26, RFC 5226, May 2008.
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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