| SPRING Working Group | R. Gandhi, Ed. |
| Internet-Draft | C. Filsfils |
| Intended status: Informational | Cisco Systems, Inc. |
| Expires: February 7, 2021 | D. Voyer |
| Bell Canada | |
| M. Chen | |
| Huawei | |
| B. Janssens | |
| Colt | |
| August 6, 2020 |
Performance Measurement Using TWAMP Light for Segment Routing Networks
draft-gandhi-spring-twamp-srpm-10
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 describes 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) for Delay Measurement, and uses the messages defined in this document for Loss Measurement. The procedure described is applicable to SR-MPLS and SRv6 data planes and is used for both Links and end-to-end SR Paths including 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 need for control-channel signaling. As described in Appendix A of [RFC8545], TWAMP Light mechanism is informative only. These protocols lack support for direct-mode Loss Measurement (LM) to detect actual Customer data traffic loss which is required in SR networks.
This document describes 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) for Delay Measurement (DM), and uses the messages defined in this document for Loss Measurement. The procedure described is applicable to SR-MPLS and SRv6 data planes and is used for both Links and end-to-end SR Paths including SR Policies and Flex-Algo IGP Paths. This document also defines mechanisms for handling ECMPs of SR Paths for performance delay measurement. Unless otherwise described, the messages defined in [RFC5357] are not modified by this document.
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.
TC: Traffic Class.
TWAMP: Two-Way Active Measurement Protocol.
In the reference topology shown below, the sender node R1 initiates a performance measurement probe query message and the reflector node R5 sends a probe response message for the query message received. The probe response message is typically sent to the sender node R1.
SR is enabled on nodes R1 and R5. The nodes R1 and R5 may be directly connected via a Link or there exists a Point-to-Point (P2P) SR Path e.g. SR Policy [I-D.ietf-spring-segment-routing-policy] on node R1 (called head-end) with destination to node R5 (called tail-end).
t1 t2
/ \
+-------+ Query +-------+
| | - - - - - - - - - ->| |
| R1 |=====================| R5 |
| |<- - - - - - - - - - | |
+-------+ Response +-------+
\ /
t4 t3
Sender Reflector
Reference Topology
For one-way and two-way delay measurements in Segment Routing networks, the probe messages defined in [RFC5357] are used. For direct-mode and inferred-mode loss measurements, the messages defined in this document are used. For both Links and end-to-end SR Paths including SR Policies and Flex-Algo IGP Paths, no PM state for delay or loss measurement need to be created on the reflector node R5.
Separate UDP destination port numbers are user-configured for delay and loss measurements. As specified in [RFC8545], the reflector supports the destination UDP port 862 for delay measurement probe messages by default. This UDP port however, is not used for loss measurement probe messages defined in this document. The sender uses the UDP port number following the guidelines specified in Section 6 in [RFC6335]. The same destination UDP port is used for Links and SR Paths and the reflector is unaware if the query is for the Links or SR Paths. The number of UDP ports with PM functionality needs to be minimized due to limited hardware resoucres.
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-mpls-ioam-sr] 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 / \
Loss Measurement Mode / \
v v
+-------+ +-------+
| | | |
| R1 |============| R5 |
| | SR Path | |
+-------+ Or Link +-------+
Sender Reflector
Figure 1: Example Provisioning Model
Example of Measurement Protocol is TWAMP Light, example of the Timestamp Format is PTPv2 [IEEE1588] or NTP and example of the Loss Measurement mode is inferred-mode or direct-mode.
The mechanisms to provision the sender and reflector nodes are outside the scope of this document. The provisioning model is not used for signaling the PM parameters between the reflector and sender nodes in SR networks.
The reflector node R5 uses the parameters for the timestamp format and delay measurement mode (i.e. one-way or two-way mode) from the received probe query message.
The probe messages defined in [RFC5357] are used for delay measurement for Links and end-to-end SR Paths including SR Policies. For loss measurement, the probe messages defined in this document are used.
The sender IPv4 or IPv6 address is used as the source address. The reflector IPv4 or IPv6 address is used as the destination address. In the case of SR Policy with IPv4 endpoint of 0.0.0.0 or IPv6 endpoint of ::0 [I-D.ietf-spring-segment-routing-policy], the address in the range of 127/8 for IPv4 or ::FFFF:127/104 for IPv6 is used as the destination address, respectively.
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 for DM, since the message does not have any indication to distinguish between the query and response message. The payload of the DM probe query message contains the delay measurement message defined in Section 4.1.2 of [RFC5357]. For symmetrical size query and response messages as defined in [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 = DM Message as specified in Section 4.2.1 of RFC 5357| . Payload = DM Message as specified in Section 4.1.2 of RFC 5357. . . +---------------------------------------------------------------+
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 for LM, 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 = LM Message as specified in Figure 7 or 8 | . . +---------------------------------------------------------------+
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 are used for Links which may be physical, virtual or LAG (bundle), LAG (bundle) member, numbered/unnumbered Links. 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 end-to-end SR-MPLS and SRv6 Policies.
The probe query messages for performance measurement of an end-to-end 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: Example 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 [RFC8754]. The SRv6 network programming is defined in [I-D.ietf-spring-srv6-network-programming]. The probe query messages for performance measurement of an end-to-end SRv6 Policy is sent using its SRH with Segment List as shown in Figure 5. 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 probe query messages.
+---------------------------------------------------------------+ | IP Header | . Source IP Address = Sender IPv6 Address . . Destination IP Address = Destination IPv6 Address . . . +---------------------------------------------------------------+ | SRH as specified in RFC 8754 | . <Segment List> . . . +---------------------------------------------------------------+ | IP Header (as needed) | . Source IP Address = Sender IPv6 Address . . Destination IP Address = Reflector IPv6 Address . . . +---------------------------------------------------------------+ | UDP Header | . Source Port = As chosen by Sender . . Destination Port = User-configured Port . . . +---------------------------------------------------------------+ | Payload = DM Message as specified in Section 4.2.1 of RFC 5357| . Payload = DM Message as specified in Section 4.1.2 of RFC 5357. . Payload = LM Message as specified in Figure 7 or 8 . . . +---------------------------------------------------------------+
Figure 5: Example Probe Query Message for SRv6 Policy
In this document, the Control Code field is defined for delay and loss measurement probe query messages for TWAMP Light in unauthenticated and authenticated modes. The modified delay measurement probe query message format is shown in Figure 6. This message format is backwards compatible with the message format defined in [RFC5357] as its reflectors ignore the received field (previously identified as MBZ). With this field, the reflector node does not require any additional SR state for PM (recall that in SR networks, the state is in the probe packet and signaling of the parameters is avoided). The usage of the Control Code is not limited to the SR paths and can be used for non-SR paths in a network.
. . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Timestamp | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Error Estimate | MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBZ |Se Control Code| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . .
Figure 6: Sender Control Code in TWAMP Light DM Message
Sender Control Code: Set as follows in TWAMP Light probe query message.
In a Query:
In this document, TWAMP Light probe query messages for loss measurement are defined as shown in Figure 7 and Figure 8. The message formats are hardware efficient due to well-known locations of the counters and payload small in size. They are stand-alone and similar to the delay measurement message formats (e.g. location of the Counter and Timestamp). They also do not require backwards compatibility and 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 | MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBZ |Se Control Code| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . Packet Padding . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 7: TWAMP Light LM Probe Query Message - 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 Counter | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |X|B| Reserved | Block Number | MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | MBZ |Se Control Code| +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | HMAC (16 octets) | | | | | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | | . . . Packet Padding . . . | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 8: TWAMP Light LM Probe Query Message - 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 correlate 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. The Block Number can also be used to aggregate performance metrics collected.
HMAC: The 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 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 . . . +---------------------------------------------------------------+ | Payload = DM Message as specified in Section 4.2.1 of RFC 5357| . Payload = LM Message as specified in Figure 12 or 13 . . . +---------------------------------------------------------------+
Figure 9: Probe Response Message
In one-way 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 Sender 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 used to measure one-way delay as (t2 - t1).
In two-way 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 Sender 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 used to measure two-way delay as ((t4 - t1) - (t3 - t2)).
Specifically, the probe response message is sent back on the incoming physical interface where the probe query message is received. This is required for example, in case of two-way measurement mode for Link delay.
The message content for sending probe response message for two-way performance measurement of an end-to-end 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: Example 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.
The message content for sending probe response message on the congruent path of the data traffic for two-way performance measurement of an end-to-end SRv6 Policy with SRH is shown in Figure 11. 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 probe response messages.
+---------------------------------------------------------------+ | IP Header | . Source IP Address = Reflector IPv6 Address . . Destination IP Address = Destination IPv6 Address . . . +---------------------------------------------------------------+ | SRH as specified in RFC 8754 | . <Segment List> . . . +---------------------------------------------------------------+ | IP Header (as needed) | . Source IP Address = Reflector IPv6 Address . . Destination IP Address = Source IPv6 Address from Query . . . +---------------------------------------------------------------+ | UDP Header | . Source Port = As chosen by Sender . . Destination Port = User-configured Port . . . +---------------------------------------------------------------+ | Payload = DM Message as specified in Section 4.2.1 of RFC 5357| . Payload = LM Message as specified in Figure 12 or 13 . . . +---------------------------------------------------------------+
Figure 11: Example Probe Response Message for SRv6 Policy
In this document, TWAMP Light probe response message formats are defined for loss measurement as shown in Figure 12 and Figure 13.
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 | MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 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 - 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 Counter | | | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ |X|B| Reserved | Block Number | MBZ | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | 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 - Authenticated Mode
The processing rules defined in this section are applicable to TWAMP Light messages for delay and loss measurement for Links and end-to-end SR Paths including 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 field in the IPv4 header is set to 1 [RFC8029]. Similarly, when using the Destination IPv6 Address from the ::FFFF:127/104 range, the Hop Limit field in the IPv6 header is set to 1.
For Link performance delay and loss measurements, the TTL or 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 (RAO) [RFC2113] is not set in the probe messages.
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 delay and loss measurements.
The Point-to-Multipoint (P2MP) SR Path that originates from a root node terminates on multiple destinations called leaf nodes (e.g. P2MP SR Policy [I-D.ietf-pim-sr-p2mp-policy] or P2MP Transport [I-D.shen-spring-p2mp-transport-chain]).
The procedures for delay and loss measurement described in this document for P2P SR Policies are also equally applicable to the P2MP SR Policies. The procedure for one-way measurement is defined 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 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Tree-SID | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Message as shown in Figure 2 for DM or Figure 3 for LM | . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+
Figure 14: Example Probe Query with Tree-SID for SR-MPLS Policy
The probe query messages can also be sent using the scheme defined for P2MP Transport using Chain Replication that may contain Bud SID as defined in [I-D.shen-spring-p2mp-transport-chain].
The considerations for two-way mode for performance measurement for P2MP SR Policy (e.g. for bidirectional SR Path) are outside the scope of this document.
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 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 IPv4 header of the probe messages, sweeping of Destination Address in 127/8 range 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.
Liveness monitoring is required for connectivity verification and continuity check in an SR network. The procedure defined in this document for delay measurement using the TWAMP Light probe messages can also be applied to liveness monitoring of Links and SR Paths. The one-way or two-way measurement mode can be used for liveness monitoring. Liveness failure is notified when consecutive N number of probe response messages are not received back at the sender node, where N is locally provisioned value. Note that failure detection interval and scale for number of probes need to account for the processing of the probe query messages which need to be punted from the forwarding fast path (to slow path or control plane) and response messages need to be injected on the reflector node. This is enhanced by using the probes in loopback mode as described in [I-D.gandhi-spring-sr-enhanced-plm].
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 [RFC8754]. Hence, probe messages for SRv6 may not need authentication mode. Cryptographic measures may be enhanced by the correct configuration of access-control lists and firewalls.
This document does not require any IANA action.
| [RFC0768] | Postel, J., "User Datagram Protocol", STD 6, RFC 768, DOI 10.17487/RFC0768, August 1980. |
| [RFC2119] | Bradner, S., "Key words for use in RFCs to Indicate Requirement Levels", BCP 14, RFC 2119, DOI 10.17487/RFC2119, March 1997. |
| [RFC4656] | Shalunov, S., Teitelbaum, B., Karp, A., Boote, J. and M. Zekauskas, "A One-way Active Measurement Protocol (OWAMP)", RFC 4656, DOI 10.17487/RFC4656, September 2006. |
| [RFC5357] | Hedayat, K., Krzanowski, R., Morton, A., Yum, K. and J. Babiarz, "A Two-Way Active Measurement Protocol (TWAMP)", RFC 5357, DOI 10.17487/RFC5357, October 2008. |
| [RFC8174] | Leiba, B., "Ambiguity of Uppercase vs Lowercase in RFC 2119 Key Words", BCP 14, RFC 8174, DOI 10.17487/RFC8174, May 2017. |
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 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.