]> Cisco Systems, Inc.

Canada rgandhi@cisco.com

Cisco Systems, Inc.

cfilsfil@cisco.com

Bell Canada

daniel.voyer@bell.ca

Huawei

mach.chen@huawei.com

Colt

Bart.Janssens@colt.net

Nokia

footer.foote@nokia.com

IPPM Working Group Segment Routing (SR) leverages the source routing paradigm. SR is applicable to both Multiprotocol Label Switching (SR-MPLS) and IPv6 (SRv6) forwarding planes. This document specifies RFC 8762 (Simple Two-Way Active Measurement Protocol (STAMP)) extensions for SR networks, for both SR-MPLS and SRv6 forwarding planes by augmenting the optional extensions defined in RFC 8972.

Introduction Segment Routing (SR) leverages the source routing paradigm for Software Defined Networks (SDNs). SR is applicable to both Multiprotocol Label Switching (SR-MPLS) and IPv6 (SRv6) forwarding 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) toolset 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. defines optional extensions, in the form of TLVs, for STAMP. Note that the YANG data model defined in can be used to provision the STAMP Session-Sender and STAMP Session-Reflector. The STAMP test packets are transmitted along an IP path between a Session-Sender and a Session-Reflector to measure performance delay and packet loss along that IP path. It may be desired in SR networks that the same path (same set of links and nodes) between the Session-Sender and Session-Reflector is used for the STAMP test packets in both directions. This is achieved by using the STAMP extensions for SR-MPLS and SRv6 networks specified in this document by augmenting the optional extensions defined in .

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 MPLS: Multiprotocol Label Switching. PM: Performance Measurement. SID: Segment ID. SL: Segment List. SR: Segment Routing. SR-MPLS: Segment Routing with MPLS forwarding plane. SRv6: Segment Routing with IPv6 forwarding plane. SSID: STAMP Session Identifier. STAMP: Simple Two-Way Active Measurement Protocol.

Reference Topology In the reference topology shown below, the STAMP Session-Sender S1 initiates a STAMP test packet and the STAMP Session-Reflector R1 transmits a reply STAMP test packet. The reply test packet may be transmitted 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 nodes S1 and R1 may be connected via a link or an SR path . The link may be a physical interface, virtual link, or Link Aggregation Group (LAG) , or LAG member. The SR path may be an SR Policy on node S1 (called head-end) with destination to node R1 (called tail-end). | | | S1 |=====================| R1 | | |<- - - - - - - - - - | | +-------+ Reply Test Packet +-------+ \ / T4 T3 STAMP Session-Sender STAMP Session-Reflector Reference Topology ]]>

TLV Verification Check The Unrecognized TLV flag (U flag) is defined in as "A Session-Reflector MUST set the U flag to 1 if the Session-Reflector has not understood the TLV." This can be interpreted as, the U flag indicates a condition when a node does not recognize the TLV Type, or does not understand the TLV contents or does not support the TLV. One way as an example this may be handled by the Session-Sender is, by simply stopping the session and removing the unsupported TLV option as the Session-Reflector is not capable. The U flag is not really indicative of the cases where the node recognizes the TLV Type and understands the TLV contents, but fails to use the instructions in the TLV to generate the reply packet. This can occur due to verification check failures such as destination is wrong (due to broken Label Switched Path (LSP)), Segment Identifier in the return path is not programmed in the forwarding table, or some transient (or dynamic) networking failures. In this case, as an example, the Session-Sender may continue to run the session and not remove the failed TLV as the failure should get corrected after troubleshooting. The V flag is defined in this section to help with these failures.

Verification Check Flag in TLV The STAMP TLV option in defines the use of the 8-bit flags field common to all STAMP TLVs. A one-bit flag called Verification Check (V) is defined at bit position 3 in the flags field of the STAMP TLV. A Session-Sender MUST set the V flag to 0 before transmitting an extended STAMP test packet. A Session-Reflector MUST set the V flag to 1 for any STAMP TLV that it supports that includes an instruction or request for data that cannot be followed or was ignored. The V flag MUST be set to 0 by the Session-Reflector when the instruction or the request for data from the TLV in the test packet was followed. The V flag is applicable to both Stateful and Stateless Session-Reflector.

Verification Check Flag in TLV Usage Examples For the STAMP Session-Reflector that supports the STAMP Return Path TLV defined in this document, the test packets carry additional instructions in a TLV for the Session-Reflector to follow. In this case, the V flag provides feedback to the Session-Sender if the Session-Reflector was able to follow that instruction to send reply on the return path. For example, Session-Reflector recognizes the TLV and it is not malformed, the STAMP test packet including all the TLVs was successfully processed but the additional instruction in the Return Path TLV was not followed or was ignored due to a forwarding table lookup failure. Another example is when using the "Direct Measurement" TLV defined in , the Session-Reflector that supports this TLV but was not able to return the requested Tx and Rx counters in the TLV (e.g., if the Session-Reflector is Stateless or the hardware is not capable, etc.). The Session-Reflector can return the packet with the error back to the Session-Sender by setting the V flag to 1.

Destination Node Address TLV The Session-Sender may need to transmit test packets to the Session-Reflector with a different destination address that is not matching an address of the Session-Reflector e.g. when the STAMP test packet is encapsulated by a tunneling protocol or an MPLS Segment List with destination IPv4 address from 127/8 range or Segment Routing Header (SRH) with destination IPv6 address ::1/128. In an ECMP environment, the hashing function in forwarding may decide the outgoing path using the source address, destination address, ports, etc. from the packet. In order to traverse different ECMP paths for measurement, different values of IPv4 destination address from 127/8 range may be used. In those cases, the STAMP test packet may reach the un-intended Session-Reflector in an error condition, and an un-intended node may transmit reply test packet resulting in reporting of invalid measurement metrics. defines STAMP test packets that can include one or more optional TLVs. In this document, the TLV type (value 9) is defined for the Destination Node Address TLV for the STAMP test packet . The format of the Destination Node Address TLV is shown in Figure 1:

Destination Node Address TLV Format

TLV fields are defined as follows: STAMP TLV Flags : The STAMP TLV Flags follow the procedures described in and this document. Type : Type (value 9) for Desatination Node Address TLV. Length : A two-octet field equal to the length of the Address field in octets. The Length field is used to decide the Address Family of the Address. The length of 4 octet is used for IPv4 address and length of 16 octet is used for IPv6 address. Address : IPv4 or IPv6 address. The Destination Node Address TLV is optional. The Destination Node Address TLV indicates the address of the intended Session-Reflector node of the test packet. The Destination Node Address is also used to uniquely identify the STAMP session on the Session-Reflector when the optional SSID is not sent. For security reasons (e.g., to avoid node discovery), the Session-Reflector SHOULD use the received Destination Node Address as the Source Address in the IP header of the reply test packet, instead of using its Node Address. The Session-Reflector MUST add the received Destination Node Address TLV in the reply test packet to ensure the symmetric reply test packet size and to transmit the STAMP TLV Flags to the Session-Sender. A Session-Sender MUST set the V flag to 0 in the Destionation Node Address TLV before transmitting an extended STAMP test packet. A Session-Reflector that supports this TLV, MUST set the V flag in the reply test packet to 1 if the Session-Reflector determined that it is not the intended Destination as identified in the Destination Node Address TLV. Otherwise, the Session-Reflector MUST set the V flag in the Destination Node Address TLV in the reply test packet to 0.

Return Path TLV For end-to-end SR paths, the Session-Reflector may need to transmit the reply test packet on a specific return path. The Session-Sender can request this in the test packet to the Session-Reflector using a Return Path TLV. With this TLV carried in the Session-Sender test packet, signaling and maintaining dynamic SR network state for the STAMP sessions on the Session-Reflector are avoided. There are two modes defined for the behaviors on the Session-Reflector in Section 4 of . A Stateful Session-Reflector that requires configuration that must match all Session-Sender parameters, including Source Address, Destination Address, Source UDP Port, Destination UDP Port, and possibly SSID (assuming the SSID is configurable and not auto-generated). In this case, a local policy can be used to direct the test packet by creating additional states for the STAMP sessions on the Session-Reflector. In the case of promiscuous operation, the Stateless Session-Reflector will require an indication of how to return the test packet on a specific path, for example, measurement in an ECMP environment. For links, the Session-Reflector may need to transmit the reply test packet on the same incoming link in the reverse direction. The Session-Sender can request this in the test packet to the Session-Reflector using a Return Path TLV. defines STAMP test packets that can include one or more optional TLVs. In this document, the TLV Type (value 10) is defined for the Return Path TLV that carries the return path for the Session-Sender test packet. The format of the Return Path TLV is shown in Figure 2:

Return Path TLV

TLV fields are defined as follows: STAMP TLV Flags : The STAMP TLV Flags follow the procedures described in and this document. Type : Type (value 10) for Return Path TLV. Length : A two-octet field equal to the length of the Return Path Sub-TLVs field in octets. Return Path Sub-TLVs : As defined in Section 5.1. The Return Path TLV is optional. The Session-Sender MUST only insert one Return Path TLV in the STAMP test packet. The Session-Reflector that supports this TLV, MUST only process the first Return Path TLV in the test packet and ignore other Return Path TLVs if present, and it MUST add the received Return Path TLV (including all Sub-TLVs) in the reply test packet to ensure the symmetric reply test packet size and to transmit the STAMP TLV Flags to the Session-Sender. The Session-Reflector that supports this TLV MUST reply using the Return Path received in the Session-Sender test packet. In the case where the Session-Reflector does not support this TLV, the procedure defined in is followed by the Session-Reflector. A Session-Sender MUST set the V flag to 0 before transmitting an extended STAMP test packet. A Session-Reflector that supports this TLV, MUST set the V flag in the reply test packet to 1 if the Session-Reflector determined that it cannot use the return path in the test packet to transmit the reply test packet. Otherwise, the Session-Reflector MUST set the V flag in the reply test packet to 0.

Return Path Sub-TLVs The Return Path TLV contains one or more Sub-TLVs to carry the information for the requested return path. A Return Path Sub-TLV can carry Return Path Control Code, Return Path IP Address or Return Path Segment List. The STAMP Sub-TLV Flags are set using the procedures described in . When Return Path Sub-TLV is present in the Session-Sender test packet, the Session-Reflector that supports this TLV, MUST transmit reply test packet using the return path information specified in the Return Path Sub-TLV. A Return Path TLV MUST NOT contain both Control Code Sub-TLV as well as Return Address or Return Segment List Sub-TLV.

Return Path Control Code Sub-TLV The format of the Return Path Control Code Sub-TLV is shown in Figure 3. The Type of the Return Path Control Code Sub-TLV is defined as following:

Control Code Sub-TLV in Return Path TLV

TLV fields are defined as follows:

• Type (value 1): Return Path Control Code. The Session-Sender can request the Session-Reflector to transmit the reply test packet based on the flags defined in the Control Code field.

STAMP TLV Flags : The STAMP TLV Flags follow the procedures described in and this document. Length : A two-octet field equal to the length of the Control Code field which is 4 octets. Control Code Flags (32-bit): Defined as follows.

0x0: No Reply Requested.

0x1: Reply Requested on the Same Link.

When Control Code flag is set to 0x0 in the Session-Sender test packet, the Session-Reflector does not transmit reply test packet to the Session-Sender and terminates the STAMP test packet. Only the one-way measurement is applicable in this case. Optionally, the Session-Reflector may locally stream performance metrics via telemetry using the information from the received test packet. All other Return Path Sub-TLVs MUST be ignored in this case. When Control Code flag is set to 0x1 in the Session-Sender test packet, the Session-Reflector transmits the reply test packet over the same incoming link where the test packet is received in the reverse direction towards the Session-Sender. The link may be a physical interface, virtual link, or Link Aggregation Group (LAG) , or LAG member. All other Return Path Sub-TLVs MUST be ignored in this case.

Return Address Sub-TLV The STAMP reply test packet may be transmitted to the Session-Sender to a different destination address on the Session-Sender using Return Path TLV. For this, the Session-Sender can specify in the test packet the receiving destination node address for the Session-Reflector reply test packet. When transmitting the STAMP test packet to a different destination address, the Session-Sender MUST follow the procedure defined in Section 4.3 of . The format of the Return Address Sub-TLV is shown in Figure 4. The Address Family field indicates the type of the address, and it SHALL be set to one of the assigned values in the "IANA Address Family Numbers" registry. The Type of the Return Address Sub-TLV is defined as following:

Return Address Sub-TLV in Return Path TLV

TLV fields are defined as follows:

• Type (value 2): Return Address. Destination node IPv4 or IPv6 address of the Session-Reflector reply test packet different than the Source Address in the Session-Sender test packet.

STAMP TLV Flags : The STAMP TLV Flags follow the procedures described in and this document. Length : A two-octet field equal to the length of the Return Address field in octets. The Length field is used to decide the Address Family of the Return Address. The length of 4 octet is used for IPv4 address and length of 16 octet is used for IPv6 address.

Return Segment List Sub-TLVs The format of the Segment List Sub-TLVs in the Return Path TLV is shown in Figures 5, 6, and 7. The Segments carried in Segment List Sub-TLVs are described in . The segment entries MUST be in network order. TLV fields are defined as follows: The Segment List Sub-TLV can be one of the following Types:

• Type (value 3): SR-MPLS Label Stack of the Return Path
• Type (value 4): SRv6 Segment List of the Return Path
• Type (value 5): Structured SRv6 Segment List of the Return Path

STAMP TLV Flags : The STAMP TLV Flags follow the procedures described in and this document. Length : A two-octet field equal to the length of the Segment List field in octets.

SR-MPLS Segment List Sub-TLV in Return Path TLV

SRv6 Segment List Sub-TLV in Return Path TLV

Structured SRv6 Segment List Sub-TLV in Return Path TLV

The SR-MPLS Label Stack contains a list of 32-bit Label Stack Entry (LSE) that includes a 20-bit label value, 8-bit Time-To-Live (TTL) value, 3-bit Traffic Class (TC) value and 1-bit End-Of-Stack (S) field. An SR-MPLS Label Stack Sub-TLV may carry only Binding SID Label of the Return SR-MPLS Policy. An SRv6 Segment List Sub-TLV and Structured SRv6 Segment List Sub-TLV may carry only Binding SID of the Return SRv6 Policy. A Structured SRv6 Segment List Sub-TLV is used carry the structure and behavior for SRv6 SIDs used in the Return SRv6 path as shown in Figure 7. The structure is intended for informational use by the control and management planes. The fields in the structure of the Sub-TLV are defined as follows :

• LB Length: 1 octet. SRv6 SID Locator Block (LB) length in bits.
• LN Length: 1 octet. SRv6 SID Locator Node (LN) length in bits.
• Fun. Length: 1 octet. SRv6 SID Function length in bits.
• Arg. Length: 1 octet. SRv6 SID Arguments length in bits.

In Structured SRv6 Segment List Sub-TLV, the sum of all four sizes MUST be less than or equal to 128 bits. If the sum of all four sizes is larger than 128 bits, the Sub-TLV MUST NOT be used by the Session-Reflector. The Session-Sender MUST only insert one Segment List Return Path Sub-TLV in the test packet. The Session-Reflector MUST only process the first Segment List Return Path Sub-TLV in the test packet and ignore other Segment List Return Path Sub-TLVs if present. Note that in addition to Point-To-Point (P2P) SR paths, the Return Segment List Sub-TLV is also applicable to Point-To-Multipoint (P2MP) SR paths. For example, for P2MP SR paths, it may only carry the Node Segment Identifier of the Session-Sender in order for the reply test packet to follow an SR path to the Session-Sender.

Interoperability with TWAMP Light This document does not introduce any additional considerations for interoperability with TWAMP Light than those described in Section 4.6 of . As desctibed in , there are two possible combinations for such a interoperability use case: - STAMP Session-Sender with TWAMP Light Session-Reflector - TWAMP Light Session-Sender with STAMP Session-Reflector If any of STAMP extensions defined in this document are used by STAMP Session-Sender, the TWAMP Light Session-Reflector will view them as the Packet Padding field. If the packet received from the TWAMP Session-Sender is larger than the STAMP base packet, the STAMP Session-Reflector that supports the extension in this document will copy the content of the remainder of the received packet to transmit a reflected packet of symmetrical size. TWAMP Light Session-Sender will view them as the packet padding.

Security Considerations The usage of STAMP protocol is intended for deployment in limited domains . As such, it assumes that a node involved in STAMP protocol operation has previously verified the integrity of the path and the identity of the far-end 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 reply test packets. The minimal state associated with these protocols also limits the extent of measurement disruption that can be caused by a corrupt or invalid test packet to a single test cycle. The security considerations specified in and also apply to the extensions defined in this document. Specifically, the message integrity protection using HMAC, as defined in Section 4.4, also apply to the procedure described in this document. STAMP uses the well-known UDP port number that could become a target of denial of service (DoS) or could be used to aid man-in-the-middle (MITM) attacks. Thus, the security considerations and measures to mitigate the risk of the attack documented in Section 6 of equally apply to the STAMP extensions in this document. The STAMP extensions defined in this document may be used for potential "proxying" attacks. For example, a Session-Sender may specify a return path that has a destination different from that of the Session-Sender. But normally, such attacks will not happen in an SR domain where the Session-Senders and Session-Reflectors belong to the same domain. In order to prevent using the extension defined in this document for proxying any possible attacks, the return path has destination to the same node where the forward path is from. The Session-Reflector may drop the Session-Sender test packet when it cannot determine whether the Return Path has the destination to the Session-Sender. That means, the Session-Sender should choose a proper source address according to the specified Return Path to help the Session-Reflector to make that decision.

IANA Considerations IANA has created the "STAMP TLV Types" registry for . IANA has early allocated a value for the Destination Address TLV Type and a value for the Return Path TLV Type from the IETF Review TLV range of the same registry. STAMP TLV Types

Value	Description	Reference
9 (Early Allocation)	Destination Node Address	This document
10 (Early Allocation)	Return Path	This document

IANA is requested to create a sub-registry for "Return Path Sub-TLV Type". All code points in the range 1 through 175 in this registry shall be allocated according to the "IETF Review" procedure as specified in . Code points in the range 176 through 239 in this registry shall be allocated according to the "First Come First Served" procedure as specified in . Remaining code points are allocated according to : Return Path Sub-TLV Type Registry

Value	Description	Reference
1 - 175	IETF Review	This document
176 - 239	First Come First Served	This document
240 - 251	Experimental Use	This document
252 - 254	Private Use	This document

IANA is requested to allocate the values for the following Sub-TLV Types from this registry. Return Path Sub-TLV Types

Type	Description	Reference
0	Reserved	This document
1	Return Path Control Code	This document
2	Return Address	This document
3	SR-MPLS Label Stack of the Return Path	This document
4	SRv6 Segment List of the Return Path	This document
5	Structured SRv6 Segment List of the Return Path	This document
255	Reserved	This document

IANA has created the "STAMP TLV Flags" subregistry. IANA has early allocated the following bit position in the "STAMP TLV Flags" subregistry. STAMP TLV Flags

Bit Position	Symbol	Description	Reference
3 (Early Allocation)	V	Verification Check	This document

References Normative References In many standards track documents several words are used to signify the requirements in the specification. These words are often capitalized. This document defines these words as they should be interpreted in IETF documents. This document specifies an Internet Best Current Practices for the Internet Community, and requests discussion and suggestions for improvements. RFC 2119 specifies common key words that may be used in protocol specifications. This document aims to reduce the ambiguity by clarifying that only UPPERCASE usage of the key words have the defined special meanings. This document describes the Simple Two-way Active Measurement Protocol (STAMP), which enables the measurement of both one-way and round-trip performance metrics, like delay, delay variation, and packet loss. This document describes optional extensions to Simple Two-way Active Measurement Protocol (STAMP) that enable measurement of performance metrics. The document also defines a STAMP Test Session Identifier and thus updates RFC 8762. The Segment Routing over IPv6 (SRv6) Network Programming framework enables a network operator or an application to specify a packet processing program by encoding a sequence of instructions in the IPv6 packet header. Each instruction is implemented on one or several nodes in the network and identified by an SRv6 Segment Identifier in the packet. This document defines the SRv6 Network Programming concept and specifies the base set of SRv6 behaviors that enables the creation of interoperable overlays with underlay optimization. Informative References Cisco Systems Cisco Systems Bell Canada British Telecom Microsoft Ciena Corporation Cisco Systems, Inc. Microsoft Corporation Huawei Technologies Huawei Technologies ZTE Corp. ZTE Corp. Ericsson IEEE Std. 802.1AX

Acknowledgments The authors would like to thank Thierry Couture for the discussions on the use-cases for Performance Measurement in Segment Routing. The authors would also like to thank Greg Mirsky, Mike Koldychev, Gyan Mishra, Tianran Zhou, Al Mortons, Reshad Rahman, Zhenqiang Li, Frank Brockners, Henrik Nydell, and Cheng Li for providing comments and suggestions.