SPRING Working Group R. Gandhi, Ed.
Internet-Draft C. Filsfils
Intended Status: Informational Cisco Systems, Inc.
Expires: August 18, 2019 D. Voyer
Bell Canada
S. Salsano
Universita di Roma "Tor Vergata"
P. L. Ventre
CNIT
M. Chen
Huawei
February 14, 2019
In-band Performance Measurement for
Segment Routing Networks with MPLS Data Plane
draft-gandhi-spring-rfc6374-srpm-mpls-00
Abstract
RFC 6374 specifies protocol mechanisms to enable the 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
using probe messages. This document reviews how these mechanisms can
be used for Delay and Loss Performance Measurements (PM) in Segment
Routing (SR) networks with MPLS data plane (SR-MPLS), for both SR
links and end-to-end SR Policies. The performance measurements for
SR links are used to compute extended Traffic Engineering (TE)
metrics for delay and loss and are advertised in the network using
the routing protocol extensions.
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
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material or to cite them other than as "work in progress."
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Copyright Notice
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . . 3
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
2.1. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 3
2.2. Reference Topology . . . . . . . . . . . . . . . . . . . . 4
2.3. In-band Probe Messages . . . . . . . . . . . . . . . . . . 5
3. Probe Query and Response Packets . . . . . . . . . . . . . . . 5
3.1. Probe Packet Header for SR-MPLS Policies . . . . . . . . . 5
3.2. Probe Packet Header for SR-MPLS Links . . . . . . . . . . 6
3.3. Probe Response Message for SR-MPLS Links and Policies . . 6
3.3.1. One-way Measurement Probe Response Message . . . . . . 6
3.3.2. Two-way Measurement Probe Response Message . . . . . . 6
4. Performance Delay Measurement . . . . . . . . . . . . . . . . 7
4.1. Delay Measurement Message Format . . . . . . . . . . . . . 7
4.2. Timestamps . . . . . . . . . . . . . . . . . . . . . . . . 7
5. Performance Loss Measurement . . . . . . . . . . . . . . . . . 7
5.1. Loss Measurement Message Format . . . . . . . . . . . . . 8
6. Performance Measurement for P2MP SR Policies . . . . . . . . . 8
7. ECMP for SR-MPLS Policies . . . . . . . . . . . . . . . . . . 8
8. SR Link Extended TE Metrics Advertisements . . . . . . . . . . 8
9. Security Considerations . . . . . . . . . . . . . . . . . . . 9
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 9
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 9
11.1. Normative References . . . . . . . . . . . . . . . . . . 9
11.2. Informative References . . . . . . . . . . . . . . . . . 9
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 11
Contributors . . . . . . . . . . . . . . . . . . . . . . . . . . . 11
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . . 11
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1. Introduction
Service provider's ability to satisfy Service Level Agreements (SLAs)
depend on the ability to measure and monitor performance metrics for
packet loss and one-way and two-way delay, as well as related metrics
such as delay variation. The ability to monitor these performance
metrics also provides operators with greater visibility into the
performance characteristics of their networks, thereby facilitating
planning, troubleshooting, and network performance evaluation.
[RFC6374] specifies protocol mechanisms to enable the efficient and
accurate measurement of performance metrics in MPLS networks using
probe messages. The One-Way Active Measurement Protocol (OWAMP)
defined in [RFC4656] and Two-Way Active Measurement Protocol (TWAMP)
defined in [RFC5357] provide capabilities for the measurement of
various performance metrics in IP networks. However, mechanisms
defined in [RFC6374] are more suitable for Segment Routing (SR) when
using MPLS data plane (SR-MPLS). The [RFC6374] also supports IEEE
1588 timestamps [IEEE1588] and "direct mode" Loss Measurement (LM),
which are required in SR networks.
[RFC7876] specifies the procedures to be used when sending and
processing out-of-band performance measurement probe replies over an
UDP return path when receiving RFC 6374 based probe queries. These
procedures can be used to send out-of-band PM replies for both SR
links and SR Policies [I-D.spring-segment-routing-policy] for one-way
measurement.
This document reviews how probe based mechanisms defined in [RFC6374]
can be used for Delay and Loss Performance Measurements (PM) in SR
networks with MPLS data plane, for both SR links and end-to-end SR
Policies. The performance measurements for SR links are used to
compute extended Traffic Engineering (TE) metrics for delay and loss
and are advertised in the network using routing protocol extensions.
2. Conventions Used in This Document
2.1. Abbreviations
ACH: Associated Channel Header.
DM: Delay Measurement.
ECMP: Equal Cost Multi-Path.
G-ACh: Generic Associated Channel (G-ACh).
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GAL: Generic Associated Channel (G-ACh) Label.
LM: Loss Measurement.
MPLS: Multiprotocol Label Switching.
NTP: Network Time Protocol.
PM: Performance Measurement.
PSID: Path Segment Identifier.
PTP: Precision Time Protocol.
SID: Segment ID.
SL: Segment List.
SR: Segment Routing.
SR-MPLS: Segment Routing with MPLS data plane.
TC: Traffic Class.
TE: Traffic Engineering.
URO: UDP Return Object.
2.2. Reference Topology
In the reference topology shown in Figure 1, the querier node R1
initiates a performance measurement probe query and the responder
node R5 sends a probe response for the query message received. The
probe response is typically sent to the querier node R1. The nodes
R1 and R5 may be directly connected via a link enabled with Segment
Routing or there exists a Point-to-Point (P2P) SR Policy
[I-D.spring-segment-routing-policy] on node R1 with destination to
node R5. In case of Point-to-Multipoint (P2MP), SR Policy
originating from source node R1 may terminate on multiple destination
leaf nodes [I-D.spring-sr-p2mp-policy].
+-------+ Query +-------+
| | - - - - - - - - - ->| |
| R1 |---------------------| R5 |
| |<- - - - - - - - - - | |
+-------+ Response +-------+
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Figure 1: Reference Topology
Both delay and loss performance measurement is performed in-band for
the traffic traversing between node R1 and node R5. One-way delay
and two-way delay measurements are defined in Section 2.4 of
[RFC6374]. Transmit and Receive packet loss measurements are defined
in Section 2.2 and Section 2.6 of [RFC6374]. One-way loss
measurement provides receive packet loss whereas two-way loss
measurement provides both transmit and receive packet loss.
2.3. In-band Probe Messages
For both Delay and Loss measurements for links and SR Policies, no PM
session is created on the responder node. The probe messages for
Delay measurement are sent in-band by the querier node to measure the
delay experienced by the actual traffic flowing on the links and SR
Policies. For Loss measurement, in-band probe messages are used to
collect the traffic counter for the incoming link or incoming SID on
which the probe query message is received at the responder node R5
(as it has no PM session state present on the node).
3. Probe Query and Response Packets
3.1. Probe Packet Header for SR-MPLS Policies
As described in Section 2.9.1 of [RFC6374], MPLS PM probe query and
response messages flow over the MPLS Generic Associated Channel (G-
ACh). A probe packet for an end-to-end measurement for SR Policy
contains SR-MPLS label stack [I-D.spring-segment-routing-policy],
with the G-ACh Label (GAL) at the bottom of the stack. The GAL is
followed by an Associated Channel Header (ACH), which identifies the
message type and the message payload following the ACH as shown in
Figure 2.
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(0) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
. .
. .
. .
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Label(n) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GAL (value 13) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Reserved | GAL Channel Type |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 2: Probe Packet Header for an End-to-end SR-MPLS Policy
The SR-MPLS label stack can be empty to indicate Implicit NULL label
case.
3.2. Probe Packet Header for SR-MPLS Links
As described in Section 2.9.1 of [RFC6374], MPLS PM probe query and
response messages flow over the MPLS Generic Associated Channel
(G-ACh). A probe packet for SR-MPLS links contains G-ACh Label
(GAL). The GAL is followed by an Associated Channel Header (ACH),
which identifies the message type, and the message payload following
the ACH as shown in Figure 3.
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| GAL (value 13) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
|0 0 0 1|Version| Reserved | GAL Channel Type |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 3: Probe Packet Header for an SR-MPLS Link
3.3. Probe Response Message for SR-MPLS Links and Policies
3.3.1. One-way Measurement Probe Response Message
For one-way performance measurement [RFC7679], the PM querier node
can receive "out-of-band" probe replies by properly setting the UDP
Return Object (URO) TLV in the probe query message. The URO TLV
(Type=131) is defined in [RFC7876] and includes the
UDP-Destination-Port and IP Address. In particular, if the querier
sets its own IP address in the URO TLV, the probe response is sent
back by the responder node to the querier node. In addition, the
"control code" in the probe query message is set to "out-of-band
response requested". The "Source Address" TLV (Type 130), and
"Return Address" TLV (Type 1), if present in the probe query message,
are not used to send probe response message.
3.3.2. Two-way Measurement Probe Response Message
For two-way performance measurement [RFC6374], when using a
bidirectional channel, the probe response message is sent back to the
querier node in-band on the reverse direction SR Link or SR Policy
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using a message with format similar to their probe query message. In
this case, the "control code" in the probe query message is set to
"in-band response requested".
A Path Segment Identifier [I-D.spring-mpls-path-segment] of the
forward SR Policy can be used to find the reverse SR Policy and to
send back the probe response message.
4. Performance Delay Measurement
4.1. Delay Measurement Message Format
As defined in [RFC6374], MPLS DM probe query and response messages
use Associated Channel Header (ACH) (value 0x000C for delay
measurement) [RFC6374], which identifies the message type, and the
message payload following the ACH. For both SR links and end-to-end
measurement for SR Policies, the same MPLS DM ACH value is used.
The DM message payload as defined in Section 3.2 of [RFC6374] is used
for SR-MPLS delay measurement, for both SR links and end-to-end SR
Policies.
4.2. Timestamps
The Section 3.4 of [RFC6374] defines timestamp format that can be
used for delay measurement. The IEEE 1588 Precision Time Protocol
(PTP) timestamp format [IEEE1588] is used by default as described in
Appendix A of [RFC6374], but it may require hardware support. As an
alternative, Network Time Protocol (NTP) timestamp format can also be
used [RFC6374].
Note that for one-way delay measurement, clock synchronization
between the querier and responder nodes using the methods detailed in
[RFC6374] is required. The two-way delay measurement does not
require clock synchronization between the querier and responder
nodes.
5. Performance Loss Measurement
The LM protocol can perform two distinct kinds of loss measurement as
described in Section 2.9.8 of [RFC6374].
o In inferred mode, LM will measure the loss of specially generated
test messages in order to infer the approximate data plane loss
level. Inferred mode LM provides only approximate loss
accounting.
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o In direct mode, LM will directly measure data plane packet loss.
Direct mode LM provides perfect loss accounting, but may require
hardware support.
For both of these modes of LM, Path Segment Identifier (PSID)
[I-D.spring-mpls-path-segment] is used for accounting received
traffic on the egress node of the SR-MPLS Policy.
5.1. Loss Measurement Message Format
As defined in [RFC6374], MPLS LM probe query and response messages
use Associated Channel Header (ACH) (value 0x000A for direct loss
measurement or value 0x000B for inferred loss measurement), which
identifies the message type, and the message payload following the
ACH. For both SR links and end-to-end measurement for SR Policies,
the same MPLS LM ACH value is used.
The LM message payload as defined in Section 3.1 of [RFC6374] is used
for SR-MPLS loss measurement, for both SR links and end-to-end SR
Policies.
6. Performance Measurement for P2MP SR Policies
The procedures for delay and loss measurement reviewed in this
document for Point-to-Point (P2P) SR-MPLS Policies are also equally
applicable to the Point-to-Multipoint (P2MP) SR Policies.
The responder node adds the "Source Address" TLV (Type 130) [RFC6374]
in the probe response message. This TLV allows the querier node to
identify the responder nodes of the P2MP SR Policy.
7. ECMP for SR-MPLS Policies
An SR Policy can have ECMPs between the source and transit nodes,
between transit nodes and between transit and destination nodes.
Usage of Anycast SID [RFC8402] by an SR Policy can result in ECMP
paths via transit nodes part of that Anycast group. The PM messages
using [RFC6374] can not traverse all ECMP paths to measure
performance delay of all paths of an SR Policy.
8. SR Link Extended TE Metrics Advertisements
The extended TE metrics for SR link delay and loss computed using the
performance measurement procedures reviewed in this document can be
advertised in the routing domain as follows:
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o For OSPF, ISIS, and BGP-LS, protocol extensions defined in
[RFC7471], [RFC7810] [I-D.lsr-isis-rfc7810bis], and
[I-D.idr-te-pm-bgp] are used, respectively for advertising the
extended TE link metrics in the network.
o The extended TE link delay metrics advertised are minimum-delay,
maximum-delay, average-delay, and delay-variance for one-way.
o The delay-variance metric is computed as specified in Section 4.2
of [RFC5481].
o The one-way delay metrics can be computed using two-way
measurement by dividing the measured delay values by 2.
o The extended TE link loss metric advertised is one-way percentage
packet loss.
9. Security Considerations
This document reviews the procedures for performance delay and loss
measurement for SR-MPLS networks, for both links and end-to-end SR
Policies using the mechanisms defined in [RFC6374]. This document
does not introduce any additional security considerations other than
those covered in [RFC6374], [RFC7471], [RFC7810], and [RFC7876].
10. IANA Considerations
This document does not require any IANA actions.
11. References
11.1. Normative References
[RFC6374] Frost, D. and S. Bryant, "Packet Loss and Delay
Measurement for MPLS networks', RFC 6374, September 2011.
[RFC7876] Bryant, S., Sivabalan, S., and Soni, S., "UDP Return Path
for Packet Loss and Delay Measurement for MPLS Networks",
RFC 7876, July 2016.
11.2. Informative References
[IEEE1588] IEEE, "1588-2008 IEEE Standard for a Precision Clock
Synchronization Protocol for Networked Measurement and
Control Systems", March 2008.
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[RFC4656] Shalunov, S., Teitelbaum, B., Karp, A., Boote, J., and M.
Zekauskas, "A One-way Active Measurement Protocol
(OWAMP)", RFC 4656, September 2006.
[RFC5357] Hedayat, K., Krzanowski, R., Morton, A., Yum, K., and J.
Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)",
RFC 5357, October 2008.
[RFC5481] Morton, A. and B. Claise, "Packet Delay Variation
Applicability Statement", RFC 5481, March 2009.
[RFC7679] Almes, G., et al., "A One-Way Delay Metric for IP
Performance Metrics (IPPM)', RFC 7679, January 2016.
[RFC7471] Giacalone, S., et al., "OSPF Traffic Engineering (TE)
Metric Extensions", RFC 7471, March 2015.
[RFC7810] Previdi, S., et al., "IS-IS Traffic Engineering (TE)
Metric Extensions", RFC 7810, May 2016.
[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>.
[I-D.lsr-isis-rfc7810bis] Ginsberg, L., et al., "IS-IS Traffic
Engineering (TE) Metric Extensions",
draft-ietf-lsr-isis-rfc7810bis, work in progress.
[I-D.idr-te-pm-bgp] Ginsberg, L. Ed., et al., "BGP-LS Advertisement
of IGP Traffic Engineering Performance Metric Extensions",
draft-ietf-idr-te-pm-bgp, work in progress.
[I-D.spring-segment-routing-policy] Filsfils, C., et al., "Segment
Routing Policy Architecture",
draft-ietf-spring-segment-routing-policy, work in
progress.
[I-D.spring-sr-p2mp-policy] Voyer, D. Ed., et al., "SR Replication
Policy for P2MP Service Delivery",
draft-voyer-spring-sr-p2mp-policy, work in progress.
[I-D.spring-mpls-path-segment] Cheng, W., et al., "Path Segment in
MPLS Based Segment Routing Network",
draft-cheng-spring-mpls-path-segment, work in progress.
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Acknowledgments
The authors would like to thank Greg Mirsky for providing many useful
comments and suggestions.
Contributors
Sagar Soni
Cisco Systems, Inc.
Email: sagsoni@cisco.com
Patrick Khordoc
Cisco Systems, Inc.
Email: pkhordoc@cisco.com
Zafar Ali
Cisco Systems, Inc.
Email: zali@cisco.com
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
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Pier Luigi Ventre
CNIT
Italy
Email: pierluigi.ventre@cnit.it
Mach(Guoyi) Chen
Huawei
Email: mach.chen@huawei.com
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