Internet-Draft Transit Measurement February 2024
Mizrahi, et al. Expires 16 August 2024 [Page]
Intended Status:
Standards Track
T. Mizrahi
T. Zhou
S. Belkar
R. Cohen

The Transit Measurement Option


This document specifies an IPv6 option that contains a compact set of fields which can be used for transit delay measurement and congestion detection. This option can be incorporated into data packets and updated by transit nodes along the path, enabling lightweight measurement and monitoring using constant-length data that does not depend on the number of hops in the network.

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

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 16 August 2024.

Table of Contents

1. Introduction

This document introduces an IPv6 option that includes a compact set of performance-related fields. This option can be incorporated into data packets and updated by transit nodes along the path.

There is a number of in-progress documents in the IETF that define IPv6 options that can be used for tracing a path and its performance, including for example, [I-D.ietf-ippm-ioam-ipv6-options], [I-D.filsfils-spring-path-tracing], [I-D.ali-spring-ioam-srv6], [I-D.kumar-ippm-ifa], [I-D.zhou-ippm-enhanced-alternate-marking]. Some of these extensions use per-hop fields which are updated by intermediate nodes, collecting information about the performance along the path. While these extension provide detailed and fine-grained information, they incur high per-packet bandwidth and processing overhead.

The Transit Measurement option, which is defined in this document, provides coarse-grained performance information using a set of fields that have a constant length that does not depend on the number of hops along the path. These fields are defined as a new IPv6 option type, referred to as the Transit Measurement option.

The Transit Measurement option includes two main fields: Accumulated Delay and Status Bitmap. The Accumulated Delay field is used for measuring the one-way delay along the path. Each transit node incrementally adds its internal transit delay to the Accumulated Delay field, and thus at the end of the path this field includes the sum of the transit delay values of the nodes along the path. The Status Bitmap field includes a per-hop bit that indicates its congestion status. Each node along the path updates its corresponding status bit, indicating whether the node is congested. The criterion for deciding whether a node is congested is similar to the "Congestion Experienced" trigger in ECN [RFC3168].

The Transit Measurement option can be incorporated into all or a subset of the traffic that is forwarded by the source node. Notably, the Transit Measurement option adds a fixed and low overhead to data packets, which remains constant along the path.

There are several potential use cases for the Transit Measurement option, including:

2. Conventions

2.1. Requirement 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. Terminology

Abbreviations used in this document:

Operations, Administration, and Maintenance
Explicit Congestion Notification

3. Transit Measurement Option

This document defines a new IPv6 Option type, the Transit Measurement type, which can be included either in the Hop-by-Hop Options header or in the Destination Options header. Figure 1 presents the format of the Transit Measurement option type.

    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
                                   |  Option Type  |  Opt Data Len |
   |                       Accumulated Delay                       |
   |   Hop Count   |            Status Bitmap                      |
Figure 1: Transit Measurement Option Type

A node that complies to this draft MUST support the following fields, as depicted in Figure 1:

Option Type:
This document assigns the value TBD-type, which indicates that this is the Transit Measurement option. The two highest order bits are "00", indicating that nodes that cannot process this option skip over it and continue processing the header, as defined in [RFC8200]. The third-highest-order bit is set to "1", indicating that this option may change en route.
Opt Data Len:
The length in octets of the two fields that follow, which is 8.
Accumulated Delay:
represents the sum of the transit delay values in nanoseconds along the path of the packet, including the current node. This field is a 4-octet unsigned integer in the range 0 to 2^31-1. A transit node that receives the Accumulated Delay field updates its value by adding the transit delay of the current node to the value of the Accumulated Delay field in the received packet. The 'transit delay' in this context is the time in nanoseconds the packet spent in the transit node. If the Accumulated Delay exceeds 2^31-1 nanoseconds then the most significant bit is set to indicate overflow and the value is set to 0x80000000. If a transit node receives this field with the value 0x80000000 or if the node is not able to update the value of the field it SHOULD forward the packet with the unmodified field.
Hop Count/Status Bitmap:

indicates the devices along the path that have experienced congestion.

Hop Count:
a one-octet field that indicates the number of hops since the source node. The source node initializes this field to 0. Every transit node that supports this option increments this field by 1. A maximum of 24 hops is supported. If a transit node receives this field with the value 24 it assigns the value of all '1's (0xFF = 255), which indicates that the number of hops has exceeded the maximum.
Status Bitmap:
a three octet field that represents the congestion status of each transit node along the path. The value '1' indicates that the current packet was enqueued in a queue that is congested. The criterion for whether a queue is congested or not is identical to the "Congestion Experienced" trigger in ECN. Every transit node that supports the Transit Measurement option updates the bit corresponding to the current Hop Count, after having updated the value of the Hop Count. For example, the first transit node along the path updates the Hop Count to 1, and then updates the first (most significant bit) of the Status Bitmap. The source and destination nodes do not update the Status Bitmap. If a node detects that the Hop Count has exceeded its maximal value (24), it does not update the Status Bitmap field.

4. IANA Considerations

4.1. IPv6 Option Type

IANA is requested to allocate a value from the IPv6 Destination Options and Hop-by-Hop Options registry:

Transit Measurement

5. Security Considerations

The Transit Option, and specifically the Accumulated Delay field, which is defined in this document, may be used for reconnaissance, which in turn can facilitate other types of attacks. As in other types of Operations, Administration and Maintenance (OAM) protocols, a malicious attacker can manipulate the Accumulated Delay value in order to create a false illusion of nonexistent network issues or prevent the detection of actual ones.

6. References

6.1. Normative References

Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, , <>.
Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, , <>.
Deering, S. and R. Hinden, "Internet Protocol, Version 6 (IPv6) Specification", STD 86, RFC 8200, DOI 10.17487/RFC8200, , <>.

6.2. Informative References

Ali, Z., Gandhi, R., Filsfils, C., Brockners, F., Nainar, N. K., Pignataro, C., Li, C., Chen, M., and G. Dawra, "Segment Routing Header encapsulation for In-situ OAM Data", Work in Progress, Internet-Draft, draft-ali-spring-ioam-srv6-06, , <>.
Filsfils, C., Abdelsalam, A., Camarillo, P., Yufit, M., Graf, T., Su, Y., Matsushima, S., Valentine, M., and Dhamija, "Path Tracing in SRv6 networks", Work in Progress, Internet-Draft, draft-filsfils-spring-path-tracing-05, , <>.
Bhandari, S. and F. Brockners, "In-situ OAM IPv6 Options", Work in Progress, Internet-Draft, draft-ietf-ippm-ioam-ipv6-options-12, , <>.
Kumar, J., Anubolu, S., Lemon, J., Manur, R., Holbrook, H., Ghanwani, A., Cai, D., Ou, H., Li, Y., and X. Wang, "Inband Flow Analyzer", Work in Progress, Internet-Draft, draft-kumar-ippm-ifa-07, , <>.
Zhou, T., Fioccola, G., Liu, Y., Cociglio, M., Pang, R., Xiong, L., Lee, S., and W. Li, "Enhanced Alternate Marking Method", Work in Progress, Internet-Draft, draft-zhou-ippm-enhanced-alternate-marking-14, , <>.
Ramakrishnan, K., Floyd, S., and D. Black, "The Addition of Explicit Congestion Notification (ECN) to IP", RFC 3168, DOI 10.17487/RFC3168, , <>.
Brockners, F., Ed., Bhandari, S., Ed., and T. Mizrahi, Ed., "Data Fields for In Situ Operations, Administration, and Maintenance (IOAM)", RFC 9197, DOI 10.17487/RFC9197, , <>.
Li, Y., Miao, R., Liu, H., Zhuang, Y., Fei Feng, F., Tang, L., Cao, Z., Zhang, M., Kelly, F., Alizadeh, M., and M. Yu, "HPCC: High Precision Congestion Control", ACM SIGCOMM Beijing, China, .

Authors' Addresses

Tal Mizrahi
8-2 Matam
Haifa 3190501
Tianran Zhou
156 Beiqing Rd.
Shahar Belkar
8-2 Matam
Haifa 3190501
Reuven Cohen
8-2 Matam
Haifa 3190501