SFC WG G. Mirsky Internet-Draft ZTE Corp. Updates: 8300 (if approved) W. Meng Intended status: Standards Track ZTE Corporation Expires: August 1, 2019 B. Khasnabish Individual contributor C. Wang January 28, 2019 Active OAM for Service Function Chains in Networks draft-ietf-sfc-multi-layer-oam-01 Abstract A set of requirements for active Operation, Administration and Maintenance (OAM) of Service Function Chains (SFCs) in networks is presented. Based on these requirements an encapsulation of active OAM message in SFC and a mechanism to detect and localize defects described. Also, this document updates RFC 8300 in the definition of O (OAM) bit in the Network Service Header (NSH) and defines how the active OAM message identified in SFC NSH. 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 working documents as Internet-Drafts. The list of current Internet- Drafts is at https://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 August 1, 2019. Copyright Notice Copyright (c) 2019 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of Mirsky, et al. Expires August 1, 2019 [Page 1] Internet-Draft Active OAM for SFC January 2019 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Conventions . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2.2. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3 3. Requirements for Active OAM in SFC Network . . . . . . . . . 4 4. Active OAM Identification in SFC NSH . . . . . . . . . . . . 5 5. Echo Request/Echo Reply for SFC in Networks . . . . . . . . . 7 5.1. SFC Echo Request Transmission . . . . . . . . . . . . . . 8 5.2. SFC Echo Request Reception . . . . . . . . . . . . . . . 9 5.3. SFC Echo Reply Transmission . . . . . . . . . . . . . . . 9 5.4. Overlay Echo Reply Reception . . . . . . . . . . . . . . 10 6. Security Considerations . . . . . . . . . . . . . . . . . . . 10 7. Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . 10 8. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 10 8.1. SFC Active OAM Protocol . . . . . . . . . . . . . . . . . 10 8.2. SFC Active OAM Message Type . . . . . . . . . . . . . . . 11 8.3. SFC Echo Request/Echo Reply Parameters . . . . . . . . . 11 8.4. SFC Echo Request/Echo Reply Message Types . . . . . . . . 12 8.5. SFC Echo Reply Modes . . . . . . . . . . . . . . . . . . 12 8.6. SFC TLV Type . . . . . . . . . . . . . . . . . . . . . . 13 8.7. SFC OAM UDP Port . . . . . . . . . . . . . . . . . . . . 13 9. References . . . . . . . . . . . . . . . . . . . . . . . . . 14 9.1. Normative References . . . . . . . . . . . . . . . . . . 14 9.2. Informative References . . . . . . . . . . . . . . . . . 14 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 15 1. Introduction [RFC7665] defines components necessary to implement Service Function Chain (SFC). These include a classifier which performs the 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 the specific treatment of received packets. Mirsky, et al. Expires August 1, 2019 [Page 2] Internet-Draft Active OAM for SFC January 2019 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, entirely abstract entity, which defines an ordered set of SFs that must be applied to packets selected as a result of classification. But SFC doesn't specify the exact mapping between SFFs and SFs. Thus there exists another semi-abstract entity referred to as SFP. SFP is the instantiation of the SFC in the network and provides a level of indirection between the entirely 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 to as Rendered Service Path (RSP). The main difference between SFP and RSP is that in the former the authority to select the SFF/SF has been delegated to the network. This document defines how active Operation, Administration and Maintenance (OAM), per [RFC7799] definition of active OAM, identified in Network Service Header (NSH) SFC, lists requirements to improve the troubleshooting efficiency, and defines SFC Echo request and Echo reply that enables on-demand Continuity Check, Connectivity Verification among other operations over SFC in networks. Also, this document updates Section 2.2 of [RFC8300] in part of the definition of O bit in the (NSH). 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 NSH: Network Service Header OAM: Operations, Administration, and Maintenance PRNG: Pseudorandom number generator Mirsky, et al. Expires August 1, 2019 [Page 3] Internet-Draft Active OAM for SFC January 2019 RDI: Remote Defect Indication RSP: Rendered Service Path SF: Service Function SFC: Service Function Chain SFF: Service Function Forwarder SFP: Service Function Path 3. Requirements for Active OAM in SFC Network To perform the OAM task of fault management (FM) in an SFC, that includes failure detection, defect characterization and localization, this document defines the set of requirements for active OAM mechanisms to be used on an SFC. +---+ +---+ +---+ +---+ +---+ +---+ |SF1| |SF2| |SF3| |SF4| |SF5| |SF6| +---+ +---+ +---+ +---+ +---+ +---+ \ / \ / \ / +----------+ +----+ +----+ +----+ |Classifier|-------|SFF1|---------|SFF2|--------|SFF3| +----------+ +----+ +----+ +----+ Figure 1: SFC reference model In the example presented in Figure 1, the service SFP1 may be realized through two RSPs, RSP1(SF1--SF3--SF5) and RSP2(SF2--SF4-- SF5). 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 follow the same RSP, in the forward direction from ingress toward egress endpoint(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 the 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 SFF1. Hence the following requirement: Mirsky, et al. Expires August 1, 2019 [Page 4] Internet-Draft Active OAM for SFC January 2019 REQ#3: SFC OAM MUST support Remote Defect Indication (RDI) notification by the egress to the ingress. REQ#4: SFC OAM MUST support connectivity verification. Definition of the misconnection 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 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 the process of localizing the SFC failure, separating SFC OAM layers is an efficient approach. To achieve that continuity among SFFs that are part of the same SFP should be verified. Once SFFs reachability along the particular SFP has been confirmed task of defect localization may focus on SF reachability verification. Because reachability of SFFs has already verified, SFF local to the SF may be used as a source of the test packets. REQ#8: SFC OAM MUST be able to trigger on-demand FM with responses being directed towards initiator of such proxy request. 4. Active OAM Identification in SFC NSH The interpretation of O bit flag in the NSH header is defined in [RFC8300] as: O bit: Setting this bit indicates an OAM packet. This document updates the definition of O bit as follows: O bit: Setting this bit indicates an OAM command and/or data in the NSH Context Header or packet payload Active SFC OAM defined as a combination of OAM commands and/or data included in a message that immediately follows the NSH. To identify the active OAM message the value on the Next Protocol field MUST be Mirsky, et al. Expires August 1, 2019 [Page 5] Internet-Draft Active OAM for SFC January 2019 set to Active SFC OAM (TBA1) according to Section 8.1. The rules of interpreting the values of O bit and the Next Protocol field are as follows: o O bit set, and the Next Protocol value is not one of identifying active or hybrid OAM protocol (per [RFC7799] definitions), e.g., defined in this specification Active SFC OAM - a Fixed-Length Context Header or Variable-Length Context Header(s) contain OAM command or data. and the type of payload determined by the Next Protocol field; o O bit set, and the Next Protocol value is one of identifying active or hybrid OAM protocol - the payload that immediately follows SFC NSH contains OAM command or data; o O bit is clear - no OAM in a Fixed-Length Context Header or Variable-Length Context Header(s) and the payload determined by the value of the Next Protocol field; o O bit is clear and the Next Protocol value is one of identifying active or hybrid OAM protocol MUST be identified and reported as the erroneous combination. An implementation MAY have control to enable processing of the OAM payload. From the above-listed rules follows the recommendation to avoid combination of OAM in a Fixed-Length Context Header or Variable- Length Context Header(s) and in the payload immediately following the SFC NSH because there is no unambiguous way to identify such combination using the O bit and the Next Protocol field. Several active OAM protocols will be needed to address all the requirements listed in Section 3. Destination UDP port number may identify protocols if IP/UDP encapsulation used. But extra IP/UDP headers, especially in the case of IPv6, add noticeable overhead. This document defines Active OAM Header Figure 2 to demultiplex active OAM protocols on an SFC. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | V | Msg Type | Flags | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ SFC Active OAM Control Packet ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: SFC Active OAM Header Mirsky, et al. Expires August 1, 2019 [Page 6] Internet-Draft Active OAM for SFC January 2019 V - two bits long field indicates the current version of the SFC active OAM header. The current value is 0. Msg Type - six bits long field identifies OAM protocol, e.g., Echo Request/Reply or BFD. Flags - eight bits long field carries bit flags that define optional capability and thus processing of the SFC active OAM control packet, e.g., optional timestamping. Length - two octets long field that is the length of the SFC active OAM control packet in octets. 5. Echo Request/Echo Reply for SFC in Networks Echo Request/Reply is a well-known active OAM mechanism that is extensively used to detect inconsistencies between a state in control and the data planes, localize defects in the data plane. The format of the Echo request/Echo reply control packet is to support ping and traceroute functionality in SFC in networks Figure 3 resembles the format of MPLS LSP Ping [RFC8029] with some exceptions. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Version Number | Global Flags | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message Type | Reply mode | Return Code | Return S.code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sender's Handle | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ TLVs ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: SFC Echo Request/Reply format The interpretation of the fields is as follows: The Version reflects the current version. The version number is to be incremented whenever a change is made that affects the ability of an implementation to parse or process control packet correctly. The Global Flags is a bit vector field. Mirsky, et al. Expires August 1, 2019 [Page 7] Internet-Draft Active OAM for SFC January 2019 The Message Type filed reflects the type of the packet. Value TBA3 identifies echo request and TBA4 - echo reply The Reply Mode defines the type of the return path requested by the sender of the echo request. Return Codes and Subcodes can be used to inform the sender about the result of processing its request. The Sender's Handle is filled in by the sender and returned unchanged by the receiver in the echo reply. The sender MAY use a pseudo-random number generator (PRNG) to set the value of the Sender's Handle field. The value of the Sender's Handle field SHOULD NOT be changed in the course of the test session. The Sequence Number is assigned by the sender and can be (for example) used to detect missed replies. The value of the Sequence Number field SHOULD be monotonically increasing in the course of the test session. TLVs (Type-Length-Value tuples) have the two octets long Type field, two octets long Length field that is the length of the Value field in octets. 5.1. SFC Echo Request Transmission SFC echo request control packet MUST use the appropriate encapsulation of the monitored SFP. If Network Service Header (NSH) is used, echo request MUST set O bit, as defined in [RFC8300]. SFC NSH MUST be immediately followed by the SFC Active OAM Header defined in Section 4. Message Type field in the SFC Active OAM Header MUST be set to SFC Echo Request/Echo Reply value (TBA2) per Section 8.2. Value of the Reply Mode field MAY be set to: o Do Not Reply (TBA5) if one-way monitoring is desired. If the echo request is used to measure synthetic packet loss; the receiver may report loss measurement results to a remote node. o Reply via an IPv4/IPv6 UDP Packet (TBA6) value likely will be the most used. o Reply via Application Level Control Channel (TBA7) value if the SFP may have bi-directional paths. o Reply via Specified Path (TBA7) value to enforce the use of the particular return path specified in the included TLV to verify bi- Mirsky, et al. Expires August 1, 2019 [Page 8] Internet-Draft Active OAM for SFC January 2019 directional continuity and also increase the robustness of the monitoring by selecting a more stable path. 5.2. SFC Echo Request Reception 5.3. SFC Echo Reply Transmission The Reply Mode field directs whether and how the echo reply message should be sent. The sender of the echo request MAY use TLVs to request that the corresponding echo reply is transmitted over the specified path. Value TBA3 is referred to as "Do not reply" mode and suppresses transmission of echo reply packet. The default value (TBA6) for the Reply mode field requests the responder to send the echo reply packet out-of-band as IPv4 or IPv6 UDP packet. 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. Because SFC NSH does not identify the ingress of the SFP the echo request, the source ID MUST be included in the message and used as the IP destination address for IP/UDP encapsulation of the SFC echo reply. The sender of the SFC echo request MUST include SFC Source TLV Figure 4. 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 4: SFC Source TLV where SFC OAM Source Id Type is two octets in length and has the value of TBA9 Section 8.6. Length is two octets long field, and the value equals the length of the Value field in octets. Value field contains the IP address of the sender of the SFC OAM control message, IPv4 or IPv6. The UDP destination port for SFC Echo Reply TBA10 will be allocated by IANA Section 8.7. Mirsky, et al. Expires August 1, 2019 [Page 9] Internet-Draft Active OAM for SFC January 2019 5.4. Overlay Echo Reply Reception 6. Security Considerations Overlay Echo Request/Reply operates within the domain of the overlay network and thus inherits any security considerations that apply to the use of that overlay technology and, consequently, underlay data plane. Also, the security needs for SFC echo request/reply are similar to those of ICMP ping [RFC0792], [RFC4443] and MPLS LSP ping [RFC8029]. There are at least three approaches of attacking a node in the overlay network using the mechanisms defined in the document. One is a Denial-of-Service attack, by sending SFC ping to overload an element of the SFC. The second may use spoofing, hijacking, replying, or otherwise tampering with SFC echo requests and/or replies to misrepresent, alter operator's view of the state of the SFC. The third is an unauthorized source using an SFC echo request/ reply to obtain information about the SFC and/or its elements, e.g. SFF or SF. It is RECOMMENDED that implementations throttle the SFC ping traffic going to the control plane to mitigate potential Denial-of-Service attacks. Reply and spoofing attacks involving faking or replying SFC echo reply messages would have to match the Sender's Handle and Sequence Number of an outstanding SFC echo request message which is highly unlikely. Thus the non-matching reply would be discarded. To protect against unauthorized sources trying to obtain information about the overlay and/or underlay an implementation MAY check that the source of the echo request is indeed part of the SFP. 7. Acknowledgments Authors greatly appreciate thorough review and the most helpful comments from Dan Wing. 8. IANA Considerations 8.1. SFC Active OAM Protocol IANA is requested to assign a new type from the SFC Next Protocol registry as follows: Mirsky, et al. Expires August 1, 2019 [Page 10] Internet-Draft Active OAM for SFC January 2019 +-------+----------------+---------------+ | Value | Description | Reference | +-------+----------------+---------------+ | TBA1 | SFC Active OAM | This document | +-------+----------------+---------------+ Table 1: SFC Active OAM Protocol 8.2. SFC Active OAM Message Type IANA is requested to create a new registry called "SFC Active OAM Message Type". All code points in the range 1 through 32767 in this registry shall be allocated according to the "IETF Review" procedure as specified in [RFC8126]. Remaining code points to be allocated according to the table Table 2: +---------------+-------------+-------------------------+ | Value | Description | Reference | +---------------+-------------+-------------------------+ | 0 | Reserved | | | 1 - 32767 | Reserved | IETF Consensus | | 32768 - 65530 | Reserved | First Come First Served | | 65531 - 65534 | Reserved | Private Use | | 65535 | Reserved | | +---------------+-------------+-------------------------+ Table 2: SFC Active OAM Message Type IANA is requested to assign new type from the SFC Active OAM Message Type registry as follows: +-------+-----------------------------+---------------+ | Value | Description | Reference | +-------+-----------------------------+---------------+ | TBA2 | SFC Echo Request/Echo Reply | This document | +-------+-----------------------------+---------------+ Table 3: SFC Echo Request/Echo Reply Type 8.3. SFC Echo Request/Echo Reply Parameters IANA is requested to create new SFC Echo Request/Echo Reply Parameters registry. Mirsky, et al. Expires August 1, 2019 [Page 11] Internet-Draft Active OAM for SFC January 2019 8.4. SFC Echo Request/Echo Reply Message Types IANA is requested to create in the SFC Echo Request/Echo Reply Parameters registry the new sub-registry Message Types. All code points in the range 1 through 191 in this registry shall be allocated according to the "IETF Review" procedure as specified in [RFC8126] and assign values as follows: +------------+------------------+-------------------------+ | Value | Description | Reference | +------------+------------------+-------------------------+ | 0 | Reserved | | | TBA3 | SFC Echo Request | This document | | TBA4 | SFC Echo Reply | This document | | TBA4+1-191 | Unassigned | IETF Review | | 192-251 | Unassigned | First Come First Served | | 252-254 | Unassigned | Private Use | | 255 | Reserved | | +------------+------------------+-------------------------+ Table 4: SFC Echo Request/Echo Reply Message Types 8.5. SFC Echo Reply Modes IANA is requested to create in the SFC Echo Request/Echo Reply Parameters registry the new sub-registry Reply Modes All code points in the range 1 through 191 in this registry shall be allocated according to the "IETF Review" procedure as specified in [RFC8126] and assign values as follows: +------------+---------------------------------+--------------------+ | Value | Description | Reference | +------------+---------------------------------+--------------------+ | 0 | Reserved | | | TBA5 | Do Not Reply | This document | | TBA6 | Reply via an IPv4/IPv6 UDP | This document | | | Packet | | | TBA7 | Reply via Application Level | This document | | | Control Channel | | | TBA8 | Reply via Specified Path | This document | | TBA8+1-191 | Unassigned | IETF Review | | 192-251 | Unassigned | First Come First | | | | Served | | 252-254 | Unassigned | Private Use | | 255 | Reserved | | +------------+---------------------------------+--------------------+ Table 5: SFC Echo Reply Modes Mirsky, et al. Expires August 1, 2019 [Page 12] Internet-Draft Active OAM for SFC January 2019 8.6. 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 [RFC8126]. 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 [RFC8126]. Remaining code points are allocated according to the Table 6: +---------------+--------------+-------------------------+ | 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 6: SFC TLV Type Registry This document defines the following new value in SFC OAM TLV Type registry: +-------+-------------------+---------------+ | Value | Description | Reference | +-------+-------------------+---------------+ | TBA9 | Source IP Address | This document | +-------+-------------------+---------------+ Table 7: SFC OAM Source IP Address Type 8.7. SFC OAM UDP Port IANA is requested to allocate UDP port number according to +--------+-------+-----------+-------------+------------+-----------+ | Servic | Port | Transport | Description | Semantics | Reference | | e Name | Numbe | Protocol | | Definition | | | | r | | | | | +--------+-------+-----------+-------------+------------+-----------+ | SFC | TBA10 | UDP | SFC OAM | Section | This | | OAM | | | | 5.3 | document | +--------+-------+-----------+-------------+------------+-----------+ Table 8: SFC OAM Port Mirsky, et al. Expires August 1, 2019 [Page 13] Internet-Draft Active OAM for SFC January 2019 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, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed., "Network Service Header (NSH)", RFC 8300, DOI 10.17487/RFC8300, January 2018, . 9.2. Informative References [RFC0792] Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, DOI 10.17487/RFC0792, September 1981, . [RFC4443] Conta, A., Deering, S., and M. Gupta, Ed., "Internet Control Message Protocol (ICMPv6) for the Internet Protocol Version 6 (IPv6) Specification", STD 89, RFC 4443, DOI 10.17487/RFC4443, March 2006, . [RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function Chaining (SFC) Architecture", RFC 7665, DOI 10.17487/RFC7665, October 2015, . [RFC7799] Morton, A., "Active and Passive Metrics and Methods (with Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799, May 2016, . [RFC8029] Kompella, K., Swallow, G., Pignataro, C., Ed., Kumar, N., Aldrin, S., and M. Chen, "Detecting Multiprotocol Label Switched (MPLS) Data-Plane Failures", RFC 8029, DOI 10.17487/RFC8029, March 2017, . Mirsky, et al. Expires August 1, 2019 [Page 14] Internet-Draft Active OAM for SFC January 2019 [RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for Writing an IANA Considerations Section in RFCs", BCP 26, RFC 8126, DOI 10.17487/RFC8126, June 2017, . 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 Bhumip Khasnabish Individual contributor Email: vumip1@gmail.com Cui Wang Email: lindawangjoy@gmail.com Mirsky, et al. Expires August 1, 2019 [Page 15]