MPLS Working Group Y. Liu Internet-Draft G. Mirsky Intended status: Standards Track ZTE Corporation Expires: April 28, 2021 October 25, 2020 MPLS-based Service Function Path(SFP) Consistency Verification draft-lm-mpls-sfc-path-verification-01 Abstract This document proposes a method to verify the correlation between Service Function Chaining control and/or management plane view of the specified Service Function Path and the state of its data. It works for both SR service programming and MPLS-based NSH SFC. This document defines the signaling of the Generic Associated Channel (G-ACh) over a Service Function Path (SFP) with an MPLS forwarding plane using the basic unit defined in RFC 8595. The document also describes the processing of the G-ACh by the elements of the SFP. 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 April 28, 2021. Copyright Notice Copyright (c) 2020 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 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect Liu & Mirsky Expires April 28, 2021 [Page 1] Internet-Draft LSP Ping for SFC October 2020 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 used in this document . . . . . . . . . . . . . . 3 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2.2. Acronyms . . . . . . . . . . . . . . . . . . . . . . . . 3 3. MPLS-based SFP Consistency Verification . . . . . . . . . . . 4 3.1. Special-purpose Label in SFC-MPLS Environment . . . . . . 5 3.1.1. G-ACh over SFC-MPLS . . . . . . . . . . . . . . . . . 6 3.2. MPLS-based SFP Consistency Verification . . . . . . . . . 6 3.3. SFC Info Sub-TLV . . . . . . . . . . . . . . . . . . . . 7 3.4. SFC Basic Unit FEC Sub-TLV . . . . . . . . . . . . . . . 8 3.5. Theory of Operation . . . . . . . . . . . . . . . . . . . 9 3.5.1. MPLS-based service programming . . . . . . . . . . . 10 3.5.2. Path Consistency in SFC-MPLS . . . . . . . . . . . . 10 3.6. Discussion . . . . . . . . . . . . . . . . . . . . . . . 10 4. Security Considerations . . . . . . . . . . . . . . . . . . . 11 5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 11 5.1. SFC Validation TLV . . . . . . . . . . . . . . . . . . . 11 5.1.1. Sub-TLVs for SFC Validation TLV . . . . . . . . . . . 11 5.2. SFC Basic Unit sub-TLV . . . . . . . . . . . . . . . . . 12 6. References . . . . . . . . . . . . . . . . . . . . . . . . . 12 6.1. Normative References . . . . . . . . . . . . . . . . . . 12 6.2. Informative References . . . . . . . . . . . . . . . . . 13 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 13 1. Introduction Service Function Chain (SFC) defined in [RFC7665] as an ordered set of service functions (SFs) to be applied to packets and/or frames, and/or flows selected as a result of classification. SFC can be achieved through a variety of encapsulation methods, such as NSH [RFC8300], SR service programming [I-D.ietf-spring-sr-service-programming] and MPLS-based NSH SFC [RFC8595]. This document describes extensions to MPLS LSP ping [RFC8029] mechanisms to support verification between the control/management plane and the data plane state for both SR-MPLS service programming and MPLS-based NSH SFC. Liu & Mirsky Expires April 28, 2021 [Page 2] Internet-Draft LSP Ping for SFC October 2020 An MPLS LSP ping is a component of the MPLS Operation, Administration, and Maintenance (OAM) toolset. OAM packets used to monitor a specific Service Function Path (SFP) can be transported over a Generic Associated Channel (G-ACh). This document defines the signaling of the G-ACh over an SFP with an MPLS forwarding plane using the basic unit defined in [RFC8595]. The document also describes the processing of the G-ACh by the elements of the SFP. 2. Conventions used in this document 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. Acronyms SFC: Service Function Chain SFF: Service Function Forwarder SF: Service Function SFI: Instance of an SF SFP: Service Function Path RSP: Rendered Service Path SFC-MPLS: SFC over an MPLS forwarding plane SPL: Special-Purpose Label bSPL: Base SPL eSPL: Extended SPL GAL: Generic Associated Channel Label ELI: Entropy Label Indicator OAM: Operation, Administration, and Maintenance G-ACh: Generic Associated Channel Liu & Mirsky Expires April 28, 2021 [Page 3] Internet-Draft LSP Ping for SFC October 2020 GAL: Generic Associated Channel Label 3. MPLS-based SFP Consistency Verification MPLS echo request and reply messages [RFC8029] can be extended to support the verification of the consistency of an MPLS-based Service Function Path (SFP). SR-MPLS/MPLS can be used to realize an SFP. Two methods have been defined: o [I-D.ietf-spring-sr-service-programming] describes how to achieve service function chaining in SR-enabled MPLS and IPv6 networks. In an SR-MPLS network, each SF is associated with an MPLS label. As a result, an SFP can be encoded as a stack of MPLS labels and pushed on top of the packet. o [RFC8595] provides another method to realize SFC in an MPLS network by means of using a logical representation of the Network Service Header (NSH) in an MPLS label stack. This method, throughout this document, is referred to as SFC over an MPLS data plane (SFC-MPLS). When an MPLS label stack is used to carry a logical NSH, a basic unit of representation is used, which can be present one or more times in the label stack. This unit comprises two MPLS labels, one carries a label to provide a context within the SFC scope (the SFC Context Label), and the other carries a label to show which SF is to be enacted (the SF Label). This two- label unit 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SFC Context Label | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SF Label | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: The Basic Unit of MPLS Label Stack for SFC In MPLS Label Switched Paths (LSPs), MPLS LSP ping [RFC8029] is used to check the correctness of the data plane functioning and to verify the data plane against the control plane. The proposed extension of MPLS LSP ping allows verification of the correlation between the control/management (if data model-based Liu & Mirsky Expires April 28, 2021 [Page 4] Internet-Draft LSP Ping for SFC October 2020 central controller used) plane and the data plane state in SR-MPLS/ MPLS-based SFC. Generally, except for the designed specific functions, the packet processing functions supported by SFs are limited. SFs may not support control and/or management protocols operated over the G-ACh defined n [RFC5586], e.g., MPLS OAM protocols like LSP ping. To avoid such packets mishandled, SFFs are responsible for MPLS echo request processing. To support that processing, the basic unit can use the mechanism described in Section 3.1. 3.1. Special-purpose Label in SFC-MPLS Environment When an SFC-MPLS is used, an SFF needs to identify an OAM packet with the SFP scope. To achieve that, this specification first defines the use of a base special-purpose label (bSPL) [RFC3032] or an extended special-purpose label (eSPL) [RFC7274] (referred in this document as SPL Unit) with the basic unit defined in [RFC8595]. And based on that, the use of Generic Associated Channel Label (GAL) [RFC5586] with the basic unit in the SFC-MPLS environment. Special-purpose label (SPL), whether bSPL or eSPL, have special significance in the data and control planes. An ability to use an SPL in the basic unit allows for a closer functional match between the NSH-based SFC and SFC-MPLS. For example, Entropy Label Indicator (ELI) [RFC6790] with the basic unit can be used as the Flow ID TLV [I-D.ietf-sfc-nsh-tlv] to allow an SFF to balance SFC flows among SFs of the same type. An SPL MAY be used with the basic unit in SFC- MPLS, as displayed in Figure 2. Note that an SPL unit MAY be present in one or more basic units when MPLS label stacking is used to carry the SFC information. 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 Context Label | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SPL Unit | ~ ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SF Label | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: Special-purpose Label Unit with the Basic Unit of MPLS Label Stack for SFC Liu & Mirsky Expires April 28, 2021 [Page 5] Internet-Draft LSP Ping for SFC October 2020 3.1.1. G-ACh over SFC-MPLS SFC-MPLS environment could include instances of an SF (SFI) or SFC proxies that cannot properly process control and/or management protocol messages that are exchanged between nodes over the G-ACh associated with the particular SFP. To support OAM over G-ACh, it is beneficial to avoid handing over a test packet to the SFI or SFC proxy. Hence, this specification defines that if the Generic Associated Channel Label (GAL) immediately follows the SFC Context label [RFC8595], then the packet is recognized as an SFP OAM packet. Below are the processing rules of an SFP OAM packet by an SFF: o An SFF MUST NOT pass the packet to a local SFI or SFC proxy. o The SFF MUST decrement SF Label entry's TTL value. If the resulting value equals zero, the SFF MUST pass the SFP OAM packet to the control plane for processing. An implementation that supports this specification MUST provide control to limit the rate of SFP OAM packets passed to the control plane for processing. o If the TTL value is not zero, the SFP OAM packet is processed as defined in Section 6, Section 7, and Section 8 [RFC8595], according to the type of MPLS forwarding used in the SFP. 3.2. MPLS-based SFP Consistency Verification An MPLS SFC validation request/reply is an MPLS echo request/reply that includes an SFC validation TLV (shown in Figure 3). Nodes examine and process the TLV only if configured to do so; other nodes MUST ignore the TLV and process the packet as a standard MPLS echo packet. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | TLV Type=TBA1 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | | SFC Information Sub-TLV(s) | ~ ~ | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: SFC Validation TLV Liu & Mirsky Expires April 28, 2021 [Page 6] Internet-Draft LSP Ping for SFC October 2020 SFC Information Sub-TLV: The Sub-TLV, as presented in Figure 4, MUST NOT be included in an MPLS SFC validation request. 3.3. SFC Info Sub-TLV Upon receiving the SFC validation request, the SFF MUST respond with an echo reply, which includes the SFC detailed information. The SFC detailed information is recorded in SFC info sub-TLV. Two types of sub-TLVs are defined in this section, and those are used in MPLS-based service programming [I-D.ietf-spring-sr-service-programming] and MPLS-based NSH [RFC8595] respectively. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-TLV Type=TBA2 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SFF Label | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SF Label | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SF Type | SR Proxy Type | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 4: SFC Info Sub-TLV for SR-MPLS-based Service Programming Type TBA2 sub-TLV: used in SR-MPLS-based service programming SFF Label: represents the SID of the SFF SF Label: represents the service SID of the SF or SR proxy SF Type: indicates the type of SF, such as DPI, firewall, etc. SR Proxy Type: It is defined in [I-D.ietf-spring-sr-service-programming] and indicates the type of SR proxy if it exists. Liu & Mirsky Expires April 28, 2021 [Page 7] Internet-Draft LSP Ping for SFC October 2020 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | sub-TLV Type=TBA3 | Length | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SFC-FWD Type | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SFC context Label | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SF Label | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SF Type | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 5: SFC Info Sub-TLV for MPLS-based NSH Figure 5 presents the format of a sub-TLV for MPLS-based NSH. The fields are as follows: Type TBA3 sub-TLV: used in MPLS-based NSH SFC-FWD Type: indicates the forwarding type of the data plane, and has the following values: 0x10: MPLS-based NSH [RFC8595] label swapping 0x11: MPLS-based NSH [RFC8595] label stacking SFC context Label: The meaning of the SFC context label depends on the SFC Type. If SFC-FWD Type is 0x10, the SFC context Label represents SPI. If SFC-FWD Type is 0x11, the SFC context Label represents the context label [RFC8595]. SF Label: The meaning of the SF label depends on the SFC-FWD Type. If SFC Type is 0x10, the SF Label represents SI. If SFC Type is 0x11, the SF Label represents the SFI index [RFC8595]. SF Type: It is defined in [I-D.ietf-bess-nsh-bgp-control-plane] and indicates the type of SF, such as DPI, firewall, etc. 3.4. SFC Basic Unit FEC Sub-TLV Unlike standard MPLS forwarding, based on a single label, packet forwarding defined in [RFC8595] is based on the basic unit of MPLS label stack for SFC(SFC Context Label+SF Label). A new SFC Basic Unit FEC sub-TLV with Type value (TBA4) is defined in this document. Liu & Mirsky Expires April 28, 2021 [Page 8] Internet-Draft LSP Ping for SFC October 2020 The SFC Basic Unit FEC sub-TLV MAY be used to carry the corresponding FEC of the basic unit. 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Route Distinguisher (RD) | | (8 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | SF Type | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 6: SFC Basic Unit sub-TLV The format of the basic unit sub-TLV is shown in Figure 6 and includes the following fields: Route Distinguisher (RD): 8 octets field in SFIR Route Type specific NLRI [I-D.ietf-bess-nsh-bgp-control-plane]. SF Type: 2 octets. It is defined in [I-D.ietf-bess-nsh-bgp- control-plane] and indicates the type of SF, such as DPI, firewall, etc. SFC Basic Unit sub-TLV is defined for Target FEC Stack TLV(Type 1 TLV). A node that receives an LSP ping with the Target FEC Stack TLV and the SFC Basic Unit FEC Sub-TLV included will check if it is its Route Distinguisher and whether it advertised that Service Function Type. If the validation is not passed, the SFF will generate an MPLS echo reply with an error code as defined in [RFC8029]. 3.5. Theory of Operation An MPLS SFC validation request is an MPLS echo request with an SFC validation TLV, and the echo request is sent with a label stack corresponding to the SFP being tested. To trace SFC-MPLS, the Generic Associated Channel Label (GAL) which immediately follows the SFC Context label is also included. Sending an SFC echo request to the control plane is triggered by one of the following packet processing exceptions: IP TTL expiration, MPLS TTL expiration, or the receiver is the terminal SFF for an SFP. Liu & Mirsky Expires April 28, 2021 [Page 9] Internet-Draft LSP Ping for SFC October 2020 After general packet sanity verifying [RFC8029], Section 3.5.1 and Section 3.5.2 in this document separately describe the following processing procedures in service programming and MPLS-based NSH. After all SFFs on the SFP send back MPLS echo reply, the sender collects information about all traversed SFFs and SFs on the rendered service path (RSP). 3.5.1. MPLS-based service programming [I-D.ietf-spring-sr-service-programming] describes how a service can be associated with a SID to achieve service function chaining. In an SR-MPLS network, the SFP is encoded as a stack of MPLS labels. That stack is pushed on top of the packet. Before generating an echo relpy, an SFF MUST parse through the label stack until the next label is not a local service SID to get all the SFs attached to the SFF on the SFP and record the corresponding Label-stack-depth. The SFF then sends an MPLS echo reply with all the SF information recorded in SFC Information Sub-TLV, including the service SID and the SF type. 3.5.2. Path Consistency in SFC-MPLS [RFC8595] describes how Service Function Chaining (SFC) can be achieved in an MPLS network using a logical representation of the Network Service Header (NSH) in an MPLS label stack. SFC forwarding can be achieved by label swapping, label stacking, or the mix of both. When an SFF receives a packet containing an MPLS label stack, it examines the top basic unit of MPLS label stack for SFC, {SPI, SI} or {context label, SFI index}, to determine where to send the packet next. As described in Section 3.1.1, the packet with GAL is recognized by the SFF as an SFP OAM packet. The SFF then decrements SF Label entry's TTL value. If the resulting value equals zero, the SFF passes the SFP OAM packet to the control plane for processing. The system that supports ths specification generates a reply message, including in it the SFC info sub-TLV as desribed in Section 3.3. 3.6. Discussion In [RFC8595], it says, "when an SFF receives a packet from any component of the SFC system (classifier, SFI, or another SFF), it MUST discard any packets with TTL set to zero". To trace SFC, it Liu & Mirsky Expires April 28, 2021 [Page 10] Internet-Draft LSP Ping for SFC October 2020 should be changed to allow punting the packet to the control plane though under throttling control. 4. Security Considerations This specification defines the processing of an SFP OAM packet. Such packets could be used as an attack vector. A system that supports this specification MUST provide control to limit the rate of SFP OAM packets sent to the control plane for processing. 5. IANA Considerations This document requests assigning type values for TLVs and sub-TLVs from the IANA "Multiprotocol Label Switching (MPLS) Label Switched Paths (LSPs) Ping Parameters" registry as described in the sub- sections below. 5.1. SFC Validation TLV IANA is requested to assign a type from the Standards Action range of the "TLVs" registry according to Table 1: +-------+----------------+---------------+ | Value | Description | Reference | +-------+----------------+---------------+ | TBA1 | SFC Validation | This document | +-------+----------------+---------------+ Table 1: Type Value for SFC Validation TLV 5.1.1. Sub-TLVs for SFC Validation TLV Two sub-TLVs of SFC Validation TLV is defined in this document according to Table 2. +-------+-------------------------------------------+---------------+ | Value | Description | Reference | +-------+-------------------------------------------+---------------+ | TBA2 | Info for SR-MPLS- | This document | | | based Service Programming | | | TBA3 | Info for MPLS-based NSH | This document | +-------+-------------------------------------------+---------------+ Table 2: Sub-TLV Values for SFC Validation TLV Liu & Mirsky Expires April 28, 2021 [Page 11] Internet-Draft LSP Ping for SFC October 2020 5.2. SFC Basic Unit sub-TLV IANA is requested to assign a type from the Standards Action range of the "Sub-TLVs for TLV Types 1, 16, and 21" registry according to Table 3: +-------+----------------+---------------+ | Value | Description | Reference | +-------+----------------+---------------+ | TBA4 | SFC Basic Unit | This document | +-------+----------------+---------------+ Table 3: Type Value for SFC Basic Unit sub-TLV 6. References 6.1. Normative References [I-D.ietf-bess-nsh-bgp-control-plane] Farrel, A., Drake, J., Rosen, E., Uttaro, J., and L. Jalil, "BGP Control Plane for the Network Service Header in Service Function Chaining", draft-ietf-bess-nsh-bgp- control-plane-18 (work in progress), August 2020. [I-D.ietf-spring-sr-service-programming] Clad, F., Xu, X., Filsfils, C., daniel.bernier@bell.ca, d., Li, C., Decraene, B., Ma, S., Yadlapalli, C., Henderickx, W., and S. Salsano, "Service Programming with Segment Routing", draft-ietf-spring-sr-service- programming-03 (work in progress), September 2020. [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y., Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001, . [RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed., "MPLS Generic Associated Channel", RFC 5586, DOI 10.17487/RFC5586, June 2009, . Liu & Mirsky Expires April 28, 2021 [Page 12] Internet-Draft LSP Ping for SFC October 2020 [RFC7274] Kompella, K., Andersson, L., and A. Farrel, "Allocating and Retiring Special-Purpose MPLS Labels", RFC 7274, DOI 10.17487/RFC7274, June 2014, . [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, . [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, . [RFC8595] Farrel, A., Bryant, S., and J. Drake, "An MPLS-Based Forwarding Plane for Service Function Chaining", RFC 8595, DOI 10.17487/RFC8595, June 2019, . 6.2. Informative References [I-D.ietf-sfc-nsh-tlv] Wei, Y., Elzur, U., and S. Majee, "Network Service Header Metadata Type 2 Variable-Length Context Headers", draft- ietf-sfc-nsh-tlv-03 (work in progress), May 2020. [RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and L. Yong, "The Use of Entropy Labels in MPLS Forwarding", RFC 6790, DOI 10.17487/RFC6790, November 2012, . [RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function Chaining (SFC) Architecture", RFC 7665, DOI 10.17487/RFC7665, October 2015, . Authors' Addresses Liu & Mirsky Expires April 28, 2021 [Page 13] Internet-Draft LSP Ping for SFC October 2020 Liu Yao ZTE Corporation No. 50 Software Ave, Yuhuatai Distinct Nanjing China Email: liu.yao71@zte.com.cn Greg Mirsky ZTE Corporation Email: gregimirsky@gmail.com Liu & Mirsky Expires April 28, 2021 [Page 14]