]> Cisco Systems, Inc.

Canada rgandhi@cisco.com

Cisco Systems, Inc.

cfilsfil@cisco.com

Reliance

Navin.Vaghamshi@ril.com

Telstra

Moses.Nagarajah@team.telstra.com

Nokia

footer.foote@nokia.com

Huawei

mach.chen@huawei.com

Rakuten

amit.dhamija@rakuten.com

SPRING Working Group 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 procedure for Enhanced Performance Measurement of end-to-end SR paths including SR Policies for both SR-MPLS and SRv6 data planes using Simple Two-Way Active Measurement Protocol (STAMP) defined in RFC 8762. The procedure allows to improve the scale for number of sessions and the interval for failure detection.

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 . SR Policies as defined in are used to steer traffic through a specific, user-defined paths using a stack of Segments. A comprehensive SR Performance Measurement (PM) for delay and packet loss as well as Connectivity Verification (CV) is one of the essential requirements to measure network performance to provide Service Level Agreements (SLAs). The Simple Two-Way Active Measurement Protocol (STAMP) provides capabilities for the measurement of various performance metrics in IP networks without the use of a control channel to pre-signal session parameters. As described in , STAMP can be used for performance measurement of one-way, two-way or round-trip delay and packet loss of end-to-end SR paths. STAMP requires RFC8762 protocol support on the Session-Reflector to process the received test packets, and hence the received test packets need to be punted from the forwarding fast path and return test packets need to be generated. This limits the scale for number test sessions and the ability to provide faster detection interval. The loopback measurement mode defined in does not require STAMP test packet processing on Session-Reflector, however, it does not provide accurate one-way delay. This document defines procedure for Enhanced Performance Measurement of end-to-end SR paths including SR Policies for both SR-MPLS and SRv6 data planes, using Simple Two-Way Active Measurement Protocol (STAMP) defined in . The procedure allows to improve the scale for number of sessions and the interval for failure detection.

Conventions Used in This Document

Requirements Language The key words "MUST", "MUST NOT", "REQUIRED", "SHALL", "SHALL NOT", "SHOULD", "SHOULD NOT", "RECOMMENDED", "MAY", and "OPTIONAL" in this document are to be interpreted as described in when, and only when, they appear in all capitals, as shown here.

Abbreviations BSID: Binding Segment ID. ECMP: Equal Cost Multi-Path. EB: Endpoint Behaviour. HMAC: Hashed Message Authentication Code. I2E: Ingress-To-Egress. IHS: Ingress-To-Egress, Hop-By-Hop or Select Scope. MBZ: Must be Zero. MNA: MPLS Network Action. MPLS: Multiprotocol Label Switching. 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. STAMP: Simple Two-way Active Measurement Protocol. TC: Traffic Class. TS: Timestamp. TSF: Timestamp and Forward. TTL: Time To Live.

Reference Topology In the reference topology shown in Figure 1, the STAMP Session-Sender S1 initiates a Session-Sender test packet and the Session-Reflector R1 returns the test packet. The return test packet may be transmitted back to the Session-Sender S1 on the same path (same set of links and nodes) or a different path in the reverse direction from the path taken towards the Session-Reflector R1. The Session-Sender S1 and Session-Reflector R1 are connected via an SR path . The SR path can be an SR Policy on node S1 (called head-end) with destination to node R1 (called tail-end).

Loopback Mode Enabled with Network Programming Function

Overview

Enhanced Loopback Mode Enabled with Network Programming Function As described in , in loopback mode, the STAMP Session-Sender S1 initiates Session-Sender test packets and the Session-Reflector R1 forwards them back to the Session-Sender S1. The received STAMP test packets are not punted out of the fast path in forwarding at the Session-Reflector. At the Session-Reflector, the loopback function simply makes the necessary changes to the encapsulation including IP and UDP headers to return the STAMP test packet to the Session-Sender S1. No STAMP test session is created on the Session-Reflector R1. As described in , only round-trip delay can be measured in the loopback mode. In SR networks, there is also a need to measure the one-way delay metric to provide low latency services. This document defines a new STAMP measurement mode, called enhanced loopback mode, that is loopback mode enabled with network programming function. In this mode, both transmit (T1) and receive (T2) timestamps in data plane are collected by the Session-Sender test packets as shown in Figure 1. The network programming function optimizes the "operations of punt test packet and generate return test packet" on the Session-Reflector as timestamping is implemented in forwarding fast path in hardware. This helps to achieve higher number of STAMP test session scale and faster detection interval. The Session-Sender adds transmit timestamp (T1) in the payload of the Session-Sender test packet. The Session-Reflector adds the receive timestamp (T2) in the payload of the received test packet in forwarding fast path in hardware without punting the test packet (e.g. to slow path or control-plane). The network programming function carried by the test packet enables the Session-Reflector to add the receive timestamp (T2) at the specified offset in the payload of the test packet.

Enhanced Performance Measurement Procedure For enhanced performance monitoring of an end-to-end SR path including SR Policy, STAMP Session-Sender test packets are transmitted in loopback mode enabled with network programming function to timestamp and forward the packet. For SR Policy, the Session-Sender test packets are transmitted using the Segment List (SL) of the Candidate-Path . When a Candidate-Path has more than one Segment Lists, multiple Session-Sender test packets MUST be transmitted, one using each Segment List as described in .

Enhanced Performance Measurement Procedure for SR-MPLS Policies An SR-MPLS Policy may contain a number of Segment Lists (SLs). A Session-Sender test packet MUST be transmitted using each Segment List of the SR-MPLS Policy. The content of an example Session-Sender test packet for an end-to-end SR-MPLS Policy is shown in Figure 3. The loopback measurement mode for SR-MPLS Policies defined in Section 4.2.3.3 of is used and enhanced as described below. In this document, MPLS Network Action (MNA) Sub-Stack defined in is used for SR-MPLS data plane to enable network programming function for "timestamp and forward" the received test packet, for unauthenticated mode and authenticated mode. The MNA Sub-Stack carries the MNA Label as defined in and it is a base special purpose label . In this document, new MNA Opcode TSF (value TBA2) is defined for the network action. The Ancillary Data field of the opcode carries 10-bits of timestamp offset in bytes and 3-bits of timestamp format (FMT) (value 1 for 64-bit PTPv2 or value 0 for NTP). In the Session-Sender test packets for SR-MPLS Policies, the MNA Sub-Stack with Opcode TSF (value TBA2) is added in the MPLS header as shown in Figure 3, to collect "Receive Timestamp" field in the payload of the test packet. The Ingress-to-Egress (I2E), Hop-By-Hop (HBH), Select scope (IHS) is set to "I2E" when return path is IP/UDP and set to "Select" when the return path is SR-MPLS. The Network Action Sub-Stack Length (NASL) is set to 0 when there is no Label Stack Entry (LSE) after this Opcode in the MNA Sub-Stack. The U flag is set to skip the network action and forward the packet (and not drop the packet). The Label Stack for the reverse direction SR-MPLS path can be added after the MNA Sub-Stack (not shown in the Figure) to receive the return test packet on a specific path. When a Session-Reflector receives a packet with this MNA Sub-Stack with Opcode TSF (value TBA2), after timestamping the packet at the specified offset in STAMP payload, the Session-Reflector pops the MNA Sub-Stack (after completing any other network actions) and forwards the packet using the next label or IP header in the packet (just like the data packets for the normal traffic).

Example STAMP Test Packet with Timestamp Label for SR-MPLS

Node Capability for MNA Sub-Stack with Opcode TSF The STAMP Session-Sender needs to know if the Session-Reflector can process the MNA Sub-Stack with Opcode TSF to avoid dropping the test packets. The signaling extension for this capability exchange or local configuration are outside the scope of this document.

Enhanced Performance Measurement Procedure for SRv6 Policies An SRv6 Policy may contain a number of Segment Lists. Each Segment List may contain a number of SRv6 SIDs as defined in , and . A Session-Sender test packet MUST be transmitted using each Segment List of the SRv6 Policy. An SRv6 Policy may contain an SRv6 Segment Routing Header (SRH) carrying a Segment List as described in . The content of an example Session-Sender test packet for an end-to-end SRv6 Policy using an SRH is shown in Figure 4. The loopback measurement mode for SRv6 Policies defined in Section 4.2.3.4 of is used and enhanced as described below. The defines SRv6 Endpoint Behaviours (EB) for SRv6 nodes. In this document, two new Timestamp Endpoint Behaviours are defined for Segment Routing Header (SRH) to enable "Timestamp and Forward (TSF)" function for the received test packets, one for unauthenticated mode and one for authenticated mode. In the Session-Sender test packets for SRv6 Policies, Timestamp Endpoint Function (End.TSF) is carried with the target Segment Identifier (SID) in SRH as shown in Figure 4, to collect "Receive Timestamp" field in the payload of the test packet. The Segment List for the reverse direction path can be added after the target SID to receive the 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 the specified offset, the Session-Reflector forwards the packet using the next SID in the SRH or inner IPv6 header in the packet (just like the data packets for the normal traffic).

Example STAMP Test Packet with Endpoint Function for SRv6 . . . . . +---------------------------------------------------------------+ | IP Header | . Source IP Address = Session-Sender IPv6 Address . . Destination IP Address = Session-Sender IPv6 Address . . Next-Header = UDP (17) . . . +---------------------------------------------------------------+ | UDP Header | . Source Port = As chosen by Session-Sender . . Destination Port = As chosen by Session-Sender . . . +---------------------------------------------------------------+ | Payload = Test Packet as specified in Section 3 of RFC 8972 | . in Figure 1 and Figure 3 . . . +---------------------------------------------------------------+ ]]>

Timestamp Endpoint Function Assignment New SRv6 Endpoint Behaviors are defined called "Endpoint Behavior bound to SID with Timestamp and Forward (TSF)" ("End.uTSF" for short when using SRv6 uSID). The End.uTSF is a node SID instantiated at STAMP Session-Reflector node. When the node receives a packet whose IPv6 Destination Address is S and S is a local End.uTEF SID, the node updates the 64-bit receive timestamp in PTPv2 format in the STAMP packet payload and forwards the packet to the next-hop router. The End.uTSF is statically configured on the STAMP Session-Reflector node and not advertised into the routing protocols. Following new endpoint behaviours are statically defined on the STAMP Session-Reflector:

Node Capability for Timestamp Endpoint Function The STAMP Session-Sender needs to know if the Session-Reflector can process the Timestamp Endpoint Function to avoid dropping test packets. The signaling extension for this capability exchange is outside the scope of this document.

Security Considerations The STAMP protocol is intended for deployment in limited domains . As such, it assumes that a node involved in the STAMP protocol operation has previously verified the integrity of the path and the identity of the far-end Session-Reflector. The security considerations specified in and also apply to the procedures defined in this document. Specifically, the message integrity protection using HMAC, as defined in Section 4.4 of also apply to the procedure described in this document.

IANA Considerations IANA maintains the "MNA Opcode" registry when created from IANA request in . IANA is requested to allocate a value for In-Stack Network Action (NA) Opcode for Timestamp and Forward from this registry:

References Normative References Cisco Systems, Inc. Cisco Systems, Inc. Bell Canada Huawei Colt Nokia Cisco Systems, Inc. Cisco Systems, Inc. Broadcom Futurewei Technologies Juniper Networks Informative References China Mobile Cisco Systems, Inc. Huawei Technologies Orange Alibaba Bell Canada Cisco Systems, Inc. Broadcom Futurewei Technologies Ltd. ZTE Corporation NTT Network Innovations Huawei Technologies Cisco Systems, Inc. Cisco Systems, Inc. Alibaba Bell Canada Broadcom Arrcus, Inc. Nokia Barefoot Networks Marvell China Mobile Futurewei Cisco Systems Cisco Systems Bell Canada British Telecom Microsoft

Acknowledgments The authors would like to thank Greg Mirsky, Kireeti Kompella, and Adrian Farrel for providing useful comments.