| SPRING Working Group | R. Gandhi, Ed. |
| Internet-Draft | C. Filsfils |
| Intended status: Standards Track | Cisco Systems, Inc. |
| Expires: September 6, 2020 | D. Voyer |
| Bell Canada | |
| M. Chen | |
| Huawei | |
| B. Janssens | |
| Colt | |
| March 5, 2020 |
Performance Measurement Using TWAMP Light and STAMP for Segment Routing Networks
draft-gandhi-spring-twamp-srpm-07
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 specifies procedure for sending and processing probe query and response messages for Performance Measurement (PM) in Segment Routing networks. The procedure uses the messages defined in RFC 5357 (Two-Way Active Measurement Protocol (TWAMP) Light) and Simple Two-Way Active Measurement Protocol (STAMP) for Delay Measurement, and uses the messages defined in this document for Loss Measurement. The procedure specified is applicable to SR-MPLS and SRv6 data planes and is used for both Links and end-to-end SR Policies.
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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 takes advantage of the Equal-Cost Multipaths (ECMPs) between source and transit nodes, between transit nodes and between transit and destination nodes. SR Policies as defined in [I-D.ietf-spring-segment-routing-policy] are used to steer traffic through a specific, user-defined paths using a stack of Segments. Built-in SR Performance Measurement (PM) is one of the essential requirements to provide Service Level Agreements (SLAs).
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 using probe messages. These protocols rely on control-channel signaling to establish a test-channel over an UDP path. The TWAMP Light [Appendix I in RFC5357] [BBF.TR-390] provides simplified mechanisms for active performance measurement in Customer IP networks by provisioning UDP paths and eliminates the control-channel signaling. These protocols lack support for direct-mode Loss Measurement (LM) to detect actual Customer data traffic loss which is required in SR networks.
The Simple Two-way Active Measurement Protocol (STAMP) [I-D.ietf-ippm-stamp] alleviates the control-channel signaling by using configuration data model to provision a test-channel. [I-D.ietf-ippm-stamp-option-tlv] defines TLV extensions for STAMP messages.
This document specifies procedures for sending and processing probe query and response messages for Performance Measurement in SR networks. The procedure uses the messages defined in [RFC5357] (TWAMP Light) and STAMP (including the TLV extensions) for Delay Measurement (DM), and uses the messages defined in this document for Loss Measurement. The procedure specified is applicable to SR-MPLS and SRv6 data planes and are used for both Links and end-to-end SR Policies. This document also defines mechanisms for handling ECMPs of SR Policies for performance delay measurement. Unless otherwise specified, the mechanisms defined in [RFC5357], [I-D.ietf-ippm-stamp], and [I-D.ietf-ippm-stamp-option-tlv] are not modified by this document. The mechanisms in this document are defined to work consistently across all of these protocols.
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 [RFC2119] [RFC8174] when, and only when, they appear in all capitals, as shown here.
BSID: Binding Segment ID.
DM: Delay Measurement.
ECMP: Equal Cost Multi-Path.
HMAC: Hashed Message Authentication Code.
LM: Loss Measurement.
MPLS: Multiprotocol Label Switching.
NTP: Network Time Protocol.
OWAMP: One-Way Active Measurement Protocol.
PM: Performance Measurement.
PSID: Path Segment Identifier.
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.
TWAMP: Two-Way Active Measurement Protocol.
In the reference topology shown below, the sender node R1 initiates a probe query for performance measurement and the reflector node R5 sends a probe response for the query message received. The probe response is sent to the sender node R1. The nodes R1 and R5 may be directly connected via a Link or there exists a Point-to-Point (P2P) SR Policy [I-D.ietf-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.voyer-spring-sr-replication-segment].
+-------+ t1 Query t2 +-------+
| | - - - - - - - - - ->| |
| R1 |---------------------| R5 |
| |<- - - - - - - - - - | |
+-------+ t4 Response t3 +-------+
Sender Reflector
Reference Topology
For one-way, two-way and round-trip delay measurements in Segment Routing networks, the TWAMP Light messages defined in Appendix I of [RFC5357] are used. For one-way and two-way direct-mode and inferred-mode loss measurements in Segment Routing networks, the messages defined in this document are used. One-way loss measurement provides receive packet loss whereas two-way loss measurement provides both transmit and receive packet loss. Separate UDP destination port numbers are user-configured for delay and loss measurements from the range specified in [I-D.ietf-ippm-stamp]. The sender uses the UDP port number following the guidelines specified in Section 6 in [RFC6335]. For both Links and end-to-end SR Policies, no PM session for delay or loss measurement is created on the reflector node R5 [RFC5357].
For Performance Measurement, probe query and response messages are sent as following:
The In-Situ Operations, Administration, and Maintenance (IOAM) mechanisms for SR-MPLS defined in [I-D.gandhi-spring-ioam-sr-mpls] and for SRv6 defined in [I-D.ali-spring-ioam-srv6] are used to carry PM information such as timestamp in-band as part of the data packets, and are outside the scope of this document.
An example of a provisioning model and typical measurement parameters for each user-configured destination UDP port for performance delay and loss measurements is shown in the following Figure 1:
+------------+
| Controller |
+------------+
Destination UDP Port / \ Destination UDP port
Measurement Protocol / \ Measurement Protocol
Measurement Type / \ Measurement Type
Delay/Loss / \ Delay/Loss
Authentication Mode & Key / \ Authentication Mode & Key
Timestamp Format / \ Loss Measurement Mode
Delay Measurement Mode / \
Padding/Packet Size / \
Loss Measurement Mode / \
v v
+-------+ +-------+
| | | |
| R1 |------------| R5 |
| | | |
+-------+ +-------+
Sender Reflector
Figure 1: Example Provisioning Model
Examples of Measurement Protocol is TWAMP Light or STAMP, the Timestamp Format is PTPv2 [IEEE1588] or NTP and the Loss Measurement mode is inferred or direct mode. The mechanisms to provision the sender and reflector nodes are outside the scope of this document.
The reflector node R5 uses the parameters for the timestamp format, delay measurement mode (i.e. one-way, two-way or loopback mode) and packet padding size from the received probe query message.
The Simple Two-way Active Measurement Protocol (STAMP) [I-D.ietf-ippm-stamp] messages and the STAMP TLVs [I-D.ietf-ippm-stamp-option-tlv] are equally applicable to the procedures specified in this document. Recall that the delay measurement message formats defined for STAMP are backwards compatible with the delay measurement message formats defined in [RFC5357].
The STAMP message with a TLV for "direct measurement" can be used for combined delay + loss measurement [I-D.ietf-ippm-stamp-option-tlv]. However, in order to use only for loss measurement purpose, it requires the node to support the delay measurement STAMP messages and timestamp the packets. Furthermore, for hardware-based counter collection, the optional TLV based processing adds unnecessary overhead (as counters are not at well-known locations). In addition, the TLV cannot be used with TWAMP Light messages and it is not compatible with the loss measurement messages defined for TWAMP Light in this document.
In this document, the probe messages defined in [RFC5357] are used for Delay and Loss measurements for Links and end-to-end SR Policies. The user-configured destination UDP ports (separate UDP ports for different delay and loss message formats) are used for identifying the PM probe messages as described in Appendix I of [RFC5357].
The Sender IPv4 or IPv6 address is used as the source address. When known, the reflector IPv4 or IPv6 address is used as the destination address. If not known, the address in the range of 127/8 for IPv4 or 0:0:0:0:0:FFFF:7F00/104 for IPv6 is used as destination address. This is the case for example, when using SR Policy with IPv4 endpoint of 0.0.0.0 or IPv6 endpoint of ::0 [I-D.ietf-spring-segment-routing-policy].
The message content for Delay Measurement probe query message using UDP header [RFC0768], is shown in Figure 2. The DM probe query message is sent with user-configured Destination UDP port number for DM. The Destination UDP port cannot be used as Source port, since the message does not have any indication to distinguish between the query and response message. The DM probe query message contains the payload for delay measurement defined in Section 4.1.2 of [RFC5357]. For symmetrical size query and response messages [RFC6038], the DM probe query message contains the payload format defined in Section 4.2.1 of [RFC5357].
+---------------------------------------------------------------+ | IP Header | . Source IP Address = Sender IPv4 or IPv6 Address . . Destination IP Address = Reflector IPv4 or IPv6 Address . . Protocol = UDP . . . +---------------------------------------------------------------+ | UDP Header | . Source Port = As chosen by Sender . . Destination Port = User-configured Port for Delay Measurement. . . +---------------------------------------------------------------+ | Payload = Message as specified in Section 4.2.1 of RFC 5357 | | . Payload = Message as specified in Section 4.1.2 of RFC 5357 | . . Payload = Message specified in Section 4.2 of ietf-ippm-stamp . . . +---------------------------------------------------------------+
Figure 2: DM Probe Query Message
Timestamp field is eight bytes and use the format defined in Section 4.2.1 of [RFC5357]. It is recommended to use the IEEE 1588v2 Precision Time Protocol (PTP) truncated 64-bit timestamp format [IEEE1588] as specified in [RFC8186], with hardware support in Segment Routing networks.
When using the authenticated mode for delay measurement, the matching authentication type (e.g. HMAC-SHA-256) and key are user-configured on both the sender and reflector nodes. A separate user-configured destination UDP port is used for the delay measurement in authentication mode due to the different probe message format.
The message content for Loss Measurement probe query message using UDP header [RFC0768] is shown in Figure 3. The LM probe query message is sent with user-configured Destination UDP port number for LM, which is a different Destination UDP port number than DM. Separate Destination UDP ports are used for direct-mode and inferred-mode loss measurements. The Destination UDP port cannot be used as Source port, since the message does not have any indication to distinguish between the query and response message. The LM probe query message contains the payload for loss measurement as defined in Figure 7 and Figure 8.
+---------------------------------------------------------------+ | IP Header | . Source IP Address = Sender IPv4 or IPv6 Address . . Destination IP Address = Reflector IPv4 or IPv6 Address . . Protocol = UDP . . . +---------------------------------------------------------------+ | UDP Header | . Source Port = As chosen by Sender . . Destination Port = User-configured Port for Loss Measurement . . . +---------------------------------------------------------------+ | Payload = Message as specified in Figure 7 or 8 | . for TWAMP Light and STAMP . . . +---------------------------------------------------------------+
Figure 3: LM Probe Query Message
When using the authenticated mode for loss measurement, the matching authentication type (e.g. HMAC-SHA-256) and key are user-configured on both the sender and reflector nodes. A separate user-configured destination UDP port is used for the loss measurement in authentication mode due to the different message format.
The probe query message as defined in Figure 2 for delay measurement and Figure 3 for loss measurement is sent on the congruent path of the data traffic. The probe messages are pre-routed over the Link for both delay and loss measurement.
The performance delay and loss measurement for segment routing is applicable to both SR-MPLS and SRv6 Policies.
The probe query messages for end-to-end performance measurement of an SR-MPLS Policy is sent using its SR-MPLS header containing the MPLS segment list as shown in Figure 4.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Segment(1) | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Segment(n) | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | PSID | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message as shown in Figure 2 for DM or Figure 3 for LM | . . +---------------------------------------------------------------+
Figure 4: Probe Query Message for SR-MPLS Policy
The Segment List (SL) can be empty to indicate Implicit NULL label case for a single-hop SR Policy.
The Path Segment Identifier (PSID) [I-D.ietf-spring-mpls-path-segment] of the SR-MPLS Policy is used for accounting received traffic on the egress node for loss measurement.
An SRv6 Policy setup using the SRv6 Segment Routing Header (SRH) and a Segment List as defined in [I-D.ietf-6man-segment-routing-header]. For SRv6, network programming is defined in [I-D.ietf-spring-srv6-network-programming]. The probe query messages for end-to-end performance measurement of an SRv6 Policy is sent using its SRH with Segment List as shown in Figure 5.
+---------------------------------------------------------------+ | SRH | . . +---------------------------------------------------------------+ | Message as shown in Figure 2 for DM or Figure 3 for LM | . (Using IPv6 Source and Destination Addresses) . . . +---------------------------------------------------------------+
Figure 5: Probe Query Message for SRv6 Policy
For delay measurement of SRv6 Policy using SRH, END function END.OTP [I-D.ietf-6man-spring-srv6-oam] is used with the target SRv6 SID to punt probe messages on the target node, as shown in Figure 5. Similarly, for loss measurement of SRv6 Policy, END function END.OP [I-D.ietf-6man-spring-srv6-oam] is used with target SRv6 SID to punt probe messages on the target node.
The Control Code field is defined for delay and loss measurement probe query and response messages for both TWAMP Light and STAMP message formats in unauthenticated and authenticated modes. The modified delay measurement probe query and response message format for both TWAMP Light and STAMP is shown in Figure 6. This message format is backwards compatible with the message format defined in [RFC5357] and STAMP [I-D.ietf-ippm-stamp] as its reflector MUST ignore the received field (identified as MBZ). Using the same field in STAMP as in TWAMP Light message format eliminates the need to define a different mechanism (e.g. using STAMP TLV) for STAMP and also maintains the consistency of the message formats. The usage of the Control Code is not limited to the SR networks and can be used for various bidirectional paths in a network.
. . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Timestamp | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Estimate | Reserved | Control Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . .
Figure 6: Control Code in TWAMP Light and STAMP DM Message
Control Code: Set as follows in TWAMP Light and STAMP probe query and response messages.
For a Query:
Reserved: Reserved for future use.
In this document, TWAMP Light probe query message formats are defined for loss measurement as shown in Figure 7 and Figure 8. The message formats are hardware efficient due to the small size payload and well-known locations of the counters. They are similar to the delay measurement message formats (e.g. location of the Counter and Timestamp) and do not require any backwards compatibility or support for the existing DM message formats from [RFC5357] as different user-configured destination UDP port is used for loss measurement.
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Transmit Counter | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |X|B| Reserved | Block Number | Reserved | Control Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Packet Padding . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: TWAMP Light LM Probe Query Message Format
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 Counter | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |X|B| Reserved | Block Number | Reserved | Control Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBZ (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | HMAC (16 octets) | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Packet Padding . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: TWAMP Light LM Probe Query Message Format - Authenticated Mode
Sequence Number (32-bit): As defined in [RFC5357].
Transmit Counter (64-bit): The number of packets or octets sent by the sender node in the query message and by the reflector node in the response message. The counter is always written at the well-known location in the probe query and response messages.
Receive Counter (64-bit): The number of packets or octets received at the reflector node. It is written by the reflector node in the probe response message.
Sender Counter (64-bit): This is the exact copy of the transmit counter from the received query message. It is written by the reflector node in the probe response message.
Sender Sequence Number (32-bit): As defined in [RFC5357].
Sender TTL: As defined in Section 7.1.
Block Number (8-bit): The Loss Measurement using Alternate-Marking method defined in [RFC8321] requires to color the data traffic. To be able to compare the transmit and receive traffic counters of the matching color, the Block Number (or color) of the traffic counters is carried by the probe query and response messages for loss measurement.
HMAC: The PM probe message in authenticated mode includes a key Hashed Message Authentication Code (HMAC) ([RFC2104]) hash. Each probe query and response messages are authenticated by adding Sequence Number with Hashed Message Authentication Code (HMAC) TLV. It can use HMAC-SHA-256 truncated to 128 bits (similarly to the use of it in IPSec defined in [RFC4868]); hence the length of the HMAC field is 16 octets.
HMAC uses its own key and the mechanism to distribute the HMAC key is outside the scope of this document.
In authenticated mode, only the sequence number is encrypted, and the other payload fields are sent in clear text. The probe message MAY include Comp.MBZ (Must Be Zero) variable length field to align the packet on 16 octets boundary.
The STAMP loss measurement probe query message uses the same message format as the TWAMP Light loss measurement probe query message, except the padding size is 28 bytes in STAMP message in unauthenticated mode (in Figure 7) and no padding is added in authenticated mode (in Figure 8). They are similar to the delay measurement message formats (e.g. location of the Counter and Timestamp) and do not require any backwards compatibility or support for the existing DM message formats from [I-D.ietf-ippm-stamp], as different user-configured destination UDP port is used for loss measurement.
The probe response message is sent using the IP/UDP information from the received probe query message. The content of the probe response message is shown in Figure 9.
+---------------------------------------------------------------+ | IP Header | . Source IP Address = Reflector IPv4 or IPv6 Address . . Destination IP Address = Source IP Address from Query . . Protocol = UDP . . . +---------------------------------------------------------------+ | UDP Header | . Source Port = As chosen by Reflector . . Destination Port = Source Port from Query . . . +---------------------------------------------------------------+ | DM Payload as specified in Section 4.2.1 of RFC 5357 | | . DM payload as specified in Section 4.3 of ietf-ippm-stamp | . . LM Payload as specified in Figure 12 or 13 . . for TWAMP Light and STAMP . . . +---------------------------------------------------------------+
Figure 9: Probe Response Message
In one-way performance measurement mode, the probe response message as defined in Figure 9 is sent back out-of-band to the sender node, for both Links and SR Policies. The Control Code is set to "Out-of-band Response Requested". In this delay measurement mode, as per Reference Topology, all timestamps t1, t2, t3, and t4 are collected by the probes. However, only timestamps t1 and t2 are needed to measure one-way delay.
In two-way performance measurement mode, when using a bidirectional path, the probe response message as defined in Figure 9 is sent back to the sender node on the congruent path of the data traffic on the same reverse direction Link or associated reverse SR Policy [I-D.ietf-pce-sr-bidir-path]. The Control Code is set to "In-band Response Requested". In this delay measurement mode, as per Reference Topology, all timestamps t1, t2, t3, and t4 are collected by the probes. All four timestamps are needed to measure two-way delay.
Specifically, the probe response message is sent back on the incoming physical interface where the probe query message is received. This is useful for example, in case of two-way measurement mode for Link delay.
The message content for sending probe response message for two-way end-to-end performance measurement of an SR-MPLS Policy is shown in Figure 10.
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Segment(1) | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Segment(n) | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message as shown in Figure 9 | . . +---------------------------------------------------------------+
Figure 10: Probe Response Message for SR-MPLS Policy
The Path Segment Identifier (PSID) [I-D.ietf-spring-mpls-path-segment] of the forward SR Policy in the probe query can be used to find the associated reverse SR Policy [I-D.ietf-pce-sr-bidir-path] to send the probe response message for two-way measurement of SR Policy unless when using STAMP message with Return Path TLV.
The message content for sending probe response message on the congruent path of the data traffic for two-way end-to-end performance measurement of an SRv6 Policy with SRH is shown in Figure 11.
+---------------------------------------------------------------+ | SRH | . . +---------------------------------------------------------------+ | Message as shown in Figure 9 | . (Using IPv6 Source and Destination Addresses) . . . +---------------------------------------------------------------+
Figure 11: Probe Response Message for SRv6 Policy
The Loopback measurement mode can be used to measure round-trip delay for a bidirectional SR Path. The IP header of the probe query message contains the destination address equals to the sender address and the source address equals to the reflector address. Optionally, the probe query message can carry the reverse path information (e.g. reverse path label stack for SR-MPLS) as part of the SR header. The probe messages are not punted at the reflector node and it does not process them and generate response messages. In this delay measurement mode, as per Reference Topology, the timestamps t1 and t4 are collected by the probes. Both these timestamps are needed to measure round-trip delay.
In this document, TWAMP Light probe response message formats are defined for loss measurement as shown in Figure 12 and Figure 13. The message formats are hardware efficient due to the small size payload and well-known locations of the counters. They do not require any backwards compatibility or support for the existing DM message formats from [RFC5357], as different user-configured destination UDP port is used for loss measurement.
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 | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Transmit Counter | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |X|B| Reserved | Block Number | Reserved | Control Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Receive Counter | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sender Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sender Counter | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |X|B| Reserved |Sender Block Nu| MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sender TTL | | +-+-+-+-+-+-+-+-+ + | Packet Padding | . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 12: TWAMP Light LM Probe Response Message Format
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 Counter | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |X|B| Reserved | Block Number | Reserved | Control Code | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBZ (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Receive Counter | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBZ (8 octets) | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sender Sequence Number | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBZ (12 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sender Counter | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |X|B| Reserved |Sender Block Nu| MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBZ (4 octets) | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Sender TTL | | +-+-+-+-+-+-+-+-+ + | MBZ (15 octets) | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | HMAC (16 octets) | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . Packet Padding . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 13: TWAMP Light LM Probe Response Message Format - Authenticated Mode
The STAMP loss measurement probe response message uses the same message format as the TWAMP Light loss measurement probe response message, except the padding size is 3 bytes in STAMP message in unauthenticated mode (in Figure 12) whereas no padding is added in authenticated mode (in Figure 13). They do not require any backwards compatibility or support for the existing DM message formats from [I-D.ietf-ippm-stamp], as different user-configured destination UDP port is used for loss measurement.
The Node Address TLV is defined for STAMP message [I-D.ietf-ippm-stamp-option-tlv] in this document and has the following format shown in Figure 14:
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Address Family | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ ~ Address ~ +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: Node Address TLV Format
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 following Type is defined in this document and it contains Node Address TLV:
Destination Node Address (value TBA1):
The Destination Node Address TLV is optional. The Destination Node Address TLV indicates the address of the intended recipient node of the probe message. The reflector node SHOULD NOT send response if it is not the intended destination node of the probe query message. This check is useful for example, for performance measurement of SR Policy when using the destination address in 127/8 range for IPv4 or in 0:0:0:0:0:FFFF:7F00/104 range for IPv6.
For two-way performance measurement, the reflector node needs to send the probe response message on a specific reverse path. The sender node can request in the probe query message to the reflector node to send a response back on a given reverse path (e.g. co-routed bidirectional path). This way the destination node does not require any additional SR Policy state.
For one-way performance measurement, the sender node address may not be reachable via IP route from the reflector node. The sender node in this case needs to send its reachability path information to the reflector node.
[I-D.ietf-ippm-stamp-option-tlv] defines STAMP probe query messages that can include one or more optional TLVs. The TLV Type (value TBA2) is defined in this document for Return Path that carries reverse path for STAMP probe response messages (in the payload of the message). The format of the Return Path TLV is shown in Figure 15:
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type = TBA2 | Length | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Return Path Sub-TLVs | . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 15: Return Path TLV
The following Type defined for the Return Path TLV contains the Node Address sub-TLV using the format shown in Figure 14:
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Type | Length | Reserved | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Segment(1) | . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Segment(n) | . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 16: Segment List Sub-TLV in Return Path TLV
The Segment List Sub-TLV (shown in Figure 16) in the Return Path TLV can be one of the following Types:
The Return Path TLV is optional. The PM sender node MUST only insert one Return Path TLV in the probe query message and the reflector node MUST only process the first Return Path TLV in the probe query message and ignore other Return Path TLVs if present. The reflector node MUST send probe response message back on the reverse path specified in the Return Path TLV and MUST NOT add Return Path TLV in the probe response message.
The procedures for delay and loss measurement described in this document for Point-to-Point (P2P) SR Policies [I-D.ietf-spring-segment-routing-policy] are also equally applicable to the Point-to-Multipoint (P2MP) SR Policies as following:
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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Replication SID | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message as shown in Figure 2 for DM or Figure 3 for LM | . . +---------------------------------------------------------------+
Figure 17: Query with Replication Segment for SR-MPLS Policy
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 probe messages need to be sent to traverse different ECMP paths to measure performance delay of an SR Policy.
Forwarding plane has various hashing functions available to forward packets on specific ECMP paths. The mechanisms described in [RFC8029] and [RFC5884] for handling ECMPs are also applicable to the performance measurement. In the IP header of the PM probe messages, sweeping of Destination Addresses in 127/8 range for IPv4 or 0:0:0:0:0:FFFF:7F00/104 range for IPv6 can be used to exercise particular ECMP paths. As specified in [RFC6437], Flow Label field in the outer IPv6 header can also be used for sweeping.
The considerations for performance loss measurement for different ECMP paths of an SR Policy are outside the scope of this document.
The processing rules defined in this section are applicable to both TWAMP Light and STAMP messages for delay and loss measurement for Links and end-to-end SR Policies.
The TTL field in the IPv4 and MPLS headers of the probe query messages is set to 255 [RFC5357]. Similarly, the Hop Limit field in the IPv6 and SRH headers of the probe query messages is set to 255 [RFC5357].
When using the Destination IPv4 Address from the 127/8 range, the TTL in the IPv4 header is set to 1 [RFC8029]. Similarly, when using the Destination IPv6 Address from the 0:0:0:0:0:FFFF:7F00/104 range, the Hop Limit field in the inner IPv6 header is set to 1 whereas in the outer IPv6 header is set to 255.
For Link performance delay and loss measurements, the TTL and Hop Limit field in the probe message is set to 1 in both one-way and two-way measurement modes.
The Router Alert IP option is not set when using the routable Destination IP Address in the probe messages.
When using the Destination IPv4 Address from the 127/8 range, to be able to punt probe packets on the reflector node, the Router Alert IP Option of value 0x0 [RFC2113] for IPv4 MAY be added [RFC8029]. Similarly, when using the Destination IPv6 Address from the 0:0:0:0:0:FFFF:7F00/104 range, the Router Alert IP Option of value 69 [RFC7506] for IPv6 MAY be added in the destination option header, Section 4.6 of [RFC8200]. For SRv6 Policy using SRH, it is added in the inner IPv6 header.
The UDP Checksum Complement for delay and loss measurement messages follows the procedure defined in [RFC7820] and can be optionally used with the procedures defined in this document.
For IPv4 and IPv6 probe messages, where the hardware is not capable of re-computing the UDP checksum or adding checksum complement [RFC7820], the sender node sets the UDP checksum to 0 [RFC6936] [RFC8085]. The receiving node bypasses the checksum validation and accepts the packets with UDP checksum value 0 for the UDP port being used for PM delay and loss measurements.
The performance measurement is intended for deployment in well-managed private and service provider networks. As such, it assumes that a node involved in a measurement operation has previously verified the integrity of the path and the identity of the far-end reflector node.
If desired, attacks can be mitigated by performing basic validation and sanity checks, at the sender, of the counter or timestamp fields in received measurement response messages. The minimal state associated with these protocols also limits the extent of measurement disruption that can be caused by a corrupt or invalid message to a single query/response cycle.
Use of HMAC-SHA-256 in the authenticated mode protects the data integrity of the probe messages. SRv6 has HMAC protection authentication defined for SRH [I-D.ietf-6man-segment-routing-header]. Hence, PM probe messages for SRv6 may not need authentication mode. Cryptographic measures may be enhanced by the correct configuration of access-control lists and firewalls.
IANA is requested to allocate a value for the following optional Destination Address TLV Type for [I-D.ietf-ippm-stamp-option-tlv] to be carried in PM probe messages:
IANA is also requested to allocate a value for the following optional Return Path TLV Type for [I-D.ietf-ippm-stamp-option-tlv] to be carried in PM probe query messages:
IANA is also requested to allocate the values for the following Sub-TLV Types for the Return Path TLV.
The authors would like to thank Thierry Couture for the discussions on the use-cases for TWAMP Light in Segment Routing. The authors would also like to thank Greg Mirsky for reviewing this document and providing useful comments and suggestions. Patrick Khordoc and Radu Valceanu, both from Cisco Systems have helped significantly improve the mechanisms defined in this document. The authors would like to acknowledge the earlier work on the loss measurement using TWAMP described in draft-xiao-ippm-twamp-ext-direct-loss. The authors would also like to thank Sam Aldrin for the discussions to check for broken path.