Huawei

Israel tal.mizrahi.phd@gmail.com

Marvell

6 Hamada Yokneam 2066721 Israel yilan@marvell.com

Marvell

6 Hamada Yokneam 2066721 Israel davidme@marvell.com

Intel

Dromore House Shannon Co. Clare Ireland rory.browne@intel.com

NSH Context Header timestamp The Network Service Header (NSH) specification defines two possible methods of including metadata (MD): MD Type 0x1 and MD Type 0x2. MD Type 0x1 uses a fixed-length Context Header. The allocation of this Context Header, i.e., its structure and semantics, has not been standardized. This memo defines the Timestamp Context Header, which is an NSH fixed-length Context Header that incorporates the packet's timestamp, a sequence number, and a source interface identifier. Although the definition of the Context Header presented in this document has not been standardized by the IETF, it has been implemented in silicon by several manufacturers and is published here to facilitate interoperability.

Status of This Memo This document is not an Internet Standards Track specification; it is published for informational purposes. This is a contribution to the RFC Series, independently of any other RFC stream. The RFC Editor has chosen to publish this document at its discretion and makes no statement about its value for implementation or deployment. Documents approved for publication by the RFC Editor are not candidates for any level of Internet Standard; see Section 2 of RFC 7841. Information about the current status of this document, any errata, and how to provide feedback on it may be obtained at .

Copyright Notice Copyright (c) 2022 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents () in effect on the date of publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document.

Table of Contents

• .  Introduction
• .  Terminology
  • .  Requirements Language
  • .  Abbreviations
• .  NSH Timestamp Context Header Allocation
• .  Timestamping Use Cases
  • .  Network Analytics
  • .  Alternate Marking
  • .  Consistent Updates
• .  Synchronization Considerations
• .  IANA Considerations
• .  Security Considerations
• .  References
  • .  Normative References
  • .  Informative References
• Acknowledgments
• Authors' Addresses

Introduction The Network Service Header (NSH), defined in , is an encapsulation header that is used as the service encapsulation in the Service Function Chaining (SFC) architecture . In order to share metadata (MD) along a service path, the NSH specification supports two methods: a fixed-length Context Header (MD Type 0x1) and a variable-length Context Header (MD Type 0x2). When using MD Type 0x1, the NSH includes 16 octets of Context Header fields. The NSH specification has not defined the semantics of the 16-octet Context Header, nor does it specify how the Context Header is used by NSH-aware Service Functions (SFs), Service Function Forwarders (SFFs), and proxies. Several Context Header formats are defined in . Furthermore, some allocation schemes were proposed in the past to accommodate specific use cases, e.g., , , and . This memo presents an allocation for the MD Type 0x1 Context Header, which incorporates the timestamp of the packet, a sequence number, and a source interface identifier. Note that other allocation schema for MD Type 0x1 might be specified in the future. Although such schema are currently not being standardized by the SFC Working Group, a consistent format (allocation schema) should be used in an SFC-enabled domain in order to allow interoperability. In a nutshell, packets that enter the SFC-enabled domain are timestamped by a classifier . Thus, the timestamp, sequence number, and source interface are incorporated in the NSH Context Header. As discussed in , if reclassification is used, it may result in an update to the NSH metadata. Specifically, when the Timestamp Context Header is used, a reclassifier may either leave it unchanged or update the three fields: Timestamp, Sequence Number, and Source Interface. The Timestamp Context Header includes three fields that may be used for various purposes. The Timestamp field may be used for logging, troubleshooting, delay measurement, packet marking for performance monitoring, and timestamp-based policies. The source interface identifier indicates the interface through which the packet was received at the classifier. This identifier may specify a physical interface or a virtual interface. The sequence numbers can be used by SFs to detect out-of-order delivery or duplicate transmissions. Note that out-of-order and duplicate packet detection is possible when packets are received by the same SF but is not necessarily possible when there are multiple instances of the same SF and multiple packets are spread across different instances of the SF. The sequence number is maintained on a per-source-interface basis. This document presents the Timestamp Context Header but does not specify the functionality of the SFs that receive the Context Header. Although a few possible use cases are described in this document, the SF behavior and application are outside the scope of this document. Key Performance Indicator (KPI) stamping defines an NSH timestamping mechanism that uses the MD Type 0x2 format. This memo defines a compact MD Type 0x1 Context Header that does not require the packet to be extended beyond the NSH. Furthermore, the mechanisms described in and this memo can be used in concert, as further discussed in . Although the definition of the Context Header presented in this document has not been standardized by the IETF, it has been implemented in silicon by several manufacturers and is published here to facilitate interoperability.

Terminology

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 when, and only when, they appear in all capitals, as shown here.

Abbreviations The following abbreviations are used in this document:

KPI

Key Performance Indicator

MD

Metadata

NSH

Network Service Header

SF

Service Function

SFC

Service Function Chaining

SFF

Service Function Forwarder

NSH Timestamp Context Header Allocation This memo defines the following fixed-length Context Header allocation, as presented in .

NSH Timestamp Allocation 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Source Interface | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Timestamp | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

The NSH Timestamp allocation defined in this memo MUST include the following fields:

Sequence Number:

A 32-bit sequence number. The sequence number is maintained on a per-source-interface basis. Sequence numbers can be used by SFs to detect out-of-order delivery or duplicate transmissions. The classifier increments the sequence number by 1 for each packet received through the source interface. This requires the classifier to maintain a per-source-interface counter. The sequence number is initialized to a random number on startup. After it reaches its maximal value (2³²-1), the sequence number wraps around back to zero.

Source Interface:

A 32-bit source interface identifier that is assigned by the classifier. The combination of the source interface and the classifier identity is unique within the context of an SFC-enabled domain. Thus, in order for an SF to be able to use the source interface as a unique identifier, the identity of the classifier needs to be known for each packet. The source interface is unique in the context of the given classifier.

Timestamp:

A 64-bit field that specifies the time at which the packet was received by the classifier. Two possible timestamp formats can be used for this field: the two 64-bit recommended formats specified in . One of the formats is based on the timestamp format defined in , and the other is based on the format defined in .

The NSH specification does not specify the possible coexistence of multiple MD Type 0x1 Context Header formats in a single SFC-enabled domain. It is assumed that the Timestamp Context Header will be deployed in an SFC-enabled domain that uniquely uses this Context Header format. Thus, operators SHOULD ensure that either a consistent Context Header format is used in the SFC-enabled domain or there is a clear policy that allows SFs to know the Context Header format of each packet. Specifically, operators are expected to ensure the consistent use of a timestamp format across the whole SFC-enabled domain. The two timestamp formats that can be used in the Timestamp field are as follows:

Truncated Timestamp Format :

This format is specified in . For the reader's convenience, this format is illustrated in .

Truncated Timestamp Format (IEEE 1588) 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Seconds | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Nanoseconds | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

NTP 64-bit Timestamp Format :

This format is specified in . For the reader's convenience, this format is illustrated in .

NTP 64-Bit Timestamp Format (RFC 5905) 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Seconds | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Fraction | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Synchronization aspects of the timestamp format in the context of the NSH Timestamp allocation are discussed in .

Timestamping Use Cases

Network Analytics Per-packet timestamping enables coarse-grained monitoring of network delays along the Service Function Chain. Once a potential problem or bottleneck is detected (for example, when the delay exceeds a certain policy), a highly granular monitoring mechanism can be triggered (for example, using the hop-by-hop measurement data defined in or ), allowing analysis and localization of the problem. Timestamping is also useful for logging, troubleshooting, and flow analytics. It is often useful to maintain the timestamp of the first and last packet of the flow. Furthermore, traffic mirroring and sampling often require a timestamp to be attached to analyzed packets. Attaching the timestamp to the NSH provides an in-band common time reference that can be used for various network analytics applications.

Alternate Marking A possible approach for passive performance monitoring is to use an Alternate-Marking Method . This method requires data packets to carry a field that marks (colors) the traffic, and enables passive measurement of packet loss, delay, and delay variation. The value of this marking field is periodically toggled between two values. When the timestamp is incorporated in the NSH, it can intrinsically be used for Alternate Marking. For example, the least significant bit of the timestamp Seconds field can be used for this purpose, since the value of this bit is inherently toggled every second.

Consistent Updates The timestamp can be used for making policy decisions, such as 'Perform action A if timestamp>=T_0'. This can be used for enforcing time-of-day policies or periodic policies in SFs. Furthermore, timestamp-based policies can be used for enforcing consistent network updates, as discussed in . It should be noted that, as in the case of Alternate Marking, this use case alone does not require a full 64-bit timestamp but could be implemented with a significantly smaller number of bits.

Synchronization Considerations Some of the applications that make use of the timestamp require the classifier and SFs to be synchronized to a common time reference -- for example, using the Network Time Protocol or the Precision Time Protocol . Although it is not a requirement to use a clock synchronization mechanism, it is expected that, depending on the applications that use the timestamp, such synchronization mechanisms will be used in most deployments that use the Timestamp allocation.

IANA Considerations This document has no IANA actions.

Security Considerations The security considerations for the NSH in general are discussed in . The NSH is typically run within a confined trust domain. However, if a trust domain is not enough to provide the operator with protection against the timestamp threats as described below, then the operator SHOULD use transport-level protection between SFC processing nodes as described in . The security considerations of in-band timestamping in the context of the NSH are discussed in ; this section is based on that discussion. In-band timestamping, as defined in this document and , can be used as a means for network reconnaissance. By passively eavesdropping on timestamped traffic, an attacker can gather information about network delays and performance bottlenecks. An on-path attacker can maliciously modify timestamps in order to attack applications that use the timestamp values, such as performance-monitoring applications. Since the timestamping mechanism relies on an underlying time synchronization protocol, by attacking the time protocol an attack can potentially compromise the integrity of the NSH Timestamp. A detailed discussion about the threats against time protocols and how to mitigate them is presented in .

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. This document describes an architecture for the specification, creation, and ongoing maintenance of Service Function Chains (SFCs) in a network. It includes architectural concepts, principles, and components used in the construction of composite services through deployment of SFCs, with a focus on those to be standardized in the IETF. This document does not propose solutions, protocols, or extensions to existing protocols. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document describes a Network Service Header (NSH) imposed on packets or frames to realize Service Function Paths (SFPs). The NSH also provides a mechanism for metadata exchange along the instantiated service paths. The NSH is the Service Function Chaining (SFC) encapsulation required to support the SFC architecture (defined in RFC 7665). Various network protocols make use of binary-encoded timestamps that are incorporated in the protocol packet format, referred to as "packet timestamps" for short. This document specifies guidelines for defining packet timestamp formats in networking protocols at various layers. It also presents three recommended timestamp formats. The target audience of this document includes network protocol designers. It is expected that a new network protocol that requires a packet timestamp will, in most cases, use one of the recommended timestamp formats. If none of the recommended formats fits the protocol requirements, the new protocol specification should specify the format of the packet timestamp according to the guidelines in this document. Informative References IEEE INFOCOM Workshop on Software-Driven Flexible and Agile Networking (SWFAN) IEEE Work in Progress Cisco Systems, Inc. Individual Contributor Nokia Nokia Orange Work in Progress Work in Progress ZTE Corporation Intel Individual contributor Cisco Futurewei Technologies Work in Progress The Network Time Protocol (NTP) is widely used to synchronize computer clocks in the Internet. This document describes NTP version 4 (NTPv4), which is backwards compatible with NTP version 3 (NTPv3), described in RFC 1305, as well as previous versions of the protocol. NTPv4 includes a modified protocol header to accommodate the Internet Protocol version 6 address family. NTPv4 includes fundamental improvements in the mitigation and discipline algorithms that extend the potential accuracy to the tens of microseconds with modern workstations and fast LANs. It includes a dynamic server discovery scheme, so that in many cases, specific server configuration is not required. It corrects certain errors in the NTPv3 design and implementation and includes an optional extension mechanism. [STANDARDS-TRACK] As time and frequency distribution protocols are becoming increasingly common and widely deployed, concern about their exposure to various security threats is increasing. This document defines a set of security requirements for time protocols, focusing on the Precision Time Protocol (PTP) and the Network Time Protocol (NTP). This document also discusses the security impacts of time protocol practices, the performance implications of external security practices on time protocols, and the dependencies between other security services and time synchronization. This document describes a method to perform packet loss, delay, and jitter measurements on live traffic. This method is based on an Alternate-Marking (coloring) technique. A report is provided in order to explain an example and show the method applicability. This technology can be applied in various situations, as detailed in this document, and could be considered Passive or Hybrid depending on the application. This document describes methods of carrying Key Performance Indicators (KPIs) using the Network Service Header (NSH). These methods may be used, for example, to monitor latency and QoS marking to identify problems on some links or service functions.

Acknowledgments The authors thank and for their thorough reviews and detailed comments.

Authors' Addresses Huawei

Israel tal.mizrahi.phd@gmail.com

Marvell

6 Hamada Yokneam 2066721 Israel yilan@marvell.com

Marvell

6 Hamada Yokneam 2066721 Israel davidme@marvell.com

Intel

Dromore House Shannon Co. Clare Ireland rory.browne@intel.com