wdiff rfc9947.original rfc9947.txt

Network Working Group

Independent Submission G. Fioccola
Internet-Draft
Request for Comments: 9947 T. Zhou
Intended status:
Category: Experimental Huawei
Expires: 28 February 2026
ISSN: 2070-1721 G. Mishra
Verizon Inc.
X. Wang
Ruijie
G. Zhang
China Mobile
M. Cociglio
27 August 2025
February 2026

Application of the Alternate Marking Alternate-Marking Method to the Segment Routing
Header
draft-fz-spring-srv6-alt-mark-17

Abstract

This document describes an alternative experimental approach for the
application of the Alternate-Marking Method to SRv6. Segment Routing for
IPv6 (SRv6). It uses an experimental TLV in the Segment Routing Header, and thus
Header (SRH); thus, participation in this experiment should be
between coordinating parties in a controlled domain. This approach
has potential scaling and simplification benefits over the technique
described in RFC 9343 9343, and the scope of the experiment is to
determine whether those are significant and attractive to the
community.

This protocol extension has been developed outside the IETF as an
alternative to the IETF's standards track Standards Track specification RFC 9343 and
it does not have IETF consensus. It is published here to guide
experimental implementation, implementation and ensure interoperability among
implementations to better determine the value of this approach.
Researchers are invited to submit their evaluations of this work to
the RFC Editor for consideration as independent submissions Independent Submissions or to the
IETF SPRING working group Working Group as Internet-Drafts.

Status of This Memo

This Internet-Draft document is submitted in full conformance with the
provisions of BCP 78 not an Internet Standards Track specification; it is
published for examination, experimental implementation, and BCP 79.

Internet-Drafts are working documents of
evaluation.

This document defines an Experimental Protocol for the Internet Engineering
Task Force (IETF). Note that
community. This is a contribution to the RFC Series, independently
of any other groups may also distribute
working documents as Internet-Drafts. RFC stream. The list of current Internet-
Drafts is RFC Editor has chosen to publish this
document at https://datatracker.ietf.org/drafts/current/.

Internet-Drafts its discretion and makes no statement about its value for
implementation or deployment. Documents approved for publication by
the RFC Editor are draft documents valid not candidates for a maximum any level of Internet Standard;
see Section 2 of RFC 7841.

Information about the current status of six months this document, any errata,
and how to provide feedback on it may be updated, replaced, or obsoleted by other documents obtained 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 28 February 2026.
https://www.rfc-editor.org/info/rfc9947.

This document is subject to BCP 78 and the IETF Trust's Legal
Provisions Relating to IETF Documents (https://trustee.ietf.org/
license-info)
(https://trustee.ietf.org/license-info) 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

1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
1.1. Observations on RFC 9343 . . . . . . . . . . . . . . . . 3
1.2. Requirements Language . . . . . . . . . . . . . . . . . . 4
2. Application of the Alternate Marking Alternate-Marking Method to SRv6 . . . . . . . . 4
2.1. Controlled Domain . . . . . . . . . . . . . . . . . . . . 5
3. Definition of the SRH AltMark TLV . . . . . . . . . . . . . . 5
3.1. Base Alternate Marking Alternate-Marking Data Fields . . . . . . . . . . . 7
3.2. Optional Extended Data Fields for Enhanced Alternate
Marking . . . . . . . . . . . . . . . . . . . . . . . . . 7
4. Use of the SRH AltMark TLV . . . . . . . . . . . . . . . . . 11
4.1. Compatibility . . . . . . . . . . . . . . . . . . . . . . 11
5. Experimentation Overview . . . . . . . . . . . . . . . . . . 12
5.1. Objective of the Experiment . . . . . . . . . . . . . . . 13
6. Security Considerations . . . . . . . . . . . . . . . . . . . 13
7. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 14
8. Acknowledgements . . . . . . . . . . . . . . . . . . . . . . 14
9. Contributors . . . . . . . . . . . . . . . . . . . . . . . . 14
10. References . . . . . . . . . . . . . . . . . . . . . . . . . 14
10.1.
8.1. Normative References . . . . . . . . . . . . . . . . . . 14
10.2.
8.2. Informative References . . . . . . . . . . . . . . . . . 15
Acknowledgements
Contributors
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 16

1. Introduction

[RFC9341] and [RFC9342] describe a passive performance measurement
method, which can be used to measure packet loss, latency latency, and jitter
on live traffic. Since this method is based on marking consecutive
batches of packets, the method is often referred as the Alternate "Alternate-
Marking Method. Method".

The Alternate Marking Alternate-Marking Method requires a marking field so that packet
flows can be distinguished and identified. [RFC9343] defines the
standard for how the marking field can be encoded in a new TLV in
either Hop-by-hop Hop-by-Hop or Destination Options Headers of IPv6 packets in
order to achieve Alternate Marking. The mechanism to carry is
equally applicable to Segment Routing for IPv6 (SRv6) networks
[RFC8402].

This document describes an alternative experimental approach that
encodes the marking field in a new TLV carried in the Segment Routing
Header (SRH) [RFC8754] of an SRv6 packet. This approach is
applicable only to SRv6 deployments. It is intended to capitalize on
the assumption that Segment Routing (SR) nodes are supposed to
support fast parsing and processing of the SRH, while the SR nodes
may not handle properly handle Destination Options, as discussed in
[RFC9098], [I-D.ietf-6man-eh-limits].
[RFC9098] and [EH-LIMITS]. The experiment is to determine whether or
not there are significant and attractive advantages to the community:
if there are, the work may be brought back for IETF consideration.

This protocol extension has been developed outside the IETF as an
alternative to the IETF's standards track Standards Track specification [RFC9343] and [RFC9343]; it
does not have IETF consensus. It is published here to guide
experimental implementation, implementation and ensure interoperability among
implementations to better determine the value of this approach. As
also highlighted in [I-D.bonica-gendispatch-exp], [IETF-EXPERIMENTS], when two protocol extensions
are proposed to solve a single problem, an experiment can be initiated
initiated, and this is the purpose of this document. See Section 5
for more details about the experimentation.

1.1. Observations on RFC 9343

Like any other IPv6 use case, Hop-by-Hop and Destination Options can
also be used when the SRH is present. As specified in [RFC8200], the
Hop-by-Hop Options Header is used to carry optional information that
needs to be examined at every hop along the path, while the
Destination Options Header is used to carry optional information that
needs to be examined only by the packet's destination node(s).

When a Routing Header exists, because the SRH is a Routing Header,
Destination Options present in the IPv6 packet before the SRH header
are processed by the destination indicated in the SRH's route list.
As specified in [RFC8754], SR segment endpoint nodes process the
local
SID Segment Identifier (SID) corresponding to the packet
destination address. Then, the destination address is updated
according to the segment list. The SRH TLV provides metadata for
segment processing, while processing the SID, if the node is locally
configured to do so. Both the Destination Options Header before the
SRH and the SRH TLV are processed at the node being indicated in the
destination address field of the IPv6 header.

The distinction between the alternatives is most notable for SRv6
packets that traverse a network where the paths between sequential
segment end points endpoints include multiple hops. If the Hop-by-Hop Option is
used, then every hop along the path will process the AltMark data.
If the Destination Option positioned before the SRH is used, or the
SRH AltMark TLV is used, then only the segment end points endpoints will process
the AltMark data.

Both [RFC9343] and the approach specified in this document can co-
exist.
coexist. Indeed, this document does not change or invalidate any
procedures defined in [RFC9343]. However, deployment issues may
arise, as further discussed below.

The rest of this document is structured as follows:

* Section 2 covers the application of the Alternate Marking Alternate-Marking Method
to SRv6,

* Section 3 specifies the AltMark SRH TLV to carry the base data
fields (Section 3.1) and the extended data fields (Section 3.2),

* Section 4 discusses the use of the AltMark TLV, and

* Section 5 describes the experiment and the objectives of the
experimentation (Section 5.1).

1.2. 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. Application of the Alternate Marking Alternate-Marking Method to SRv6

SRv6 leverages the IPv6 SRH, that which can embed TLVs to provide metadata
for segment processing, as described in [RFC8754]. This document
defines the SRH AltMark TLV to carry Alternate Marking Alternate-Marking data fields
for use in SRv6 networks networks, and it is an alternative to the method
described in [RFC9343]. [RFC9343] defines how the Alternate Marking Alternate-Marking
Method can be carried in the Option Headers (Hop-by-hop (Hop-by-Hop or
Destination) of an IPv6 packet. The AltMark data fields format
defined in [RFC9343] is the basis of the AltMark SRH TLV introduced
in Section 3.

In addition to the base data fields of [RFC9343], it is also allowed
the insertion of optional extended data fields which that are not present
in [RFC9343]. These extended data fields can support metadata for
additional telemetry requirements, as further described below.

2.1. Controlled Domain

[RFC8799] introduces the concept of specific limited domain solutions
and notes the application of the Alternate Marking Alternate-Marking Method as an
example.

Despite the flexibility of IPv6, when innovative applications are
proposed
proposed, they are often applied within controlled domains to help
constrain the domain-wide policies, options supported, the style of
network management, and security requirements. This is also the case
for applying the application of the Alternate Marking Alternate-Marking Method to SRv6.

Therefore, the experimentation of the Alternate Marking Alternate-Marking Method to
SRv6 MUST be deployed only within a controlled domain. For SRv6, the
controlled domain corresponds to an SR domain, as defined in
[RFC8402]. The Alternate-Marking measurement domain overlaps with
the controlled domain.

The use of a controlled domain is also appropriate for the deployment
of an experimental protocol extension. Carefully bounding the domain
reduces the risk of the experiment leaking out and clashing with
other experiments of causing unforeseen consequences in wider
deployments.

3. Definition of the SRH AltMark TLV

The AltMark SRH TLV is defined to carry the data fields associated
with the Alternate Marking Alternate-Marking Method. The TLV has some initial fields
that are always present, present and further extension fields that are present
when Enhanced Alternate Marking is in use.

Figure 1 shows the format of the AltMark TLV.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| SRH TLV Type | SRH TLV Len | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FlowMonID |L|D| Reserved | NH |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Optional extended data fields (variable) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 1: AltMark: The AltMark SRH TLV for alternate marking Alternate Marking

The fields of this TLV are as follows:

SRH TLV Type: 8 bit The 8-bit identifier of the Alternate Marking Alternate-Marking SRH TLV.
The value for this field is taken from the range 124-126. It is
an Experimental code point that indicates a TLV that does not
change en route. Experimentation of this document must coordinate
the value used by all implementations participating in the
experiment. Therefore, experiments should carefully consider any
other implementations running in the controlled domain to avoid
clashes with other SRH TLVs.

SRH TLV Len: The length of the Data Fields of this TLV in bytes.
This is set to 6 when Enhanced Alternate Marking is not in use.

Reserved: Reserved for future use. These bits MUST be set to zero
on transmission and ignored on receipt.

FlowMonID: The Flow Monitoring Identification field, 20 bits unsigned
integer. field. It is a 20-bit
unsigned integer as defined in [RFC9343].

L: The Loss flag, as defined in [RFC9343].

D: The Delay flag, as defined in [RFC9343].

NH: The NH (NextHeader) field NextHeader field. It is used to indicate extended data
fields are present to support Enhanced Alternate Marking as
follows:

* NextHeader value of 0x0 means that there is no extended data
field attached.

* NextHeader values of 0x1-0x8 are reserved for further usage.

* NextHeader value of 0x9 indicates the extended data fields are
present as described in Section 3.2.

* NextHeader values of 0xA-0xF are reserved for further usage.

Optional extended data fields may be present according to the setting
of the NH field and as described in Section 3.2.

3.1. Base Alternate Marking Alternate-Marking Data Fields

The base AltMark data fields are: the Loss Flag (L), (L) flag, the Delay Flag (D)
flag, and the Flow Monitoring Identification field (FlowMonID), (FlowMonID) field, as in
[RFC9343].

L and D are the marking fields of the Alternate Marking Method Alternate-Marking Method, while
FlowMonID is used to identify monitored flows and aids the
optimization of implementation and scaling of the Alternate Marking Alternate-Marking
Method. Note that, as already highlighted in [RFC9343], the
FlowMonID is used to identify the monitored flow because it is not
possible to utilize the Flow Label field of the IPv6 Header.

It is important to note that if the 20 bit 20-bit FlowMonID is set by the
domain entry nodes, there is a chance of collision even when the
values are chosen using a pseudo-random pseudorandom algorithm; therefore therefore, it may
be
not be sufficient to uniquely identify a monitored flow. In such
cases
cases, the packets need to be tagged with additional flow information
to allow disambiguation. Such additional tagging can be carried in
the extended data fields described in Section 3.2.

3.2. Optional Extended Data Fields for Enhanced Alternate Marking

The optional extended data fields to support Enhanced Alternate
Marking are illustrated in Figure 2. They are present when the NH
field of the AltMark TLV is set to 0x9.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| FlowMonID Ext |M|F|W|R| Len | Rsvd |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MetaInfo | Optional MetaData ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
~ Optional MetaData (variable) ~
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 2: Optional Extended Data Fields for Enhanced Alternate
Marking

The extended data fields are as follows:

FlowMonID Ext - 20 bits Ext: 20-bit unsigned integer. This is integer used to extend the FlowMonID
in order to reduce the conflict when random allocation is applied.
The disambiguation of the FlowMonID field is discussed in IPv6 AltMark Option "IPv6
Application of the Alternate-Marking Method" [RFC9343].

Four bit-flags different bit flags indicate special-purpose usage.

M bit: Measurement mode. If M=0, it indicates that it is for
segment-by-segment monitoring. If M=1, it indicates that it is
for end-to-end monitoring.

F bit: Fragmentation. If F=1, it indicates that the original
packet is fragmented, therefore fragmented; therefore, it is necessary to only count
a single packet, ignoring all the following fragments with F
set to 1. Note that F is set to 0 for the first fragment.

W bit: Flow direction identification. This flag is used if
backward direction flow monitoring is requested to be set up
automatically, so that the egress node is instructed to setup
the backward flow monitoring. If W=1, it indicates that the
flow direction is forward. If W=0, it indicates that the flow
direction is backward.

R bit: Reserved. This bit MUST be set to zero and ignored on
receipt.

* Len -

Len: Length. Indicates the length of the extended data fields in
bytes for enhanced alternate marking. Enhanced Alternate Marking. It includes all of the
fields shown in Figure 2 including any meta data metadata that is present.

* Rsvd -

Rsvd: Reserved for further use. These bits MUST be set to zero on
transmission and ignored on receipt.

* MetaInfo -

MetaInfo: A 16-bit Bitmap to indicate more meta data metadata attached in the
Optional MetaData field for enhanced functions. More than one bit
may be set, in which case the additional meta data metadata is present in
the order that the bits are set. MetaInfo bits are numbered from
0 as the most significant bit. Three bits and associated
meta data metadata
are defined as follows:

bit 0: If set to 1, it indicates that a 6 byte 6-byte Timestamp is
present as shown 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp(s) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp(ns) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 3: The Timestamp Extended Data Field

This Timestamp can be filled by the encapsulation node, node and is
taken all the way to the decapsulation node so that all the
intermediate nodes can compare it against their local time, time and
measure the one way one-way delay. The timestamp Timestamp consists of two
fields:

Timestamp(s) is a 16 bit

Timestamp(s): A 16-bit integer that carries the number of
seconds.

Timestamp(ns) is a 32 bit

Timestamp(ns): A 32-bit integer that carries the number of
nanoseconds.

Note that the timestamp Timestamp data field enables all the intermediate
nodes to measure the one way one-way delay. It can be correlated with
the implementation of [I-D.ietf-opsawg-ipfix-on-path-telemetry] [IPFIX] and [I-D.ietf-ippm-on-path-telemetry-yang].
[I-D.ietf-opsawg-ipfix-on-path-telemetry] [YANG-TELEMETRY]. [IPFIX]
introduces new IP Flow Information Export (IPFIX) information
elements to expose the On-Path Telemetry measured delay, similarly,
[I-D.ietf-ippm-on-path-telemetry-yang] delay.
Similarly, [YANG-TELEMETRY] defines a YANG data model for
monitoring On-Path Telemetry data, including the path delay.

bit 1: If set to 1, it indicates the control information to set
up the backward direction flow monitoring based on the trigger
packet presence as shown in Figure 4.

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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| DIP Mask | SIP Mask |P|I|O|V|S|T| Period |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 4: Control Information for Backward Direction Flow
Monitoring

The control information includes several fields and flags to
match in order to set up the backward direction:

DIP Mask: The length of the destination IP prefix used to
match the flow.

SIP Mask: The length of the source IP prefix used to match the
flow.

P bit: If set to 1, it indicates to match the flow using the
protocol identifier in the trigger packet.

I bit: If set to 1, it indicates to match the source port.

O bit: If set to 1, it indicates to match the destination
port.

V bit: If set to 1, the node will automatically set up reverse
direction monitoring, monitoring and allocate a FlowMonID.

S bit: If set to 1, it indicates to match the DSCP. Differentiated
Services Code Point (DSCP).

T bit: Used to control the scope of tunnel measurement. T=1
means measure between Network-to-Network Interfaces (i.e.,
NNI to NNI). T=0 means measure between User-to-Network
Interfaces (i.e., UNI to UNI).

Period: Indicates the alternate marking Alternate-Marking period counted in
seconds.

bit 2: If set to 1, it indicates that a 4 byte sequence number 4-byte Sequence Number is
present as shown in 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+

Figure 5: Sequence Number Data Field

The unique Sequence Number can be used to detect the out-of-
order packets, in addition to enabling packet loss measurement.
Moreover, the Sequence Number can be used together with the
latency measurement, measurement to access per packet timestamps. per-packet Timestamps.

4. Use of the SRH AltMark TLV

Since the measurement domain is congruent with the SR controlled SR-controlled
domain, the procedure for AltMark data encapsulation in the SRv6 SRH
is summarized as follows:

* Ingress SR Node: As part of the SRH encapsulation, the Ingress SR
Node of an SR domain or an SR Policy [RFC9256] that supports the
mechanisms defined in this document and that wishes to perform the
Alternate Marking
Alternate-Marking Method adds the AltMark TLV in the SRH of the
data packets.

* Intermediate SR Node: The Intermediate SR Node is any node
receiving an IPv6 packet where the destination address of that
packet is a local Segment Identifier (SID). If an Intermediate SR
Node is not capable of processing the AltMark TLV, it simply
ignores it according to the processing rules of [RFC8754]. If an
Intermediate SR Node is capable of processing the AltMark TLV, it
checks if the SRH AltMark TLV is present in the packet and
processes it.

* Egress SR Node: The Egress SR Node is the last node in the segment
list of the SRH. The processing of AltMark TLV at the Egress SR
Node is the same as the processing of AltMark TLV at the
Intermediate SR Nodes.

The use of the AltMark TLV may be combined with the network
programming capability of SRv6 ([RFC8986]). [RFC8986]. Specifically, the ability
for an SRv6 endpoint to determine whether to process or ignore some
specific SRH TLVs (such as the AltMark TLV) may be based on the SID
function associated with the SID advertised by an Intermediate or
Egress SR Node and used in the Destination Address field of the SRv6
packet. When a packet is addressed to a SID which that does not support
the Alternate Marking Alternate-Marking functionality, the receiving node does not have
to look for or process the SRH AltMark TLV and can simply ignore it.
This also enables collection of Alternate Marking Alternate-Marking data only from the
supporting segment endpoints.

4.1. Compatibility

As highlighted in Section 1.1, the use of the Destination Option to
carry the AltMark data preceding the SRH is equivalent to the SRH
AltMark TLV. Therefore, it is important to analyze what happens when
both the SRH AltMArk AltMark TLV and the Destination Option are present, and
how that would impact processing and complexity.

It is worth mentioning that the SRH AltMark TLV and the the Destination
Option carrying AltMark data can coexist without problems. If both
are present, the only issue could be the duplication of information information,
but this will not affect in any way the device and the network
services. The security requirement of controlled domain applies to
both this document and [RFC9343], and it also confines this
duplication to a single service provider networks. However,
duplication of the same information in different places should be avoided
avoided, and it is recommended to only analyze the use of the SRH
AltMark TLV for the experimentation.

5. Experimentation Overview

The protocol extension, extension described in this document, document is built on
existing technology using an Experimental code point.
Experimentation of this document must use a code point chosen from
the Experimental range, as noted in Section 3, and should make it
possible for the operator to configure the value used in a deployment
such that it is possible to conduct multiple non-conflicting
experiments within the same network.

This experiment aims to determine whether or not the use of the SRH
AltMark TLV brings advantages, in particular particular, in consideration of
implementations that cannot support multiple IPv6 extension headers
in the same packet, or which do not support Destination Options
Header processing, or which process the Destination Options Header on
the slow path.

This experiment also needs to determine whether the proposed protocol
extensions achieve the desired function and can be supported in the
presence of normal SRv6 processing. In particular, the experiment
needs to verify the ability to support SR network programming, SID
function control control, and the support or non-support of the AltMark TLV.

It is anticipated that this experiment will be contained within a
single service provider network in keeping with the constraints of an
SR Domain, domain, and also in keeping with the limits in sharing performance
monitoring data collected on the path of packets in the network. The
scope of the experimental deployment may depend on the availability
of implementations and the willingness of operators to deploy it on
live networks.

The results of this experiment will be collected and shared with the
RFC Editor for consideration as independent submission an Independent Submission or with the
IETF SPRING working group Working Group as an Internet-Draft, to help forward the
discussions that will determine the correct development of Alternate Alternate-
Marking Method solutions in SRv6 networks. It is expected that a
first set of
initial results will be made available within two years of the
publication of this document as an RFC.

5.1. Objective of the Experiment

Researchers are invited to evaluate the SRH AltMark TLV against the
existing approach in [RFC9343]. There are several potential areas of
exploration for this experimentation that need to be analyzed:

* Does the use of the SRH AltMark TLV survive across a network
better or worse than the use of an extension headers usage? header?

* Does the SRH TLV processing represent a performance improvement or
hindrance on the device as compared to the Destination Option?

* Is the forwarding plane performance impacted across different
device architecture types comparing compared to the use of the SRH TLV and
Destination Option?

* How does the use of the extended data fields, introduced in
Section 3.2, compare to other on path on-path telemetry methods from the
point of view of the operators?

6. Security Considerations

The security considerations of SRv6 are discussed in [RFC8754] and
[RFC8986], and the security considerations of Alternate Marking in
general and its application to IPv6 are discussed in [RFC9341] and
[RFC9343].

[RFC9343] analyzes different security concerns and related solutions.
These aspects are valid and applicable also to this document. In
particular
particular, the fundamental security requirement is that Alternate
Marking MUST only be applied in a limited domain, as also mentioned
in [RFC8799] and Section 2.1.

Alternate Marking is a feature applied to a trusted domain, where a
single operator decides on leveraging and configuring Alternate
Marking according to their needs. Additionally, operators need to
properly secure the Alternate Marking Alternate-Marking domain to avoid malicious
configuration and attacks, which could include injecting malicious
packets into a domain. So Therefore, the implementation of Alternate
Marking is applied within a controlled domain where the network nodes
are locally administered and where packets containing the AltMark TLV
are prevented from entering or leaving the domain. A limited
administrative domain provides the network administrator with the
means to select, monitor monitor, and control the access to the network.

7. IANA Considerations

This document makes has no requests for IANA actions.

8. Acknowledgements

The authors would like to thank Eliot Lear, Adrian Farrel, Joel M.
Halpern and Haoyu Song for the precious comments and suggestions.

9. Contributors

The following people provided relevant contributions to this
document:

Fabio Bulgarella
Telecom Italia
Email: fabio.bulgarella@guest.telecomitalia.it

Massimo Nilo
Telecom Italia
Email: massimo.nilo@telecomitalia.it

Fabrizio Milan
Telecom Italia
Email: fabrizio.milan@telecomitalia.it

10. References

10.1.

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,
<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,
May 2017, <https://www.rfc-editor.org/info/rfc8174>.

[RFC8402] Filsfils, C., Ed., Previdi, S., Ed., Ginsberg, L.,
Decraene, B., Litkowski, S., and R. Shakir, "Segment
Routing Architecture", RFC 8402, DOI 10.17487/RFC8402,
July 2018, <https://www.rfc-editor.org/info/rfc8402>.

[RFC9341] Fioccola, G., Ed., Cociglio, M., Mirsky, G., Mizrahi, T.,
and T. Zhou, "Alternate-Marking Method", RFC 9341,
DOI 10.17487/RFC9341, December 2022,
<https://www.rfc-editor.org/info/rfc9341>.

[RFC9342] Fioccola, G., Ed., Cociglio, M., Sapio, A., Sisto, R., and
T. Zhou, "Clustered Alternate-Marking Method", RFC 9342,
DOI 10.17487/RFC9342, December 2022,
<https://www.rfc-editor.org/info/rfc9342>.

[RFC9343] Fioccola, G., Zhou, T., Cociglio, M., Qin, F., and R.
Pang, "IPv6 Application of the Alternate-Marking Method",
RFC 9343, DOI 10.17487/RFC9343, December 2022,
<https://www.rfc-editor.org/info/rfc9343>.

10.2.

8.2. Informative References

[I-D.bonica-gendispatch-exp]
Bonica, R. and A. Farrel, "IETF Experiments", Work in
Progress, Internet-Draft, draft-bonica-gendispatch-exp-06,
22 July 2025, <https://datatracker.ietf.org/doc/html/
draft-bonica-gendispatch-exp-06>.

[I-D.ietf-6man-eh-limits]

[EH-LIMITS]
Herbert, T., "Limits on Sending and Processing IPv6
Extension Headers", Work in Progress, Internet-Draft,
draft-ietf-6man-eh-limits-19, 27 February 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-6man-eh-
limits-19>.

[I-D.ietf-ippm-on-path-telemetry-yang]
Fioccola, G., Zhou, T., Zhu, Y., Zhang, W.,

[IETF-EXPERIMENTS]
Bonica, R. and K. Zhu,
"On-Path Telemetry YANG Data Model", A. Farrel, "IETF Experiments", Work in
Progress, Internet-Draft, draft-ietf-ippm-on-path-telemetry-yang-01,
2 July 2025, <https://datatracker.ietf.org/doc/html/draft-
ietf-ippm-on-path-telemetry-yang-01>.

[I-D.ietf-opsawg-ipfix-on-path-telemetry] draft-bonica-gendispatch-exp-07,
19 January 2026, <https://datatracker.ietf.org/doc/html/
draft-bonica-gendispatch-exp-07>.

[IPFIX] Graf, T., Claise, B., and A. H. Feng, "Export of Delay
Performance Metrics in IP Flow Information eXport
(IPFIX)", Work in Progress, Internet-Draft, draft-ietf-
opsawg-ipfix-on-path-telemetry-20, 23 July
opsawg-ipfix-on-path-telemetry-23, 30 September 2025,
<https://datatracker.ietf.org/doc/html/draft-ietf-opsawg-
ipfix-on-path-telemetry-20>.
ipfix-on-path-telemetry-23>.

[RFC8200] Deering, S. and R. Hinden, "Internet Protocol, Version 6
(IPv6) Specification", STD 86, RFC 8200,
DOI 10.17487/RFC8200, July 2017,
<https://www.rfc-editor.org/info/rfc8200>.

[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.

[RFC8799] Carpenter, B. and B. Liu, "Limited Domains and Internet
Protocols", RFC 8799, DOI 10.17487/RFC8799, July 2020,
<https://www.rfc-editor.org/info/rfc8799>.

[RFC8986] Filsfils, C., Ed., Camarillo, P., Ed., Leddy, J., Voyer,
D., Matsushima, S., and Z. Li, "Segment Routing over IPv6
(SRv6) Network Programming", RFC 8986,
DOI 10.17487/RFC8986, February 2021,
<https://www.rfc-editor.org/info/rfc8986>.

[RFC9098] Gont, F., Hilliard, N., Doering, G., Kumari, W., Huston,
G., and W. Liu, "Operational Implications of IPv6 Packets
with Extension Headers", RFC 9098, DOI 10.17487/RFC9098,
September 2021, <https://www.rfc-editor.org/info/rfc9098>.

[RFC9256] Filsfils, C., Talaulikar, K., Ed., Voyer, D., Bogdanov,
A., and P. Mattes, "Segment Routing Policy Architecture",
RFC 9256, DOI 10.17487/RFC9256, July 2022,
<https://www.rfc-editor.org/info/rfc9256>.

[YANG-TELEMETRY]
Fioccola, G., Zhou, T., Zhu, Y., Zhang, W., and K. Zhu,
"On-Path Telemetry YANG Data Model", Work in Progress,
Internet-Draft, draft-ietf-ippm-on-path-telemetry-yang-02,
2 January 2026, <https://datatracker.ietf.org/doc/html/
draft-ietf-ippm-on-path-telemetry-yang-02>.

Acknowledgements

The authors would like to thank Eliot Lear, Adrian Farrel, Joel
M. Halpern, and Haoyu Song for the precious comments and suggestions.

Contributors

The following people provided relevant contributions to this
document:

Fabio Bulgarella
Telecom Italia
Email: fabio.bulgarella@guest.telecomitalia.it

Massimo Nilo
Telecom Italia
Email: massimo.nilo@telecomitalia.it

Fabrizio Milan
Telecom Italia
Email: fabrizio.milan@telecomitalia.it

Authors' Addresses

Giuseppe Fioccola
Huawei
Viale Martesana, 12
20055 Vimodrone (Milan)
Italy
Email: giuseppe.fioccola@huawei.com

Tianran Zhou
Huawei
156 Beiqing Rd.
Beijing
100095
China
Email: zhoutianran@huawei.com

Gyan S. Mishra
Verizon Inc.
Email: gyan.s.mishra@verizon.com

Xuewei Wang
Ruijie
Email: wangxuewei1@ruijie.com.cn

Geng Zhang
China Mobile
Email: zhanggeng@chinamobile.com

Mauro Cociglio
Email: mauro.cociglio@outlook.com