SFC WG G. Mirsky
Internet-Draft ZTE Corp.
Intended status: Standards Track W. Meng
Expires: December 14, 2017 ZTE Corporation
B. Khasnabish
ZTE TX, Inc.
C. Wang
June 12, 2017
Multi-Layer OAM for Service Function Chains in Networks
draft-wang-sfc-multi-layer-oam-08
Abstract
A multi-layer approach to the task of Operation, Administration and
Maintenance (OAM) of Service Function Chains (SFCs) in networks is
presented. Based on the SFC OAM requirements, a multi-layer model is
introduced. A mechanism to detect and localize defects using the
multi-layer model is also described.
Status of This Memo
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
3. Multi-layer Model of SFC OAM . . . . . . . . . . . . . . . . 3
4. Requirements for SFC OAM Multi-layer Model . . . . . . . . . 4
5. SFC OAM multi-layer model . . . . . . . . . . . . . . . . . . 5
6. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 6
7. Security Considerations . . . . . . . . . . . . . . . . . . . 7
8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
8.1. SFC TLV Type . . . . . . . . . . . . . . . . . . . . . . 7
8.2. SFC OAM UDP Port . . . . . . . . . . . . . . . . . . . . 8
9. References . . . . . . . . . . . . . . . . . . . . . . . . . 8
9.1. Normative References . . . . . . . . . . . . . . . . . . 8
9.2. Informative References . . . . . . . . . . . . . . . . . 9
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
[RFC7665] defines components necessary to implement Service Function
Chain (SFC). These include a classifier which performs
classification of incoming packets. A Service Function Forwarder
(SFF) is responsible for forwarding traffic to one or more connected
Service Functions (SFs) according to the information carried in the
SFC encapsulation. SFF also handles traffic coming back from the SF
and transports the data packets to the next SFF. And the SFF serves
as termination element of the Service Function Path (SFP). SF is
responsible for specific treatment of received packets.
Resulting from that SFC is constructed by a number of these
components, there are different views from different levels of the
SFC. One is the SFC, fully abstract entity, that defines an ordered
set of SFs that must be applied to packets selected as a result of
classification. But SFC doesn't define exact mapping between SFFs
and SFs. Thus there exists another semi-abstract entity referred as
SFP. SFP is the instantiation of the SFC in the network and provides
a level of indirection between the fully abstract SFC and a fully
specified ordered list of SFFs and SFs identities that the packet
will visit when it traverses the SFC. The latter entity is being
referred as Rendered Service Path (RSP). The main difference between
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SFP and RSP is that in the former the authority to select the SFF/SF
has been delegated to the network.
This document proposes the multi-layer model of SFC Operation,
Administration and Maintenance (OAM) and requirements to improve the
troubleshooting efficiency.
2. Conventions
2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
2.2. Terminology
Unless explicitly specified in this document, active OAM in SFC and
SFC OAM are being used interchangeably.
e2e: End-to-End
FM: Fault Management
OAM: Operations, Administration, and Maintenance
RDI: Remote Defect Indication
RSP: Rendered Service Path
SF: Service Function
SFC: Service Function Chain
SFF: Service Function Forwarder
SFP: Service Function Path
3. Multi-layer Model of SFC OAM
As described in [I-D.ietf-sfc-oam-framework], multiple layers come
into play to realize the SFC, including the Service layer, the
underlying Network layer, as well as the Link layer, which are
depicted in Figure 1:
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o The Service layer consists of classifiers and/or service
functions/SFs.
o Network and Transport layers leverage various overlay network
technologies interconnecting SFs to establish SFP.
o The Link layer is technology specific and reflects the technology
used in the underlay network.
+---+ +---+ +---+ +---+ +---+
|SF1| |SF2| |SF3| |SF4| |SF5|
+---+ +---+ +---+ +---+ +---+
\ / \ / |
+----------+ +----+ +----+ +----+
|Classifier|-------|SFF1|---------|SFF2|--------|SFF3|
+----------+ +----+ +----+ +----+
0---------------------------------------------0 Service layer
0----------------0--------------0-------------0 Network layer
0-------------0------0-------0------0---------0 Link layer
Figure 1: SFC OAM Multi-Layer model
4. Requirements for SFC OAM Multi-layer Model
To perfrom the OAM task of fault management (FM) in an SFC, that
inculdes failure detection, defect characterzation and localization,
this document defines the multi-layer model of OAM, presented in
Section 3, and set of requirements towards active OAM mechanisms to
be used on an SFC.
In example presented in Figure 1 the service SFP1 may be realized
through two RSPs, RSP1(SF1--SF3--SF5) and RSP2(SF2--SF4--SF6). To
perform end-to-end (e2e) FM SFC OAM:
REQ#1: Packets of active OAM in SFC SHOULD be fate sharing with
data traffic, i.e. in-band with the monitored traffic, i.e. follow
exactly the same RSP, in forward direction, i.e. from ingress
toward egress end point(s) of the OAM test.
REQ#2: SFC OAM MUST support pro-active monitoring of any element
in the SFC availability.
The egress, SFF3 in example in Figure 1, is the entity that detects
the failure of the SFC. It must be able to signal the new defect
state to the ingress, i.e. SFF1. Hence the following requirement:
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REQ#3: SFC OAM MUST support Remote Defect Indication (RDI)
notification by egress to the ingress, i.e. source of continuity
checking.
REQ#4: SFC OAM MUST support connectivity verification. Definition
of mis-connectivity defect entry and exit criteria are outside the
scope of this document.
Once the SFF1 detects the defect objective of OAM switches from
failure detection to defect characterization and localization.
REQ#5: SFC OAM MUST support fault localization of Loss of
Continuity check in the SFC.
REQ#6: SFC OAM MUST support tracing an SFP in order to realize the
RSP.
It is practical, as presented in Figure 1, that several SFs share the
same SFF. In such case SFP1 may be realized over two RSPs,
RSP1(SF1--SF3--SF5) and RSP2(SF2--SF4--SF6).
REQ#7: SFC OAM MUST have the ability to discover and exercise all
available RSPs in the transport network.
In process of localizing the SFC failure separating SFC OAM layers is
very attractive and efficient approach. To achieve that continuity
among SFFs that are part of the same SFP should be verified. Once
SFFs reacheability along the particular SFP has been confirmed task
of defect localization may focus on SF reacheability verification.
Because reacheability of SFFs has already been verified, SFF local to
the SF may be used as source.
REQ#8: SFC OAM MUST be able to trigger on-demand FM with responses
being directed towards initiator of such proxy request.
By using the multi-layer model OAM that confirms to the above listed
requirements is capable to perform efficient defect localization on
an SFC.
5. SFC OAM multi-layer model
Figure 2 presents a use case of applying the proposed SFC OAM multi-
layer model. In this scenario operator needs to discover SFFs and
SFs of the same SFC. The Layer 1 includes the SFFs that are part of
the SFP. The Layer 2 - the SFs along the RSP. When trying to do SFC
OAM, classifier or service nodes select and confirm which SFC OAM
layering they plan to do, then encapsulate the layering information
in the SFC OAM packets, and send the SFC OAM packets along the
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service function paths to the destination. When receiving the SFC
OAM packets, service nodes analyze the layering information and then
decide whether sending these packets to next SFFs directly without
being processed by SFs for Layer 1 process or sending to SFs for
Layer 2 process.
+---+ +---+ +----+ +----+ +-----+ +-----+ +------+ +------+
|SF1|.|SFn| |SF1'|.|SFn'| |SF1''|.|SFn''| |SF1'''|.|SFn'''|
+---+ +---+ +----+ +----+ +-----+ +-----+ +------+ +------+
\ / \ / | \ / \ / |
+------+ +----+ +----+ | +-----+ +-----+ |
|Class.|---|SFF1| ... |SFFn| | |SFF1'| ... |SFFn'| |
+------+ +----+ +----+ | +-----+ +-----+ |
| | | |
| | | |
|----|------Layer 1---------------| |
| |
|-------------Layer 2-------------|
Figure 2: SFC OAM multi-layering model
6. Theory of Operation
Echo Request/Reply is well-known OAM mechanism that is extecively
used to detect inconsitencies between states in control plane and
data plane, localize defects in the data plane. In SFC OAM Echo
Request/Reply is built as extension of Overlay Echo Request/Reply
functions [I-D.ooamdt-rtgwg-demand-cc-cv].
Responder to the SFC Echo Request sends the Echo Reply over IP
network if the reply mode is Reply via an IPv4/IPv6 UDP Packet
[I-D.ooamdt-rtgwg-demand-cc-cv]. Because SFC NSH does not identify
the ingress of the SFP the Echo Request MUST include this information
that to be used as IP destination address for IP/UDP encapsulation of
the SFC Echo Reply. Sender of the SFC Echo Request MUST include SFC
Source TLV Figure 3.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SFC OAM Source ID Type | Length |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Value |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Segment Routing Static MPLS Tunnel sub-TLV
where
SFC OAM Source Id Type is two octets in length and has the value
of TBD1 Section 8.1.
Length is two octets long field and the valuse is equal to the
length of the Value field.
Value field contains IP address of the sender of the SFC OAM
control message, IPv4 or IPv6.
The UDP destination port for SFC Echo Reply TBD2 will be allocated by
IANA Section 8.2.
7. Security Considerations
TBD
8. IANA Considerations
8.1. SFC TLV Type
IANA is requested to create SFC OAM TLV Type registry. All code
points in the range 1 through 32759 in this registry shall be
allocated according to the "IETF Review" procedure as specified in
[RFC5226]. Code points in the range 32760 through 65279 in this
registry shall be allocated according to the "First Come First
Served" procedure as specified in [RFC5226]. Remaining code points
are allocated according to the Table 1:
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+---------------+--------------+-------------------------+
| Value | Description | Reference |
+---------------+--------------+-------------------------+
| 0 | Reserved | This document |
| 1- 32759 | Unassigned | IETF Review |
| 32760 - 65279 | Unassigned | First Come First Served |
| 65280 - 65519 | Experimental | This document |
| 65520 - 65534 | Private Use | This document |
| 65535 | Reserved | This document |
+---------------+--------------+-------------------------+
Table 1: SFC TLV Type Registry
This document defines the following new value in SFC OAM TLV Type
registry:
+-------+-------------------+---------------+
| Value | Description | Reference |
+-------+-------------------+---------------+
| TBD1 | Source IP Address | This document |
+-------+-------------------+---------------+
Table 2: SFC OAM Source IP Address Type
8.2. SFC OAM UDP Port
IANA is requested to allocate UDP port number according to
+---------+--------+------------+---------+--------------+----------+
| Service | Port | Transport | Descrip | Semantics | Referenc |
| Name | Number | Protocol | tion | Definition | e |
+---------+--------+------------+---------+--------------+----------+
| SFC OAM | TBD2 | UDP | SFC OAM | Section 6 | This |
| | | | | | document |
+---------+--------+------------+---------+--------------+----------+
Table 3: SFC OAM Port
9. References
9.1. Normative References
[I-D.ooamdt-rtgwg-demand-cc-cv]
Mirsky, G., Kumar, N., Kumar, D., Chen, M., Yizhou, L.,
and D. Dolson, "Echo Request and Echo Reply for Overlay
Networks", draft-ooamdt-rtgwg-demand-cc-cv-03 (work in
progress), March 2017.
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[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<http://www.rfc-editor.org/info/rfc2119>.
[RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC
2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174,
May 2017, <http://www.rfc-editor.org/info/rfc8174>.
9.2. Informative References
[I-D.ietf-sfc-oam-framework]
Aldrin, S., Krishnan, R., Akiya, N., Pignataro, C., and A.
Ghanwani, "Service Function Chaining Operation,
Administration and Maintenance Framework", draft-ietf-sfc-
oam-framework-01 (work in progress), February 2016.
[RFC5226] Narten, T. and H. Alvestrand, "Guidelines for Writing an
IANA Considerations Section in RFCs", BCP 26, RFC 5226,
DOI 10.17487/RFC5226, May 2008,
<http://www.rfc-editor.org/info/rfc5226>.
[RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function
Chaining (SFC) Architecture", RFC 7665,
DOI 10.17487/RFC7665, October 2015,
<http://www.rfc-editor.org/info/rfc7665>.
Authors' Addresses
Greg Mirsky
ZTE Corp.
Email: gregimirsky@gmail.com
Wei Meng
ZTE Corporation
No.50 Software Avenue, Yuhuatai District
Nanjing
China
Email: meng.wei2@zte.com.cn,vally.meng@gmail.com
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Bhumip Khasnabish
ZTE TX, Inc.
55 Madison Avenue, Suite 160
Morristown, New Jersey 07960
USA
Email: bhumip.khasnabish@ztetx.com
Cui Wang
Email: lindawangjoy@gmail.com
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