Internet DRAFT - draft-ietf-mpls-tp-csf
draft-ietf-mpls-tp-csf
Network Working Group J.He
Internet Draft Huawei Technologies
Intended status: Standard Track
H.Li
China Mobile
E. Bellagamba
Ericsson
Expires: March 2012 September 13, 2011
Indication of Client Failure in MPLS-TP
draft-ietf-mpls-tp-csf-02.txt
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Abstract
This document describes a Multi-Protocol Label Switching Transport
Profile (MPLS-TP) Operations, Administration and Maintenance (OAM)
protocol to propagate a client failure indication across an MPLS-TP
network in the case that propagation of failure status in the client
layer is not supported as required in [RFC5860].
Table of Contents
1. Introduction ................................................ 2
2. Conventions used in this document............................ 3
2.1. Terminology ............................................ 3
3. Mechanisms of CSF ........................................... 4
3.1. General ................................................ 4
3.2. Transmission of CSF..................................... 5
3.3. Reception of CSF........................................ 6
3.4. Configuration of CSF.................................... 6
4. Frame format of CSF ......................................... 7
5. Consequent actions .......................................... 8
6. Security Considerations...................................... 9
7. IANA Considerations ......................................... 9
8. Acknowledgments ............................................. 9
9. References .................................................. 9
9.1. Normative References.................................... 9
9.2. Informative References................................. 10
10. Authors' Addresses ........................................ 10
1. Introduction
In transport networks, OAM functions are important and fundamental to
ease operational complexity, enhance network availability and meet
service performance objectives. This is achieved through automatic
detection, handling, diagnosis, appropriate reporting of defects and
performance monitoring.
As defined in [RFC 5860] MPLS-TP OAM MUST provide a function to
enable the propagation, from edge to edge of an MPLS-TP network, of
information pertaining to a client (i.e., external to the MPLS-TP
network) defect or fault condition detected at an End Point of a PW
or LSP, if the client layer OAM functionality does not provide an
alarm notification/propagation functionality (e.g. not needed in the
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original application of the client signal, or the signal was
originally at the bottom of the layer stack and it was not expected
to be transported over a server layer), while such an indication is
needed by the downstream.
This document defines a Client Signal Fail (CSF) indication protocol
in order to propagate client failures and their clearance across a
MPLS-TP domain.
According to [RFC 5921], MPLS-TP supports two native service
adaptation mechanisms via:
1) a Pseudowire, to emulate certain services, for example, Ethernet,
Frame Relay, or PPP / High-Level Data Link Control (HDLC).
2) an LSP, to provide adaptation for any native service traffic type
supported by [RFC3031] and [RFC3032]. Examples of such traffic
types include IP packets and MPLS-labeled packets (i.e.: PW over
LSP, or IP over LSP).
As to the first adaptation mechanism via a PW, the mechanism of CSF
function to support propagation of client failure indication follows
[static-pw-status]. The PW status relevant to CSF function is AC
fault as defined in [RFC 4447] and [RFC 4446].
As to the second adaptation mechanism via LSP, the mechanism is
detailed in this draft and is used in case the client of MPLS-TP can
not provide itself with such failure notification/propagation.
2. Conventions used in this document
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].
2.1. Terminology
The reader is assumed to be familiar with the terminology in MPLS-TP.
The relationship between ITU-T and IETF terminologies on MPLS-TP can
be found in [Rosetta stone].
ACH: Associated Channel Header
AIS: Alarm Indication Signal
CSF: Client Signal Fail indication
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FDI: Forward Defect Indication
G-ACh: Generic Associated Channel
GAL: G-ACh Label
LSR: Label Switching Router
MEP: Maintenance Entity Group End Point
MIP: Maintenance Entity Group Intermediate Point
OAM: Operations, Administration, and Maintenance
MPLS-TP: MPLS Transport Profile
PW: Pseudowire
RDI: Remote Defect Indication
3. Mechanisms of CSF
3.1. General
Client Signal Fail(CSF) indication provides a function to enable a
MEP to propagate a client failure indication to its peer MEP across a
MPLS-TP network in case the client service itself does not support
propagation of its failure status. A MIP is not intended to generate
or process CSF information.
Packets with CSF information can be issued by a MEP, upon receiving
failure information from its client service. Detection rules for
client failure events are client-specific and are therefore outside
the scope of this document.
+---+ +---+ +---+ +---+
| | | |-->CSF | | | |
| A |--X--| B |-----------------| C |------| D |
+---+ +---+ +---+ +---+
|<--MPLS-TP domain-->|
Figure 1 Use case of CSF
Figure 1 depicts a typical connection scenario between two client
network elements (Node A and Node D) interconnected through MPLS-TP
transport network. Client Node A connects to MPLS-TP Node B and
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Client Node D connects to MPLS-TP Node C. Node B and C support MPLS-
TP MEP function.
If a failure is detected between Node A and Node B and is taken as a
native client failure condition, the MEP function in Node B will
initiate CSF signal and it will be sent to Node C through MPLS-TP
network. CSF signal will be extracted at Node C as an indication of
client signal failure. Further, this may be mapped back into native
client failure indication and regenerated towards client Node D.
Node B learns the failure between A and B either by direct detection
of signal fail (e.g. loss of signal) or by some fault indications
between A and B (e.g. RDI, AIS/FDI).
If the connection between Node A and B recovers, Node B may stop
sending CSF signals to Node C (implicit failure clearance mechanism)
or explicitly send failure clearance indication (e.g. by flags in CSF
PDU format) to Node C to help expedite clearance of native client
failure conditions.
Accordingly, Node C will clear client failure condition when a valid
client data frame is received and no CSF is received (implicit
failure clearance mechanism) or upon receiving explicit failure
clearance indication.
3.2. Transmission of CSF
When CSF function is enabled, upon learning signal failure condition
of its client-layer, the MEP can immediately start transmitting
periodic packets with CSF information to its peer MEP. A MEP
continues to transmit periodic packets with CSF information until the
client-layer signal failure condition is cleared.
The clearance of CSF condition can be communicated to the peer MEP
via:
- Stopping of the transmission of CSF signal but forwarding client
data frames, or
- Forwarding CSF PDUs with a clearance indication.
Transmission of packets with CSF information can be enabled or
disabled on a MEP (e.g. through management plane).
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Detection and clearance rules for CSF events are client and
application specific and outside the scope of this draft.
The period of CSF transmission is client and application specific.
Examples are as follows:
- 3.33ms: for protection switching application.
- 1s: for fault management application.
However, the value 0 is invalid.
3.3. Reception of CSF
Upon receiving a packet with CSF information a MEP either declares or
clears a client-layer signal fail condition according to the received
CSF information and propagates this as a signal fail indication to
its client-layer.
CSF condition is cleared when the receiving MEP
- does not receive CSF signal within an interval of N times the CSF
transmission period (Suggested value of N is 3.5), or
- receives a valid client data frame, or
- receives CSF PDU with CSF-Clear information
3.4. Configuration of CSF
Specific configuration information required by a MEP to support CSF
transmission is the following:
CSF transmission period - this is application dependent. Examples are
3.3 ms and 1s.
PHB - identifies the per-hop behavior of packet with CSF information.
A MIP is transparent to packets with CSF information and therefore
does not require any information to support CSF functionality.
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4. Frame format of CSF
Figure 2 depicts the frame format of CSF. CSF PDUs are encapsulated
using the ACH, according to [RFC 5586]. GAL is used as an alert based
exception mechanism to differentiate CSF packets (with ACH as G-ACh
packets) from user-plane packets as defined in [RFC 5586].
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|0 0 0 0|0 0 0 0 0 0 0 0| MPLS-TP CSF(0xXX) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Version | Reserved 1 | Flags | Reserved 2 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Total TLV Len | ~
+-+-+-+-+-+-+-+-+ TLVs ~
~ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2 Frame format of CSF
The first four bytes represent the Generic ACH ([RFC 5586]):
- first nibble: set to 0001b to indicate a control channel
associated with a PW, a LSP or a Section;
- ACH Version(bits 4 to 7): set to 0, as specified in [RFC 5586]
- ACH Reserved (bits 8 to 15): set to 0 and ignored on reception,
as specified in [RFC 5586];
- ACH Channel Type (Bits 16 to 31): value 0xXX identifies the
payload as CSF PDU. To be assigned by IANA.
- CSF Version (Bits 32 to 39): Set to 0;
- CSF Reserved 1 (Bits 40 to 47): This field MUST be set to zero
on transmission and ignored on receipt;
- CSF Reserved 2 (Bits 56 to 63): This field MUST be set to zero
on transmission and ignored on receipt;
- Total TLV Length: Total of all included TLVs. No TLVs are
defined currently. The value is 0.
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- TLVs: No TLVs are defined currently.
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
| Res | Type | Period |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3 Format of Flags in CSF PDU
Figure 3 depicts the format of Flags in CSF PDU.
- Flag Reserved (Bits 48 to 49): Set to 0;
- Type (Bits 50 to 52): Set to the following values to indicate
CSF types
Value Type
111 Client Signal Fail - Loss of Signal (CSF-LOS)
001 Client Signal Fail - Forward Defect Indication (CSF-FDI)
010 Client Signal Fail - Reverse Defect Indication (CSF-RDI)
000 Clearance of Client Signal Fail - (CSF-Clear)
- Period (Bits 53 to 55): CSF transmission period and can be
configured.
5. Consequent actions
The primary intention of CSF is to transport a client signal fail
condition at the input of the MPLS-TP network to the output port of
the MPLS-TP network for clients that do not have alarm
notification/propagation mechanism defined.
Further, CSF allows creating a condition at the output port of the
MPLS-TP network such that the customer input port is able to detect
and alarm that there is no data arriving i.e. the connection is
interrupted. In this case, customers may choose another transport
network or another port to continue communication.
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6. Security Considerations
Malicious insertion of spurious CSF signals (e.g. DoS) is not quite
likely in a transport network since transport networks are usually
self-managed by operators and providers.
7. IANA Considerations
MPLS-TP CSF function requires a new Associated Channel Type to be
assigned by IANA from the Pseudowire Associated Channel Types
Registry.
Registry:
Value Description
----- -----------------------
0xXX MPLS-TP Client Signal Fail indication (CSF)
8. Acknowledgments
The authors would like to thank Haiyan Zhang, Adrian Farrel, Loa
Andersson, Matthew Bocci, Andy Malis and Thomas D. Nadeau for their
guidance and input to this work.
9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119, March 1997.
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031, January 2001.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci,
D., Li, T., and A. Conta, "MPLS Label Stack Encoding", RFC
3032, January 2001.
[RFC4446] Martini, L., "IANA Allocations for Pseudowire Edge to Edge
Emulation (PWE3)", RFC4446, April 2006
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[RFC4447] Martini, L., et al., "Pseudowire Setup and Maintenance
Using the Label Distribution Protocol (LDP)", RFC4447,
April 2006.
[RFC5586] Vigoureux, M., Bocci, M., Swallow, G., Ward, D., and R.
Aggarwal, "MPLS Generic Associated Channel", RFC5586, June
2009
[ITU-T Recommendation G.7041] "Generic framing procedure (GFP)", ITU-
T G.7041, October 2008
[RFC 5654] Niven-Jenkins, B., Brungard, D., and M. Betts,
"Requirements of an MPLS Transport Profile", RFC 5654,
September 2009
[RFC 5860] Vigoureux, M., Ward, D., and M. Betts, "Requirements for
OAM in MPLS Transport Networks", RFC5860, May 2010
[RFC 5921] Bocci, M., Bryant, S., and D. Frost, "A Framework for MPLS
in Transport Networks", RFC 5921, July 2010
[static-pw-status] Martini, L., Swallow, G., Heron, G., and M. Bocci,
"Pseudowire Status for Static Pseudowires", draft-ietf-
pwe3-static-pw-status-06 (work in progress), July 2011
9.2. Informative References
[MPLS-TP OAM Frmk] Busi,I., and D. Allan, "MPLS-TP OAM Framework and
Overview", draft-ietf-mpls-tp-oam-framework-11(work in
progress), February 2011
[Rosetta stone] Van Helvoort, H., Andersson, L., Sprecher, N., "A
Thesaurus for the Terminology used in Multiprotocol Label
Switching Transport Profile (MPLS-TP) drafts/RFCs and ITU-
T's Transport Network Recommendations", draft-ietf-mpls-tp-
rosetta-stone-04 (work in progress), June 2011
10. Authors' Addresses
Jia He
Huawei Technologies Co., Ltd.
Email: hejia@huawei.com
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Han Li
China Mobile Communications Corporation
Email: lihan@chinamobile.com
Elisa Bellagamba
Ericsson
Email: elisa.bellagamba@ericsson.com
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