Internet-Draft Active OAM for SFC July 2023
Mirsky, et al. Expires 8 January 2024 [Page]
Workgroup:
SFC WG
Internet-Draft:
draft-ietf-sfc-multi-layer-oam-28
Published:
Intended Status:
Standards Track
Expires:
Authors:
G. Mirsky
Ericsson
W. Meng
ZTE Corporation
T. Ao
China Mobile
B. Khasnabish
Individual contributor
K. Leung
Individual contributor
G. Mishra
Verizon Inc.

Active OAM for Service Function Chaining (SFC)

Abstract

A set of requirements for active Operation, Administration, and Maintenance (OAM) of Service Function Chains (SFCs) in a network is presented in this document. Based on these requirements, an encapsulation of active OAM messages in SFC and a mechanism to detect and localize defects are described.

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 8 January 2024.

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Table of Contents

1. Introduction

[RFC7665] defines data plane elements necessary to implement a Service Function Chaining (SFC). These include:

  1. Classifiers that perform the classification of incoming packets. Such classification may result in associating a received packet to a service function chain.
  2. Service Function Forwarders (SFFs) that are responsible for forwarding traffic to one or more connected Service Functions (SFs) according to the information carried in the SFC encapsulation and handling traffic coming back from the SFs and forwarding it to the next SFF.
  3. SFs that are responsible for executing specific service treatment on received packets.

There are different views from different levels of the SFC. One is the service function chain, an entirely abstract view, which defines an ordered set of SFs that must be applied to packets selected based on classification rules. But service function chain doesn't specify the exact mapping between SFFs and SFs. Thus, another logical construct used in SFC is a Service Function Path (SFP). According to [RFC7665], SFP is the instantiation of the SFC in the network and provides a level of indirection between the entirely abstract SFCs 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 referred to as Rendered Service Path (RSP). The main difference between SFP and RSP is that the former is the logical construct, while the latter is the realization of the SFP via the sequence of specific SFC data plane elements.

This document defines how active Operation, Administration and Maintenance (OAM), per [RFC7799] definition of active OAM, is implemented when Network Service Header (NSH) [RFC8300] is used as the SFC encapsulation. Following the analysis of SFC OAM in [RFC8924], this document applies and, when necessary, extends requirements listed in Section 4 of [RFC8924] for the use of active OAM in an SFP supporting fault management and performance monitoring. Active OAM tools, conformant to this specification, improve OAM's ability for Fault Management (FM) by, for example, using the query mechanism to troubleshoot and localize defects, which conforms to the stateless character of transactions in SFC NSH [RFC8300]. Note that Performance Monitoring OAM, as mentioned in [RFC8924], as a requirement, is not satisfied by this document and is out of scope. For the purpose of FM OAM in SFC, SFC Echo Request and Echo Reply are specified in Section 6. These mechanisms enable on-demand Continuity Check and Connectivity Verification, among other operations, over SFC in networks and addresses functionalities discussed in Sections 4.1, 4.2, and 4.3 of [RFC8924]. SFC Echo Request and Echo Reply can be used with encapsulations other than NSH, for example, using MPLS encapsulation, as described in [RFC8595]. The applicability of the SFC Echo Request/Reply mechanism in SFC encapsulations other than NSH is outside the scope of this document.

The intended scope of active SFC OAM is for use within a single provider operational domain. Active SFC OAM deployment scope is deliberately constrained, as explained in [RFC7665] and [RFC8300], and limited to a single network administrative domain.

2. Terminology and Conventions

The terminology defined in [RFC7665] is used extensively throughout this document, and the reader is expected to be familiar with it.

In this document, SFC OAM refers to an active OAM [RFC7799] in an SFC architecture. In this document, "Echo Request/Reply" and "SFC Echo Request/Reply" are used interchangeably.

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

E2E: End-to-End

FM: Fault Management

NSH: Network Service Header

OAM: Operations, Administration, and Maintenance

RSP: Rendered Service Path

SF: Service Function

SFC: Service Function Chain

SFF: Service Function Forwarder

SFI: Service Function Instance

SFP: Service Function Path

MAC: Message Authentication Code

3. Requirements for Active OAM in SFC

As discussed in [RFC8924], SFC-specific means are needed to perform the FM OAM task in an SFC architecture, including failure detection, defect characterization, and localization. This document defines the set of requirements for active FM OAM mechanisms to be used in an SFC architecture.


              +-----+ +-----+ +-----+ +-----+ +-----+ +-----+
              |SFI11| |SFI12| |SFI21| |SFI22| |SFI31| |SFI32|
              +-----+ +-----+ +-----+ +-----+ +-----+ +-----+
                  \    /          \   /           \    /
   +----------+   +----+         +----+          +----+
   |Classifier|---|SFF1|---------|SFF2|----------|SFF3|
   +----------+   +----+         +----+          +----+
Figure 1: An Example of SFC Data Plane Architecture

The architecture example depicted in Figure 1 considers a service function chain that includes three distinct service functions. In this example, the SFP traverses SFF1, SFF2, and SFF3. Each SFF is connected to two service function instances (SFIs) of the same service function. End-to-end (E2E) SFC OAM has the Classifier as the ingress and SFF3 as its egress. The scope of Segment SFC OAM is between two elements that are part of the same SFP. Following are the requirements for an FM SFC OAM, whether with the E2E or segment scope:

REQ#1: Packets of active SFC OAM SHOULD be fate sharing with the monitored SFC data in the forward direction from ingress toward egress endpoint(s) of the OAM test.

The fate sharing, in the SFC environment, is achieved when a test packet traverses the same path and receives the same treatment in the underlay network layer as an SFC-encapsulated packet.

REQ#2: SFC OAM MUST support monitoring of the continuity of the SFP between any of its elements.

An SFC failure might be declared when several consecutive test packets are not received within a pre-determined time. For example, in the E2E FM SFC OAM case, the egress, SFF3 (Figure 1) could be the entity that detects the SFP's failure by monitoring a flow of periodic test packets. The ingress may be capable of recovering from the failure, e.g., using redundant SFC elements. Thus, it is beneficial for the egress to signal the new defect state to the ingress, which in this example is the Classifier. Hence the following requirement:

REQ#3: SFC OAM MUST support Remote Defect Indication notification by the egress to the ingress.
REQ#4: SFC OAM MUST support connectivity verification of the SFP. Definition of the misconnection defect, entry, and exit criteria are outside the scope of this document.

Once an SFF detects the defect, the objective of the SFC OAM changes from the detection of a defect to defect characterization and localization.

REQ#5: SFC OAM MUST support fault localization of the Loss of Continuity Check within an SFP.
REQ#6: SFC OAM MUST support an SFP tracing to discover the RSP.

In the example presented in Figure 1, two distinct instances of the same service function share the same SFF. In this example, the SFP can be realized over several RSPs that use different instances of SF of the same type. For instance, RSP1(SFI11--SFI21--SFI31) and RSP2(SFI12--SFI22--SFI32). Available RSPs can be discovered using the trace function discussed in Section 4.3 of [RFC8924] or the procedure defined in Section 6.5.4.

REQ#7: SFC OAM MUST have the ability to discover and exercise all available RSPs in the network.

The SFC OAM layer model described in [RFC8924] offers an approach for defect localization within a service function chain. As the first step, the SFP's continuity for SFFs that are part of the same SFP could be verified. After the reachability of SFFs has already been verified, SFFs that serve an SF may be used as a test packet source. In such a case, SFF can act as a proxy for another element within the service function chain.

REQ#8: SFC OAM MUST be able to trigger on-demand FM remotely with responses being directed toward the initiator of the remote request.

The conformance of the SFC Echo Request/Reply mechanism to these requirements reflected below:

4. Active OAM Identification in the NSH

Active SFC OAM combines OAM commands and/or data included in a message that immediately follows the NSH. To identify the active SFC OAM message, the "Next Protocol" field MUST be set to Active SFC OAM (TBA1) (Section 10.1). The O bit in the NSH MUST be set, according to [I-D.ietf-sfc-oam-packet]. A case when the O bit is clear and the "Next Protocol" field value is set to Active SFC OAM (TBA1) is considered an erroneous combination. An implementation MUST report it. Although the notification mechanism is outside the scope of this specification, note that it MUST include rate-limiting control. The packet SHOULD be dropped. An implementation MAY have control to enable the processing of the OAM payload.

5. Active SFC OAM Header

SFC OAM is required to perform multiple tasks. Several active OAM protocols could be used to address all the requirements. When IP/UDP encapsulation of an SFC OAM control message is used, protocols can be demultiplexed using the destination UDP port number. But an extra IP/UDP header, especially in an IPv6 network, adds overhead compared to the length of an active OAM control packet (e.g., BFD Control packet [RFC5880]). In some environments, for example, when measuring performance metrics, it is beneficial to transmit OAM packets in a broad range of lengths to emulate application traffic closer. This document defines an 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  | Reserved  |          Length               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~              SFC Active OAM Control Packet                    ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: SFC Active OAM Header

6. Echo Request/Echo Reply for SFC

Echo Request/Reply is a well-known active OAM mechanism extensively used to verify a path's continuity, detect inconsistencies between a state in control and the data planes, and localize defects in the data plane. ICMP ([RFC0792] for IPv4 and [RFC4443] for IPv6 networks) and [RFC8029] are examples of broadly used active OAM protocols based on the Echo Request/Reply principle. The SFC Echo Request/Reply control message (format is presented in Figure 3) is an instance of the SFC Active OAM Control Packet that is a part of the SFC Active OAM Header (Figure 2).

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      Echo Request Flags       |          Reserved             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Echo Type   |   Reply mode  |  Return Code  |Return Subcode |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                        Sender's Handle                        |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                         Sequence Number                       |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                              TLVs                             ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: SFC Echo Request/Reply Format

The interpretation of the fields is as follows:

TLV is a variable-length construct whose length is multiple of four-octet words. Multiple TLVs MAY be placed in an SFC Echo Request/Reply packet. None, one or more sub-TLVs may be enclosed in the value part of a TLV, subject to the semantics of the (outer) TLV. If no TLVs are included in an SFC Echo Request/Reply, the value of the Length field in the SFC Active OAM Header MUST be 16 octets. Figure 4 presents the format of an SFC Echo Request/Reply TLV, where fields are defined as follows:

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|      Type     |    Reserved   |           Length              |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                            Value                              ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: SFC Echo Request/Reply TLV Format

6.1. Return Codes

The value of the Return Code field MUST be set to zero by the sender of an Echo Request. The receiver of said Echo Request MUST set it to one of the values in IANA's SFC Echo Return Codes sub-registry (Section 10.3.4) in the corresponding Echo Reply that it generates.

6.2. Authentication in Echo Request/Reply

Authentication can be used to protect the integrity of the information in SFC Echo Request and/or Echo Reply. In the [RFC9145] a variable-length Context Header has been defined to protect the integrity of the NSH and the payload. The header can also be used for the optional encryption of sensitive metadata. MAC#1 (Message Authentication Code) Context Header is more suitable for the integrity protection of active SFC OAM, particularly of the SFC Echo Request and Echo Reply, defined in this document. On the other hand, using MAC#2 Context Header allows the detection of mishandling of the O-bit by a transient SFC element.

6.3. SFC Echo Request Transmission

SFC Echo Request control packet MUST use the appropriate underlay network encapsulation of the monitored SFP. Echo Request MUST set O bit in the NSH, as defined in [I-D.ietf-sfc-oam-packet]. NSH MUST be immediately followed by the SFC Active OAM Header defined in Section 4. The Echo Type field's value in the SFC Active OAM Header MUST be set to SFC Echo Request/Echo Reply value (1) per Section 10.2.1.

Value of the Reply Mode field MUST be set to one of the following:

  • Do Not Reply (1) 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. Ways of learning the identity of that node are outside the scope of this specification.
  • Reply via an IPv4/IPv6 UDP Packet (2). If an SFC Echo Request is not encapsulated in IP/UDP, then this value requests the use of the Source ID TLV (Section 6.3.1).
  • Reply via Specified Path (4). This value requests the use of the particular return path specified in the included TLV to verify bi-directional continuity and may also increase the robustness of the monitoring by selecting a more stable path. Section 6.5.1 provides an example of communicating an explicit path for the Echo Reply.
  • Reply via an IPv4/IPv6 UDP Packet with the data integrity protection (5). This value requests the use of the MAC Context Header [RFC9145].
  • Reply via Specified Path with the the data integrity protection (7). This value requests the use of the MAC Context Header [RFC9145].

6.3.1. Source ID TLV

The responder to the SFC Echo Request encapsulates the SFC Echo Reply message in IP/UDP packet if the Reply mode is "Reply via an IPv4/IPv6 UDP Packet" or "Reply via an IPv4/IPv6 UDP Packet with the data integrity protection". Because the NSH does not identify the ingress node that generated the Echo Request, information that sufficiently identifies the source MUST be included in the message so that the IP destination address and destination UDP port number for IP/UDP encapsulation of the SFC Echo Reply could be derived. The sender of the SFC Echo Request MUST include the Source ID TLV (Figure 5).

  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
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |    Source ID  |   Reserved1   |           Length              |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 |          Port Number          |           Reserved2           |
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
 ~                         IP Address                            ~
 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: SFC Source ID TLV

where

  • Source ID - the value MUST be set to 1 (Section 10.4).
  • Reserved1 - a one-octet field. The field MUST be zeroed on transmission and ignored on receipt.
  • Length - the value equals the length of the data following the Length field counted in octets. The value of the Length field can be 8 or 20. If the value of the field is neither, the Source ID TLV is considered to be malformed.
  • Port Number is a two-octet field. It contains the UDP port number of the sender of the SFC OAM control message. The value of the field MUST be used as the destination UDP port number in the IP/UDP encapsulation of the SFC Echo Reply message.
  • Reserved2 is a two-octet field. The field MUST be zeroed on transmit and ignored on receipt.
  • IP Address field contains the IP address of the sender of the SFC OAM control message, IPv4 or IPv6. The value of the field MUST be used as the destination IP address in the IP/UDP encapsulation of the SFC Echo Reply message.

A single Source ID TLV for each address family, i.e., IPv4 and IPv6, MAY be present in an SFC Echo Request message. If the Source ID TLVs for both address families are present in an SFC Echo Request message, the SFF MUST NOT replicate an SFC Echo Reply but choose the destination IP address for the one SFC Echo Reply it sends based on the local policy. The source IP address used in the IP/UDP encapsulation of SFC Echo Reply is one of the IP addresses associated with the responder. The value of the Port Number field MUST be used as the destination UDP port number in the IP/UDP encapsulation of the SFC Echo Reply message. The responder selects the source UDP port number from the dynamic range of port numbers. If more than one Source ID TLV per the address family is present, the receiver MUST use the first TLV and ignore the rest. The Echo Reply message, including relevant TLVs, follows the IP/UDP headers immediately.

6.4. Processing Received SFC Echo Request

Punting a received SFC Echo Request to the control plane for validation and processing is triggered by one of the following packet processing exceptions: NSH TTL expiration, NSH Service Index (SI) expiration, or the receiver is the terminal SFF for an SFP.

An SFF that received the SFC Echo Request MUST validate the packet as follows:

  • 1. If the SFC Echo Request is integrity-protected, the receiving SFF first MUST verify the authentication.
  • 1.1 Suppose the authentication validation has failed and the Source ID TLV is considered properly formatted. In that case, the SFF MUST send to the system identified in the Source ID TLV (see Section 6.5), according to a rate-limit control mechanism, an SFC Echo Reply with the Return Code set to "Authentication failed" and the Subcode set to zero.
  • 1.2 If the authentication is validated successfully, the SFF that has received an SFC Echo Request verifies the rest of the packet's general sanity.
  • 2. Validate the Source ID TLV, as defined in Section 6.3.1.
  • 2.1 If the Source ID TLV is determined malformed, the received SFC Echo Request processing is stopped, the message is dropped, and the event SHOULD be logged, according to a rate-limiting control for logging.
  • 3. Sender's Handle and Sequence Number fields are not examined but are copied in the SFC Echo Reply message.
  • 4. If the packet is not well-formed, i.e., not formed according to this specification, the receiver SFF SHOULD send an SFC Echo Reply with the Return Code set to "Malformed Echo Request received" and the Subcode set to zero under the control of the rate-limiting mechanism to the system identified in the Source ID TLV (see Section 6.5).
  • 5. If there are any TLVs that the SFF does not understand, the SFF MUST send an SFC Echo Reply with the Return Code set to 2 ("One or more TLVs was not understood") and set the Subcode to zero. Also, the SFF MAY include an Errored TLVs TLV (Section 6.4.1) that, as sub-TLVs, contains only the misunderstood TLVs.
  • 6. If the sanity check of the received Echo Request succeeded, i.e., the Echo Request is deemed properly formed, then the SFF at the end of the SFP MUST send an SFC Echo Reply with the Return Code value to 5 ("End of the SFP") and the Subcode set to zero.
  • 7. If the SFF is not at the end of the SFP and the NSH TTL value is 1, the SFF MUST send an SFC Echo Reply with the Return Code set to 4 ("SFC TTL Exceeded") and the Subcode set to zero.
  • 8. In all other cases, for the validated Echo Request message, a transit, i.e., not at the end of the SFP, SFF MUST send an SFC Echo Reply with the Return Code value to 0 ("No Error") and the Subcode set to zero.

6.4.1. Errored TLVs TLV

If the Return Code for the Echo Reply is determined as 2 ("One or more TLVs was not understood"), the Errored TLVs TLV might be included in an Echo Reply. The use of this TLV is meant to inform the sender of an Echo Request of TLVs either not supported by an implementation or parsed and found to be in error.

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  Errored TLVs |    Reserved   |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                             Value                             |
.                                                               .
.                                                               .
.                                                               .
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: Errored TLVs TLV

where

  • The Errored TLVs Type MUST be set to 2 (Section 10.4).
  • Reserved - the field MUST be zeroed on transmission and ignored on receipt.
  • Length - the value equals to the length of the Value field in octets.
  • The Value field contains the TLVs, encoded as sub-TLVs (as shown in Figure 7), that were not understood or failed to be parsed correctly. 
 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 |    Reserved   |        Sub-TLV Length         |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~                        Sub-TLV   Value                        ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Not Understood or Failed TLV as Sub-TLV

where

  • The Sub-TLV's Type - a copy of the first octet of the not understood or failed to be parsed TLV.
  • Reserved - MUST be zeroed on transmission and ignored on receipt.
  • Sub-TLV Length - the value equals to the value of the Length field of the errored TLV.
  • The Sub-TLV Value field contains data that follow the Length field in the errored TLV.

6.5. SFC Echo Reply Transmission

The "Reply Mode" field directs whether and how the Echo Reply message should be sent. The Echo Request sender MAY use TLVs to request that the corresponding Echo Reply be transmitted over the specified path. For example, a TLV that specifies the return path of the Echo Reply if the Return Mode in the Echo Request is set to Reply via Specified Path (4) is described in Section 6.5.1. Value 1 is the "Do not reply" mode and suppresses the Echo Reply packet transmission. The value 2 of the Reply mode field requests sending the Echo Reply packet out-of-band as an IPv4 or IPv6 UDP packet.

6.5.1. Reply Service Function Path TLV

While SFC Echo Request always traverses the SFP it is directed to by using NSH, the corresponding Echo Reply usually is sent without NSH. In some cases, an operator might choose to direct the responder to send the Echo Reply with NSH over a particular SFP. This section defines a new Type-Length-Value (TLV), Reply Service Function Path TLV, for Reply via Specified Path mode of SFC Echo Reply.

The Reply Service Function Path TLV can provide an efficient mechanism to test SFCs, such as bidirectional and hybrid SFC, as defined in Section 2.2 of [RFC7665]. For example, it allows an operator to test both directions of the bidirectional or hybrid SFP with a single SFC Echo Request/Echo Reply operation.

The Reply Service Function Path TLV carries the information that sufficiently identifies the return SFP that the SFC Echo Reply message is expected to follow. The format of Reply Service Function Path TLV is shown in Figure 8.

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|   Reply SFP   |    Reserved   |          Length               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|    Reply Service Function Path Identifier     | Service Index |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: SFC Reply TLV Format

where:

  • Reply SFP (Service Function Path) (3) - identifies the TLV that contains information about the SFC Reply path.
  • Reserved MUST be zeroed on transmission and ignored on receipt.
  • Length - the value MUST be equal to 4
  • Reply Service Function Path Identifier - a three-octet field that contains SFP identifier for the path that the SFC Echo Reply message is requested to be sent over.
  • Service Index - a one-octet field. The value is set to the value of the Service Index field in the NSH of the SFC Echo Reply message.

6.5.2. Theory of Operation

[RFC7110] defined mechanism to control return path for MPLS LSP Echo Reply. In SFC's case, the return path is an SFP along which the SFC Echo Reply message MUST be transmitted. Hence, the Reply Service Function Path TLV included in the SFC Echo Request message MUST sufficiently identify the SFP that the sender of the Echo Request message expects the receiver to use for the corresponding SFC Echo Reply.

When sending an Echo Request, the sender MUST set the value of Reply Mode field to "Reply via Specified Path", defined in Section 6.3, and if the specified path is an SFC path, the Request MUST include Reply Service Function Path TLV. The Reply Service Function Path TLV consists of the identifier of the reverse SFP and an appropriate Service Index.

If the NSH of the received SFC Echo Request includes the MAC Context Header, the packet's authentication MUST be verified before using any data as defined in Section 6.4.

The destination SFF of the SFP being tested or the SFF at which NSH TTL expired (as per [RFC8300]) are referred to as responding SFF. The processing described below equally applies to both cases.

If the Echo Request message with Reply Service Function Path TLV, received by the responding SFF, has Reply Mode value of "Reply via Specified Path" but no Reply Service Function Path TLV is present, then the responding SFF MUST send Echo Reply with Return Code set to 6 ("Reply Service Function Path TLV is missing"). If the responding SFF cannot find the requested SFP it MUST send Echo Reply with Return Code set to 7 ("Reply SFP was not found") and include the Reply Service Function Path TLV from the Echo Request message.

Suppose the SFC Echo Request receiver cannot determine whether the specified return path SFP has the route to the initiator. In that case, it SHOULD set the value of the Return Codes field to 8 ("Unverifiable Reply Service Function Path"). The receiver MAY drop the Echo Request when it cannot determine whether SFP's return path has the route to the initiator. When sending Echo Request, the sender SHOULD choose a proper source address according to the specified return path SFP to help the receiver find the viable return path.

6.5.2.1. Bi-directional SFC Case

The ability to specify the return path for an Echo Reply might be used in the case of bi-directional SFC. The egress SFF of the forward SFP might not be co-located with a classifier of the reverse SFP, and thus the egress SFF has no information about the reverse path of an SFC. Because of that, even for bi-directional SFC, a reverse SFP needs to be indicated in a Reply Service Function Path TLV in the Echo Request message.

6.5.3. SFC Echo Reply Reception

An SFF SHOULD NOT accept SFC Echo Reply unless the received message passes the following checks:

  • the received SFC Echo Reply is well-formed;
  • the matching SFC Echo Request is found, that is, the value of the Sender's Handle in the Echo Request sent is equal to the value of Sender's Handle in the Echo Reply received;
  • all other checks passed, and the Sequence Number in the Echo Reply received matches the Sequence Number of one of outstanding transmitted Echo Requests.

6.5.4. Tracing an SFP

SFC Echo Request/Reply can be used to isolate a defect detected in the SFP and trace an RSP. As with ICMP echo request/reply [RFC0792] and MPLS echo request/reply [RFC8029], this mode is referred to as "traceroute". In the traceroute mode, the sender transmits a sequence of SFC Echo Request messages starting with the NSH TTL value set to 1 and is incremented by 1 in each next Echo Request packet. The sender stops transmitting SFC Echo Request packets when the Return Code in the received Echo Reply equals 5 ("End of the SFP").

Suppose a specialized information element (e.g., IPv6 Flow Label [RFC6437] or Flow ID [RFC9263]) is used for distributing the load across Equal Cost Multi-Path or Link Aggregation Group paths. In that case, such an element SHOULD also be used for the SFC OAM traffic. Doing so is meant to induce the SFC Echo Request to follow the same RSP as the monitored flow.

6.6. The Use of Consistency Verification Request Message

The consistency of an SFP can be verified by comparing the view of the SFP from the control or management plane with information collected from traversing by an SFC Echo Request/Reply message (Figure 3). The sender of an SFP Consistency Verification Request (CVReq) message MUST set the value of the SFC Echo Request/Reply Echo Type field to SFP Consistency Verification Request (3). The sender of an SFP Consistency Verification Reply (CVRep) message MUST set the value of the SFC Echo Request/Reply Echo Type field to SFP Consistency Verification Reply (4). All processing steps of SFC Echo Request and Echo Reply messages described in Section 6.3 through Section 6.5 apply to the processing of CVReq and CVRep respectively.

Every SFF that receives a CVReq message MUST perform the following actions:

  • Collect information about the SFs traversed by the CVReq packet and send it to the ingress SFF as CVRep packet over IP network;
  • Forward the CVReq to the next downstream SFF if the one exists.

As a result, the ingress SFF collects information about all traversed SFFs and SFs, information on the actual path the CVReq packet has traveled. That information can be used to verify the SFC's path consistency. The mechanism for the SFP consistency verification is outside the scope of this document.

6.6.1. SFF Information Record TLV

For the received CVReq, an SFF, that supports this specification, MUST include in the CVRep message the information about SFs that are available from that SFF instance for the specified SFP. The SFF MUST include SFF Information Record TLV (Figure 9) in CVRep message. Every SFF sends back a single CVRep message, including information on all the SFs attached to that SFF on the SFP, as requested in the received CVReq message using the SF Information sub-TLV (Section 6.6.2).

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|SFF Record TLV |    Reserved   |            Length             |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|       Service Path Identifier (SPI)           |   Reserved    |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                                                               |
|                   SF Information  Sub-TLV                     |
~                                                               ~
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 9: SFF Information Record TLV

The SFF Information Record TLV is a variable-length TLV that includes the information of all SFs available from the particular SFF instance for the specified SFP. Figure 9 presents the format of an SFF Information Record TLV, where fields are defined as the following:

  • SFF Record TLV - The value is (4) (Section 10.4).
  • Reserved - MUST be zeroed on transmission and ignored on receipt.
  • Service Path Identifier (SPI): The identifier of SFP to which all the SFs in this TLV belong.
  • SF Information Sub-TLV: The sub-TLV is as defined in Section 6.6.2.

If the NSH of the received SFC Echo Reply includes the MAC Context Header [RFC9145], the authentication of the packet MUST be verified before using any data. If the verification fails, the receiver MUST stop processing the SFF Information Record TLV and notify an operator. The notification mechanism SHOULD include control of rate-limited messages. Specification of the notification mechanism is outside the scope of this document.

6.6.2. SF Information Sub-TLV

Every SFF receiving a CVReq packet MUST include the SF characteristic data into the CVRep packet. The format of an SF Information sub-TLV, included in a CVRep packet, is shown in Figure 10.

After the CVReq message traverses the SFP, all the information about the SFs on the SFP is available from the TLVs included in CVRep messages.

 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|  SF sub-TLV   |    Reserved   |          Length               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|Service Index  |          SF Type              |   SF ID Type  |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|                          SF Identifier                        |
~                                                               ~
|                                                               |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 10: Service Function Information Sub-TLV

  • SF sub-TLV Type: one-octet long field. The value is (5) (Section 10.4).
  • Reserved - one-octet field. The field MUST be zeroed on transmission and ignored on receipt.
  • Length - two-octet long field. The value of this field is the length of the data following the Length field counted in octets.
  • Service Index - indicates the SF's position on the SFP.
  • SF Type - two-octet field. It is defined in [RFC9015] and indicates the type of SF, e.g., Firewall, Deep Packet Inspection, WAN optimization controller, etc.
  • SF ID Type - one-octet field with values defined as Section 10.5.
  • SF Identifier - an identifier of the SF. The length of the SF Identifier depends on the type of the SF ID Type. For example, if the SF Identifier is its IPv4 address, the SF Identifier should be 32 bits.

6.6.3. SF Information Sub-TLV Construction

Each SFF in the SFP MUST send one and only one CVRep corresponding to the CVReq. If only one SF is attached to the SFF in such SFP, only one SF information sub-TLV is included in the CVRep. If several SFs attached to the SFF in the SFP, SF Information sub-TLV MUST be constructed as described below in either Section 6.6.3.1 and Section 6.6.3.2.

6.6.3.1. Multiple SFs as Hops of an SFP

Multiple SFs attached to the same SFF can be the hops of the SFP. The service indexes of these SFs on that SFP will be different. Service function types of these SFs could be different or be the same. Information about all SFs MAY be included in the CVRep message. Information about each SF MUST be listed as separate SF Information sub-TLVs in the CVRep message. The same SF can even appear more than once in an SFP with a different service index.

An example of the SFP consistency verification procedure for this case is shown in Figure 11. The Service Function Path (SPI=x) is SF1->SF2->SF4->SF3. The SF1, SF2, and SF3 are attached to SFF1, and SF4 is attached to SFF2. The CVReq message is sent to the SFFs in the sequence of the SFP(SFF1->SFF2->SFF1). Every SFF(SFF1, SFF2) replies with the information of SFs belonging to the SFP. The SF information Sub-TLV in Figure 10 contains information for each SF (SF1, SF2, SF3, and SF4).

                SF1         SF2           SF4                SF3
                +------+------+            |                  |
   CVReq  ......>  SFF1       ......>  SFF2       ......> SFF1
   (SPI=x)             .                   .                  .
           <............         <..........       <...........
             CVRep1(SF1,SF2)    CVRep2(SF4)    CVRep3(SF3)
Figure 11: Example 1 for CVRep with multiple SFs

6.6.3.2. Multiple SFs for load balance

Multiple SFs may be attached to the same SFF to spread the load; in other words, that means that the particular traffic flow will traverse only one of these SFs. These SFs have the same Service Function Type and Service Index. For this case, the SF ID Type, which must be the same for all of these SFs, appears once but all of their SF Identifiers will appear concatenated in the SF Identifier area of the Sub-TLV (see Figure 10). The number of these SFs can be calculated from the SF ID Type and the value of the Length field of the sub-TLV.

An example of the SFP consistency verification procedure for this case is shown in Figure 12. The Service Function Path (SPI=x) is SF1a/SF1b->SF2a/SF2b. The Service Functions SF1a and SF1b are attached to SFF1, which balances the load among them. The Service Functions SF2a and SF2b are attached to SFF2, which, in turn, balances its load between them. The CVReq message is sent to the SFFs in the sequence of the SFP (i.e. SFF1->SFF2). Every SFF (SFF1, SFF2) replies with the information of SFs belonging to the SFP. The SF information Sub-TLV in Figure 10 contains information for all SFs at that hop.

                      /SF1a                   /SF2a
                      \SF1b                   \SF2b
                        |                       |
                       SFF1                    SFF2
   CVReq   .........>  .           .........>  .
   (SPI=x)                .                       .
              <............        <...............
       CVRep1(SF1a,SF1b)       CVRep2(SF2a,SF2b)
Figure 12: Example 2 for CVRep with multiple SFs

7. Security Considerations

As an element of SFC OAM and, specifically, NSH-based, the Echo Request/Reply mechanism described in this document inherits Security Considerations discussed in [RFC7665] and [RFC8300].

When the integrity protection for SFC active OAM, and SFC Echo Request/Reply in particular, is required, using one of the Context Headers defined in [RFC9145] is RECOMMENDED. MAC#1 Context Header could be more suitable for active SFC OAM because it does not require re-calculation of the MAC when the value of the NSH Base Header's TTL field is changed. Integrity protection for SFC active OAM can also be achieved using mechanisms in the underlay data plane. For example, if the underlay is an IPv6 network, IP Authentication Header [RFC4302] or IP Encapsulating Security Payload Header [RFC4303] can be used to provide integrity protection. Confidentiality for the SFC Echo Request/Reply exchanges can be achieved using the IP Encapsulating Security Payload Header [RFC4303]. 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 to attacking a node in the overlay network using the mechanisms defined in the document. One is a Denial-of-Service attack, sending SFC Echo Requests 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 the 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., SFFs and/or SFs.

It is RECOMMENDED that implementations throttle the number of SFC Echo Request/Echo Reply messages going to the control plane to mitigate potential Denial-of-Service attacks.

Reply and spoofing attacks involving faking or replying to 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 for off-path attackers. A non-matching reply would be discarded.

To protect against unauthorized sources trying to obtain information about the overlay and/or underlay, an implementation MUST have means to check that the source of the Echo Request is part of the SFP.

Also, since the Service Function Information sub-TLV discloses information about the SFP, the spoofed CVReq packet may be used to obtain network information. Thus, implementations MUST provide a means of checking the source addresses of CVReq messages, specified in Source ID TLV (Section 6.3.1), against an access list before accepting the message.

8. Operational Considerations

This section provides information about operational aspects of the SFC NSH Echo Request/Reply according to recommendations in [RFC5706].

SFC NSH Echo Request/Reply provides essential OAM functions for network operators. SFC NSH Echo Request/Reply is intended to detect and localize defects in an SFC. For example, by comparing results of the trace function in operational and failed states, an operator can locate the defect, e.g., the connection between SFF1 and SFF2 (Figure 1). After narrowing down a failure to an overlay link, a more specific failure location can be determined using OAM tools in the underlay network. The mechanism defined in this document can be used on-demand or for periodic validation of an SFP or RSP. Because the protocol makes use of the control plane which may have limited capacity, an operator must be able to rate limit Echo Request and Echo Reply messages. A reasonably selected default interval between Echo Request control packets can provide additional benefit for an operator. If the protocol is incrementally deployed in the NSH domain, SFC elements, e.g., Classifier or SFF, that don't support Active SFC OAM will discard protocol's packets. If an SFC uses a re-classification along the SFP or when the principle of load balancing is unknown, the fate-sharing between data and active OAM packets cannot be guaranteed. As a result, the OAM outcome might not reflect the state of the entire SFC properly but only its segment. In general, it is an operational task to consider the cases where active OAM may not share fate with monitored SFP. SFC NSH Echo Request/Reply also can be used in combination with the existing mechanisms discussed in [RFC8924], filling the gaps and extending their functionalities.

Management of the SFC NSH Echo Request/Reply protocol can be provided by a proprietary tool, e.g., command line interface, or based on a data model, structured or standardized.

9. Acknowledgments

The authors greatly appreciate the thorough review and the most helpful comments from Dan Wing, Dirk von Hugo, Mohamed Boucadair, Donald Eastlake, Carlos Pignataro, and Frank Brockners. The authors are thankful to John Drake for his review and the reference to the work on BGP Control Plane for NSH SFC. The authors express their appreciation to Joel M. Halpern for his suggestion about the load-balancing scenario. The authors greatly appreciate the thoroughness of comments and thoughtful suggestions by Darren Dukes that significantly improved the document.

10. IANA Considerations

The terms used in the IANA Considerations below are intended to be consistent with [RFC8126].

10.1. SFC Active OAM Protocol

IANA is requested to assign a new type from the sub-registry NSH Next Protocol of the Network Service Header (NSH) Parameters registry as follows:

Table 1: SFC Active OAM Protocol
Value Description Reference
TBA1 SFC Active OAM This document

10.2. SFC Active OAM

IANA is requested to create an SFC Active OAM registry containing the sub-registries listed below.

10.2.1. SFC Active OAM Message Type

IANA is requested to create in the SFC Active OAM registry a sub-registry as follows:

  • Sub-registry Name: SFC Active OAM Message Type.
  • Assignment Policy:
  • 2-31 IETF Review
  • 32-62 First Come First Served
  • Reference: [this document]
Table 2: SFC Active OAM Message Type
Value Description Reference
0 Reserved This document
1 SFC Echo Request/Echo Reply This document
2 - 31 Unassigned This document
32-62 Unassigned This document
63 Reserved This document

10.3. SFC Echo Request/Echo Reply Parameters

IANA is requested to create in the SFC Active OAM Registry the sub-registry SFC Echo Request/Echo Reply Parameters.

10.3.1. SFC Echo Request Flags

IANA is requested to create in the SFC Echo Request/Echo Reply Parameters the SFC Echo Request Flags sub-registry.

This sub-registry tracks the assignment of 16 flags in the SFC Echo Request Flags field of the SFC Echo Request message. The flags are numbered from 0 (most significant bit, transmitted first) to 15.

New entries are assigned by Standards Action.

Table 3: SFC Echo Request Flags
Bit Number Description Reference
15-0 Unassigned This document

10.3.2. SFC Echo Types

IANA is requested to create in the SFC Echo Request/Echo Reply Parameters the SFC Echo Types sub-registry as follows:

  • Sub-registry Name: SFC Echo Types
  • Assignment Policy:
  • 5 - 175 IETF Review
  • 176 - 239 First Come First Served
  • Reference: [this document]
Table 4: SFC Echo Types
Value Description Reference
0 Reserved This document
1 SFC Echo Request This document
2 SFC Echo Reply This document
3 SFP Consistency Verification Request This document
4 SFP Consistency Verification Reply This document
5 - 175 Unassigned This document
176 - 239 Unassigned This document
240 - 251 Experimental This document
252 - 254 Private Use This document
255 Reserved This document

10.3.3. SFC Echo Reply Modes

IANA is requested to create in the SFC Echo Request/Echo Reply Parameters registry the new sub-registry as follows:

  • Sub-registry Name: SFC Echo Reply Mode
  • Assignment Policy:
  • 8 - 175 IETF Review
  • 176 - 239 First Come First Served
  • Reference: [this document]
Table 5: SFC Echo Reply Modes
Value Description Reference
0 Reserved This document
1 Do Not Reply This document
2 Reply via an IPv4/IPv6 UDP Packet This document
3 Unassigned This document
4 Reply via Specified Path This document
5 Reply via an IPv4/IPv6 UDP Packet with the data integrity protection This document
6 Unassigned This document
7 Reply via Specified Path with the data integrity protection This document
8 - 175 Unassigned This document
176 - 239 Unassigned This document
240 - 251 Experiemntal This document
252 - 254 Private Use This document
255 Reserved This document

10.3.4. SFC Echo Return Codes

IANA is requested to create in the SFC Echo Request/Echo Reply Parameters registry the new sub-registry as follows:

  • Sub-registry Name: SFC Echo Return Codes
  • Assignment Policy:
  • 9 - 191 IETF Review
  • 192 - 251 First Come First Served
  • Reference: [this document]
Table 6: SFC Echo Return Codes
Value Description Reference
0 No Error This document
1 Malformed Echo Request received This document
2 One or more of the TLVs was not understood This document
3 Authentication failed This document
4 SFC TTL Exceeded This document
5 End of the SFP This document
6  Reply Service Function Path TLV is missing  This document
7  Reply SFP was not found  This document
8  Unverifiable Reply Service Function Path  This document
9 -191 Unassigned This document
192-251 Unassigned This document
252-254 Private Use This document
255 Reserved This document

10.4. SFC Active OAM TLV Type

IANA is requested to create in the in the SFC Active OAM Registry the sub-registry as follows:

  • Registry Name: SFC Active OAM TLV Type
  • Assignment Policy:
  • 6 -175 IETF Review
  • 176 - 239 First Come First Served
  • Reference: [this document]
Table 7: SFC Active OAM TLV Type Registry
Value Description Reference
0 Reserved This document
1 Source ID TLV This document
2 Errored TLVs This document
3  Reply Service Function Path Type  This document
4 SFF Information Record Type This document
5 SF Information This document
6 - 175 Unassigned This document
176 - 239 Unassigned This document
240 - 251 Experimental This document
252 - 254 Private Use This document
255 Reserved This document

10.5. SF Identifier Types

IANA is requested to create in the SF Types registry [RFC9263] the sub-registry as follows:

  • Registry Name: SF Identifier Types
  • Assignment Policy:
  • 4 -191 IETF Review
  • 192 - 251 First Come First Served
  • Reference: [this document]
Table 8: SF Identifier Type
Value Description Reference
0 Reserved This document
1 IPv4 This document
2 IPv6 This document
3 MAC This document
4 -191 Unassigned This document
192-251 Unassigned This document
252-254 Private Use This document
255 Reserved This document

11. References

11.1. Normative References

[I-D.ietf-sfc-oam-packet]
Boucadair, M., "OAM Packet and Behavior in the Network Service Header (NSH)", Work in Progress, Internet-Draft, draft-ietf-sfc-oam-packet-03, , <https://datatracker.ietf.org/doc/html/draft-ietf-sfc-oam-packet-03>.
[RFC2119]
Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <https://www.rfc-editor.org/info/rfc2119>.
[RFC7665]
Halpern, J., Ed. and C. Pignataro, Ed., "Service Function Chaining (SFC) Architecture", RFC 7665, DOI 10.17487/RFC7665, , <https://www.rfc-editor.org/info/rfc7665>.
[RFC8174]
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <https://www.rfc-editor.org/info/rfc8174>.
[RFC8300]
Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed., "Network Service Header (NSH)", RFC 8300, DOI 10.17487/RFC8300, , <https://www.rfc-editor.org/info/rfc8300>.
[RFC9015]
Farrel, A., Drake, J., Rosen, E., Uttaro, J., and L. Jalil, "BGP Control Plane for the Network Service Header in Service Function Chaining", RFC 9015, DOI 10.17487/RFC9015, , <https://www.rfc-editor.org/info/rfc9015>.
[RFC9145]
Boucadair, M., Reddy.K, T., and D. Wing, "Integrity Protection for the Network Service Header (NSH) and Encryption of Sensitive Context Headers", RFC 9145, DOI 10.17487/RFC9145, , <https://www.rfc-editor.org/info/rfc9145>.

11.2. Informative References

[RFC0792]
Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, DOI 10.17487/RFC0792, , <https://www.rfc-editor.org/info/rfc792>.
[RFC4086]
Eastlake 3rd, D., Schiller, J., and S. Crocker, "Randomness Requirements for Security", BCP 106, RFC 4086, DOI 10.17487/RFC4086, , <https://www.rfc-editor.org/info/rfc4086>.
[RFC4302]
Kent, S., "IP Authentication Header", RFC 4302, DOI 10.17487/RFC4302, , <https://www.rfc-editor.org/info/rfc4302>.
[RFC4303]
Kent, S., "IP Encapsulating Security Payload (ESP)", RFC 4303, DOI 10.17487/RFC4303, , <https://www.rfc-editor.org/info/rfc4303>.
[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, , <https://www.rfc-editor.org/info/rfc4443>.
[RFC5706]
Harrington, D., "Guidelines for Considering Operations and Management of New Protocols and Protocol Extensions", RFC 5706, DOI 10.17487/RFC5706, , <https://www.rfc-editor.org/info/rfc5706>.
[RFC5880]
Katz, D. and D. Ward, "Bidirectional Forwarding Detection (BFD)", RFC 5880, DOI 10.17487/RFC5880, , <https://www.rfc-editor.org/info/rfc5880>.
[RFC6437]
Amante, S., Carpenter, B., Jiang, S., and J. Rajahalme, "IPv6 Flow Label Specification", RFC 6437, DOI 10.17487/RFC6437, , <https://www.rfc-editor.org/info/rfc6437>.
[RFC7110]
Chen, M., Cao, W., Ning, S., Jounay, F., and S. Delord, "Return Path Specified Label Switched Path (LSP) Ping", RFC 7110, DOI 10.17487/RFC7110, , <https://www.rfc-editor.org/info/rfc7110>.
[RFC7555]
Swallow, G., Lim, V., and S. Aldrin, "Proxy MPLS Echo Request", RFC 7555, DOI 10.17487/RFC7555, , <https://www.rfc-editor.org/info/rfc7555>.
[RFC7799]
Morton, A., "Active and Passive Metrics and Methods (with Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799, , <https://www.rfc-editor.org/info/rfc7799>.
[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, , <https://www.rfc-editor.org/info/rfc8029>.
[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, , <https://www.rfc-editor.org/info/rfc8126>.
[RFC8595]
Farrel, A., Bryant, S., and J. Drake, "An MPLS-Based Forwarding Plane for Service Function Chaining", RFC 8595, DOI 10.17487/RFC8595, , <https://www.rfc-editor.org/info/rfc8595>.
[RFC8924]
Aldrin, S., Pignataro, C., Ed., Kumar, N., Ed., Krishnan, R., and A. Ghanwani, "Service Function Chaining (SFC) Operations, Administration, and Maintenance (OAM) Framework", RFC 8924, DOI 10.17487/RFC8924, , <https://www.rfc-editor.org/info/rfc8924>.
[RFC9263]
Wei, Y., Ed., Elzur, U., Majee, S., Pignataro, C., and D. Eastlake 3rd, "Network Service Header (NSH) Metadata Type 2 Variable-Length Context Headers", RFC 9263, DOI 10.17487/RFC9263, , <https://www.rfc-editor.org/info/rfc9263>.

Contributors' Addresses

Cui Wang
Individual contributor
Zhonghua Chen
China Telecom
No.1835, South PuDong Road
Shanghai
201203
China
Phone: +86 18918588897

Authors' Addresses

Greg Mirsky
Ericsson
Wei Meng
ZTE Corporation
No.50 Software Avenue, Yuhuatai District
Nanjing,
China
Ting Ao
China Mobile
No.889, BiBo Road
Shanghai
201203
China
Phone: +86 17721209283
Bhumip Khasnabish
Individual contributor
Kent Leung
Individual contributor
530 Showers Drive Ste 7
Mountain View, CA 94040,
United States of America
Gyan Mishra
Verizon Inc.