Performance Measurement Using Simple Two-Way Active Measurement Protocol (STAMP) for Segment Routing over the MPLS Data Plane
draft-ietf-spring-stamp-srpm-mpls-02
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| Authors | Rakesh Gandhi , Clarence Filsfils , Bart Janssens , Mach Chen , Richard "Footer" Foote | ||
| Last updated | 2026-06-30 (Latest revision 2026-04-02) | ||
| Replaces | draft-ietf-spring-stamp-srpm | ||
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draft-ietf-spring-stamp-srpm-mpls-02
SPRING Working Group R. Gandhi, Ed.
Internet-Draft C. Filsfils
Intended status: Informational Cisco Systems, Inc.
Expires: 1 January 2027 B. Janssens
Colt
M. Chen
Huawei
R. Foote
Nokia
30 June 2026
Performance Measurement Using Simple Two-Way Active Measurement Protocol
(STAMP) for Segment Routing over the MPLS Data Plane
draft-ietf-spring-stamp-srpm-mpls-02
Abstract
Segment Routing (SR) can be used to steer packets through a network
employing source routing. SR can be applied to both MPLS (SR-MPLS)
and IPv6 (SRv6) data planes. This document describes the procedures
for Performance Measurement in SR-MPLS networks using the Simple Two-
Way Active Measurement Protocol (STAMP), as defined in RFC 8762,
along with its optional extensions defined in RFC 8972 and further
augmented in RFC 9503. The described procedures are used for SR-MPLS
paths (including Segment Lists of SR-MPLS Policies, SR-MPLS IGP best
paths, and SR-MPLS IGP Flexible Algorithm paths), as well as Layer-3
and Layer-2 services over the SR-MPLS paths.
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 1 January 2027.
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Copyright Notice
Copyright (c) 2026 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 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 Revised BSD License text as
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provided without warranty as described in the Revised BSD License.
Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 4
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 4
2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. STAMP Reference Model . . . . . . . . . . . . . . . . . . 6
4. Two-Way Measurement Mode . . . . . . . . . . . . . . . . . . 8
4.1. Session-Sender Test Packet . . . . . . . . . . . . . . . 9
4.2. Session-Sender Test Packet for SR-MPLS Data Plane . . . . 10
4.2.1. Session-Sender Test Packet for SR-MPLS Paths . . . . 10
4.2.2. Session-Sender Test Packet for Layer-3 Services over
SR-MPLS Path . . . . . . . . . . . . . . . . . . . . 12
4.2.3. Session-Sender Test Packet for Layer-2 Services over
SR-MPLS Path . . . . . . . . . . . . . . . . . . . . 13
4.3. Session-Reflector Test Packet . . . . . . . . . . . . . . 13
5. One-Way Measurement Mode . . . . . . . . . . . . . . . . . . 14
5.1. STAMP Reference Model Considerations for One-Way
Measurement Mode . . . . . . . . . . . . . . . . . . . . 15
6. Loopback Measurement Mode . . . . . . . . . . . . . . . . . . 16
6.1. STAMP Reference Model Considerations for Loopback
Measurement Mode . . . . . . . . . . . . . . . . . . . . 16
6.2. Loopback Measurement Mode for SR-MPLS Paths . . . . . . . 18
6.2.1. SR-MPLS Return Path . . . . . . . . . . . . . . . . . 20
6.2.2. IP Return Path . . . . . . . . . . . . . . . . . . . 20
6.3. Loopback Measurement Mode for Layer-3 Services over SR-MPLS
Path . . . . . . . . . . . . . . . . . . . . . . . . . . 20
6.3.1. SR-MPLS Return Path . . . . . . . . . . . . . . . . . 22
6.3.2. IP Return Path . . . . . . . . . . . . . . . . . . . 22
6.4. Loopback Measurement Mode for Layer-2 Services over SR-MPLS
Path . . . . . . . . . . . . . . . . . . . . . . . . . . 22
6.4.1. SR-MPLS Return Path . . . . . . . . . . . . . . . . . 23
6.4.2. IP Return Path . . . . . . . . . . . . . . . . . . . 23
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7. Loopback Measurement Mode with Timestamp and Forward . . . . 24
7.1. Loopback Measurement Mode with Timestamp and Forward
Network Action for SR-MPLS Data Plane . . . . . . . . . . 25
7.1.1. Timestamp and Forward Network Action Assignment and
Node Capability . . . . . . . . . . . . . . . . . . . 26
8. Packet Loss Measurement in SR-MPLS Networks . . . . . . . . . 26
9. Direct Measurement in SR-MPLS Networks . . . . . . . . . . . 27
10. ECMP Measurement in SR-MPLS Networks . . . . . . . . . . . . 27
11. STAMP Session State . . . . . . . . . . . . . . . . . . . . . 28
12. Additional STAMP Test Packet Processing Rules . . . . . . . . 28
12.1. TTL . . . . . . . . . . . . . . . . . . . . . . . . . . 29
12.2. IPv6 Hop Limit . . . . . . . . . . . . . . . . . . . . . 29
12.3. Router Alert Option . . . . . . . . . . . . . . . . . . 29
12.4. IPv6 Flow Label . . . . . . . . . . . . . . . . . . . . 29
12.5. UDP Checksum . . . . . . . . . . . . . . . . . . . . . . 29
13. Implementation Status . . . . . . . . . . . . . . . . . . . . 29
13.1. Cisco Implementation . . . . . . . . . . . . . . . . . . 30
14. Operational and Manageability Considerations . . . . . . . . 30
15. Security Considerations . . . . . . . . . . . . . . . . . . . 30
16. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 31
17. References . . . . . . . . . . . . . . . . . . . . . . . . . 31
17.1. Normative References . . . . . . . . . . . . . . . . . . 31
17.2. Informative References . . . . . . . . . . . . . . . . . 32
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 34
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . 34
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 34
1. Introduction
Segment Routing (SR) [RFC8402] can be used to steer packets through a
network employing source routing. SR can be applied to both MPLS
(SR-MPLS) and IPv6 (SRv6) data planes. SR takes advantage of Equal-
Cost Multipath (ECMP) between source and transit nodes, between
transit nodes, and between transit and destination nodes. SR
Policies, as defined in [RFC9256], are used to steer traffic through
specific user-defined paths using a list of segments.
A comprehensive SR Performance Measurement toolset is an essential
requirement for measuring network performance to provide Service
Level Agreements (SLAs).
The Simple Two-Way Active Measurement Protocol (STAMP), as specified
in [RFC8762], provides capabilities for measuring various performance
metrics in IP networks without the use of a control channel to pre-
signal session parameters. [RFC8972] defines optional extensions in
the form of TLVs for STAMP. [RFC9503] further augments that
framework to define STAMP extensions for SR networks.
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This document describes the procedures for Performance Measurement in
SR-MPLS networks, using STAMP as defined in [RFC8762], along with its
optional extensions defined in [RFC8972] and augmented in [RFC9503].
The described procedures are used for SR-MPLS paths [RFC8402]
(including Segment Lists of SR-MPLS Policies [RFC9256], SR-MPLS IGP
best paths, and Flexible Algorithm (Flex-Algo) paths [RFC9350]), as
well as Layer-3 (L3) and Layer-2 (L2) services over the SR-MPLS
paths.
STAMP requires protocol support on the Session-Reflector to process
the received test packets. As a result, the received test packets
need to be punted from the fast path in the data plane, and return
test packets need to be generated. This limits the frequency of
STAMP test packets and the ability to provide faster measurement
intervals. This document adds new mechanisms to enhance the
procedures for Performance Measurement using STAMP to improve the
scalability of the number of STAMP sessions and the measurement
interval for SR-MPLS paths by defining new measurement modes: one-
way, loopback, and loopback with "timestamp and forward."
2. Conventions Used in This Document
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
ECMP: Equal Cost Multi-Path.
HMAC: Hashed Message Authentication Code.
I2E: Ingress-To-Egress.
IHS: Ingress-To-Egress, Hop-By-Hop or Select Scope.
L2: Layer-2.
L3: Layer-3.
LSE: Label Stack Entry.
MBZ: Must be Zero.
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MNA: MPLS Network Action.
MPLS: Multiprotocol Label Switching.
PSID: Path Segment Identifier.
SHA: Secure Hash Algorithm.
SID: Segment ID.
SR: Segment Routing.
SR-MPLS: Segment Routing with MPLS data plane.
SSID: STAMP Session Identifier.
STAMP: Simple Two-Way Active Measurement Protocol.
TC: Traffic Class.
TSF: Timestamp and Forward.
TTL: Time-To-Live.
VPN: Virtual Private Network.
3. Overview
For performance measurement in SR-MPLS networks, the STAMP Session-
Sender and Session-Reflector use the STAMP test packets defined in
[RFC8762], along with optional extensions defined in [RFC8972]. The
STAMP test packets are encapsulated using an IP/UDP header, as
specified in [RFC8762]. In this document, the STAMP test packets
using the IP/UDP header are used for SR-MPLS networks, where the
STAMP test packets are further encapsulated with an MPLS header.
STAMP test packets are transmitted in performance measurement modes,
including two-way, one-way, loopback, and loopback with "timestamp
and forward" in SR-MPLS networks. Note that the two-way measurement
mode is referenced in the STAMP process in [RFC8762] and is further
described for SR-MPLS networks in this document. The other
measurement modes, which are new and specifically described for SR-
MPLS networks in this document, are not defined by the STAMP process
in [RFC8762].
STAMP test packets are transmitted on the same path as the data
traffic flow under measurement to measure the delay and packet loss
experienced by the data traffic flow, using the same SR-MPLS
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encapsulation as the data traffic flow. Similarly, STAMP test
packets are transmitted on various transport data paths in the
network to measure the delay and packet loss experienced by the
traffic forwarded on those transport data paths. The STAMP test
packets carry the same MPLS headers as the data packets transmitted
on the SR-MPLS path and on the L3 and L2 services for the data
traffic forwarded on those services.
Typically, STAMP Session-Reflector test packets are transmitted along
an IP path between the Session-Reflector and Session-Sender.
Matching the forward direction path and the return path for STAMP
test packets, even for directly connected nodes, is not guaranteed.
In SR-MPLS networks, it may be desired that the same path (i.e., the
same set of links and nodes) between the Session-Sender and Session-
Reflector be used for the STAMP test packets in both directions, for
example, in an ECMP environment.
In two-way measurement mode, this is achieved by using the optional
STAMP extensions for SR-MPLS, as specified in [RFC9503]. The STAMP
Session-Reflector uses the return path parameters for the Session-
Reflector test packet from the STAMP extensions in the received
Session-Sender test packet, as described in [RFC9503]. In loopback
measurement mode, this is achieved by adding both the forward
direction path and the return path in the SR-MPLS encapsulation of
the Session-Sender test packets.
The performance measurement procedures defined in this document are
used to measure both delay and packet loss in SR-MPLS networks based
on the transmission and reception of STAMP test packets. The
optional STAMP extensions, as defined in [RFC8972], are used for
direct measurement in SR-MPLS networks.
3.1. STAMP Reference Model
The STAMP Reference Model, along with some typical measurement
parameters, as defined in [RFC8972] for a STAMP session, is shown in
Figure 1.
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+------------+
| SDN |
| Controller |
+------------+
/ \
Performance Measurement Mode / \ Stateful or Stateless
Destination UDP Port / \ Destination UDP Port
Authentication Mode / \ Authentication Mode
Keychain / \ Keychain
Timestamp Format / \ Timestamp Format
SSID / \ SSID (Stateful)
Metric Type / \
v v
+-------+ +-------+
| | STAMP | |
| S1 |==========| R1 |
| | Session | |
+-------+ +-------+
STAMP Session-Sender STAMP Session-Reflector
Figure 1: STAMP Reference Model
The procedure defined in [RFC8972] uses the two-way measurement mode.
The destination UDP port number is selected for the STAMP function as
described in [RFC8762]. By default, the reflector UDP port 862 is
selected as the destination UDP port for STAMP sessions [RFC8762] for
SR-MPLS paths, and for L3 and L2 services over the SR-MPLS paths.
The source UDP port is selected by the Session-Sender. The same or
different source UDP ports may be used for different STAMP sessions.
Session-Reflector mode can be either Stateful or Stateless, as
described in Section 4 of [RFC8762]. Stateless Session-Reflector
mode is applicable only in two-way measurement mode.
The SSID field in the STAMP test packets [RFC8972], along with the
local configuration for the performance measurement mode, is used to
identify the STAMP sessions.
When authentication mode is enabled for STAMP sessions, the matching
Authentication Type (e.g., HMAC-SHA-256) and Keychain must be
configured on both the Session-Sender and Session-Reflector
[RFC8762].
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Examples of the Timestamp Format include 64-bit truncated Precision
Time Protocol (PTPv2) [IEEE.1588] and 64-bit Network Time Protocol
(NTPv4) [RFC5905]. By default, the Session-Reflector replies using
the same timestamp format as received in the Session-Sender test
packet, as indicated by the "Z" flag in the Error Estimate field, as
described in [RFC8762]. This behaviour can be based on the Session-
Reflector's capability.
The destination IP address in the STAMP test packets with SR-MPLS
encapsulation is chosen as described in [I-D.ietf-mpls-stamp-pw].
Examples of Delay Metrics are one-way delay, round-trip delay, near-
end delay (forward direction), and far-end delay (backward
direction), as defined in [RFC8762].
Examples of Packet Loss Metric Types are round-trip packet loss,
near-end packet loss (forward direction) and far-end packet loss
(backward direction), as defined in [RFC8762].
A Software-Defined Networking (SDN) controller can be used for the
configuration and management of STAMP sessions, as described in
[RFC8762]. The controller can also receive streaming telemetry of
operational data. The YANG data model for STAMP, defined in
[I-D.ietf-ippm-stamp-yang], can be used to configure Session-Senders
and Session-Reflectors and to stream telemetry of operational data.
4. Two-Way Measurement Mode
As shown in Figure 2, in the reference topology for two-way
measurement mode, the STAMP Session-Sender S1 initiates a STAMP
Session-Sender test packet, and the STAMP Session-Reflector R1
generates and transmits a reply Session-Reflector test packet. The
Session-Reflector test packets are transmitted to the STAMP Session-
Sender S1 on the same path (i.e., the same set of links and nodes) or
on a different path in the reverse direction from the path taken
towards the Session-Reflector R1.
T1 is a transmit timestamp, and T4 is a receive timestamp added by
node S1. T2 is a receive timestamp, and T3 is a transmit timestamp
added by node R1. All four timestamps are used by the Session-Sender
to measure the round-trip delay metric as ((T4 - T1) - (T3 - T2)).
Timestamps T1 and T2 are used by the Session-Sender to measure the
one-way delay metric as (T2 - T1), also referred to as the near-end
(forward direction) delay metric. Note that the delay value (T4 -
T3), measured by the Session-Sender, is referred to as the far-end
(backward direction) one-way delay metric.
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The computation of the one-way delay metric requires the clocks on
the Session-Sender and Session-Reflector to be synchronized using
either PTPv2 or NTPv4.
T1 T2
/ \
+-------+ Test Packet +-------+
| | - - - - - - - - - ->| |
| S1 |=====================| R1 |
| |<- - - - - - - - - - | |
+-------+ Reply Test Packet +-------+
\ /
T4 T3
STAMP Session-Sender STAMP Session-Reflector
Figure 2: Reference Topology for Two-Way Measurement Mode
The nodes S1 and R1 may be connected via an SR-MPLS path [RFC8402].
The SR-MPLS path may be a Segment List (i.e., a stack of MPLS labels)
of an SR-MPLS Policy [RFC9256] on node S1 (referred to as the "head-
end") with a destination to node R1 (referred to as the "endpoint"),
an SR-MPLS IGP best path, or an SR-MPLS IGP Flex-Algo path [RFC9350].
Additionally, a Layer-3 (L3) or Layer-2 (L2) VPN service may be
carried over the SR-MPLS path between nodes S1 and R1.
4.1. Session-Sender Test Packet
The content of a Session-Sender test packet is shown in Figure 3.
The payload containing the Session-Sender test packet, as defined in
Section 3 of [RFC8972], is transmitted with an IP and UDP header
[RFC0768].
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+---------------------------------------------------------------+
| IP Header |
. Source IP Address = Session-Sender IP Address .
. Destination IP Address = Session-Reflector IP Address .
. IPv4 Protocol or IPv6 Next-header = 17 (UDP) .
. .
+---------------------------------------------------------------+
| UDP Header |
. Source Port = Chosen by Session-Sender .
. Destination Port = User-configured Destination Port | 862 .
. .
+---------------------------------------------------------------+
| Payload = Test Packet as specified in Section 3 of RFC 8972 |
. in Figures 1 and 3 .
. .
+---------------------------------------------------------------+
Figure 3: Content of Session-Sender Test Packet
4.2. Session-Sender Test Packet for SR-MPLS Data Plane
4.2.1. Session-Sender Test Packet for SR-MPLS Paths
An SR-MPLS Policy Candidate-Path contains one or more Segment Lists
(i.e., a stack of MPLS labels) [RFC9256]. For delay measurement of
an SR-MPLS Policy, the Session-Sender test packets are transmitted
for every Segment List of the Candidate-Path of the SR-MPLS Policy,
by creating a separate STAMP session for each Segment List.
Each SR-MPLS Segment List contains a list of 32-bit Label Stack
Entries (LSE), where each LSE includes a 20-bit label value, an 8-bit
Time-To-Live (TTL) field, a 3-bit Traffic-Class (TC) field, and a
1-bit Bottom of Stack (S) field [RFC3032].
The content of a Session-Sender test packet for an SR-MPLS path,
using the SR-MPLS encapsulation of the data traffic transmitted over
the path, is shown in Figure 4.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label[1] (Top of Stack) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label[n] | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PSID (optional) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Test Packet as shown in Figure 3 |
. .
+---------------------------------------------------------------+
Figure 4: Content of Session-Sender Test Packet for SR-MPLS Path
The head-end node address of the SR-MPLS Policy is used as the Source
Address in the IP header of the Session-Sender test packet. The
endpoint address of the SR-MPLS Policy is used as the Destination
Address in the IP header of the Session-Sender test packet.
In the case of Penultimate Hop Popping (PHP), the MPLS header is
removed by the penultimate node. In this case, the Destination
Address in the IP header ensures that the test packets reach the
Session-Reflector at the SR-MPLS Policy endpoint.
In the case of an SR-MPLS Policy with Color-Only Destination
Steering, where the endpoint is an unspecified address (the null
endpoint is 0.0.0.0 for IPv4, as defined in Section 8.8.1 of
[RFC9256]), the loopback address from the range 127/8 for IPv4 is
used as the Destination Address in the IPv4 header of the Session-
Sender test packets as the Session-Reflector Address. In this case,
the SR-MPLS encapsulation ensures that the Session-Sender test
packets reach the SR-MPLS Policy endpoint, for example, by adding the
Prefix SID label of the SR-MPLS Policy endpoint to the Segment List.
In addition, the Session-Sender test packets carry the "Destination
Node IPv4 or IPv6 Address" STAMP TLV as defined in [RFC9503] to
identify the intended Session-Reflector IPv4 address.
The Path Segment Identifier (PSID) [RFC9545] of an SR-MPLS Policy
(for the Segment List or for the Candidate-Path) is added to the
Segment List of the STAMP test packets when the egress node supports
PSID processing.
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Each IGP Flex-Algo path in SR-MPLS networks [RFC9350] has Prefix SID
labels advertised by the nodes. For delay measurement of SR-MPLS IGP
Flex-Algo paths, the Session-Sender test packets carry the Flex-Algo
Prefix SID labels of the Session-Sender and Session-Reflector in the
MPLS header for that IGP Flex-Algo path under measurement.
Similarly, each IGP best path in SR-MPLS networks [RFC9350] has
Prefix SID labels advertised by the nodes. For delay measurement of
SR-MPLS IGP best paths, the Session-Sender test packets carry the IGP
Prefix SID labels of the Session-Sender and Session-Reflector in the
MPLS header for that IGP best path under measurement.
4.2.2. Session-Sender Test Packet for Layer-3 Services over SR-MPLS
Path
For delay measurement of the L3 service over an SR-MPLS path, the SR-
MPLS label stack of the data packets transmitted over the L3 service,
including the L3VPN label (advertised by the Session-Reflector), is
used to encapsulate the Session-Sender test packets, 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label[1] (Top of Stack) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L3VPN Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Test Packet as shown in Figure 3 |
. Destination IP Address in L3VPN table .
. Source IP Address in L3VPN table-reverse direction .
. .
+---------------------------------------------------------------+
Figure 5: Content of Session-Sender Test Packet for L3 Service
over SR-MPLS Path
An IP header, as shown in Figure 3, is added to the Session-Sender
test packets after the SR-MPLS encapsulation. The Destination
Address in the IP header is reachable via the IP table lookup
associated with the L3VPN label added for the L3 service on the
Session-Reflector. The Source Address in the IP header of the
Session-Sender test packets is reachable via the IP table lookup
associated with the L3 service in the reverse direction.
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4.2.3. Session-Sender Test Packet for Layer-2 Services over SR-MPLS
Path
For delay measurement of the L2 service over an SR-MPLS path, the SR-
MPLS label stack of the data packets transmitted over the L2 service,
including the L2VPN label (as advertised by the Session-Reflector),
is used to encapsulate the Session-Sender test packets, as shown in
Figure 6.
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label[1] (Top of Stack) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L2VPN Label | TC |1| TTL=1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Test Packet as shown in Figure 3 |
. .
+---------------------------------------------------------------+
Figure 6: Content of Session-Sender Test Packet for L2 Service
over SR-MPLS Path
The L2VPN label is added with a TTL value of 1 to punt the Session-
Sender test packet from the data plane to the CPU or the slow path on
the Session-Reflector for STAMP processing.
An IP header, as shown in Figure 3, is added to the Session-Sender
test packets after the MPLS header. This header contains the
Session-Sender Address as the Source Address and the Session-
Reflector Address as the Destination Address.
4.3. Session-Reflector Test Packet
In two-way measurement mode, the Session-Reflector test packets are
transmitted on the same SR-MPLS path (i.e., the same set of links and
nodes) in the reverse direction to the Session-Sender to perform
accurate two-way delay measurement.
The Session-Reflector decapsulates the MPLS header, if present, from
the received Session-Sender test packets. The Session-Reflector test
packet is generated using the information from the received IP/UDP
header of the Session-Sender test packet, as shown in Figure 7.
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+---------------------------------------------------------------+
| IP Header |
. Source IP Address .
. = Session-Reflector IP Address .
. Destination IP Address .
. = Source IP Address from Session-Sender Test Packet .
. IPv4 Protocol or IPv6 Next-header = 17 (UDP) .
. .
+---------------------------------------------------------------+
| UDP Header |
. Source Port = Chosen by Session-Reflector .
. Destination Port .
. = Source Port from Session-Sender Test Packet .
. .
+---------------------------------------------------------------+
| Payload = Test Packet as specified in Section 3 of RFC 8972 |
. in Figures 2 and 4 .
. .
+---------------------------------------------------------------+
Figure 7: Content of Session-Reflector Test Packet
The payload contains the Session-Reflector test packet defined in
Section 3 of [RFC8972].
For SR-MPLS paths, the Session-Sender uses the Segment List sub-TLV
in the Return Path TLV defined in [RFC9503] to request that the
Session-Reflector transmit the Session-Reflector test packet on a
specific SR-MPLS return path. Examples of specific SR-MPLS return
paths include: the reverse SR-MPLS path associated with the forward
direction SR-MPLS path, the Binding SID of the reverse SR-MPLS
Policy, or the Prefix SID of the Session-Sender.
For SR-MPLS IGP Flex-Algo paths, the Session-Sender uses the Segment
List sub-TLV in the Return Path TLV defined in [RFC9503] to request
that the Session-Reflector transmit the Session-Reflector test packet
on the same SR-MPLS IGP Flex-Algo path in the reverse direction.
5. One-Way Measurement Mode
As shown in Figure 8, in the reference topology for one-way
measurement mode, the STAMP Session-Sender S1 initiates a Session-
Sender test packet. The STAMP Session-Reflector does not transmit
Session-Reflector test packets upon receiving the Session-Sender test
packets.
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T1 is a transmit timestamp added by node S1, and T2 is a receive
timestamp added by node R1. Timestamps T1 and T2 are used by the
Session-Reflector to measure the one-way delay metric as (T2 - T1).
The computation of the one-way delay metric requires the clocks on
the Session-Sender and Session-Reflector to be synchronized using
either PTPv2 or NTPv4.
T1 T2
/ \
+-------+ Test Packet +-------+
| | - - - - - - - - - ->| |
| S1 |=====================| R1 |
| | | |
+-------+ +-------+
STAMP Session-Sender STAMP Session-Reflector
Figure 8: Reference Topology for One-Way Measurement Mode
5.1. STAMP Reference Model Considerations for One-Way Measurement Mode
In one-way measurement mode, for SR-MPLS paths and for L3 and L2
services over the SR-MPLS paths, the Session-Sender test packets, as
defined in Section 4 for STAMP sessions, are transmitted.
The Stateful mode of the Session-Reflector [RFC8762] is used as the
Session-Receiver in one-way measurement mode. The SSID field in the
received Session-Sender test packets [RFC8972] at the Session-
Reflector, along with the local configuration, is used to identify
the STAMP sessions that use one-way measurement mode on the Stateful
Session-Reflector.
Typically, a different destination UDP port is selected for one-way
measurement mode than the one used by the STAMP Session-Reflector for
two-way measurement mode. When the same STAMP Session-Reflector UDP
port is selected for one-way measurement mode, the Session-Sender
requests, in the test packets, that the Session-Reflector not
transmit Session-Reflector test packets. To achieve this, it uses
the "No Reply Requested" flag in the Control Code Sub-TLV within the
Return Path TLV defined in [RFC9503].
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6. Loopback Measurement Mode
As shown in Figure 9, in the reference topology for loopback
measurement mode, the STAMP Session-Sender S1 initiates a Session-
Sender test packet to measure the loopback delay of a bidirectional
path. At the STAMP Session-Reflector, the received Session-Sender
test packets are not punted out of the fast path in the data plane
(i.e., to the CPU or the slow path) but are simply forwarded. In
other words, the Session-Reflector does not perform STAMP functions
or generate Session-Reflector test packets.
T1
/
+-------+ Test Packet +-------+
| | - - - - - - - - - - | |
| S1 |====================|| R1 |
| |<- - - - - - - - - - | |
+-------+ Return Test Packet +-------+
\
T4
STAMP Session-Sender STAMP Session-Reflector
(Loopback,
Forward)
Figure 9: Reference Topology for Loopback Measurement Mode
The Session-Sender retrieves the timestamp T1 from the received
Session-Sender test packet and collects the receive timestamp T4
locally. Both timestamps, T1 and T4, are used to measure the
loopback delay metric as (T4 - T1). The loopback delay includes the
STAMP test packet processing delay on the Session-Reflector
component. The Session-Reflector processing delay component includes
only the time required to loop the STAMP test packet from the
incoming interface to the outgoing interface in the data plane. The
Session-Reflector does not timestamp the test packets and, therefore,
does not require timestamping capability.
6.1. STAMP Reference Model Considerations for Loopback Measurement Mode
The Session-Sender test packets are encapsulated with the forward
direction SR-MPLS path and transmitted to the Session-Reflector, as
defined in Section 4 for STAMP sessions. An IP header is added for
the return path in the Session-Sender test packets, setting the
Destination Address equal to the Session-Sender address, as shown in
Figure 10, to return the test packets to the Session-Sender.
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+---------------------------------------------------------------+
| IP Header (Return Path) |
. Source IP Address = Session-Sender IP Address .
. Destination IP Address = Session-Sender IP Address .
. IPv4 Protocol or IPv6 Next-header = 17 (UDP) .
. .
+---------------------------------------------------------------+
| UDP Header |
. Source Port = Chosen by Session-Sender .
. Destination Port = Source Port .
. .
+---------------------------------------------------------------+
| Payload = Test Packet as specified in Section 3 of RFC 8972 |
. in Figures 1 and 3 .
. .
+---------------------------------------------------------------+
Figure 10: Content of Session-Sender Return Test Packet in
Loopback Measurement Mode
The Session-Reflector does not perform the STAMP process, as the
loopback function simply processes the encapsulation including the IP
and MPLS headers (but does not process the UDP header) to forward the
received Session-Sender test packet to the Session-Sender without
STAMP modifications, as defined in [RFC8762].
The SSID field in the received Session-Sender test packets [RFC8972]
at the Session-Sender, along with the local configuration, is used to
identify the STAMP sessions that use loopback measurement mode.
The Session-Sender sets the destination UDP port to the UDP port it
uses to receive the return Session-Reflector test packets (other than
the destination UDP port 862, which is used by the Session-
Reflector). The same UDP port is used as both the destination and
source UDP port in the Session-Sender test packets, as shown in
Figure 10.
At the Session-Sender, the "Session-Sender Sequence Number", the
"Session-Sender Timestamp", the "Session-Sender Error Estimate", and
the "Session-Sender TTL" fields are all set to zero in the
transmitted Session-Sender test packets and are ignored in the
received test packets.
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6.2. Loopback Measurement Mode for SR-MPLS Paths
In loopback measurement mode for SR-MPLS paths, the Session-Sender
test packet carries either the Segment List of the forward direction
path only or both the forward direction and return paths in the MPLS
header, as specified in [RFC8403], as shown in Figure 11.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label[1] (Top of Stack) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label[n] | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Return Path Label[1] | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Return Path Label[n] | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Return Path PSID (optional)| TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Test Packet as shown in Figure 10 (Return Path) |
. .
+---------------------------------------------------------------+
Example 1: Encapsulation Using SR-MPLS Return Path
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label[1] (Top of Stack) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label[n] | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PSID (optional) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Test Packet as shown in Figure 10 (Return Path) |
. .
+---------------------------------------------------------------+
Example 2: Encapsulation Using IP Return Path
Figure 11: Content of Session-Sender Test Packet in Loopback
Measurement Mode for SR-MPLS Path
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In the case of an SR-MPLS Policy using Penultimate Hop Popping (PHP),
the Session-Sender ensures that the STAMP test packets reach the SR-
MPLS Policy endpoint, for example, by adding the Prefix SID label of
the SR-MPLS Policy endpoint to the Segment List of the forward
direction path.
The IP header for the return path is added to the Session-Sender test
packets, and the Destination Address is set to the Session-Sender
address in the IP header.
6.2.1. SR-MPLS Return Path
The Session-Sender test packets, in the SR-MPLS label stack, carry
the return path in addition to the forward direction path, as shown
in Example 1 of Figure 11. For example, they carry the SR-MPLS label
stack of the Segment List of the associated reverse Candidate-Path,
the Binding SID label of the reverse SR-MPLS Policy, or the SR-MPLS
Prefix SID label of the Session-Sender. The Binding SID of the
reverse SR-MPLS Policy can be configured on the Session-Sender using
an SDN controller, for example.
For SR-MPLS IGP Flex-Algo paths, the Session-Sender test packets
carry the SR-MPLS Prefix SID label of the Session-Sender on the same
SR-MPLS IGP Flex-Algo path in the reverse direction.
The PSID is added to the Segment List of the Session-Sender test
packets for the SR-MPLS return path when the head-end node supports
PSID allocation.
6.2.2. IP Return Path
The Session-Sender test packets, in the MPLS header, carry only the
SR-MPLS label stack of the forward direction path, as shown in
Example 2 of Figure 11.
The Session-Reflector decapsulates the MPLS header and forwards the
test packet using the IP header back to the Session-Sender.
The optional PSID added to the Session-Sender test packet is for the
SR-MPLS forward direction path and is allocated by the Session-
Reflector.
6.3. Loopback Measurement Mode for Layer-3 Services over SR-MPLS Path
In loopback measurement mode for the L3 service over an SR-MPLS path,
the SR-MPLS label stack of the data packets transmitted over the L3
service is used to encapsulate the Session-Sender test packets, as
shown in Figure 12.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label[1] (Top of Stack) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label[n] | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Return Path Label[1] | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L3VPN Label (Return Path) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Test Packet as shown in Figure 10 (Return Path) |
. Source and Destination IP Address in L3VPN table .
. .
+---------------------------------------------------------------+
Example 1: Encapsulation Using SR-MPLS Return Path
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label[1] (Top of Stack) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L3VPN Label(Forward Path) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Test Packet as shown in Figure 10 (Return Path) |
. Source and Destination IP Address in L3VPN table .
. .
+---------------------------------------------------------------+
Example 2: Encapsulation Using IP Return Path
Figure 12: Content of Session-Sender Test Packet in Loopback
Measurement Mode for L3 Service over SR-MPLS Path
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The IP header for the return path of the Session-Sender test packets
is added, setting the Destination Address to the Session-Sender
address. The Destination Address added in the IP header for the
return path MUST be reachable via the IP table lookup associated with
the L3VPN label added in the test packets.
6.3.1. SR-MPLS Return Path
The SR-MPLS label stack, except for the L3VPN label (advertised by
the Session-Reflector) of the forward direction L3 service, is added
in the Session-Sender test packets. In addition, the SR-MPLS label
stack, including the L3VPN label for the reverse direction L3
service, is also added in the Session-Sender test packets.
6.3.2. IP Return Path
The SR-MPLS label stack, including the L3VPN label (advertised by the
Session-Reflector) for the forward direction L3 service, is added to
the Session-Sender test packets.
The Session-Reflector decapsulates the MPLS header and forwards the
Session-Sender test packet using the IP header back to the Session-
Sender, after adding SR-MPLS encapsulation for the reverse direction
L3 service.
6.4. Loopback Measurement Mode for Layer-2 Services over SR-MPLS Path
In loopback measurement mode for the L2 service over an SR-MPLS path,
the SR-MPLS label stack of the data packets transmitted over the L2
service is used to encapsulate the Session-Sender test packets, as
shown in Figure 13.
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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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label[1] (Top of Stack) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label[n] | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Return Path Label[1] | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| L2VPN Label (Return Path) | TC |1| TTL=1 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Test Packet as shown in Figure 10 (Return Path) |
. .
+---------------------------------------------------------------+
Encapsulation Using SR-MPLS Return Path
Figure 13: Content of Session-Sender Test Packet in Loopback
Measurement Mode for L2 Service over SR-MPLS Path
The IP header for the return path is added to the Session-Sender test
packets, and the Destination Address set to the Session-Sender
address.
6.4.1. SR-MPLS Return Path
The SR-MPLS label stack, except for the L2VPN label (advertised by
the Session-Reflector) for the forward direction L2 service, is added
to the Session-Sender test packets. In addition, the SR-MPLS label
stack, including the L2VPN label for the reverse direction L2
service, is added to the Session-Sender test packets with a TTL value
of 1 to punt the test packets from the data plane to the CPU or the
slow path on the Session-Sender for STAMP processing.
6.4.2. IP Return Path
The STAMP test packets that do not use the SR-MPLS return path are
not supported.
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7. Loopback Measurement Mode with Timestamp and Forward
As shown in Figure 14, in the reference topology for "loopback
measurement mode with timestamp and forward", the STAMP Session-
Sender S1 initiates a Session-Sender test packet in loopback
measurement mode. The "timestamp and forward" is used to optimize
the "operation of punting the test packet and generating the return
test packet" on the STAMP Session-Reflector, as timestamping is
implemented in the fast path in the data plane. This helps achieve a
higher number of STAMP sessions and faster measurement intervals.
T1 T2
/ \
+-------+ Test Packet +-------+
| | - - - - - - - - - - | |
| S1 |====================|| R1 |
| |<- - - - - - - - - - | |
+-------+ Return Test Packet +-------+
\
T4
STAMP Session-Sender STAMP Session-Reflector
(Loopback,
Timestamp and Forward)
Figure 14: Reference Topology for Loopback Measurement Mode with
Timestamp and Forward
The Session-Sender retrieves the timestamps T1 and T2 from the
received Session-Sender test packet and collects the receive
timestamp T4 locally. Timestamps T1 and T2 are used by the Session-
Sender to measure the one-way delay metric as (T2 - T1). Timestamps
T1 and T4 are used by the Session-Sender to measure the loopback
delay metric as (T4 - T1).
The Session-Sender adds the transmit timestamp (T1) to the payload of
the Session-Sender test packet. The Session-Reflector adds the
receive timestamp (T2) to the payload of the received test packet in
the fast path in the data plane, without punting the test packet
(e.g., to the CPU or the slow path) for STAMP packet processing.
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7.1. Loopback Measurement Mode with Timestamp and Forward Network
Action for SR-MPLS Data Plane
The MPLS Network Action (MNA) Sub-Stack defined in [RFC9994] is used
for the STAMP test packets in the loopback measurement mode with
timestamp and forward. A locally configured MPLS Network Action
opcode, referred to as MNA.TSF in this document, is used for the
"Timestamp and Forward Network Action".
In the Session-Sender test packets for SR-MPLS paths, the MNA Sub-
Stack with the opcode MNA.TSF is added in the MPLS header, as shown
in Figure 15, to collect the timestamp in the "Receive Timestamp"
field in the payload of the STAMP test packet from the Session-
Reflector. The Ingress-to-Egress (I2E), Hop-By-Hop (HBH), or Select
scope field (IHS) is set to "I2E" when the return path is IP/UDP.
The Network Action Sub-Stack Length (NASL) and Network Action Length
(NAL) are set as defined in [RFC9994]. The U flag is set to value 0
(to skip the network action) as defined in [RFC9994] and to forward
the test packet (and not drop the packet).
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label[1] (Top of Stack) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label[n] | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MNA Label | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|7-bit MNA.TSF| 13-bit (value 0x0) |R|IHS|S| NASL |U| NAL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Test Packet as shown in Figure 10 (Return Path) |
. .
+---------------------------------------------------------------+
Figure 15: Content of Session-Sender Test Packet in Loopback
Measurement Mode with MNA.TSF for SR-MPLS Paths
The SR-MPLS label stack of the return path can be added after the MNA
Sub-Stack to receive the return test packet on a specific path, as
described in the loopback measurement for SR-MPLS paths in this
document. The IHS scope is set to "Select" in this case [RFC9994].
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When a Session-Reflector receives a test packet with the MNA Sub-
Stack with opcode MNA.TSF, it timestamps the test packet payload at a
fixed offset, pops the MNA Sub-Stack (after completing any other
network actions), and forwards the test packet as defined in the
loopback measurement mode for SR-MPLS paths in this document.
7.1.1. Timestamp and Forward Network Action Assignment and Node
Capability
The new locally configured MPLS Network Action opcode MNA.TSF, called
"Timestamp and Forward Network Action", described in this document,
is assigned a value from the "Private Use Range: 111-126" on the
Session-Reflector node.
The timestamp format (e.g., 64-bit PTPv2 or NTPv4), to be added to
the Session-Sender test packet payload, is also locally configured
for the opcode MNA.TSF. The offset in the Session-Sender test packet
payload (e.g., STAMP test packet in Figure 5 of [RFC8762] with an
offset of 16 bytes for Receive Timestamp) is similarly locally
configured for the opcode MNA.TSF.
The Session-Sender needs to know if the Session-Reflector is capable
of processing the "Timestamp and Forward" network action to avoid
dropping the test packets. The signaling extension for this
capability exchange or its configuration through local settings is
outside the scope of this document.
8. Packet Loss Measurement in SR-MPLS Networks
The procedure described for two-way measurement mode allows for
round-trip, near-end (forward direction), and far-end (backward
direction) inferred packet loss measurement. However, this provides
only an approximate view of the data packet loss.
The loopback measurement mode and loopback measurement mode with
"timestamp and forward", defined in this document, allow only round-
trip packet loss measurement.
Note that the packet loss measurement does not require the clocks on
the Session-Sender and Session-Reflector to be synchronized using
either PTPv2 or NTPv4.
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9. Direct Measurement in SR-MPLS Networks
The STAMP "Direct Measurement" TLV (Type 5), defined in [RFC8972], is
used in SR-MPLS networks for data packet loss measurement. The STAMP
test packets with this TLV are transmitted using the procedure
described for two-way measurement mode using STAMP test packets and
collecting the Session-Sender transmit counters and Session-Reflector
receive and transmit counters of the data packet flows for direct
measurement.
The PSID carried in the data packets is used to measure received data
packets (for the receive traffic counter) on the associated SR-MPLS
path on the Session-Reflector.
In the case of L3 and L2 services in SR-MPLS networks, the associated
SR-MPLS service labels are used to measure received data packets (for
the receive traffic counters) on the Session-Reflector.
In loopback measurement mode and loopback measurement mode with
"timestamp and forward", defined in this document, direct measurement
is not applicable.
10. ECMP Measurement in SR-MPLS Networks
The Segment List of an SR-MPLS path can have ECMP paths between the
source and transit nodes, between transit nodes, and between transit
and destination nodes. The usage of a node SID [RFC8402] by the
Segment List of an SR-MPLS path can result in ECMP paths. In
addition, the usage of an Anycast SID [RFC8402] by the Segment List
of an SR-MPLS path can result in ECMP paths via transit nodes that
are part of that anycast group. The STAMP test packets are
transmitted to traverse different ECMP paths to measure the delay of
each ECMP path of a Segment List.
For SR-MPLS path delay measurement, different entropy label values
[RFC6790] are used in the Session-Sender and Session-Reflector test
packets to take advantage of the hashing function in the forwarding
plane to influence the ECMP path taken by them.
In the IPv4 header of the Session-Sender and Session-Reflector test
packets, different values of the Destination Address from the range
127/8 are used to traverse different IPv4 ECMP paths as described in
Section 2.1 of [RFC8029]. In this case, the Session-Sender test
packets may carry the "Destination Node IPv4 or IPv6 Address" STAMP
TLV as defined in [RFC9503] to identify the intended Session-
Reflector IP address.
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The considerations for loss measurement for different ECMP paths of
an SR-MPLS path are outside the scope of this document.
11. STAMP Session State
The threshold-based notification for delay and packet loss metrics is
not generated if the delay and packet loss metrics do not change
significantly. For unambiguous monitoring, the controller needs to
distinguish whether the STAMP session is active but delay and packet
loss metrics did not cross the thresholds, or if the STAMP session
has failed and is not transmitting or receiving test packets.
The STAMP session state monitoring allows the node to determine
whether the performance measurement test is active, idle, or failed.
The STAMP session state is notified as idle when the Session-Sender
is not transmitting test packets.
In the two-way and loopback measurement modes, the STAMP session
state is initially notified as active when the Session-Sender is
transmitting test packets and as soon as one or more Session-
Reflector test packets are received at the Session-Sender. The STAMP
session state is notified as failed when N consecutive Session-
Reflector test packets are not received at the Session-Sender after
the STAMP session state is notified as active, where N (the
consecutive packet loss count) is a locally provisioned value.
Similarly, in the one-way measurement mode, the STAMP session state
is initially notified as active when the Session-Sender is
transmitting test packets and as soon as one or more Session-Sender
test packets are received at the Session-Reflector. The STAMP
session state is notified as failed when N consecutive Session-Sender
test packets are not received at the Session-Reflector after the
STAMP session state is notified as active, where N (the consecutive
packet loss count) is a locally provisioned value.
The failed state of the STAMP session also indicates the connectivity
failure of the SR-MPLS path or of the L3/L2 service over the SR-MPLS
path, where the STAMP session was active.
12. Additional STAMP Test Packet Processing Rules
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12.1. TTL
The TTL field in the IPv4 and MPLS headers of the Session-Sender and
Session-Reflector test packets is set to 255, as per the Generalized
TTL Security Mechanism (GTSM) [RFC5082]. The service labels such as
the L2VPN label, where a specific TTL value is required for correct
forwarding behavior are not subject to this rule.
12.2. IPv6 Hop Limit
The Hop Limit (HL) field in all IPv6 headers of the Session-Sender
and Session-Reflector test packets is set to 255, as per the
Generalized TTL Security Mechanism (GTSM) [RFC5082].
12.3. Router Alert Option
The Router Alert IP option (RAO) [RFC2113] is not required in the
Session-Sender and Session-Reflector test packets to punt the STAMP
test packets from the data plane to the CPU or the slow path.
12.4. IPv6 Flow Label
The Flow Label field in the IPv6 header of the Session-Sender test
packets is set to the value used by the data packets for the IPv6
traffic flow being measured by the Session-Sender.
The Session-Reflector uses the Flow Label value received in the IPv6
header of the Session-Sender test packet for the Session-Reflector
test packet, which can be based on a local policy.
12.5. UDP Checksum
For IPv4 STAMP test packets, where the local processor, after adding
the timestamp, is not capable of re-computing the UDP checksum or
adding a checksum complement [RFC7820], the Session-Sender and
Session-Reflector set the UDP checksum value to 0 [RFC8085].
For IPv6 STAMP test packets, where the local processor, after adding
the timestamp, is not capable of re-computing the UDP checksum or
adding a checksum complement [RFC7820], the Session-Sender and
Session-Reflector use the procedure defined in [RFC6936] for the UDP
checksum (with the value set to 0) for UDP ports used in STAMP
sessions, which can be based on a local policy.
13. Implementation Status
Editorial note: Please remove this section prior to publication.
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13.1. Cisco Implementation
The following Cisco routing platforms running the IOS-XR operating
system have participated in interoperability testing for one-way,
two-way, and loopback measurement modes for SR-MPLS:
* Cisco 8000 (based on Cisco Silicon One ASIC)
* Cisco ASR9904 with Lightspeed linecard and Tomahawk linecard
* Cisco NCS5500 (based on Broadcom Jericho1 ASIC)
* Cisco NCS5700 (based on Broadcom Jericho2 ASIC)
14. Operational and Manageability Considerations
The operational considerations described in Section 5 of [RFC8762]
and the manageability considerations described in Section 9 of
[RFC8402] apply to this specification.
The operational considerations specified in [RFC9994] and
[I-D.ietf-mpls-stamp-pw] are also applicable to the procedures
described in this document.
Various statistics for one-way (near-end, far-end), round-trip, and
loopback delay metrics (such as average delay, minimum delay, maximum
delay, and delay variance) as well as for one-way (near-end, far-end)
or round-trip packet loss metrics (such as percentage loss and
consecutive packets lost) and the STAMP session state changes can be
computed using the performance measurement procedures described in
this document. Operator alerts are generated for anomaly detection
when delay or loss metrics cross user-configured thresholds or when
the STAMP session state changes.
When STAMP sessions are created for the Segment Lists of the SR-MPLS
Policies, the scalability regarding the number of STAMP sessions
needs to be carefully considered.
15. Security Considerations
The security considerations specified in [RFC8762], [RFC8972], and
[RFC9503] also apply to the procedures described in this document.
The use of HMAC-SHA-256 in authenticated mode protects the data
integrity of the STAMP test packets. The message integrity
protection using HMAC, as defined in Section 4.4 of [RFC8762], can be
used with the procedures described in this document.
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The procedures defined in this document are intended for deployment
in a single network administrative domain. As such, the Session-
Sender address, Session-Reflector address, and the forward direction
and return paths are provisioned by the operator for the STAMP
session. It is assumed that the operator has verified the integrity
of the forward direction and return paths of the STAMP test packets.
When using the procedures defined in [RFC6936], the security
considerations specified in [RFC6936] also apply.
The security considerations specified in [RFC9994] and
[I-D.ietf-mpls-stamp-pw] are also applicable to the procedures
described in this document.
16. IANA Considerations
This document does not require any IANA action.
17. References
17.1. Normative References
[RFC0768] Postel, J., "User Datagram Protocol", STD 6, RFC 768,
DOI 10.17487/RFC0768, August 1980,
<https://www.rfc-editor.org/info/rfc768>.
[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>.
[RFC5082] Gill, V., Heasley, J., Meyer, D., Savola, P., Ed., and C.
Pignataro, "The Generalized TTL Security Mechanism
(GTSM)", RFC 5082, DOI 10.17487/RFC5082, October 2007,
<https://www.rfc-editor.org/info/rfc5082>.
[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>.
[RFC8762] Mirsky, G., Jun, G., Nydell, H., and R. Foote, "Simple
Two-Way Active Measurement Protocol", RFC 8762,
DOI 10.17487/RFC8762, March 2020,
<https://www.rfc-editor.org/info/rfc8762>.
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[RFC8972] Mirsky, G., Min, X., Nydell, H., Foote, R., Masputra, A.,
and E. Ruffini, "Simple Two-Way Active Measurement
Protocol Optional Extensions", RFC 8972,
DOI 10.17487/RFC8972, January 2021,
<https://www.rfc-editor.org/info/rfc8972>.
[RFC9503] Gandhi, R., Ed., Filsfils, C., Chen, M., Janssens, B., and
R. Foote, "Simple Two-Way Active Measurement Protocol
(STAMP) Extensions for Segment Routing Networks",
RFC 9503, DOI 10.17487/RFC9503, October 2023,
<https://www.rfc-editor.org/info/rfc9503>.
[RFC9545] Cheng, W., Ed., Li, H., Li, C., Ed., Gandhi, R., and R.
Zigler, "Path Segment Identifier in MPLS-Based Segment
Routing Networks", RFC 9545, DOI 10.17487/RFC9545,
February 2024, <https://www.rfc-editor.org/info/rfc9545>.
[RFC9994] Rajamanickam, J., Ed., Gandhi, R., Ed., Zigler, R., Song,
H., and K. Kompella, "MPLS Network Action (MNA) Sub-Stack
Specification Including In-Stack Network Actions and
Data", RFC 9994, DOI 10.17487/RFC9994, June 2026,
<https://www.rfc-editor.org/info/rfc9994>.
17.2. Informative References
[RFC2113] Katz, D., "IP Router Alert Option", RFC 2113,
DOI 10.17487/RFC2113, February 1997,
<https://www.rfc-editor.org/info/rfc2113>.
[RFC3032] Rosen, E., Tappan, D., Fedorkow, G., Rekhter, Y.,
Farinacci, D., Li, T., and A. Conta, "MPLS Label Stack
Encoding", RFC 3032, DOI 10.17487/RFC3032, January 2001,
<https://www.rfc-editor.org/info/rfc3032>.
[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,
<https://www.rfc-editor.org/info/rfc5905>.
[RFC6790] Kompella, K., Drake, J., Amante, S., Henderickx, W., and
L. Yong, "The Use of Entropy Labels in MPLS Forwarding",
RFC 6790, DOI 10.17487/RFC6790, November 2012,
<https://www.rfc-editor.org/info/rfc6790>.
[RFC6936] Fairhurst, G. and M. Westerlund, "Applicability Statement
for the Use of IPv6 UDP Datagrams with Zero Checksums",
RFC 6936, DOI 10.17487/RFC6936, April 2013,
<https://www.rfc-editor.org/info/rfc6936>.
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[RFC7820] Mizrahi, T., "UDP Checksum Complement in the One-Way
Active Measurement Protocol (OWAMP) and Two-Way Active
Measurement Protocol (TWAMP)", RFC 7820,
DOI 10.17487/RFC7820, March 2016,
<https://www.rfc-editor.org/info/rfc7820>.
[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, March 2017,
<https://www.rfc-editor.org/info/rfc8029>.
[RFC8085] Eggert, L., Fairhurst, G., and G. Shepherd, "UDP Usage
Guidelines", BCP 145, RFC 8085, DOI 10.17487/RFC8085,
March 2017, <https://www.rfc-editor.org/info/rfc8085>.
[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>.
[RFC8403] Geib, R., Ed., Filsfils, C., Pignataro, C., Ed., and N.
Kumar, "A Scalable and Topology-Aware MPLS Data-Plane
Monitoring System", RFC 8403, DOI 10.17487/RFC8403, July
2018, <https://www.rfc-editor.org/info/rfc8403>.
[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>.
[RFC9350] Psenak, P., Ed., Hegde, S., Filsfils, C., Talaulikar, K.,
and A. Gulko, "IGP Flexible Algorithm", RFC 9350,
DOI 10.17487/RFC9350, February 2023,
<https://www.rfc-editor.org/info/rfc9350>.
[I-D.ietf-ippm-stamp-yang]
Mirsky, G., Min, X., Luo, W. S., and R. Gandhi, "Simple
Two-way Active Measurement Protocol (STAMP) Data Model",
Work in Progress, Internet-Draft, draft-ietf-ippm-stamp-
yang-12, 5 November 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-ippm-
stamp-yang-12>.
[I-D.ietf-mpls-stamp-pw]
Gandhi, R., Brissette, P., Leyton, E., and X. Min,
"Encapsulation of Simple Two-Way Active Measurement
Protocol for LSPs and Pseudowires in MPLS Networks", Work
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in Progress, Internet-Draft, draft-ietf-mpls-stamp-pw-06,
21 June 2026, <https://datatracker.ietf.org/doc/html/
draft-ietf-mpls-stamp-pw-06>.
[IEEE.1588]
IEEE, "1588-2008 IEEE Standard for a Precision Clock
Synchronization Protocol for Networked Measurement and
Control Systems", March 2008.
Acknowledgments
The authors would like to thank Ianik Semco and Thierry Couture for
their discussions on the use cases for Performance Measurement in
Segment Routing. The authors would also like to thank Greg Mirsky,
Gyan Mishra, Xie Jingrong, Zafar Ali, Boris Hassanov, Ruediger Geib,
Liyan Gong, Zhenqiang Li, Maria Matejka, William Hawkins, and Mike
Koldychev for reviewing this document and providing useful comments
and suggestions. Additionally, Patrick Khordoc, Haowei Shi, Amila
Tharaperiya Gamage, Pengyan Zhang, Ruby Lin, Senni Tan, and Radu
Valceanu have helped improve the mechanisms described in this
document.
Contributors
The following people have substantially contributed to this document:
Daniel Voyer
Cisco Systems, Inc.
Email: davoyer@cisco.com
Navin Vaghamshi
Reliance
Email: Navin.Vaghamshi@ril.com
Moses Nagarajah
Telstra
Email: Moses.Nagarajah@team.telstra.com
Amit Dhamija
Arrcus
India
Email: amitd@arrcus.com
Authors' Addresses
Rakesh Gandhi (editor)
Cisco Systems, Inc.
Canada
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Email: rgandhi@cisco.com
Clarence Filsfils
Cisco Systems, Inc.
Email: cfilsfil@cisco.com
Bart Janssens
Colt
Email: Bart.Janssens@colt.net
Mach(Guoyi) Chen
Huawei
Email: mach.chen@huawei.com
Richard Foote
Nokia
Email: footer.foote@nokia.com
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