MPLS Working Group L. Han
Internet-Draft China Mobile
Intended status: Standards Track F. Yang
Expires: January 14, 2021 Huawei Technologies
July 13, 2020
Signal Degrade Indication Used in Segment Routing over MPLS Network
draft-han-mpls-sdi-sr-00
Abstract
This document describes the typical use cases for signal degrade
indication used in SR over MPLS networks. To satisfy the use cases
and requirements of signal degrade indication, two extensions based
on the BFD protocol and MPLS-TP OAM mechanisms are given
respectively.
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 [RFC2119].
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 3
4. BFD Indication Mechanism . . . . . . . . . . . . . . . . . . 4
5. MPLS-TP Indication Mechanism . . . . . . . . . . . . . . . . 5
6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 6
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 6
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
9.1. Normative References . . . . . . . . . . . . . . . . . . 7
9.2. Informative References . . . . . . . . . . . . . . . . . 7
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 7
1. Introduction
The importance and necessity of signal degrade notification used in
Segment Routing over MPLS networks is discussed in
[I-D.yang-mpls-ps-sdi-sr]. When signal degrade is detected, this
information could be extended by means of protocols to perform the
performance monitoring, fault management, and trigger of protection
mechanism etc. Extensions on control plane, forwarding plane,
management plane, and/or combination of any of them could be utilized
to support the function of signal degrade indication. This document
provides two protocol extensions used in SR over MPLS networks, by
specifying the encapsulations and behaviors in detail.
In some of SR over MPLS networks, BFD [RFC5880] or enhanced SBFD
[RFC7880] is widely utilized as the failure detection mechanism
because of its' simplicity and efficiency characteristics. The
indication of signal degrade could be adopted as one of the reasons
of BFD state changes. In other SR over MPLS networks, MPLS-TP OAM
[ITU-T G.8113.1] mechanisms are used instead of BFD or SBFD. In this
scenario, the extension based on the OAM PDU format is proposed in
this document to support the signal degarde indication.
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2. Terminology
MPLS: Multiprotocol Label Switching
SR: Segment Routing
BFD: Bidirectional Forwarding Detection
SBFD: Seamless BFD
LER: Label Edge Router
LSR: Label Switching Router
MPLS-TP: Multiprotocol Label Switching - Tranport Profile
OAM: Operation, Administration and Maintena
GAL: Generic Associated Channel Label
G-ACh: Generic Associated Channel (G-ACh)
PDU: Protocol Data Unit
CCM: Continuity Check Message
3. Overview
The use cases and requirements have been discussed in
[I-D.yang-mpls-ps-sdi-sr]. This document narrows the scope to the
multi-hop SR over MPLS network, signal degrade is detected simply
based on the physical bit error statistic on port level, no matter if
the PHY is with or without forward error correction (FEC). Port
level statistic is the intuitive approach to be best understood in
the equipment and network systems. In practice of deployment,
flexible configuration of the watermark to trigger the indication of
signal degrade is preferred.
As mentioned in [I-D.yang-mpls-ps-sdi-sr], signal degrade can happen
in any link or node in SR over MPLS networks, such as LERs and LSRs.
LERs can detect the signal degrade fault, or directly trigger the
protecton switch mechanisms once it detects the signal degrade
reaches at a certain level. However, LSRs may need further
considerations. In SR over MPLS networks, since only the headend LER
knows all the segments in the label stack, the intermediate LSRs does
not know the entire label stack. There is no other choice of
forwarding path to avoid the impact of signal degrade on the LSR.
Thus, the signal degrade information should be spread to other LSRs
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and LERs, and consequent behaviors on LSRs or LERs are executed
depending on the choices of the protection mechanisms.
The notification mechanism is best used through a forwarding
protocol, not through the centralized Network Management System (NMS)
or a SDN controller, to make sure the notification could be fast
enough. Furthermore, carrying the signal degrade information in a
control protocol is considered as well. In this case, the extensions
of BFD control packet format and MPLS-TP CCM OAM PDU format are made
to spread the signal degrade information.
Though the signal degrade detection is limited to be monitored based
on the physical link, the indication of signal degrade is preferred
at the transport path level, e.g. MPLS PWs, MPLS LSPs, or MPLS
Sections. In this case, Generic Associated Channel (G-ACh) defined
in [RFC5586] is proposed as the best choice to satisfy this
requirement. The Generic Associated Channel packet format used in SR
over MPLS network is shown in Figure 1.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label | EXP |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GAL Label (13) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0001 | 0000 | 00000000 | Channel Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 1 G-ACh Packet Format in SR over MPLS
4. BFD Indication Mechanism
Working together with the G-Ach, IP/UDP/BFD packet formats are
encapsulated and shown in Figure 2. The IP, UDP and BFD headers stay
intact within the generic associated channel. The Diagnostic code
specifies the local system's reason for the last change in session
state. The definition of the Values is specified in Section 4.1 of
[RFC5880]. The Reserved values from 9 to 31 can be extended to
support the signal degrade indication. The registration to support
the indication and removal of the signal degrade indication should be
applied to IANA.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GAL Label (13) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0001 | 0000 | 00000000 | Channel Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Vers | IHL | TOS | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Identifier | Flag | Fragment Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| TTL | Prot | Header Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Destination Address |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Source Port | Destination Port |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Length | Checksum |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Vers | Diag |Sta|P|F|C|A|D|M| Detect Mult | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| My Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Your Discriminator |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Desired Min TX Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Required Min RX Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Required Min Echo RX Interval |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Authentication (optional) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: BFD Packet Format in SR over MPLS
5. MPLS-TP Indication Mechanism
ITU-T G.8113.1 defines the OAM PDU formats used in MPLS-TP networks.
Figure 3 shows the OAM PDU format used within the SR over MPLS
networks. If the LSR node detects the signal degrade, OAM CCM
message is chosen to indicate the signal degrade via the forwarding
plane. The OpCode value 0x01 in OAM PDU field indicates the CCM PDU
message type.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GAL Label (13) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| 0001 | 0000 | 00000000 | Channel Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MEL | Version | OpCode(0x01) | Flag | TLV Offset |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| OAM PDU |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|End TLV|
+-+-+-+-+
Figure 3 G.8113.1 OAM PDU Format in SR over MPLS
The reservation bits in Flag format in CCM OAM PDU message can be
used as the error notification indication (EI) to indicate signal
degrade, as shown in Figure 4. LSRs fills the EI field and transmits
the OAM message to the other LSRs or LERs so that the degrade
information can be learned.
0
0 1 2 3 4 5 6 7
+---+---+---+---+---+---+---+---+
|RDI| EI| Resv | Period |
+---+---+---+---+---+---+---+---+
Figure 4 Extended Flags Format
EI (1 bit): Error notification indication, 0 indicates no error, 1
indicates error, to notify the signal degradation error.
6. IANA Considerations
The document requires the definition of the new indication and
removal of the signal degrade indication in BFD Value code.
Moreover, the EI bit definition is required to be assigned by ITU-T.
7. Security Considerations
This document has no security consideration.
8. Acknowledgements
TBD
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9. References
9.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
9.2. Informative References
[I-D.yang-mpls-ps-sdi-sr]
Yang, F., Han, L., and J. Zhao, "Problem Statement of
Signal Degrade Indication for Segment Routing over MPLS
Network", draft-yang-mpls-ps-sdi-sr-00 (work in progress),
March 2020.
[ITU-T_G8113.1]
ITU-T, "ITU-T G.8113.1: Operations, administration
and maintenance mechanisms for MPLS-TP in packet
and maintenance mechanisms for MPLS-TP in packet
transport networks", April 2016.
[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586,
DOI 10.17487/RFC5586, June 2009,
<https://www.rfc-editor.org/info/rfc5586>.
[RFC5880] Katz, D. and D. Ward, "Bidirectional Forwarding Detection
(BFD)", RFC 5880, DOI 10.17487/RFC5880, June 2010,
<https://www.rfc-editor.org/info/rfc5880>.
[RFC7880] Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.
Pallagatti, "Seamless Bidirectional Forwarding Detection
(S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016,
<https://www.rfc-editor.org/info/rfc7880>.
[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.
Authors' Addresses
Liuyan Han
China Mobile
No.32 Xuanwumen west street
Beijing 100053
China
Email: hanliuyan@chinamobile.com
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Fan Yang
Huawei Technologies
Huawei Campus, No. 156 Beiqing Rd.
Beijing 100095
China
Email: shirley.yangfan@huawei.com
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