Internet DRAFT - draft-ietf-bier-pmmm-oam
draft-ietf-bier-pmmm-oam
BIER Working Group G. Mirsky
Internet-Draft Ericsson
Intended status: Standards Track L. Zheng
Expires: 14 July 2024 Individual Contributor
M. Chen
G. Fioccola
Huawei Technologies
11 January 2024
Performance Measurement (PM) with Marking Method in Bit Index Explicit
Replication (BIER) Layer
draft-ietf-bier-pmmm-oam-15
Abstract
This document describes the applicability of a hybrid performance
measurement method for packet loss and packet delay measurements of a
multicast service through a Bit Index Explicit Replication domain.
Status of This Memo
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This Internet-Draft will expire on 14 July 2024.
Copyright Notice
Copyright (c) 2024 IETF Trust and the persons identified as the
document authors. All rights reserved.
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Please review these documents carefully, as they describe your rights
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions used in this document . . . . . . . . . . . . . . 3
2.1. Terminology . . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Requirements Language . . . . . . . . . . . . . . . . . . 3
3. OAM Field in BIER Header . . . . . . . . . . . . . . . . . . 3
4. Theory of Operation . . . . . . . . . . . . . . . . . . . . . 4
4.1. Single-Marking Enabled Measurement . . . . . . . . . . . 5
4.2. Double-Marking Enabled Measurement . . . . . . . . . . . 6
4.3. Operational Considerations . . . . . . . . . . . . . . . 6
5. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 7
6. Security Considerations . . . . . . . . . . . . . . . . . . . 7
7. Acknowledgement . . . . . . . . . . . . . . . . . . . . . . . 7
8. References . . . . . . . . . . . . . . . . . . . . . . . . . 7
8.1. Normative References . . . . . . . . . . . . . . . . . . 7
8.2. Informative References . . . . . . . . . . . . . . . . . 8
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 9
1. Introduction
[RFC8279] introduces and explains the Bit Index Explicit Replication
(BIER) architecture and how it supports the forwarding of multicast
data packets. [RFC8296] specified that in the case of BIER
encapsulation in an MPLS network, a BIER-MPLS label, the label that
is at the bottom of the label stack, uniquely identifies the
multicast flow. [RFC9341] and [RFC9342] describe a hybrid
performance measurement method, according to the classification of
measurement methods in [RFC7799]. The method, called Packet Network
Performance Monitoring (PNPM), can be used to measure packet loss,
latency, and jitter on live traffic complies with requirements R-5
and R-12 listed in [I-D.ietf-bier-oam-requirements]. Because this
method is based on marking consecutive batches of packets, the method
is often referred to as a marking method. Terms PNPM and "marking
method" in this document are used interchangeably.
This document defines how the marking method can be used on the BIER
layer to measure packet loss and delay metrics of a multicast flow in
an MPLS network.
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2. Conventions used in this document
2.1. Terminology
This document uses the terms related to the Alternate Marking Method
as defined in [RFC9341], [RFC9342]. This document uses the terms
related to the Bit Indexed Explicit Replication as defined in
[RFC8296].
2.2. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "NOT RECOMMENDED", "MAY", and
"OPTIONAL" in this document are to be interpreted as described in BCP
14 [RFC2119] [RFC8174] when, and only when, they appear in all
capitals, as shown here.
3. OAM Field in BIER Header
[RFC8296] defined the two-bits long field, referred to as OAM. The
OAM field can be used for the marking performance measurement method.
Because the setting of the field to any value does not affect
forwarding and/or quality of service treatment of a packet, using the
OAM field for PNPM in BIER layer can be viewed as the example of the
hybrid performance measurement method.
Figure 1 displays the interpretation of the OAM field defined in this
specification for the use of the PNPM method. The context of
interpretation of the OAM field MAY be signaled via the control plane
or configured using an extension to the BIER YANG data model
[I-D.ietf-bier-bier-yang]. These extensions are outside the scope of
this document.
0
0 1
+-+-+-+-+
| S | D |
+-+-+-+-+
Figure 1: OAM field of BIER Header format
where:
* S - Single-Marking flag;
* D - Double-Marking flag.
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4. Theory of Operation
The marking method can be used in the multicast environment supported
by BIER layer. Without limiting any generality consider multicast
network presented in Figure 2. Any combination of markings can be
applied to a multicast flow by the Bit Forwarding Ingress Router
(BFIR) at either ingress or egress point to perform node, link,
segment or end-to-end measurement to detect performance degradation
defect and localize it efficiently.
-----
--| D |
----- / -----
--| B |--
/ ----- \ -----
/ --| E |
----- / -----
| A |--- -----
----- \ --| F |
\ ----- / -----
--| C |--
----- \ -----
--| G |
-----
Figure 2: Multicast network
Using the marking method, a BFIR creates distinct sub-flows in the
particular multicast traffic over BIER layer. Each sub-flow consists
of consecutive blocks of identically marked packets. For example, a
block of N packets, with each packet being marked as X, is followed
by the block of M packets with each packet being marked as Y. These
blocks are unambiguously recognizable by a monitoring point at any
Bit Forwarding Router (BFR) and can be measured to calculate packet
loss and/or packet delay metrics. The marking method can be used on
multiple flows concurently. Demultiplexing of monitored flows might
be achived using n-tuple, for example, two-tuple as combination of
the values in the Entropy and BFIR-id fields [RFC8296]. Also, that
can be achieved by using an explicit Flow Identifiier. The
definition of the Flow Identifier is outside the scope of this
specification. It is expected that the marking values be set and
cleared at the edge of BIER domain. Thus for the scenario presented
in Figure 2 if the operator initially monitors the A-C-G and A-B-D
segments he may enable measurements on segments C-F and B-E at any
time.
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4.1. Single-Marking Enabled Measurement
As explained in [RFC9341], marking can be applied to delineate blocks
of packets based either on the equal number of packets in a block or
based on the equal time interval. The latter method offers better
control as it allows a better account for capabilities of downstream
nodes to report statistics related to batches of packets and, at the
same time, time resolution that affects defect detection interval.
If the Single-Marking measurement is used to measure packet loss,
then the D flag MUST be set to zero on transmit and ignored by the
monitoring point.
The S flag is used to create sub-flows to measure the packet loss by
switching the value of the S flag every N-th packet or at certain
time intervals. Delay metrics MAY be calculated with the sub-flow
using any of the following methods:
* First/Last Packet Delay calculation: whenever the marking, i.e.,
the value of S flag changes, a BFR can store the timestamp of the
first/last packet of the block. The timestamp can be compared
with the timestamp of the packet that arrived in the same order
through a monitoring point at a downstream BFR to compute packet
delay. Because timestamps collected based on the order of arrival
this method is sensitive to packet loss and re-ordering of packets
(see Section 4.3 for more details).
* Average Packet Delay calculation: an average delay is calculated
by considering the average arrival time of the packets within a
single block. A BFR may collect timestamps for each packet
received within a single block. Average of the timestamp is the
sum of all the timestamps divided by the total number of packets
received. Then the difference between the average packet arrival
time calculated for the downstream monitoring point and the same
metric but calculated at the upstream monitoring point is the
average packet delay on the segment between these two points.
This method is robust to out of order packets and also to packet
loss on the segment between the measurement points (packet loss
may cause a minor loss of accuracy in the calculated metric
because the number of packets used is different at each
measurement point). This method only provides a single metric for
the duration of the block, and it doesn't give the minimum and
maximum delay values. This limitation of producing only the
single metric could be overcome by reducing the duration of the
block. As a result, the calculated value of the average delay
will better reflect the minimum and maximum delay values of the
block's duration time.
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4.2. Double-Marking Enabled Measurement
Double-Marking method allows measurement of minimum and maximum
delays for the monitored flow, but it requires more nodal and network
resources. If the Double-Marking method used, then the S flag is
used to create the sub-flow, i.e., mark blocks of packets. The D
flag is used to mark single packets within a block to measure delay
and jitter.
The first marking (S flag alternation) is needed for packet loss and
also for average delay measurement. The second marking (D flag is
put to one) creates a new set of marked packets that are fully
identified over the BIER network, so that a BFR can store the
timestamps of these packets; these timestamps can be compared with
the timestamps of the same packets on a second BFR to compute packet
delay values for each packet. The number of measurements can be
easily increased by changing the frequency of the second marking. On
the other hand, the higher frequency of the second marking will cause
a higher volume of the measurement data being transported through the
BIER domain. An operator should consider and balance both effects.
This method is useful to measure not only the average delay but also
the minimum and maximum delay values and, in wider terms, to know
more about the statistic distribution of delay values.
4.3. Operational Considerations
For the ease of operational procedures, the initial marking of a
multicast flow is performed at BFIR. and cleared, by way of removing
BIER encapsulation form a payload packet, at the edge of the BIER
domain by BFERs.
Since at the time of writing this specification, there are no
proposals to using auto-discovery or signaling mechanism to inform
downstream nodes what methodology is used each monitoring point MUST
be configured beforehand.
Section 5 [RFC9341] provides a detailed analysis of how packet re-
ordering and the duration of the block in the Single-Marking mode of
the marking method impact the accuracy of the packet loss
measurement. Re-ordering of packets in the Single-Marking mode will
be noticeable only at the edge of a block of packets (re-ordering
within the block cannot be detected in the Single-Marking mode). If
the extra delay for some packets is much smaller than half of the
duration of a block, then it should be easier to attribute re-ordered
packets to the proper block and thus maintain the accuracy of the
packet loss measurement.
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Selection of a time interval to switch the marking of a batch of
packets should be based on the service requirements. In the course
of the regular operation, reports, including performance metrics like
packet loss ratio, packet delay, and inter-packet delay variation,
are logged every 15 minutes. Thus, it is reasonable to maintain the
duration of the measurement interval at 5 minutes with 100
measurements per each interval. To support these measurements,
marking of the packet batch is switched every 3 seconds. In case
when performance metrics are required in near-real-time, the duration
interval of a single batch of identically marked packets will be in
the range of tens of milliseconds.
5. IANA Considerations
This document sets no requirements to IANA. This section can be
removed before the publication.
6. Security Considerations
Regarding using the marking method, [RFC9341] stressed two types of
security concerns. First, the potential harm caused by the
measurements, is a lesser threat as [RFC8296] defines OAM field used
by the marking method so that the value of "two bits have no effect
on the path taken by a BIER packet and have no effect on the quality
of service applied to a BIER packet." Second security concern,
potential harm to the measurements can be mitigated by using policy,
suggested in [RFC8296], to accept BIER packets only from trusted
routers, not from customer-facing interfaces.
All the security considerations for BIER discussed in [RFC8296] are
inherited by this document.
7. Acknowledgement
Comments from Alvaro Retana helped improve the document and are much
appreciated.
Reviews and comments from Quan Xiong and Xiao Min are thankfully
acknowledged.
8. References
8.1. Normative References
[RFC2119] Bradner, S., "Key words for use in RFCs to Indicate
Requirement Levels", BCP 14, RFC 2119,
DOI 10.17487/RFC2119, March 1997,
<https://www.rfc-editor.org/info/rfc2119>.
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[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>.
[RFC8296] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Tantsura, J., Aldrin, S., and I. Meilik, "Encapsulation
for Bit Index Explicit Replication (BIER) in MPLS and Non-
MPLS Networks", RFC 8296, DOI 10.17487/RFC8296, January
2018, <https://www.rfc-editor.org/info/rfc8296>.
[RFC9341] Fioccola, G., Ed., Cociglio, M., Mirsky, G., Mizrahi, T.,
and T. Zhou, "Alternate-Marking Method", RFC 9341,
DOI 10.17487/RFC9341, December 2022,
<https://www.rfc-editor.org/info/rfc9341>.
[RFC9342] Fioccola, G., Ed., Cociglio, M., Sapio, A., Sisto, R., and
T. Zhou, "Clustered Alternate-Marking Method", RFC 9342,
DOI 10.17487/RFC9342, December 2022,
<https://www.rfc-editor.org/info/rfc9342>.
8.2. Informative References
[I-D.ietf-bier-bier-yang]
Chen, R., hu, F., Zhang, Z., dai.xianxian@zte.com.cn, and
M. Sivakumar, "YANG Data Model for BIER Protocol", Work in
Progress, Internet-Draft, draft-ietf-bier-bier-yang-08, 18
September 2023, <https://datatracker.ietf.org/doc/html/
draft-ietf-bier-bier-yang-08>.
[I-D.ietf-bier-oam-requirements]
Mirsky, G., Nainar, N. K., Chen, M., and S. Pallagatti,
"Operations, Administration and Maintenance (OAM)
Requirements for Bit Index Explicit Replication (BIER)
Layer", Work in Progress, Internet-Draft, draft-ietf-bier-
oam-requirements-13, 10 August 2023,
<https://datatracker.ietf.org/doc/html/draft-ietf-bier-
oam-requirements-13>.
[RFC7799] Morton, A., "Active and Passive Metrics and Methods (with
Hybrid Types In-Between)", RFC 7799, DOI 10.17487/RFC7799,
May 2016, <https://www.rfc-editor.org/info/rfc7799>.
[RFC8279] Wijnands, IJ., Ed., Rosen, E., Ed., Dolganow, A.,
Przygienda, T., and S. Aldrin, "Multicast Using Bit Index
Explicit Replication (BIER)", RFC 8279,
DOI 10.17487/RFC8279, November 2017,
<https://www.rfc-editor.org/info/rfc8279>.
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Authors' Addresses
Greg Mirsky
Ericsson
Email: gregimirsky@gmail.com
Lianshu Zheng
Individual Contributor
Email: veronique_zheng@hotmail.com
Mach Chen
Huawei Technologies
Email: mach.chen@huawei.com
Giuseppe Fioccola
Huawei Technologies
Email: giuseppe.fioccola@huawei.com
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