Internet Engineering Task Force (IETF) R. Gandhi, Ed.
Request for Comments: 9779 C. Filsfils
Category: Standards Track Cisco Systems, Inc.
ISSN: 2070-1721 D. Voyer
Bell Canada
S. Salsano
Universita di Roma "Tor Vergata"
M. Chen
Huawei
April 2025
Performance Measurement for Segment Routing Networks with the MPLS Data
Plane
Abstract
This document specifies the application of the MPLS loss and delay
measurement techniques (originally defined in RFCs 6374, 7876, and
9341) within Segment Routing (SR) networks that utilize the MPLS data
plane, also referred to as Segment Routing over MPLS (SR-MPLS). SR
enables the forwarding of packets through an ordered list of
instructions, known as segments, which are imposed at the ingress
node. This document defines the procedures and extensions necessary
to perform accurate measurement of packet loss and delay in SR-MPLS
environments, ensuring that network operators can effectively measure
and maintain the quality of service across their SR-based MPLS
networks. This includes coverage of links and end-to-end SR-MPLS
paths, as well as SR Policies.
Status of This Memo
This is an Internet Standards Track document.
This document is a product of the Internet Engineering Task Force
(IETF). It represents the consensus of the IETF community. It has
received public review and has been approved for publication by the
Internet Engineering Steering Group (IESG). Further information on
Internet Standards is available in Section 2 of RFC 7841.
Information about the current status of this document, any errata,
and how to provide feedback on it may be obtained at
https://www.rfc-editor.org/info/rfc9779.
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Table of Contents
1. Introduction
2. Conventions Used in This Document
2.1. Requirements Language
2.2. Abbreviations
2.3. Reference Topology
3. Overview
4. Query and Response Messages
4.1. Query Message for Links and SR-MPLS Policies
4.1.1. Query Message for Links
4.1.2. Query Message for SR-MPLS Policies
4.2. Response Message for Links and SR-MPLS Policies
4.2.1. One-Way Measurement Mode
4.2.2. Two-Way Measurement Mode
4.2.3. Loopback Measurement Mode
5. Delay and Loss Measurement
5.1. Delay Measurement Message
5.2. Loss Measurement Message
5.3. Combined Loss/Delay Measurement Message
5.4. Counters
5.5. Block Number for Counters
6. TLV Extensions
6.1. Return Path TLV Extension
6.1.1. Return Path Sub-TLV Extension
6.2. Block Number TLV Extension
7. ECMP for SR-MPLS Policies
8. Extended TE Link Metrics Advertisement
9. Backwards Compatibility
10. Manageability Considerations
11. Security Considerations
12. IANA Considerations
13. References
13.1. Normative References
13.2. Informative References
Acknowledgments
Contributors
Authors' Addresses
1. Introduction
Segment Routing (SR), as specified in [RFC8402], leverages the source
routing paradigm and applies to both the Multiprotocol Label
Switching (MPLS) and Internet Protocol version 6 (IPv6) data planes.
These are referred to as Segment Routing over MPLS (SR-MPLS) and
Segment Routing over IPv6 (SRv6), respectively. SR takes advantage
of Equal-Cost Multipaths (ECMPs) between source and transit nodes,
between transit nodes, and between transit and destination nodes. SR
Policies, 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 one of the
essential requirements for measuring network performance to provide
Service Level Agreements (SLAs).
[RFC6374] specifies protocol mechanisms to enable efficient and
accurate measurement of packet loss, one-way and two-way delay, as
well as related metrics such as delay-variation in MPLS networks.
[RFC7876] specifies mechanisms for sending and processing out-of-band
responses over a UDP return path when receiving query messages
defined in [RFC6374]. These mechanisms can be applied to SR-MPLS
networks.
[RFC9341] defines the Alternate-Marking Method using Block Numbers as
a data correlation mechanism for packet loss measurement.
This document utilizes the mechanisms from [RFC6374], [RFC7876], and
[RFC9341] for delay and loss measurements in SR-MPLS networks. This
includes coverage of links and end-to-end SR-MPLS paths, as well as
SR Policies.
This document extends [RFC6374] by defining Return Path and Block
Number TLVs (see Section 6) for delay and loss measurement in SR-MPLS
networks. These TLVs can also apply to be used in MPLS Label Switched Paths
(LSPs) [RFC3031]. However, the procedure for delay and loss
measurement of MPLS LSPs is outside the scope of this document.
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
ACH: Associated Channel Header
DM: Delay Measurement
ECMP: Equal-Cost Multipath
G-ACh: Generic Associated Channel
GAL: Generic Associated Channel Label
LM: Loss Measurement
LSE: Label Stack Entry
MPLS: Multiprotocol Label Switching
PSID: Path Segment Identifier
SID: Segment Identifier
SL: Segment List
SR: Segment Routing
SR-MPLS: Segment Routing over MPLS
TC: Traffic Class
TE: Traffic Engineering
TTL: Time to Live
URO: UDP Return Object
2.3. Reference Topology
In the reference topology shown in Figure 1, the querier node Q1
initiates a query message, and the responder node R1 transmits a
response message for the query message received. The response
message may be sent back to the querier node Q1 on the same path (the
same set of links and nodes) or on a different path in the reverse
direction from the path taken towards the responder R1.
T1 is a transmit timestamp, and T4 is a receive timestamp; both are
added by node Q1. T2 is a receive timestamp, and T3 is a transmit
timestamp; both are added by node R1.
SR is enabled with the MPLS data plane on nodes Q1 and R1. The nodes
Q1 and R1 are connected via a channel (Section 2.9.1 of [RFC6374]).
The channel may be a directly connected link enabled with MPLS
(Section 2.9.1 of [RFC6374]) or an SR-MPLS path [RFC8402]. The link
may be a physical interface, a virtual link, a Link Aggregation Group
(LAG) [IEEE802.1AX], or a LAG member link. The SR-MPLS path may be
an SR-MPLS Policy [RFC9256] on node Q1 (called the "head-end") with
the destination to node R1 (called the "tail-end").
T1 T2
/ \
+-------+ Query +-------+
| | - - - - - - - - - ->| |
| Q1 |=====================| R1 |
| |<- - - - - - - - - - | |
+-------+ Response +-------+
\ /
T4 T3
Querier Responder
Figure 1: Reference Topology
3. Overview
In this document, the procedures defined in [RFC6374], [RFC7876], and
[RFC9341] are utilized for delay and loss measurement in SR-MPLS
networks. Specifically, the one-way, two-way, and round-trip delay
measurements described in Section 2.4 of [RFC6374] are further
elaborated for application within SR-MPLS networks. Similarly, the
packet loss measurement procedures outlined in Section 2.2 of
[RFC6374] are extended for use in SR-MPLS networks.
Packet loss measurement using the Alternate-Marking Method defined in
[RFC9341] may employ the Block Number for data correlation. This is
achieved by utilizing the Block Number TLV extension defined in this
document.
In SR-MPLS networks, the query messages defined in [RFC6374] MUST be
transmitted along the same path as the data traffic for links and
end-to-end SR-MPLS paths. This is to collect both transmit and
receive timestamps for delay measurement and to collect both transmit
and receive traffic counters for loss measurement.
If it is desired in SR-MPLS networks that the same path (i.e., the
same set of links and nodes) between the querier and responder be
used in both directions of the measurement, then this can be achieved
by using the Return Path TLV extension defined in this document.
The performance measurement procedures for links can be used to
compute extended Traffic Engineering (TE) metrics for delay and loss,
as described herein. These metrics are advertised in the network
using the routing protocol extensions defined in [RFC7471],
[RFC8570], and [RFC8571].
4. Query and Response Messages
4.1. Query Message for Links and SR-MPLS Policies
4.1.1. Query Message for Links
The query message, as defined in [RFC6374], is sent over the links
for both delay and loss measurement. In each Label Stack Entry (LSE)
[RFC3032] in the MPLS label stack, the TTL value MUST be set to 255
[RFC5082].
4.1.2. Query Message for SR-MPLS Policies
An SR-MPLS Policy Candidate-Path may contain a number of Segment
Lists (SLs) (i.e., a stack of MPLS labels) [RFC9256]. For delay and/
or loss measurement for an end-to-end SR-MPLS Policy, the query
messages MUST be transmitted for every SL of the SR-MPLS Policy
Candidate-Path. This is done by creating a separate session for each
SL. Each query message of a session contains an SR-MPLS label stack
of the Candidate-Path, with the G-ACh Label (GAL) at the bottom of
the stack (with S=1) as shown in Figure 2. In each LSE in the MPLS
label stack, the TTL value MUST be set to 255 [RFC5082].
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) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label(n) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GAL (value 13) | TC |1| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Reserved | Channel Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Example Query Message Header for an End-to-End SR-MPLS
Policy
The fields 0001, Version, Reserved, and Channel Type shown in
Figure 2 are specified in [RFC5586].
The SR-MPLS label stack can be empty in the case of a one-hop SR-MPLS
Policy with an Implicit NULL label.
For an SR-MPLS Policy, to ensure that the query message is processed
by the intended responder, the Destination Address TLV (Type 129)
[RFC6374] containing an address of the responder can be sent in the
query messages. The responder that supports this TLV MUST return
Success in "Control Code"
Control Code 0x1 (Success) [RFC6374] if it is the intended
destination for the query. Otherwise, it MUST return Error 0x15:
Invalid Destination Node Identifier [RFC6374].
4.2. Response Message for Links and SR-MPLS Policies
4.2.1. One-Way Measurement Mode
In the one-way measurement mode defined in Section 2.4 of [RFC6374],
the querier can receive out-of-band response messages with an IP/UDP header "out-
of-band" by properly setting the UDP Return Object (URO) TLV in the
query message. The URO TLV (Type 131) is defined in [RFC7876] and
includes the UDP-Destination-Port and IP address. When the querier
sets an IP address and a UDP port in the URO TLV, the response
message MUST be sent to that IP address, with that IP address as the
destination address and the UDP port as the destination port. In
addition, the Control Code in the query message MUST be set to Out-of-Band Out-
of-band Response Requested [RFC6374].
4.2.2. Two-Way Measurement Mode
In the two-way measurement mode defined in Section 2.4 of [RFC6374],
the response messages SHOULD be sent back one of two ways: either
they are sent back in-band on the same link link, or they are sent back on
the same end-to-end SR-MPLS path (same (i.e., the same set of links and
nodes) in the reverse direction to the querier, querier. This is done in
order to perform accurate two- way delay measurement.
For links, the response message as defined in [RFC6374] is sent back
on the same incoming link where the query message is received. In
this case, the Control Code in the query message MUST be set to In-
band Response Requested [RFC6374].
For end-to-end SR-MPLS paths, the responder transmits the response
message (see the example as shown in Figure 2) on a specific return
SR-MPLS path. The In the query message, the querier can request in the query message for that the
responder to send the response message back on a given return path using
the MPLS Label Stack Sub-TLV in the Return Path TLV defined in this
document.
4.2.3. Loopback Measurement Mode
The loopback measurement mode defined in Section 2.8 of [RFC6374] is
used to measure round-trip delay for a bidirectional circular path
[RFC6374] in SR-MPLS networks. In this mode for SR-MPLS, the
received query messages are not punted out of the fast path in
forwarding (i.e., to the slow path or control plane) at the
responder. In other words, the responder does not process the
payload or generate response messages. The loopback function simply
returns the received query message to the querier without responder
modifications [RFC6374].
The loopback mode is done by generating "queries" with the Response
flag set to 1 and adding the Loopback Request object (Type 3)
[RFC6374]. In query messages, the label stack, as shown in Figure 3,
carries both the forward and reverse path labels in the MPLS header.
The GAL is still carried at the bottom of the label stack (with S=1).
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) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label(n) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reverse Path Label(1)| TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Reverse Path Label(n)| TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GAL (value 13) | TC |1| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Reserved | Channel Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Example Query Message Header for an End-to-End SR-MPLS
Policy in the Loopback Measurement Mode
5. Delay and Loss Measurement
5.1. Delay Measurement Message
As defined in [RFC6374], MPLS Delay Measurement (DM) query and
response messages use the Associated Channel Header (ACH) (value (with the
value 0x000C for delay measurement) [RFC6374], which measurement). This value identifies the
message type and the message payload that follow the ACH, as defined in
Section 3.2 of [RFC6374]
following the ACH. [RFC6374]. For delay measurement, the same ACH value
is used for both links and end-to-end SR-MPLS Policies.
5.2. Loss Measurement Message
The Loss Measurement (LM) protocol can perform two distinct kinds of
loss measurement as described in Section 2.9.8 of [RFC6374].
* In the inferred mode, LM will measure the loss of specially
generated test messages to infer the approximate data plane loss
level. Inferred mode LM provides only approximate loss
accounting.
* In the direct mode, LM will directly measure data plane packet
loss. Direct mode LM provides perfect loss accounting but may
require hardware support.
As defined in [RFC6374], MPLS LM query and response messages use the
ACH (value (with the value 0x000A for direct loss measurement or value
0x000B for inferred loss measurement), which measurement). This value identifies the
message type and the message payload that follow the ACH, as defined in
Section 3.1 of [RFC6374] following the
ACH. [RFC6374]. For loss measurement, the same ACH value
is used for both links and end-to-end SR-MPLS Policies.
5.3. Combined Loss/Delay Measurement Message
As defined in [RFC6374], combined DM+LM LM/DM query and response messages
use the ACH (value (with the value 0x000D for direct loss and delay
measurement or the value 0x000E for inferred loss and delay measurement), which
identifies
measurement). The value identies the message type and the message
payload that follows the ACH, as defined in Section 3.3 of [RFC6374] following the ACH. [RFC6374].
For combined loss and delay measurement, the same ACH value is used
for both links and end-
to-end end-to-end SR-MPLS Policies.
5.4. Counters
The Path Segment Identifier (PSID) [RFC9545] MUST be carried in the
received data packet for the traffic flow under measurement, in order
to account for received traffic on the egress node of the SR-MPLS
Policy. In the direct mode, the PSID in the received query message
(as shown in Figure 4) can be used to associate the received traffic
counter on the responder to detect the transmit packet loss for the
end-to-end SR-MPLS Policy.
In the inferred mode, the PSID in the received query messages (as
shown in Figure 4) can be used to count the received query messages
on the responder to detect the transmit packet loss for an end-to-end
SR-MPLS Policy.
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) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label(n) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| PSID | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GAL (value 13) | TC |1| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Reserved | Channel Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 4: Example with the PSID for SR-MPLS Policy
The fields 0001, Version, Reserved, and Channel Type shown in
Figure 4 are specified in [RFC5586].
Different values of the PSID can be used per Candidate-Path to
account for received traffic and to measure packet loss at the
Candidate-Path level. Similarly, different values of the PSID can be
used per Segment List (SL) of the Candidate-Path for accounting
received traffic to measure packet loss at the SL level. The same
value of the PSID can be used for all SLs of the SR-MPLS Policy to
measure packet loss at the SR-MPLS Policy level.
5.5. Block Number for Counters
The packet loss measurement using the Alternate-Marking Method
defined in [RFC9341] may use the block number for data correlation
for the traffic flow under measurement. As defined in Section 3.1 of
[RFC9341], the block number is used to divide the traffic flow into
consecutive blocks and count the number of packets transmitted and
received in each block for loss measurement.
As described in Section 4.3 of [RFC9341], a protocol-based
distributed solution can be used to exchange values of counters on
the nodes for loss measurement. That solution is further described
in this document using the LM messages defined in [RFC6374].
The querier node assigns a block number to the block of data packets
of the traffic flow under measurement. The querier counts the number
of packets transmitted in each block. The mechanism for the
assignment of the block number is a local decision on the querier and
is outside the scope of this document.
As an example, the querier can use the procedure defined in [RFC9714]
for alternate marking of the data packets of the traffic flow under
measurement. The responder counts the number of received packets in
each block based on the marking in the received data packets. The
querier and responder maintain separate sets of transmit and receive
counters for each marking. The marking can be used as a block
number, or a separate block number can be incremented when the
marking changes. Other methods can be defined for alternate marking
of the data packets of the traffic flow under measurement to assign a
block number for the counters.
The LM query and response messages defined in [RFC6374] are used to
measure packet loss for the block of data packets transmitted with
the previous marking while marking, whereas data packets carry alternate marking.
Specifically, LM query and response messages carry the transmit and
receive counters (which are currently not incrementing) along with
their block number to correlate for loss measurement.
Section 4.3 of [RFC9341] specifies that: "The assumption of this BN
mechanism is that the measurement nodes are time synchronized."
However, this is not necessary, as the block number on the responder
can be synchronized based on the received LM query messages.
6. TLV Extensions
6.1. Return Path TLV Extension
In the two-way measurement mode, the responder may transmit the
response message on a specific return path, for example, in an ECMP
environment. The querier can request in the query message for the
responder to send a response message back on a given return path
(e.g., a co-routed bidirectional path). This allows the responder to
avoid creating and maintaining additional states (containing return
paths) for the sessions.
The querier may not be directly reachable from the responder in a
network. In this case, the querier MUST send its reachability path
information to the responder using the Return Path TLV.
[RFC6374] defines query and response messages that can include one or
more optional TLVs. This document defines the the Return Path TLV
(5) to carry return path information in query messages. The Return
Path TLV is specific to a measurement session. The format of the
Return Path TLV is shown in Figure 5 below:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type = 5 | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Return Path Sub-TLV |
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 5: Return Path TLV
The Length is a one-byte field and is equal to the length of the
Return Path Sub-TLV and the Reserved field in bytes. The Length MUST
NOT be 0 or 1.
The Return Path TLV is defined in the "Mandatory TLV Type" registry
space [RFC6374]. The querier MUST only insert one Return Path TLV in
the query message. The responder that supports this TLV MUST only
process the first Return Path TLV and ignore the other Return Path
TLVs if present. The responder that supports this TLV also MUST send
the response message back on the return path specified in the Return
Path TLV. The responder also MUST NOT add a Return Path TLV in the
response message.
The Reserved field MUST be set to 0 and MUST be ignored on the
receive side.
6.1.1. Return Path Sub-TLV Extension
The Return Path TLV contains a Sub-TLV to carry the return path. The
format of the MPLS Label Stack Sub-TLV is shown in Figure 6. The
label entries in the Sub-TLV MUST be in network order. The MPLS
Label Stack Sub-TLV in the Return Path TLV is of the following type:
* Type (value 1): MPLS Label Stack of the 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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=1 | Length | Reserved |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label(1) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label(n) | TC |1| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 6: MPLS Label Stack Sub-TLV in the Return Path TLV
The MPLS Label Stack label stack contains a list of 32-bit LSE LSEs that includes a
20-bit label value, an 8-bit TTL value, a 3-bit TC value, and a 1-bit
EOS
End of Stack (S) field. An MPLS Label Stack Sub-TLV may carry a
stack of labels or a Binding SID label [RFC8402] of the Return SR-MPLS SR-
MPLS Policy.
The Length is a one-byte field and is equal to the length of the
label stack field and the Reserved field in bytes. The Length MUST
NOT be 0 or 1.
The Return Path TLV MUST carry only one Return Path Sub-TLV. The
MPLS Label Stack in the Return Path Sub-TLV MUST contain at least one
MPLS Label. The responder that supports this Sub-TLV MUST only
process the first Return Path Sub-TLV and ignore the other Return
Path Sub-TLVs if present. The responder that supports this Sub-TLV
MUST send the response message back on the return path specified in
the Return Path Sub-TLV.
The Reserved field MUST be set to 0 and MUST be ignored on the
receive side.
6.2. Block Number TLV Extension
[RFC6374] defines query and response messages that can include one or
more optional TLVs. This document defines the Block Number TLV (6)
to carry (8-bit) Block Number of the traffic counters in the LM query
and response messages. The format of the Block Number TLV is shown
in Figure 7:
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
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Type=6 | Length | Reserved |R| Block Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: Block Number TLV
The Length is a one-byte field and is equal to 2 bytes.
The Block Number TLV is defined in the "Mandatory TLV Type" registry
space [RFC6374]. The querier MUST only insert one Block Number TLV
in the query message to identify the Block Number for the traffic
counters in the forward direction. The responder that supports this
TLV MUST only insert one Block Number TLV in the response message to
identify the Block Number for the traffic counters in the reverse
direction. The responder also MUST return the first Block Number TLV
from the query message and ignore the other Block Number TLVs if
present. The Block Number TLV is specific to a measurement session.
The R flag is used to indicate the query and response message
direction associated with the Block Number. The R flag MUST be clear
in the query message for the Block Number associated with Counter 1
and Counter 2, and set in the response message for the Block Number
associated with Counter 3 and Counter 4.
The Reserved field MUST be set to 0 and MUST be ignored on the
receive side.
7. ECMP for SR-MPLS Policies
The SLs of an SR-MPLS Policy can have ECMPs between the source and
transit nodes, between transit nodes, and between transit and
destination nodes. Usage of a node SID node-SID [RFC8402] by the SLs of an
SR-MPLS Policy can result in ECMP paths. In addition, usage of an
Anycast SID
Anycast-SID [RFC8402] by the SLs of an SR-MPLS Policy can result in
ECMP paths via transit nodes that are part of that anycast group.
The query and response messages are sent to traverse different ECMP
paths to measure the delay of each ECMP path of an SL.
The forwarding plane has various hashing functions available to
forward packets on specific ECMP paths. For end-to-end SR-MPLS
Policy delay measurement, different entropy label values [RFC6790]
can be used in query and response messages to take advantage of the
hashing function in the forwarding plane to influence the ECMP path
taken by them.
The considerations for loss measurement for different ECMP paths of
an SR-MPLS Policy are outside the scope of this document.
8. Extended TE Link Metrics Advertisement
The extended TE metrics for link delay (namely, average delay,
minimum delay, maximum delay, and delay-variance) and packet loss can
be computed using the performance measurement procedures described in
this document and can be advertised in the routing domain as follows:
* For OSPF, IS-IS, and the Border Gateway Protocol - Link State
(BGP-LS), the protocol extensions defined in [RFC7471], [RFC8570],
and [RFC8571], respectively, are used for advertising the extended
TE link delay and loss metrics in the network.
* The extended TE link delay and loss metrics are advertised for
Layer-2 LAG bundle member links in OSPF [RFC9356] and IS-IS
[RFC8668] using the same protocol extensions defined in [RFC7471]
and [RFC8570], respectively.
* The advertised delay-variance metric is computed as Packet Delay
Variation (PDV), as described in Section 4.2 of [RFC5481].
9. Backwards Compatibility
The procedures defined in this document are backwards compatible with
the procedures defined in [RFC6374] at both the querier and the
responder. If the responder does not support the new Mandatory TLV
Types defined in this document, it will return Error 0x17:
Unsupported Mandatory TLV Object as per [RFC6374].
10. Manageability Considerations
The manageability considerations described in Section 7 of [RFC6374]
and Section 6 of [RFC7876] are applicable to this specification.
11. Security Considerations
The security considerations specified in [RFC6374], [RFC7471],
[RFC8570], [RFC8571], [RFC7876], and [RFC9341] also apply to the
procedures described in this document.
The procedure defined in this document is intended for deployment in
a single operator administrative domain. As such, the querier node,
the responder node, the forward path, and the return paths are
provisioned by the operator for the probe session. It is assumed
that the operator has verified the integrity of the forward and
return paths of the probe packets.
The Return Path TLV extensions defined in this document may be used
for potential address spoofing. For example, a query message may
carry a return path that has a destination that is not local at the
querier. To prevent such possible attacks, the responder may drop
the query messages when it cannot determine whether the return path
has the destination local at the querier. The querier may send a
proper source address in the Source Address TLV. The responder can
use this to make that determination, for example, by checking the
access control list provisioned by the operator.
12. IANA Considerations
IANA has allocated values for the following Mandatory TLV Types
[RFC6374] from the "MPLS Loss/Delay Measurement TLV Object" registry
contained within the "Generic Associated Channel (G-ACh) Parameters"
registry group:
+======+==============+===========+
| Code | Description | Reference |
+======+==============+===========+
| 5 | Return Path | RFC 9779 |
+------+--------------+-----------+
| 6 | Block Number | RFC 9779 |
+------+--------------+-----------+
Table 1: MPLS Loss/Delay
Measurement TLV Types
The Block Number TLV is carried in the query and response messages,
and the Return Path TLV is carried in the query messages.
IANA has created the "Return Path Sub-TLV Type" Types" registry. All code
points in the range 0 through 175 in this registry shall be allocated
according to the "IETF Review" procedure as specified in [RFC8126].
Code points in the range 176 through 239 in this registry shall be are allocated according to per the "First Come First Served" procedure as
specified registration policies shown in [RFC8126]. Remaining code points are allocated
according to Table 2: 2
(see [RFC8126]).
+===========+=========================+===========+
| Value | Description | Reference |
+===========+=========================+===========+
| 1 - 175 | IETF Review | RFC 9779 |
+-----------+-------------------------+-----------+
| 176 - 239 | First Come First Served | RFC 9779 |
+-----------+-------------------------+-----------+
| 240 - 251 | Experimental Use | RFC 9779 |
+-----------+-------------------------+-----------+
| 252 - 254 | Private Use | RFC 9779 |
+-----------+-------------------------+-----------+
Table 2: Return Path Sub-TLV Type Registry
This document defines the following values in the "Return Path Sub-
TLV Type" registry:
+=======+=====================================+===========+
| Value | Description | Reference |
+=======+=====================================+===========+
| 0 | Reserved | RFC 9779 |
+-------+-------------------------------------+-----------+
| 1 | MPLS Label Stack of the Return Path | RFC 9779 |
+-------+-------------------------------------+-----------+
| 255 | Reserved | RFC 9779 |
+-------+-------------------------------------+-----------+
Table 3: Return Path Sub-TLV Types
13. References
13.1. 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>.
[RFC6374] Frost, D. and S. Bryant, "Packet Loss and Delay
Measurement for MPLS Networks", RFC 6374,
DOI 10.17487/RFC6374, September 2011,
<https://www.rfc-editor.org/info/rfc6374>.
[RFC7876] Bryant, S., Sivabalan, S., and S. Soni, "UDP Return Path
for Packet Loss and Delay Measurement for MPLS Networks",
RFC 7876, DOI 10.17487/RFC7876, July 2016,
<https://www.rfc-editor.org/info/rfc7876>.
[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>.
[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>.
13.2. Informative References
[RFC3031] Rosen, E., Viswanathan, A., and R. Callon, "Multiprotocol
Label Switching Architecture", RFC 3031,
DOI 10.17487/RFC3031, January 2001,
<https://www.rfc-editor.org/info/rfc3031>.
[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>.
[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>.
[RFC5481] Morton, A. and B. Claise, "Packet Delay Variation
Applicability Statement", RFC 5481, DOI 10.17487/RFC5481,
March 2009, <https://www.rfc-editor.org/info/rfc5481>.
[RFC5586] Bocci, M., Ed., Vigoureux, M., Ed., and S. Bryant, Ed.,
"MPLS Generic Associated Channel", RFC 5586,
DOI 10.17487/RFC5586, June 2009,
<https://www.rfc-editor.org/info/rfc5586>.
[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>.
[RFC7471] Giacalone, S., Ward, D., Drake, J., Atlas, A., and S.
Previdi, "OSPF Traffic Engineering (TE) Metric
Extensions", RFC 7471, DOI 10.17487/RFC7471, March 2015,
<https://www.rfc-editor.org/info/rfc7471>.
[RFC8126] Cotton, M., Leiba, B., and T. Narten, "Guidelines for
Writing an IANA Considerations Section in RFCs", BCP 26,
RFC 8126, DOI 10.17487/RFC8126, June 2017,
<https://www.rfc-editor.org/info/rfc8126>.
[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>.
[RFC8570] Ginsberg, L., Ed., Previdi, S., Ed., Giacalone, S., Ward,
D., Drake, J., and Q. Wu, "IS-IS Traffic Engineering (TE)
Metric Extensions", RFC 8570, DOI 10.17487/RFC8570, March
2019, <https://www.rfc-editor.org/info/rfc8570>.
[RFC8571] Ginsberg, L., Ed., Previdi, S., Wu, Q., Tantsura, J., and
C. Filsfils, "BGP - Link State (BGP-LS) Advertisement of
IGP Traffic Engineering Performance Metric Extensions",
RFC 8571, DOI 10.17487/RFC8571, March 2019,
<https://www.rfc-editor.org/info/rfc8571>.
[RFC8668] Ginsberg, L., Ed., Bashandy, A., Filsfils, C., Nanduri,
M., and E. Aries, "Advertising Layer 2 Bundle Member Link
Attributes in IS-IS", RFC 8668, DOI 10.17487/RFC8668,
December 2019, <https://www.rfc-editor.org/info/rfc8668>.
[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>.
[RFC9356] Talaulikar, K., Ed. and P. Psenak, "Advertising Layer 2
Bundle Member Link Attributes in OSPF", RFC 9356,
DOI 10.17487/RFC9356, January 2023,
<https://www.rfc-editor.org/info/rfc9356>.
[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>.
[RFC9714] Cheng, W., Ed., Min, X., Ed., Zhou, T., Dai, J., and Y.
Peleg, "Encapsulation for MPLS Performance Measurement
with the Alternate-Marking Method", RFC 9714,
DOI 10.17487/RFC9714, February 2025,
<https://www.rfc-editor.org/info/rfc9714>.
[IEEE802.1AX]
IEEE, "IEEE Standard for Local and Metropolitan Area
Networks - Link Aggregation", IEEE Std 802.1AX-2008,
November 2008. 802.1AX-2020,
DOI 10.1109/IEEESTD.2020.9105034, May 2020,
<https://doi.org/10.1109/IEEESTD.2020.9105034>.
Acknowledgments
The authors would like to thank Thierry Couture and Ianik Semco for
the discussions on the use cases for performance measurement in
segment routing networks. The authors would like to thank Patrick
Khordoc, Ruby Lin, and Haowei Shi for implementing the mechanisms
defined in this document. The authors would like to thank Greg
Mirsky and Xiao Min for providing many useful comments and
suggestions. The authors would also like to thank Stewart Bryant,
Sam Aldrin, Tarek Saad, and Rajiv Asati for their review comments.
Thanks to Huaimo Chen, Yimin Shen, and Xufeng Liu for the MPLS-RT MPLS expert
review; Zhaohui Zhang for the RTGDIR early review; Tony Li for
shepherd's review; Ned Smith for the SECDIR review; Roni Even for the
Gen-ART review; Marcus Ihlar for the TSV-ART review; Dhruv Dhody for
the OPSDIR review; and Gunter Van de Velde, Paul Wouters, Éric
Vyncke, Murray Kucherawy, John Scudder, and Roman Danyliw for the
IESG review.
Contributors
Sagar Soni
Cisco Systems, Inc.
Email: sagsoni@cisco.com
Zafar Ali
Cisco Systems, Inc.
Email: zali@cisco.com
Pier Luigi Ventre
CNIT
Italy
Email: pierluigi.ventre@cnit.it
Authors' Addresses
Rakesh Gandhi (editor)
Cisco Systems, Inc.
Canada
Email: rgandhi@cisco.com
Clarence Filsfils
Cisco Systems, Inc.
Email: cfilsfil@cisco.com
Daniel Voyer
Bell Canada
Email: daniel.voyer@bell.ca
Stefano Salsano
Universita di Roma "Tor Vergata"
Italy
Email: stefano.salsano@uniroma2.it
Mach(Guoyi) Chen
Huawei
Email: mach.chen@huawei.com