Internet-Draft Active OAM for SFC June 2021
Mirsky, et al. Expires 18 December 2021 [Page]
Workgroup:
SFC WG
Internet-Draft:
draft-ietf-sfc-multi-layer-oam-13
Updates:
8300 (if approved)
Published:
Intended Status:
Standards Track
Expires:
Authors:
G. Mirsky
ZTE Corp.
W. Meng
ZTE Corporation
B. Khasnabish
Individual contributor
C. Wang
Individual contributor

Active OAM for Service Function Chaining

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.

This document updates RFC 8300. Particularly, it updates the definition of O (OAM) bit in the Network Service Header (NSH) (RFC 8300) and defines how an active OAM message is identified in the 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 18 December 2021.

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 identified when Network Service Header (NSH) 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 the requirements listed in Section 3, improve, for example, troubleshooting efficiency and defect localization in SFP because they specifically address the architectural principles of NSH. For that purpose, SFC Echo Request and Echo Reply are specified in Section 6. This mechanism enables on-demand Continuity Check, Connectivity Verification among other operations over SFC in networks, addresses functionalities discussed in Sections 4.1, 4.2, and 4.3 of [RFC8924]. SFC Echo Request and Echo Reply, defined in this document, 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. Also, this document updates Section 2.2 of [RFC8300] in part of the definition of O bit in the NSH.

2. Terminology and Conventions

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

In this document, SFC OAM refers to an active OAM [RFC7799] in an SFC architecture.

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

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 OAM task of fault management (FM) 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 being connected to two instances of the same service function. End-to-end (E2E) SFC OAM has the Classifier as the ingress and SFF3 as its egress. 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 transport layer as an SFC-encapsulated packet (e.g., NSH).

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, in the example in 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 the SFF1 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 example, RSP1(SFI11--SFI21--SFI31) and RSP2(SFI12--SFI22--SFI32). Available RSPs can be discovered using the trace function discussed in Section 4.3 [RFC8924] or the procedure defined in Section 6.7.

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 with responses being directed towards the initiator of such proxy request.

4. Active OAM Identification in the NSH

The O bit in the NSH is defined in [RFC8300] as follows:

This document updates that definition as follows:

Active SFC OAM is 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 "Next Protocol" field MUST be set to Active SFC OAM (TBA1) (Section 9.1). The rules for interpreting the values of the O bit and the "Next Protocol" field are as follows:

One conclusion from the above-listed rules of processing the O bit and the "Next Protocol" field is to avoid the combination of OAM in an NSH Context Header (Fixed-Length or Variable-Length) and the payload immediately following the NSH because there is no unambiguous way to identify such combination using the O bit and the Next Protocol field.

5. Active SFC OAM Header

As demonstrated in Section 4 [RFC8924] and Section 3 of this document, 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 extra IP/UDP headers, especially in an IPv6 network, 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

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, respectively) and [RFC8029] are examples of broadly used active OAM protocols based on the Echo Request/Reply principle. The SFC Echo Request/Reply defined in this document addresses several requirements listed in Section 3. Specifically, it can be used to check the continuity of an SFP, trace an SFP, or localize the failure within an SFP. The SFC Echo Request/Reply control message format is presented in Figure 3.

       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 |        Reserved           |      Echo Request Flags       |
      +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
      | Message 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:

       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

TLV is a variable-length field. Multiple TLVs MAY be placed in an SFC Echo Request/Reply packet. Additional TLVs may be enclosed within a given TLV, subject to the semantics of the (outer) TLV in question. If more than one TLV is to be included, the value of the Type field of the outmost outer TLV MUST be set to "Multiple TLVs Used" (TBA12), as assigned by IANA according to Section 9.4. Figure 4 presents the format of an SFC Echo Request/Reply TLV, where fields are defined as follows:

6.1. Return Codes

The value of the Return Code field is set to zero by the sender of an Echo Request. The receiver of said Echo Request can set it to one of the values listed in Table 1 in the corresponding Echo Reply that it generates (in cases when the reply is requested).

Table 1: SFC Echo Return Codes
Value Description
0 No Return Code
1 Malformed Echo Request received
2 One or more of the TLVs was not understood
3 Authentication failed

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 [I-D.ietf-sfc-nsh-integrity] 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 Context Header is more suitable for the integrity protection of active SFC OAM, particularly of the defined in this document SFC Echo Request and Echo Reply. 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 transport encapsulation of the monitored SFP. If the NSH is used, Echo Request MUST set O bit, as defined in [RFC8300]. NSH MUST be immediately followed by the SFC Active OAM Header defined in Section 4. The Message Type field's value in the SFC Active OAM Header MUST be set to SFC Echo Request/Echo Reply value (TBA2) per Section 9.2.2.

Value of the Reply Mode field MAY be set to:

  • 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. Note that ways of learning the identity of that node are outside the scope of this specification.
  • Reply via an IPv4/IPv6 UDP Packet (TBA6) value likely will be the most used.
  • Reply via Application Level Control Channel (TBA7) value if the SFP may have bi-directional paths.
  • Reply via Specified Path (TBA8) value to enforce the use of the particular return path specified in the included TLV to verify bi-directional continuity and also increase the robustness of the monitoring by selecting a more stable path. [I-D.ao-sfc-oam-return-path-specified] provides an example of communicating an explicit path for the Echo Reply.

6.3.1. Source TLV

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". Because the NSH does not identify the ingress node that generated the Echo Request, the source ID MUST be included in the message and used as the IP destination address and destination UDP port number of the SFC Echo Reply. The sender of the SFC Echo Request MUST include an SFC Source 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 TLV

where

  • Source ID Type is a one-octet-long field and has the value of TBA13 Section 9.4.
  • Reserved1 - one-octet-long field.
  • Length is a two-octets-long field, and the value equals the length of the Value field in octets. The value of the Length field can be 8 or 20. If the value of the field is neither, the Source TLV is considered to be malformed.
  • Port Number is a two-octets-long 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-octets-long 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 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 SFC Echo Reply based on the local policy. If more than one Source ID TLV per the address family is present, the receiver MUST use the first TLV and ignore the rest.

6.4. SFC Echo Request Reception

Punting received SFC Echo Request to the control plane 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.

Firstly, if the SFC Echo Request is integrity-protected, the receiving SFF first MUST verify the authentication. Then the receiver SFF MUST validate the Source TLV, as defined in Section 6.3.1. If the authentication validation has failed and the Source TLV is considered properly formatted, the SFF MUST send to the system identified in the Source 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. If the Source 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. Then, the SFF that has received an SFC Echo Request verifies the rest of the received packet's general sanity. If the packet is not well-formed, 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 TLV (see Section 6.5). 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. In the latter case, the SFF MAY include an Errored TLVs TLV (Section 6.4.1) that, as sub-TLVs, contains only the misunderstood TLVs. Sender's Handle and Sequence Number fields are not examined but are included in the SFC Echo Reply message. If the sanity check of the received Echo Request succeeded, then the SFF at the end of the SFP MUST set the Return Code value to 5 ("End of the SFP") and the Subcode set to zero. If the SFF is not at the end of the SFP and the TTL value is 1, the value of the Return Code MUST be set to 4 ("TTL Exceeded") and the Subcode set to zero. In all other cases, SFF MUST set the Return Code value to 0 ("No Return Code") 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 TBA14 Section 9.4.
  • Reserved - one-octet-long field.
  • Length - two-octet-long field equal to the length of the Value field in octets.
  • The Value field contains the TLVs, encoded as sub-TLVs, that were not understood or failed to be parsed correctly.

6.5. 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. [I-D.ao-sfc-oam-return-path-specified] provides an example of a TLV that can be used to specify the return path of the Echo Reply. Value TBA3 is referred to as the "Do not reply" mode and suppresses the Echo Reply packet transmission. 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.

6.6. 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;
  • it has an outstanding SFC Echo Request sent from the UDP port that matches destination UDP port number of the received packet;
  • if the matching to the Echo Request found, 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;
  • if all checks passed, the SFF checks if the Sequence Number in the Echo Request sent matches to the Sequence Number in the Echo Reply received.

6.7. Tracing an SFP

SFC Echo Request/Reply can be used to isolate a defect detected in the SFP and trace an RSP. As for 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 [I-D.ietf-sfc-nsh-tlv]) is used for distributing the load across Equal Cost Multi-Path or Link Aggregation Group paths. In that case, such an element MAY also be used for the SFC OAM traffic. Doing so is meant to control whether the SFC Echo Request follows the same RSP as the monitored flow.

7. Security Considerations

When the integrity protection for SFC active OAM, and SFC Echo Request/Reply in particular, is required, it is RECOMMENDED to use one of the Context Headers defined in [I-D.ietf-sfc-nsh-integrity]. MAC#1 (Message Authentication Code) 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. The 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 an SFC Echo Request 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., 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 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. 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.

8. Acknowledgments

Authors greatly appreciate thorough review and the most helpful comments from Dan Wing, Dirk von Hugo, and Mohamed Boucadair.

9. IANA Considerations

9.1. SFC Active OAM Protocol

IANA is requested to assign a new type from the SFC Next Protocol registry as follows:

Table 2: SFC Active OAM Protocol
Value Description Reference
TBA1 SFC Active OAM This document

9.2. SFC Active OAM

IANA is requested to create a new SFC Active OAM registry.

9.2.1. Version in the Active SFC OAM Header

IANA is requested to create in the SFC Active OAM registry a new sub-registry called "SFC Active OAM Header Version". All code points are assigned according to the "IETF Review" procedure specified in [RFC8126]. The remaining code points to be allocated according to Table 3:

Table 3: SFC Active OAM Header Version
Version Description Reference
Version 0b00 Protocol as defined by this specification This document
Version 0b01 Unassigned This document
Version 0b10 Unassigned This document
Version 0b11 Unassigned This document

9.2.2. SFC Active OAM Message Type

IANA is requested to create in the SFC Active OAM registry a new sub-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 specified in [RFC8126]. The remaining code points to be allocated according to Table 4:

Table 4: SFC Active OAM Message Type
Value Description Reference
0 Reserved
1 - 32767 Reserved IETF Consensus
32768 - 65530 Reserved First Come First Served
65531 - 65534 Reserved Private Use
65535 Reserved

IANA is requested to assign a new type from the SFC Active OAM Message Type sub-registry as follows:

Table 5: SFC Echo Request/Echo Reply Type
Value Description Reference
TBA2 SFC Echo Request/Echo Reply This document

9.2.3. SFC Active OAM Header Flags

IANA is requested to create in the SFC Active OAM registry the new sub-registry SFC Active OAM Flags.

This sub-registry tracks the assignment of 8 flags in the Flags field of the SFC Active OAM Header. The flags are numbered from 0 (most significant bit, transmitted first) to 7.

New entries are assigned by Standards Action.

Table 6: SFC Active OAM Header Flags
Bit Number Description Reference
7-0 Unassigned This document

9.3. SFC Echo Request/Echo Reply Parameters

IANA is requested to create a new SFC Echo Request/Echo Reply Parameters registry.

9.3.1. SFC Echo Request/Reply Version

IANA is requested to create in the SFC Echo Request/Echo Reply Parameters registry a new sub-registry called "SFC Echo Request/Reply Version". All code points assigned according to the "IETF Review" procedure specified in [RFC8126]. The remaining code points to be allocated according to Table 7:

Table 7: SFC Echo Request/Reply Version
Version Description Reference
Version 0b00 Protocol as defined by this specification This document
Version 0b01 Unassigned This document
Version 0b10 Unassigned This document
Version 0b11 Unassigned This document

9.3.2. SFC Echo Request Flags

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

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

9.3.3. 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 175 in this registry shall be allocated according to the "IETF Review" procedure specified in [RFC8126]. Code points in the range 176 through 239 in this registry shall be allocated according to the "First Come First Served" procedure specified in [RFC8126]. The remaining code points are allocated as specified in Table 9.

Table 9: SFC Echo Request/Echo Reply Message Types
Value Description Reference
0 Reserved This document
1- 175 Unassigned This document
176 - 239 Unassigned This document
240 - 251 Experimental This document
252 - 254 Private Use This document
255 Reserved This document

IANA is requested to assign values as listed in Table 10.

Table 10: SFC Echo Request/Echo Reply Message Types Values
Value Description Reference
TBA3 SFC Echo Request This document
TBA4 SFC Echo Reply This document

9.3.4. SFC Echo Reply Modes

IANA is requested to create in the SFC Echo Request/Echo Reply Parameters registry the new sub-registry Reply Mode. All code points in the range 1 through 175 in this registry shall be allocated according to the "IETF Review" procedure specified in [RFC8126]. Code points in the range 176 through 239 in this registry shall be allocated according to the "First Come First Served" procedure specified in [RFC8126]. The remaining code points are allocated according to Table 11.

Table 11: SFC Echo Reply Mode
Value Description Reference
0 Reserved This document
1- 175 Unassigned This document
176 - 239 Unassigned This document
240 - 251 Experimental This document
252 - 254 Private Use This document
255 Reserved This document

All code points in the range 1 through 191 in this registry shall be allocated according to the "IETF Review" procedure specified in [RFC8126] and assign values as listed in Table 12.

Table 12: SFC Echo Reply Mode Values
Value Description Reference
0 Reserved
TBA5 Do Not Reply This document
TBA6 Reply via an IPv4/IPv6 UDP Packet This document
TBA7 Reply via Application Level Control Channel This document
TBA8 Reply via Specified Path This document
TBA9 Reply via an IPv4/IPv6 UDP Packet with the data integrity protection This document
TBA10 Reply via Application Level Control Channel with the data integrity protection This document
TBA11 Reply via Specified Path with the data integrity protection This document

9.3.5. SFC Echo Return Codes

IANA is requested to create in the SFC Echo Request/Echo Reply Parameters registry the new sub-registry Return Codes as described in Table 13.

Table 13: SFC Echo Return Codes
Value Description Reference
0-191 Unassigned IETF Review
192-251 Unassigned First Come First Served
252-254 Unassigned Private Use
255 Reserved

Values defined for the Return Codes sub-registry are listed in Table 14.

Table 14: SFC Echo Return Codes Values
Value Description Reference
0 No Return Code 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 TTL Exceeded This document
5 End of the SFP This document

9.4. SFC Active OAM TLV Type

IANA is requested to create the SFC Active OAM TLV Type registry. All code points in the range 1 through 175 in this registry shall be allocated according to the "IETF Review" procedure specified in [RFC8126]. Code points in the range 176 through 239 in this registry shall be allocated according to the "First Come First Served" procedure specified in [RFC8126]. The remaining code points are allocated according to Table 15:

Table 15: SFC Active OAM TLV Type Registry
Value Description Reference
0 Reserved This document
1- 175 Unassigned This document
176 - 239 Unassigned This document
240 - 251 Experimental This document
252 - 254 Private Use This document
255 Reserved This document

This document defines the following new values in SFC Active OAM TLV Type registry:

Table 16: SFC OAM Type Values
Value Description Reference
TBA12 Multiple TLVs Used This document
TBA13 Source ID TLV This document
TBA14 Errored TLVs This document

10. References

10.1. Normative References

[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>.
[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>.

10.2. Informative References

[I-D.ao-sfc-oam-return-path-specified]
Mirsky, G., Ao, T., Chen, Z., and G. Mishra, "Controlled Return Path for Service Function Chain (SFC) OAM", Work in Progress, Internet-Draft, draft-ao-sfc-oam-return-path-specified-09, , <https://tools.ietf.org/html/draft-ao-sfc-oam-return-path-specified-09>.
[I-D.ietf-sfc-nsh-integrity]
Boucadair, M., Reddy, T., and D. Wing, "Integrity Protection for the Network Service Header (NSH) and Encryption of Sensitive Context Headers", Work in Progress, Internet-Draft, draft-ietf-sfc-nsh-integrity-05, , <https://tools.ietf.org/html/draft-ietf-sfc-nsh-integrity-05>.
[I-D.ietf-sfc-nsh-tlv]
Wei, Y. (., Elzur, U., Majee, S., and C. Pignataro, "Network Service Header Metadata Type 2 Variable-Length Context Headers", Work in Progress, Internet-Draft, draft-ietf-sfc-nsh-tlv-06, , <https://tools.ietf.org/html/draft-ietf-sfc-nsh-tlv-06>.
[RFC0792]
Postel, J., "Internet Control Message Protocol", STD 5, RFC 792, DOI 10.17487/RFC0792, , <https://www.rfc-editor.org/info/rfc792>.
[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>.
[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>.
[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>.
[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>.

Authors' Addresses

Greg Mirsky
ZTE Corp.
Wei Meng
ZTE Corporation
No.50 Software Avenue, Yuhuatai District
Nanjing,
China
Bhumip Khasnabish
Individual contributor
Cui Wang
Individual contributor