| SPRING Working Group | R. Gandhi, Ed. |
| Internet-Draft | C. Filsfils |
| Intended status: Standards Track | Cisco Systems, Inc. |
| Expires: December 7, 2020 | N. Vaghamshi |
| Reliance | |
| M. Nagarajah | |
| Telstra | |
| June 5, 2020 |
Enhanced Performance Delay and Liveness Monitoring in Segment Routing Networks
draft-gandhi-spring-sr-enhanced-plm-01
Segment Routing (SR) leverages the source routing paradigm. SR is applicable to both Multiprotocol Label Switching (SR-MPLS) and IPv6 (SRv6) data planes. This document defines procedure for Performance Delay and Liveness Monitoring (PDLM) in Segment Routing networks. The procedure uses the probe messages defined in RFC 5357 (Two-Way Active Measurement Protocol (TWAMP) Light) and RFC 8762 (Simple Two-Way Active Measurement Protocol (STAMP)) for SR Paths including SR Policies with both SR-MPLS and SRv6 data planes.
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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 [RFC8402]. 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 Liveness Monitoring for detecting faults as well as Performance Delay Measurement (DM) and Loss Measurement (LM) are essential requirements to provide Service Level Agreements (SLAs) in SR networks.
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. The TWAMP Light [Appendix I in RFC 5357] provides simplified mechanisms for active performance measurement in Customer IP networks by provisioning UDP paths that eliminates the need for control-channel signaling. Similarly, the Simple Two-way Active Measurement Protocol (STAMP) [RFC8762] alleviates the need for control-channel signaling by using configuration data model to provision a test-channel.
[I-D.gandhi-spring-twamp-srpm] defines procedure for performance measurement using TWAMP Light messages with user-defined IP/UDP paths in SR networks. [I-D.gandhi-spring-stamp-srpm] defines similar procedure using STAMP messages in SR networks. The procedure for one-way and two-way modes defined for delay measurement can also be applied to liveness monitoring of SR Paths. However, it limits the scale for number of PM sessions and fault detection interval since the probe query messages need to be punted from the forwarding path (to slow path or control plane) and response messages need to be injected.
For Liveness Monitoring, Seamless Bidirectional Forwarding Detection (S-BFD) [RFC7880] can be used in Segment Routing networks. However, S-BFD requires protocol support on the reflector node to process the S-BFD packets as packets need to be punted from the forwarding path in order to send the reply thereby limiting the scale for number of PM sessions and fault detection interval. In addition, S-BFD protocol does not have the capability today to enable performance delay monitoring in SR networks. Enabling multiple protocols in SR networks, S-BFD for liveness monitoring and TWAMP Light or STAMP for performance delay monitoring increases the deployment and operational complexities in SR networks.
This document defines procedure for Performance Delay and Liveness Monitoring (PDLM) in Segment Routing networks. The procedure uses the probe messages defined in [RFC5357] (TWAMP Light) and [RFC8762] (STAMP) for SR Paths including SR Policies with both SR-MPLS and SRv6 data planes.
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.
BFD: Bidirectional Forwarding Detection.
BSID: Binding Segment ID.
DM: Delay Measurement.
ECMP: Equal Cost Multi-Path.
LM: Loss Measurement.
MPLS: Multiprotocol Label Switching.
OWAMP: One-Way Active Measurement Protocol.
PDLM: Performance Delay and Liveness Monitoring.
PM: Performance Measurement.
PTP: Precision Time Protocol.
SID: Segment ID.
SL: Segment List.
SR: Segment Routing.
SRH: Segment Routing Header.
SR-MPLS: Segment Routing with MPLS data plane.
SRv6: Segment Routing with IPv6 data plane.
STAMP: Simple Two-way Active Measurement Protocol.
TWAMP: Two-Way Active Measurement Protocol.
In the reference topology shown below, the nodes R1 and R5 are connected via Point-to-Point (P2P) SR Path such as SR Policy [I-D.ietf-spring-segment-routing-policy] originating on node R1 with endpoint on node R5.
+-------+ t1 Probe +-------+
| | - - - - - - - - - - | |
| R1 |====================|| R5 |
| |<- - - - - - - - - - | |
+-------+ t4 Return Probe +-------+
Sender Reflector
(Simply Forward)
Figure 1: Reference Topology
In loopback mode, the sender node R1 initiates probe messages and the reflector node R5 forwards them back to the sender node R1 just like data packets for the normal traffic. The probe messages are not punted at the reflector node and it does not process them and generate response messages. The reflector node must not drop the loopback probe messages, for example, due to a local policy provisioned on the node.
The TWAMP Light probe messages for delay measurement as defined in [RFC5357] or STAMP probe messages as defined in [RFC8762] are sent by the sender node R1 towards the reflector node R5 in loopback mode as shown in Figure 1. The probe messages are sent by the sender node on the congruent path of the data traffic flowing on the SR Path.
The destination UDP port number in the probe message is user-configured from the range specified in [RFC8762]. As specified in [RFC8762], the destination UDP port 862 is used in the probe messages by default. The Source and Destination IP addresses in the probe messages are set to the reflector and the sender node addresses, respectively (representing the reverse path). The IPv4 Time To Live (TTL) and IPv6 Hop Limit (HL) are set to 255.
No PM session is created on the reflector node R5. As the probe message is not punted on the reflector node for processing, the Sender copies the 'Sequence Number' in 'Session-Sender Sequence Number' field directly. Also, the Sender Timestamp, Sender Error Estimate and Sender TTL fields [RFC5357] [RFC8762] in the probe message are not used. The rest of the fields are set as defined in [RFC5357] [RFC8762]
Timestamp format recommended is 64-bit PTPv2 [IEEE1588] as specified in [RFC8186] implemented in hardware. In addition to adding the timestamp in the message, the "Error Estimate" field in the payload of the message can be updated using the procedure defined in [RFC4656].
An example of a provisioning model and typical measurement parameters for the user-configured destination UDP port is shown in Figure 2:
+------------+
| Controller |
+------------+
Destination UDP Port / \ Network Programming Label
Measurement Protocol / \ Timestamp2 Offset
PDLM Mode / \ Timestamp Format
LB or Enhanced LB / \
Network Programming Label / \
Timestamp Format / \
/ \
/ \
v v
+-------+ +-------+
| | | |
| R1 |============| R5 |
| | SR Path | |
+-------+ +-------+
Sender Reflector
Figure 2: Example Provisioning Model
Example of Measurement Protocol is TWAMP Light and STAMP, example of Timestamp Format is 64-bit PTPv2 [IEEE1588] and NTP, etc.
The mechanisms to provision the sender and reflector nodes are outside the scope of this document.
For performance delay and liveness monitoring of an SR Path including SR Policy, PM probes in loopback mode is used. The PM probe messages are sent by the sender (head-end) node R1 to the reflector (endpoint) node R5 of the SR Policy as shown in Figure 1.
The probe messages are sent using the Segment List (SL) of the Candidate-paths of the SR Policy [I-D.ietf-spring-segment-routing-policy]. When a Candidate-path has more than one Segment Lists, multiple probe messages are sent, one using each Segment List. The return probe messages are received by the sender node via IP/UDP [RFC0768] return path by default. The Segment List of the return SR path can be added in the probe message header to receive the return probe message on a specific path using the mechanisms defined in [I-D.ietf-pce-binding-label-sid] and [I-D.ietf-pce-sr-bidir-path].
The TWAMP Light or STAMP probe messages for SR-MPLS data plane are sent using the MPLS header containing the label stack of the SR Policy as shown in Figure 3. In case of IP/UDP return path, the MPLS header is removed by the reflector node. The label stack can contain a reverse SR-MPLS path to receive the return probe message on a specific path. In this case, the MPLS header will not be removed by the reflector node.
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label(1) | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label(n) | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IP Header | . Source IP Address = Reflector IPv4 or IPv6 Address . . Destination IP Address = Sender IPv4 or IPv6 Address . . Protocol = UDP . . . +---------------------------------------------------------------+ | UDP Header | . Source Port = As chosen by Sender . . Destination Port = User-configured Port . . . +---------------------------------------------------------------+ | Payload as defined in Section 4.2.1 of RFC 5357 | | | Payload as defined in Section 4.2 of RFC 8762 | . . +---------------------------------------------------------------+
Figure 3: Example Probe Message for SR-MPLS
The TWAMP Light or STAMP probe messages for SRv6 data plane are sent using the Segment Routing Header (SRH) [RFC8754] containing the Segment List of the SR Policy as shown in Figure 4. In case of IP/UDP return path, the SRH is removed by the reflector node. The Segment List can contain a reverse SRv6 path to receive the return probe message on a specific path. In this case, the SRH will not be removed by the reflector node.
+---------------------------------------------------------------+ | IP Header | . Source IP Address = Sender IPv6 Address . . Destination IP Address = Destination IPv6 Address . . . +---------------------------------------------------------------+ | SRH as specified in RFC 8754 | . <Segment List> . . . +---------------------------------------------------------------+ | IP Header | . Source IP Address = Reflector IPv6 Address . . Destination IP Address = Sender IPv6 Address . . . +---------------------------------------------------------------+ | UDP Header | . Source Port = As chosen by Sender . . Destination Port = User-configured Port . . . +---------------------------------------------------------------+ | Payload as defined in Section 4.2.1 of RFC 5357 | | | Payload as defined in Section 4.2 of RFC 8762 | . . +---------------------------------------------------------------+
Figure 4: Example Probe Message for SRv6
The enhanced performance delay and liveness monitoring of an SR Path including SR Policy is defined using the PM probes in loopback mode enabled with network programming.
In loopback mode enabled with network programming, both transmit (t1) and receive (t2) timestamps in data plane are collected by the probe messages sent in loopback mode as shown in Figure 5. The network programming function optimizes the "operations of punt, add receive timestamp and inject the probe packet" on the reflector node and is implemented in hardware. The payload of the probe message is not modified by any intermediate nodes.
+-------+ t1 Probe t2 +-------+
| | - - - - - - - - - - | |
| R1 |====================|| R5 |
| |<- - - - - - - - - - | |
+-------+ Return Probe +-------+
Sender Reflector
(Timestamp,
Pop and Forward)
Figure 5: Loopback Mode Enabled with Network Programming
The sender node adds transmit (t1) timestamp in the payload of the TWAMP Light or STAMP probe message and clears the receive (t2) timestamp. The reflector node adds the receive timestamp in the payload of the received probe message without punting the message to slow-path (or control-plane). The reflector node only adds the receive timestamp if the source or destination address in the probe message matches the local node address to ensure that the receive timestamp is returned by the intended reflector node.
The network programming function enables the node to add receive timestamp in the payload of the probe message at a specific location which is locally provisioned consistently in the network. In TWAMP Light message defined in Section 4.2.1 of [RFC5357] or STAMP message defined in [RFC8762] for delay measurement, the 64-bit receive timestamp is added at byte-offset 16 which is from the start of the payload.
In this document, new Timestamp Label (value TBD1) is defined for SR-MPLS data plane to enable network programming function for "timestamp, pop and forward" the received packet.
In the probe message for SR-MPLS, Timestamp Label is added in the MPLS header as shown in Figure 6, to collect "Receive Timestamp" field in the payload of the TWAMP Light [RFC5357] or STAMP probe message. The label stack for the reverse SR-MPLS path can be added after the Timestamp Label to receive the return probe message on a specific path. When a node receives a message with Timestamp Label, after timestamping the message at a fixed location, the node pops the Timestamp Label and forwards the message using the next label or IP header in the message (just like the data packets for the normal traffic).
0 1 2 3 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 2 3 4 5 6 7 8 9 0 1 +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label(1) | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ . . . . . . +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Label(n) | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | Timestamp Label (TBA1) | TC |S| TTL | +-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+-+ | IP Header | . Source IP Address = Reflector IPv4 or IPv6 Address . . Destination IP Address = Sender IPv4 or IPv6 Address . . Protocol = UDP . . . +---------------------------------------------------------------+ | UDP Header | . Source Port = As chosen by Sender . . Destination Port = User-configured Port . . . +---------------------------------------------------------------+ | Payload as defined in Section 4.2.1 of RFC 5357 Or | | Payload as defined in Section 4.2 of RFC 8762 | . . +---------------------------------------------------------------+
Figure 6: Example Probe Message with Timestamp Label for SR-MPLS
The ingress node needs to know if the egress node can process the Timestamp Label. The signaling extension for this capability exchange is outside the scope of this document.
Another way is to leverage a centralized controller (e.g., SDN controller) to program the ingress and egress nodes. In this case, the controller MUST make sure (e.g., by some capability discovery mechanisms outside the scope of this document) that the egress node can process the Timestamp Label.
Timestamp Label (value TBA1) can be allocated using one of the following methods:
In this document, new Endpoint function "Timestamp and Forward (TSF)" (value TBD2) is defined for Segment Routing Header (SRH) [RFC8754] for SRv6 data plane to enable network programming function for "timestamp and forward" the received message.
In the probe message for SRv6, END.TSF function is added for the Endpoint Segment Identifier (SID) in SRH [RFC8754] as shown in Figure 7, to collect "Receive Timestamp" field in the payload of the TWAMP Light [RFC5357] or STAMP probe message. When a node receives a packet with END.TSF function for the target SID which is local, after timestamping the packet at a fixed location, the node forwards the packet using the next SID or IP header in the packet (just like the packets for the normal traffic).
+---------------------------------------------------------------+ | IP Header | . Source IP Address = Sender IPv6 Address . . Destination IP Address = Destination IPv6 Address . . . +---------------------------------------------------------------+ | SRH as specified in RFC 8754 | . <Segment List> . . . +---------------------------------------------------------------+ | IP Header | . Source IP Address = Reflector IPv6 Address . . Destination IP Address = Sender IPv6 Address . . . +---------------------------------------------------------------+ | UDP Header | . Source Port = As chosen by Sender . . Destination Port = User-configured Port . . . +---------------------------------------------------------------+ | Payload as defined in Section 4.2.1 of RFC 5357 Or | | Payload as defined in Section 4.2 of RFC 8762 | . . +---------------------------------------------------------------+
Figure 7: Example Probe Message with Endpoint Function for SRv6
An SR Policy can have ECMPs between the source and transit nodes, between transit nodes and between transit and destination nodes. The PM probe messages need to be sent to traverse different ECMP paths to monitor the liveness for an SR Policy.
Forwarding plane has various hashing functions available to forward packets on specific ECMP paths. In IPv4 header of the PM probe messages, sweeping of Destination Address in 127/8 range can be used to exercise different ECMP paths in the loopback mode as long as the return path is also SR-MPLS. The Flow Label field in the outer IPv6 header can also be used for sweeping to exercise different ECMP paths.
Liveness failure for SR Path is notified when consecutive N number of return probe messages are not received at the sender node, where N is locally provisioned value. Similarly, delay metrics are notified when consecutive M number of probe messages have measured delay values exceed user-configured thresholds (absolute and percentage), where M is also locally provisioned value.
In loopback mode, the timestamps t1 and t4 are used to measure round-trip delay. In loopback mode enabled with network programming, the timestamps t1 and t2 are used to measure one-way delay.
The Performance Delay and Liveness Monitoring is intended for deployment in the well-managed private and service provider networks. As such, it assumes that a node involved in a monitoring operation has previously verified the integrity of the path and the identity of the reflector node. If desired, attacks can be mitigated by performing basic validation and sanity checks, at the sender, of the timestamp fields in received probe messages. The minimal state associated with these protocols also limits the extent of disruption that can be caused by a corrupt or invalid message to a single probe cycle. Use of HMAC-SHA-256 in the authenticated mode protects the data integrity of the probe messages. Cryptographic measures may be enhanced by the correct configuration of access-control lists and firewalls.
IANA maintains the "Special-Purpose Multiprotocol Label Switching (MPLS) Label Values" registry (see <https://www.iana.org/assignments/mpls-label-values/mpls-label-values.xml>). IANA is requested to allocate Timestamp Label value from the "Extended Special-Purpose MPLS Label Values" registry:
+-------------+---------------------------------+---------------+
| Value | Description | Reference |
+-------------+---------------------------------+---------------+
| TBA1 | Timestamp Label | This document |
+-------------+---------------------------------+---------------+
IANA is requested to allocate, within the "SRv6 Endpoint Behaviors Registry" sub-registry belonging to the top-level "Segment-routing with IPv6 data plane (SRv6) Parameters" registry [I-D.ietf-spring-srv6-network-programming], the following allocation:
+-------------+---------------------------------+---------------+
| Value | Endpoint Behavior | Reference |
+-------------+---------------------------------+---------------+
| TBA2 | END.TSF (Timestamp and Forward) | This document |
+-------------+---------------------------------+---------------+
| [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. |
| [RFC8762] | Mirsky, G., Jun, G., Nydell, H. and R. Foote, "Simple Two-Way Active Measurement Protocol", RFC 8762, DOI 10.17487/RFC8762, March 2020. |
TBD