Network Working Group T. Mizrahi Internet-Draft Huawei Intended status: Informational I. Yerushalmi Expires: August 21, 2021 D. Melman Marvell R. Browne Intel February 17, 2021 Network Service Header (NSH) Context Header Allocation: Timestamp draft-mymb-sfc-nsh-allocation-timestamp-08 Abstract 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 presents an allocation for the Context Headers of NSH, which incorporates the packet's timestamp, a sequence number, and a source interface identifier. Status of This Memo This Internet-Draft is submitted in full conformance with the provisions of BCP 78 and BCP 79. Internet-Drafts are working documents of the Internet Engineering Task Force (IETF). Note that other groups may also distribute working documents as Internet-Drafts. The list of current Internet- Drafts is at https://datatracker.ietf.org/drafts/current/. Internet-Drafts are draft documents valid for a maximum of six months and may be updated, replaced, or obsoleted by other documents at any time. It is inappropriate to use Internet-Drafts as reference material or to cite them other than as "work in progress." This Internet-Draft will expire on August 21, 2021. Copyright Notice Copyright (c) 2021 IETF Trust and the persons identified as the document authors. All rights reserved. This document is subject to BCP 78 and the IETF Trust's Legal Provisions Relating to IETF Documents (https://trustee.ietf.org/license-info) in effect on the date of Mizrahi, et al. Expires August 21, 2021 [Page 1] Internet-Draft NSH Timestamp February 2021 publication of this document. Please review these documents carefully, as they describe your rights and restrictions with respect to this document. Code Components extracted from this document must include Simplified BSD License text as described in Section 4.e of the Trust Legal Provisions and are provided without warranty as described in the Simplified BSD License. Table of Contents 1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2 2. Terminology . . . . . . . . . . . . . . . . . . . . . . . . . 3 2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3 2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 3 3. NSH Context Header Allocation . . . . . . . . . . . . . . . . 3 4. Timestamping Use Cases . . . . . . . . . . . . . . . . . . . 5 4.1. Network Analytics . . . . . . . . . . . . . . . . . . . . 5 4.2. Alternate Marking . . . . . . . . . . . . . . . . . . . . 6 4.3. Consistent Updates . . . . . . . . . . . . . . . . . . . 6 5. Synchronization Considerations . . . . . . . . . . . . . . . 6 6. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 6 7. Security Considerations . . . . . . . . . . . . . . . . . . . 6 8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7 8.1. Normative References . . . . . . . . . . . . . . . . . . 7 8.2. Informative References . . . . . . . . . . . . . . . . . 8 Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 8 1. Introduction The Network Service Header (NSH), defined in [RFC8300], is an encapsulation header that is used in Service Function Chains (SFC). The NSH specification [RFC8300] supports two possible methods of including metadata in the NSH; MD Type 0x1 and MD Type 0x2. When using MD Type 0x1 the NSH includes 16 octets of Context Header fields. The current memo defines an allocation for the MD Type 0x1 Context Headers, which incorporates the timestamp of the packet, a sequence number, and a source interface identifier. It is noted that other MD Type 0x1 allocations might be specified in the future. Although MD Type 0x1 allocations are currently not being standardized by the SFC working group, a consistent format (allocation) should be used in an SFC domain in order to allow interoperability. In a nutshell, packets that enter the SFC-Enabled Domain are timestamped. The timestamp is measured by the Classifier [RFC7665], and incorporated in the NSH. The timestamp may be used for various different purposes, including delay measurement, packet marking for Mizrahi, et al. Expires August 21, 2021 [Page 2] Internet-Draft NSH Timestamp February 2021 passive performance monitoring, and timestamp-based policies. Notably, the timestamp does not increase the packet length, since it is incorporated in the MD Type 0x1 Mandatory Context Headers. The source interface identifier indicates the interface through which the packet was received at the classifier. This identifer may specify a physical or a virtual interface. The sequence numbers can be used by Service Functions (SFs) to detect out-of-order delivery or duplicate transmissions. The sequence number is maintained on a per- source-interface basis. KPI-stamping [RFC8592] defines an NSH timestamping mechanism that uses the MD Type 0x2 format. The current memo defines a compact MD Type 0x1 Context Header that does not require the packet to be extended beyond the NSH header. Furthermore, the two timestamping mechanisms can be used in concert, as further discussed below. 2. Terminology 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. Abbreviations The following abbreviations are used in this document: KPI Key Performance Indicators [RFC8592] NSH Network Service Header [RFC8300] MD Metadata [RFC8300] SF Service Function [RFC7665] SFC Service Function Chaining [RFC7665] 3. NSH Context Header Allocation This memo defines the following Context Header allocation, as presented in Figure 1. Mizrahi, et al. Expires August 21, 2021 [Page 3] Internet-Draft NSH Timestamp February 2021 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 | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 1: NSH Timestamp Allocation. The NSH Timestamp Allocation that is defined in this memo MUST include the following fields: o 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 (2^32-1) the sequence number wraps around back to zero. o Source Interface - a 32-bit source interface identifier that is assigned by the Classifier. o Timestamp - this field is 8 octets long, and 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 [RFC8877]. One of the formats is based on the [IEEE1588] timestamp format, and the other is based on the [RFC5905] format. Consistent use of one format or the other is necessary to ensure correct understanding of the Timestamp field. Operators SHOULD ensure the consistent use of a timestamp format across the whole SFC domain. The two timestamp formats that can be used in the timestamp field are: o IEEE 1588 Truncated Timestamp Format: as specified in Section 4.3 of [RFC8877]. This format is illustrated in Figure 2. Mizrahi, et al. Expires August 21, 2021 [Page 4] Internet-Draft NSH Timestamp February 2021 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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 2: IEEE 1588 Truncated Timestamp Format [IEEE1588]. o NTP [RFC5905] 64-bit Timestamp Format: as specified in Section 4.2.1 of [RFC8877]. This format is illustrated 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Seconds | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Fraction | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ Figure 3: NTP [RFC5905] 64-bit Timestamp Format Synchronization aspects of the timestamp format in the context of the NSH timestamp allocation are discussed in Section 5. 4. Timestamping Use Cases 4.1. Network Analytics Per-packet timestamping enables coarse-grained monitoring of the network delay 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 hop-by-hop monitoring mechanism, such as [RFC8592] or [I-D.ietf-ippm-ioam-data], can be triggered, allowing to analyze and localize the problem. Timestamping is also useful for logging and for 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 requires a timestamp to be attached to analyzed packets. Attaching the timestamp to the NSH Context Header provides an in-band common time reference that can be used for various network analytics applications. Mizrahi, et al. Expires August 21, 2021 [Page 5] Internet-Draft NSH Timestamp February 2021 4.2. Alternate Marking A possible approach for passive performance monitoring is to use an alternate marking method [RFC8321]. 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 Context Header, it can natively 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. 4.3. Consistent Updates The timestamp can be used for taking 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 service functions. Furthermore, timestamp-based policies can be used for enforcing consistent network updates, as discussed in [DPT]. 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. 5. Synchronization Considerations Some of the applications that make use of the timestamp require the Classifer and SFs to be synchronized to a common time reference, for example using the Network Time Protocol [RFC5905], or the Precision Time Protocol [IEEE1588]. 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. 6. IANA Considerations This memo includes no request to IANA. 7. Security Considerations The security considerations of NSH in general are discussed in [RFC8300]. NSH is typically run within a confined trust domain. However, if a trust domain is not enough to provide the operator with the protection against the timestamp threats described below, then the operator SHOULD use transport-level protection between SFC processing nodes as described in [RFC8300]. Mizrahi, et al. Expires August 21, 2021 [Page 6] Internet-Draft NSH Timestamp February 2021 The security considerations of in-band timestamping in the context of NSH is discussed in [RFC8592], and the current section is based on that discussion. The use of in-band timestamping, as defined in this document, can be used as a means for network reconnaissance. By passively eavesdropping to timestamped traffic, an attacker can gather information about network delays and performance bottlenecks. A man- in-the-middle 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 [RFC7384]. 8. References 8.1. Normative References [RFC2119] Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997, . [RFC7665] Halpern, J., Ed. and C. Pignataro, Ed., "Service Function Chaining (SFC) Architecture", RFC 7665, DOI 10.17487/RFC7665, October 2015, . [RFC8174] Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017, . [RFC8300] Quinn, P., Ed., Elzur, U., Ed., and C. Pignataro, Ed., "Network Service Header (NSH)", RFC 8300, DOI 10.17487/RFC8300, January 2018, . [RFC8877] Mizrahi, T., Fabini, J., and A. Morton, "Guidelines for Defining Packet Timestamps", RFC 8877, DOI 10.17487/RFC8877, September 2020, . Mizrahi, et al. Expires August 21, 2021 [Page 7] Internet-Draft NSH Timestamp February 2021 8.2. Informative References [DPT] Mizrahi, T., Moses, Y., "The Case for Data Plane Timestamping in SDN", IEEE INFOCOM Workshop on Software- Driven Flexible and Agile Networking (SWFAN), 2016. [I-D.ietf-ippm-ioam-data] Brockners, F., Bhandari, S., and T. Mizrahi, "Data Fields for In-situ OAM", draft-ietf-ippm-ioam-data-11 (work in progress), November 2020. [IEEE1588] IEEE, "IEEE 1588 Standard for a Precision Clock Synchronization Protocol for Networked Measurement and Control Systems Version 2", 2008. [RFC5905] Mills, D., Martin, J., Ed., Burbank, J., and W. Kasch, "Network Time Protocol Version 4: Protocol and Algorithms Specification", RFC 5905, DOI 10.17487/RFC5905, June 2010, . [RFC7384] Mizrahi, T., "Security Requirements of Time Protocols in Packet Switched Networks", RFC 7384, DOI 10.17487/RFC7384, October 2014, . [RFC8321] Fioccola, G., Ed., Capello, A., Cociglio, M., Castaldelli, L., Chen, M., Zheng, L., Mirsky, G., and T. Mizrahi, "Alternate-Marking Method for Passive and Hybrid Performance Monitoring", RFC 8321, DOI 10.17487/RFC8321, January 2018, . [RFC8592] Browne, R., Chilikin, A., and T. Mizrahi, "Key Performance Indicator (KPI) Stamping for the Network Service Header (NSH)", RFC 8592, DOI 10.17487/RFC8592, May 2019, . Authors' Addresses Tal Mizrahi Huawei Israel Email: tal.mizrahi.phd@gmail.com Mizrahi, et al. Expires August 21, 2021 [Page 8] Internet-Draft NSH Timestamp February 2021 Ilan Yerushalmi Marvell 6 Hamada Yokneam 2066721 Israel Email: yilan@marvell.com David Melman Marvell 6 Hamada Yokneam 2066721 Israel Email: davidme@marvell.com Rory Browne Intel Dromore House Shannon, Co.Clare Ireland Email: rory.browne@intel.com Mizrahi, et al. Expires August 21, 2021 [Page 9]