Internet DRAFT - draft-gandhi-spring-sr-enhanced-plm
draft-gandhi-spring-sr-enhanced-plm
SPRING Working Group R. Gandhi, Ed.
Internet-Draft C. Filsfils
Intended status: Standards Track Cisco Systems, Inc.
Expires: August 13, 2021 N. Vaghamshi
Reliance
M. Nagarajah
Telstra
R. Foote
Nokia
February 09, 2021
Enhanced Performance and Liveness Monitoring in Segment Routing Networks
draft-gandhi-spring-sr-enhanced-plm-04
Abstract
Segment Routing (SR) leverages the source routing paradigm. SR is
applicable to both Multiprotocol Label Switching (SR-MPLS) and IPv6
(SRv6) data planes. This document defines procedures for Enhanced
Performance and Liveness Monitoring (PLM) for end-to-end SR paths
including SR Policies for both SR-MPLS and SRv6 data planes, those
reduce the deployment and operational complexities in a network.
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
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material or to cite them other than as "work in progress."
This Internet-Draft will expire on August 13, 2021.
Copyright Notice
Copyright (c) 2021 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
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Table of Contents
1. Introduction . . . . . . . . . . . . . . . . . . . . . . . . 2
2. Conventions Used in This Document . . . . . . . . . . . . . . 3
2.1. Requirements Language . . . . . . . . . . . . . . . . . . 3
2.2. Abbreviations . . . . . . . . . . . . . . . . . . . . . . 4
2.3. Reference Topology . . . . . . . . . . . . . . . . . . . 5
3. Overview . . . . . . . . . . . . . . . . . . . . . . . . . . 5
3.1. Loopback Mode . . . . . . . . . . . . . . . . . . . . . . 5
3.2. Loopback Mode Enabled with Network Programming Function . 6
3.3. Example Provisioning Model . . . . . . . . . . . . . . . 6
4. PLM Test Packet Formats . . . . . . . . . . . . . . . . . . . 7
5. PLM Procedure . . . . . . . . . . . . . . . . . . . . . . . . 9
5.1. PLM for SR-MPLS Policies . . . . . . . . . . . . . . . . 10
5.2. PLM for SRv6 Policies . . . . . . . . . . . . . . . . . . 10
6. Enhanced PLM Procedure . . . . . . . . . . . . . . . . . . . 11
6.1. Enhanced PLM with Timestamp Label for SR-MPLS Policies . 11
6.1.1. Timestamp Label Allocation . . . . . . . . . . . . . 12
6.1.2. Node Capability for Timestamp Label . . . . . . . . . 13
6.2. Enhanced PLM with Timestamp Endpoint Function for SRv6
Policies . . . . . . . . . . . . . . . . . . . . . . . . 13
6.2.1. Timestamp Endpoint Function Assignment . . . . . . . 14
6.2.2. Node Capability for Timestamp Endpoint Function . . . 15
7. ECMP Handling . . . . . . . . . . . . . . . . . . . . . . . . 15
8. Example PLM Failure Notifications . . . . . . . . . . . . . . 15
9. Security Considerations . . . . . . . . . . . . . . . . . . . 16
10. IANA Considerations . . . . . . . . . . . . . . . . . . . . . 16
11. References . . . . . . . . . . . . . . . . . . . . . . . . . 17
11.1. Normative References . . . . . . . . . . . . . . . . . . 17
11.2. Informative References . . . . . . . . . . . . . . . . . 18
Acknowledgments . . . . . . . . . . . . . . . . . . . . . . . . . 19
Authors' Addresses . . . . . . . . . . . . . . . . . . . . . . . 19
1. Introduction
Segment Routing (SR) leverages the source routing paradigm and
greatly simplifies network operations for Software Defined Networks
(SDNs). SR is applicable to both Multiprotocol Label Switching (SR-
MPLS) and IPv6 (SRv6) data planes [RFC8402]. SR Policies as defined
in [I-D.ietf-spring-segment-routing-policy] are used to steer traffic
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through a specific, user-defined paths using a stack of Segments.
Built-in Performance Measurement as well as Liveness Monitoring for
Connectivity Verification (CV) and Continuity Check (CC) are
essential requirements to provide Service Level Agreements (SLAs) in
SR networks.
The Simple Two-way Active Measurement Protocol (STAMP) provides
capabilities for the measurement of various performance metrics in IP
networks [RFC8762]. It eliminates the need for control protocol by
using configuration and management model to provision and manage test
sessions. The STAMP can be used for Performance Measurement (PM) in
SR networks as well as liveness monitoring and connectivity loss
detection of SR paths. However, the STAMP requires protocol support
on the Session-Reflector to process the STAMP test packets as packets
need to be punted from the forwarding fast path (to slow path or
control plane) on the Session-Reflector and STAMP reply test packets
need to be generated. This limits the scale for number of STAMP test
sessions and faster fault detection intervals.
For Liveness Monitoring, Seamless Bidirectional Forwarding Detection
(S-BFD) [RFC7880] can be used in SR networks. However, S-BFD
requires protocol support on the BFD-Reflector to process the S-BFD
packets as packets need to be punted from the forwarding fast path
and generate the reply packets thereby limiting the scale for number
S-BFD sessions and faster fault detection intervals. In addition,
S-BFD protocol is not defined to enable performance measurement in a
network.
Enabling multiple protocols, S-BFD for liveness monitoring and STAMP
for performance measurement increases the deployment and operational
complexities a network. Also, implementing multiple protocols in a
hardware significantly increases the development cost.
This document defines procedures for Enhanced Performance and
Liveness Monitoring (PLM) for end-to-end SR paths including SR
Policies for both SR-MPLS and SRv6 data planes, those reduce the
deployment and operational complexities in a network. The procedures
use the new test packet formats those have the timestamps at the same
locations as the base STAMP test packets to leverage the existing
hardware support for STAMP.
2. Conventions Used in This Document
2.1. Requirements Language
The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT",
"SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this
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document are to be interpreted as described in [RFC2119] [RFC8174]
when, and only when, they appear in all capitals, as shown here.
2.2. Abbreviations
S-BFD: Seamless Bidirectional Forwarding Detection.
BSID: Binding Segment ID.
ECMP: Equal Cost Multi-Path.
EB: Endpoint Behaviour.
HMAC: Hashed Message Authentication Code.
MBZ: Must be Zero.
MPLS: Multiprotocol Label Switching.
PLM: Performance and Liveness Monitoring.
PM: Performance Measurement.
PTP: Precision Time Protocol.
SID: Segment ID.
SL: Segment List.
SR: Segment Routing.
SRH: Segment Routing Header.
SR-MPLS: Segment Routing with MPLS data plane.
SRv6: Segment Routing with IPv6 data plane.
SSID: Sender Session Identifier.
STAMP: Simple Two-way Active Measurement Protocol.
TC: Traffic Class.
TTL: Time To Live.
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2.3. Reference Topology
In the reference topology shown below, the Session-Sender R1
initiates a PLM test packet and the Session-Reflector R3 transmits a
PLM return test packet. The PLM return test packet is transmitted
back to the Session-Sender R1 on the same path or a different path in
the reverse direction.
The Session-Sender R1 and Session-Reflector R3 are connected via an
SR path [RFC8402]. The SR path may be an SR Policy
[I-D.ietf-spring-segment-routing-policy] on node R1 (called head-end)
with destination to node R3 (called tail-end).
T1
/
+-------+ PLM Test Packet +-------+
| | - - - - - - - - - - - | |
| R1 |======================|| R3 |
| |<- - - - - - - - - - - | |
+-------+ Return Test Packet +-------+
\
T4
Session-Sender Session-Reflector
(Simply Forward)
Reference Topology
3. Overview
3.1. Loopback Mode
In loopback mode, the Session-Sender R1 initiates PLM test packets
and the Session-Reflector R3 forwards them just like data packets for
the regular traffic back to the Session-Sender R1. The PLM test
packets are not punted at the Session-Reflector and does not process
them and generate PLM return test packets. The Session-Reflector
must not drop the loopback PLM test packets, for example, due to a
local policy provisioned. No PLM test session is created on the
Session-Reflector.
The Source and Destination IP addresses in the PLM test packets are
set to the Session-Reflector and the Session-Sender IP addresses,
respectively (representing the reverse direction path). The Source
and Destination UDP ports in the PLM test packets follow the
procedure defined in [RFC8762]. The IPv4 Time To Live (TTL) and IPv6
Hop Limit (HL) are set to 255.
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3.2. Loopback Mode Enabled with Network Programming Function
In loopback mode enabled with network programming function, both
transmit (T1) and receive (T2) timestamps in data plane are collected
by the PLM test packets transmitted in loopback mode as shown in
Figure 1. The network programming function optimizes the "operations
of punt and generate the PLM test packet" on the Session-Reflector as
timestamping is implemented in forwarding fast path in hardware.
This helps to achieve higher test session scale and faster failure
detection interval.
T1 T2
/ \
+-------+ PLM Test Packet +-------+
| | - - - - - - - - - - - | |
| R1 |======================|| R3 |
| |<- - - - - - - - - - - | |
+-------+ Return Test Packet +-------+
\
T4
Session-Sender Session-Reflector
(Timestamp,
Pop and Forward)
Figure 1: Loopback Mode Enabled with Network Programming Function
The Session-Sender adds transmit timestamp (T1) in the payload of the
PLM test packet and clears the receive (T2) timestamp. The Session-
Reflector adds the receive timestamp (T2) in the payload of the
received PLM test packet in forwarding fast path in hardware without
punting the test packet to the slow path (or control-plane). The
network programming function enables Session-Reflector to add the
receive timestamp (T2) at a specific offset in the payload which is
locally provisioned consistently in the network. The payload of the
PLM test packet is not modified by the intermediate nodes.
The Session-Reflector only adds the receive timestamp if the source
IP address (in case of SR-MPLS) or destination IP address (in case of
SRv6) in the PLM test packet matches the local node address to ensure
that the PLM test packet reaches the intended Session-Reflector and
the receive timestamp is returned by the intended Session-Reflector.
3.3. Example Provisioning Model
An example provisioning model and typical measurement parameters are
shown in Figure 2:
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+------------+
| Controller |
+------------+
PLM Mode / \ Timestamp Label/SRV6 EB
Loopback or Enhanced Mode / \ Timestamp Offset
Timestamp Label/SRv6 EB / \ Timestamp Format
Timestamp Format / \
Missed Packet Count (N) / \
Delay Threshold/Count (T/M) / \
Packet Loss Threshold (XofY)/ \
v v
+-------+ +-------+
| | | |
| R1 |==========| R3 |
| | | |
+-------+ +-------+
Session-Sender Session-Reflector
Figure 2: Example Provisioning Model
Example of PLM mode is loopback mode. The values for Timestamp Label
and SRv6 Endpoint Behaviour may be provisioned as described in
Section 6. Example of Timestamp Format is 64-bit PTPv2 [IEEE1588].
Example of Timestamp Offset is 16 and 32 bytes for the PLM test
packet formats defined in this document. Example threshold values
configured for generating notifications are: Missed Packet Count (N),
Delay Exceeded Threshold and Packet Count (T/M) and Packet Loss
Threshold (XofY), as described in Section 7.
The mechanisms to provision the Session-Sender and Session-Reflector
are outside the scope of this document.
4. PLM Test Packet Formats
The PLM test packet formats for unauthenticated and authenticated
modes are defined in this document as shown in Figure 3 those have
the transmit and receive timestamps at the same locations as the base
STAMP test packets to leverage the existing hardware support for
STAMP.
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transmit Timestamp (T1) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transmit Error Estimate | SSID |
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+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receive Timestamp (T2) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MBZ (12 Octets) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receive Error Estimate | MBZ |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (4 Octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PLM Test Packet Format in Unauthenticated Mode
0 1 2 3
0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Sequence Number |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (12 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transmit Timestamp (T1) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Transmit Error Estimate | SSID |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| MBZ (4 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receive Timestamp (T2) |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MBZ (32 octets) |
| |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Receive Error Estimate | |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ +
| MBZ (6 octets) |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| MBZ (16 octets) |
| |
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| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| |
| HMAC (16 octets) |
| |
| |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
PLM Test Packet Format in Authenticated Mode
Figure 3: PLM Test Packet Formats
Sequence Number is the sequence number of the PLM test packet
according to its transmit order. It starts with zero and is
incremented by one for each subsequent PLM test packet.
SSID (16-bits): PLM Sender Session Identifier. Uses the procedure
for SSID defined in [RFC8762].
Transmit Timestamp and Transmit Error Estimate are the Session-
Sender's transmit timestamp and error estimate for the PLM test
packet, respectively.
Receive Timestamp and Receive Error Estimate are the Session-
Reflector's receive timestamp and error estimate, respectively.
The timestamp and error estimate fields follow the definition and
formats defined in Section 4.1.2 in [RFC8762]. The timestamp format
used by default is 64-bit PTPv2 [IEEE1588].
HMAC: The use of the HMAC field is described in Section 4.4 of
[RFC8762].
MBZ: Must be Zero. It MUST be all zeroed on the transmission and
MUST be ignored on receipt.
5. PLM Procedure
For performance and liveness monitoring of an end-to-end SR path
including SR Policy, PLM test packets in loopback mode are used.
For SR Policy, the PLM test packets are transmitted using the Segment
List (SL) of the Candidate-Path
[I-D.ietf-spring-segment-routing-policy]. When a Candidate-Path has
more than one Segment Lists, multiple PLM test packets are sent, one
using each Segment List. The PLM return test packets are received by
the Session-Sender via IP/UDP [RFC0768] return path by default. The
Segment List of the return SR path can be added in the PLM test
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packet header to receive the return test packet on a specific path
using the Binding SID [I-D.ietf-pce-binding-label-sid] or Segment
List of the Reverse SR Policy [I-D.ietf-pce-sr-bidir-path].
5.1. PLM for SR-MPLS Policies
The PLM test packets are transmitted using the MPLS header for each
Label Stack of the SR-MPLS Policy Candidate-Path(s) as shown in
Figure 4. In case of IP/UDP return path, the MPLS header is removed
by the Session-Reflector. The Label Stack can contain a reverse SR-
MPLS path to receive the PLM return test packet on a specific path.
In this case, the MPLS header will not be removed by the Session-
Reflector.
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Header |
. Source IP Address = Session-Reflector IPv4 or IPv6 Address .
. Destination IP Address = Session-Sender IPv4 or IPv6 Address .
. Protocol = UDP .
. .
+---------------------------------------------------------------+
| UDP Header |
. Source Port = As chosen by Session-Sender .
. Destination Port = As chosen by Session-Sender .
. .
+---------------------------------------------------------------+
| Payload as defined in Figure 3 |
. .
+---------------------------------------------------------------+
Figure 4: Example PLM Test Packet for SR-MPLS
5.2. PLM for SRv6 Policies
The PLM test packets for SRv6 data plane are transmitted using the
Segment Routing Header (SRH) [RFC8754] for each Segment List of the
SRv6 Policy Candidate-Path(s) as shown in Figure 5. In case of IP/
UDP return path, the SRH is removed by the Session-Reflector. The
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Segment List can contain a reverse SRv6 path to receive the PLM
return test packet on a specific path. In this case, the SRH will
not be removed by the Session-Reflector. When the PLM return test
packet contains an SRH at the Session-Sender, the procedure defined
for upper-layer header processing for SRv6 SIDs in
[I-D.ietf-spring-srv6-network-programming] is used to process the UDP
header in the received PLM test packets.
+---------------------------------------------------------------+
| IP Header |
. Source IP Address = Session-Sender IPv6 Address .
. Destination IP Address = Destination IPv6 Address .
. .
+---------------------------------------------------------------+
| SRH as specified in RFC 8754 |
. <Segment List> .
. .
+---------------------------------------------------------------+
| IP Header |
. Source IP Address = Session-Reflector IPv6 Address .
. Destination IP Address = Session-Sender IPv6 Address .
. .
+---------------------------------------------------------------+
| UDP Header |
. Source Port = As chosen by Session-Sender .
. Destination Port = As chosen by Session-Sender .
. .
+---------------------------------------------------------------+
| Payload as defined in Figure 3 |
. .
+---------------------------------------------------------------+
Figure 5: Example PLM Test Packet for SRv6
6. Enhanced PLM Procedure
The enhanced performance and liveness monitoring of an end-to-end SR
path including SR Policy is defined using the PLM test packets in
loopback mode enabled with network programming function.
6.1. Enhanced PLM with Timestamp Label for SR-MPLS Policies
In this document, two new Timestamp Labels are defined for SR-MPLS
data plane to enable network programming function for "timestamp, pop
and forward" the received test packet.
In the PLM test packets for SR-MPLS Policies, a Timestamp Label is
added in the MPLS header as shown in Figure 6, to collect "Receive
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Timestamp" field in the payload of the PLM test packet. The Label
Stack for the reverse SR-MPLS path can be added after the Timestamp
Label to receive the PLM return test packet on a specific path. When
a Session-Reflector receives a packet with Timestamp Label, after
timestamping the packet at a specific offset, the Session-Reflector
pops the Timestamp Label and forwards the packet using the next label
or IP header in the packet (just like the data packets for the
regular traffic).
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 |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Extension Label (15) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| Timestamp Label (TBA1 or TBA2) | TC |S| TTL |
+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
| IP Header |
. Source IP Address = Session-Reflector IPv4 or IPv6 Address .
. Destination IP Address = Session-Sender IPv4 or IPv6 Address .
. Protocol = UDP .
. .
+---------------------------------------------------------------+
| UDP Header |
. Source Port = As chosen by Session-Sender .
. Destination Port = As chosen by Session-Sender .
. .
+---------------------------------------------------------------+
| Payload as defined in Figure 3 |
. .
+---------------------------------------------------------------+
Figure 6: Example PLM Test Packet with Timestamp Label for SR-MPLS
6.1.1. Timestamp Label Allocation
The timestamp Labels for unauthenticated and authenticated modes can
be allocated using one of the following methods:
o Labels (values TBA1 and TBA2) assigned by IANA from the "Extended
Special-Purpose MPLS Values" [I-D.ietf-mpls-spl-terminology]. For
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Label (value TBA1), the timestamp offset is fixed at byte-offset
16 from the start of the payload for the unauthenticated mode, and
Label (value TBA2) at byte-offset 32 from the start of the payload
for the authenticated mode, both using the timestamp format 64-bit
PTPv2.
o Labels allocated by a Controller from the global table of the
Session-Reflector. The Controller provisions the labels on both
Session-Sender and Session-Reflector, as well as timestamp offsets
and timestamp formats.
o Labels allocated by the Session-Reflector. The signaling and IGP
flooding extension for the labels (including timestamp offsets and
timestamp formats) are outside the scope of this document.
6.1.2. Node Capability for Timestamp Label
The PLM Session-Sender needs to know if the Session-Reflector can
process the Timestamp Label to avoid dropping PLM test packets. The
signaling extension for this capability exchange is outside the scope
of this document.
6.2. Enhanced PLM with Timestamp Endpoint Function for SRv6 Policies
The [I-D.ietf-spring-srv6-network-programming] defines SRv6 Endpoint
Behaviours (EB) for SRv6 nodes. In this document, two new Timestamp
Endpoint Behaviours are defined for Segment Routing Header (SRH)
[RFC8754] to enable "Timestamp and Forward (TSF)" function for the
received test packets.
In the PLM test packets for SRv6 Policies, Timestamp Endpoint
Function (End.TSF) is carried with the target Segment Identifier
(SID) in SRH [RFC8754] as shown in Figure 7, to collect "Receive
Timestamp" field in the payload of the PLM test packet. The Segment
List for the reverse path can be added after the target SID to
receive the PLM return test packet on a specific path. When a
Session-Reflector receives a packet with Timestamp Endpoint (End.TSF)
for the target SID which is local, after timestamping the packet at a
specific offset, the Session-Reflector forwards the packet using the
next SID or IP header in the packet (just like the data packets for
the regular traffic).
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+---------------------------------------------------------------+
| IP Header |
. Source IP Address = Session-Sender IPv6 Address .
. Destination IP Address = Destination IPv6 Address .
. .
+---------------------------------------------------------------+
| SRH as specified in RFC 8754 |
. <Segment List> .
. SRv6 Endpoint End.TSF (value TBA3 or TBA4) .
. .
+---------------------------------------------------------------+
| IP Header |
. Source IP Address = Session-Reflector IPv6 Address .
. Destination IP Address = Session-Sender IPv6 Address .
. .
+---------------------------------------------------------------+
| UDP Header |
. Source Port = As chosen by Session-Sender .
. Destination Port = As chosen by Session-Sender .
. .
+---------------------------------------------------------------+
| Payload as defined in Figure 3 |
. .
+---------------------------------------------------------------+
Figure 7: Example PLM Test Packet with Endpoint Function for SRv6
6.2.1. Timestamp Endpoint Function Assignment
The Timestamp Endpoint Functions for "Timestamp and Forward" can be
signaled using one of the following methods:
o Timestamp Endpoint Functions (values TBA3 and TBA4) assigned by
IANA from the "SRv6 Endpoint Behaviors Registry". For endpoint
behaviour (value TBA3), the timestamp offset is fixed at byte-
offset 16 from the start of the payload for the unauthenticated
mode, and endpoint behaviour (value TBA4) at byte-offset 32 from
the start of the payload for the authenticated mode, both using
the timestamp format 64-bit PTPv2.
o Timestamp Endpoint Functions assigned by a Controller. The
Controller provisions the values on both Session-Sender and
Session-Reflector, as well as timestamp offsets and timestamp
formats.
o Timestamp Endpoint Functions assigned by the Session-Reflector.
The signaling and IGP flooding extension for the endpoint
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functions (including timestamp offsets and timestamp formats) are
outside the scope of this document.
6.2.2. Node Capability for Timestamp Endpoint Function
The PLM Session-Sender needs to know if the Session-Reflector can
process the Timestamp Endpoint Function to avoid dropping PLM test
packets. The signaling extension for this capability exchange is
outside the scope of this document.
7. ECMP Handling
An SR Policy can have ECMPs between the source and transit nodes,
between transit nodes and between transit and destination nodes. The
PLM test packets need to be sent to traverse different ECMP paths to
monitor an end-to-end SR Policy.
Forwarding plane has various hashing functions available to forward
packets on specific ECMP paths. In IPv4 header of the PLM test
packets, sweeping of Destination Address from the 127/8 range can be
used to exercise different IPv4 ECMP paths in both loopback modes as
long as the forward and the return paths are SR-MPLS paths. In this
case, the TTL field in the IPv4 header is set to 1.
The Flow Label field in the outer IPv6 header can also be used for
sweeping to exercise different IPv6 ECMP paths.
8. Example PLM Failure Notifications
Liveness or connectivity success for an end-to-end SR path is
initially notified as soon as one or more PLM return test packets are
received at the Session-Sender.
Liveness or connectivity failure for an end-to-end SR path is
notified when consecutive N number of PLM return test packets are not
received at the Session-Sender, where N (Missed PLM Packet Count) is
a locally provisioned value.
The round-trip packet loss for an end-to-end SR path is calculated
using the Sequence Number in the PLM test packets. The packet loss
metric is notified when X number of PLM test packets were lost out of
last Y number of PLM test packets transmitted by the Session-Sender,
where Threshold XofY is locally provisioned value.
Similarly, the delay metrics are notified, as an example, when
consecutive M number of PLM test packets have measured delay values
exceed user-configured threshold T, where M (Delay Exceeded Packet
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Count) and T (Absolute and Percentage Delay Exceeded Threshold) are
also locally provisioned values.
In both loopback modes, the timestamps T1 and T4 are used to measure
round-trip delay. In loopback mode enabled with network programming
function, the timestamps T1 and T2 are used to measure one-way delay.
In both loopback modes, a failure on the reverse direction path can
cause the PLM return test packets to not reach the Session-Sender.
This is also true in the case where the PLM return test packets were
generated by the Session-Reflector e.g. to indicate Session-Sender of
a failure on the forward direction path. As such, the test packet
based methods have a limitation of false detection due to a reverse
direction failure.
9. Security Considerations
The Performance and Liveness Monitoring is intended for deployment in
the well-managed private and service provider networks. As such, it
assumes that a node involved in a monitoring operation has previously
verified the integrity of the path and the identity of the Session-
Reflector.
If desired, attacks can be mitigated by performing basic validation
and sanity checks, at the Session-Sender, of the timestamp fields in
received PLM packets. The minimal state associated with these
protocols also limits the extent of disruption that can be caused by
a corrupt or invalid packet to a single test cycle.
Use of HMAC-SHA-256 in the authenticated mode protects the data
integrity of the test packets. Cryptographic measures may be
enhanced by the correct configuration of access-control lists and
firewalls.
The security considerations specified in [RFC8762] also apply to the
procedures defined in this document.
10. IANA Considerations
IANA maintains the "Special-Purpose Multiprotocol Label Switching
(MPLS) Label Values" registry (see <https://www.iana.org/assignments/
mpls-label-values/mpls-label-values.xml>). IANA is requested to
allocate Timestamp Label value from the "Extended Special-Purpose
MPLS Label Values" registry:
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+-------------+---------------------------------+---------------+
| Value | Description | Reference |
+-------------+---------------------------------+---------------+
| TBA1 | Timestamp Label | This document |
| | for offset 16 | |
| | for Unauthenticated Mode | |
+-------------+---------------------------------+---------------+
| TBA2 | Timestamp Label | This document |
| | for offset 32 | |
| | for Authenticated Mode | |
+-------------+---------------------------------+---------------+
IANA is requested to allocate, within the "SRv6 Endpoint Behaviors
Registry" sub-registry belonging to the top-level "Segment Routing
Parameters" registry [I-D.ietf-spring-srv6-network-programming], the
following allocation:
+-------------+---------------------------------+---------------+
| Value | Endpoint Behavior | Reference |
+-------------+---------------------------------+---------------+
| TBA3 | End.TSF (Timestamp and Forward) | This document |
| | for offset 16 | |
| | for Unauthenticated Mode | |
+-------------+---------------------------------+---------------+
| TBA4 | End.TSF (Timestamp and Forward) | This document |
| | for offset 32 | |
| | for Authenticated Mode | |
+-------------+---------------------------------+---------------+
11. References
11.1. 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>.
[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>.
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[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>.
[I-D.ietf-spring-srv6-network-programming]
Filsfils, C., Camarillo, P., Leddy, J., Voyer, D.,
Matsushima, S., and Z. Li, "SRv6 Network Programming",
draft-ietf-spring-srv6-network-programming-28 (work in
progress), December 2020.
11.2. Informative References
[IEEE1588]
IEEE, "1588-2008 IEEE Standard for a Precision Clock
Synchronization Protocol for Networked Measurement and
Control Systems", March 2008.
[RFC7880] Pignataro, C., Ward, D., Akiya, N., Bhatia, M., and S.
Pallagatti, "Seamless Bidirectional Forwarding Detection
(S-BFD)", RFC 7880, DOI 10.17487/RFC7880, July 2016,
<https://www.rfc-editor.org/info/rfc7880>.
[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>.
[RFC8754] Filsfils, C., Ed., Dukes, D., Ed., Previdi, S., Leddy, J.,
Matsushima, S., and D. Voyer, "IPv6 Segment Routing Header
(SRH)", RFC 8754, DOI 10.17487/RFC8754, March 2020,
<https://www.rfc-editor.org/info/rfc8754>.
[I-D.ietf-spring-segment-routing-policy]
Filsfils, C., Talaulikar, K., Voyer, D., Bogdanov, A., and
P. Mattes, "Segment Routing Policy Architecture", draft-
ietf-spring-segment-routing-policy-09 (work in progress),
November 2020.
[I-D.ietf-mpls-spl-terminology]
Andersson, L., Kompella, K., and A. Farrel, "Special
Purpose Label terminology", draft-ietf-mpls-spl-
terminology-06 (work in progress), January 2021.
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[I-D.ietf-pce-binding-label-sid]
Sivabalan, S., Filsfils, C., Tantsura, J., Hardwick, J.,
Previdi, S., and C. Li, "Carrying Binding Label/Segment-ID
in PCE-based Networks.", draft-ietf-pce-binding-label-
sid-05 (work in progress), October 2020.
[I-D.ietf-pce-sr-bidir-path]
Li, C., Chen, M., Cheng, W., Gandhi, R., and Q. Xiong,
"Path Computation Element Communication Protocol (PCEP)
Extensions for Associated Bidirectional Segment Routing
(SR) Paths", draft-ietf-pce-sr-bidir-path-05 (work in
progress), January 2021.
Acknowledgments
The authors would like to thank Greg Mirsky, Mach Chen, Kireeti
Kompella, and Adrian Farrel for providing the review comments.
Authors' Addresses
Rakesh Gandhi (editor)
Cisco Systems, Inc.
Canada
Email: rgandhi@cisco.com
Clarence Filsfils
Cisco Systems, Inc.
Email: cfilsfil@cisco.com
Navin Vaghamshi
Reliance
Email: Navin.Vaghamshi@ril.com
Moses Nagarajah
Telstra
Email: Moses.Nagarajah@team.telstra.com
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Richard Foote
Nokia
Email: footer.foote@nokia.com
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