| SPRING Working Group | R. Gandhi, Ed. |
| Internet-Draft | C. Filsfils |
| Intended status: Standards Track | Cisco Systems, Inc. |
| Expires: September 6, 2020 | N. Vaghamshi |
| Reliance | |
| M. Nagarajah | |
| Telstra | |
| March 5, 2020 |
Enhanced Performance and Liveness Monitoring in Segment Routing Networks
draft-gandhi-spring-sr-enhanced-plm-00
Segment Routing (SR) leverages the source routing paradigm. SR is applicable to both Multiprotocol Label Switching (SR-MPLS) and IPv6 (SRv6) data planes. This document defines procedure for Enhanced Performance and Liveness Monitoring (PLM) in Segment Routing networks. The procedure uses the probe messages defined in RFC 5357 (Two-Way Active Measurement Protocol (TWAMP) Light) as well as STAMP and is applicable to 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 and Loss Monitoring 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 control-channel signaling. 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.gandhi-spring-twamp-srpm] defines procedure for using TWAMP Light and STAMP messages with user-defined IP/UDP paths in SR networks and is applicable to both SR-MPLS and SRv6 data planes.
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 are punted from forwarding path in order to send reply thereby limiting the scale for number of sessions and fault detection interval. In addition, S-BFD protocol does not have the capability today to enable performance delay and loss monitoring in SR networks. Enabling multiple protocols in SR networks, S-BFD for liveness monitoring and TWAMP Light or STAMP for performance delay and loss monitoring increases the operational complexity in SR networks.
This document defines procedure for Enhanced Performance and Liveness Monitoring (PLM) in Segment Routing networks. The procedure uses the probe messages defined in [RFC5357] (Two-Way Active Measurement Protocol (TWAMP) Light) as well as STAMP defined in [I-D.ietf-ippm-stamp] in loopback mode. The procedure specified is applicable to both SR-MPLS and SRv6 data planes.
The procedure defined in this document will be updated in a future revision to include performance loss monitoring as well.
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.
PLM: Performance 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.
For liveness monitoring for an SR Policy, the loopback mode as defined in Section 4.2.3 of [I-D.gandhi-spring-twamp-srpm] is used. The TWAMP Light probe messages for delay measurement defined in Section 4.2.1 of [RFC5357] or STAMP probe messages as defined in [I-D.ietf-ippm-stamp] are sent by the sender (head-end) node R1 to the reflector endpoint node R5 of the SR Policy using the user-configured IP/UDP path as shown in Figure 1.
+-------+ t1 Probe +-------+
| | - - - - - - - - - - | |
| R1 |--------------------|| R5 |
| |<- - - - - - - - - - | |
+-------+ t4 Return Probe +-------+
Sender Reflector Endpoint
(Simply Forward)
Figure 1: Loopback Mode
The probe messages are sent using the Segment List (SL) of the SR Policy. When an SR Policy has more than one Segment List, multiple probe messages are sent, one using each Segment List. The Source and Destination IP addresses in the probe messages are set to the reflector endpoint and the sender head-end node addresses, respectively. The IPv4 Time To Live (TTL), IPv6 Hop Limit (HL), Router Alert (RA) Option and UDP checksum fields in the probe messages are set using the procedures defined in [I-D.gandhi-spring-twamp-srpm].
The probe packets are not punted on the reflector node but are simply forwarded just like data traffic. The probe messages are received back 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 probe message on a specific reverse path using the mechanisms defined in [I-D.ietf-pce-binding-label-sid] and [I-D.ietf-pce-sr-bidir-path]. In either case, the reflector node must not drop the loopback probe messages, for example, due to a local policy provisioned on the node.
Liveness failure is notified when consecutive N number of probe messages are not received back at the sender, where N is locally provisioned value.
The TWAMP Light or STAMP probe messages are sent using the label stack of the SR Policy as shown in Figure 2 using the procedure specified in [I-D.gandhi-spring-twamp-srpm]. The label stack can contain a reverse SR-MPLS path to receive the reply on a specific path.
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 = Endpoint 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 STAMP | . . +---------------------------------------------------------------+
Figure 2: Probe Message Header for SR-MPLS
The TWAMP Light or STAMP probe messages are sent using the SRH containing the Segment Identifier (SID) List of the SR Policy as shown in Figure 3 using the procedure specified in [I-D.gandhi-spring-twamp-srpm]. The SID List can contain a reverse SRv6 path to receive the reply on a specific path.
+---------------------------------------------------------------+ | SRH | . <Segment List> . . . +---------------------------------------------------------------+ | IP Header | . Source IP Address = Endpoint IPv6 Address . . Destination IP Address = Sender 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 STAMP | . . +---------------------------------------------------------------+
Figure 3: Probe Message Header for SRv6
The enhanced performance and liveness monitoring for an SR Policy is defined using the loopback mode enabled with network programming. 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. In this mode, both transmit (t1) and receive (t2) timestamps in data plane are collected by the probe messages sent in loopback mode as shown in Figure 4. The payload of the probe message is not modified by any intermediate nodes.
+-------+ t1 Probe t2 +-------+
| | - - - - - - - - - - | |
| R1 |--------------------|| R5 |
| |<- - - - - - - - - - | |
+-------+ Return Probe +-------+
Sender Reflector Endpoint
(Timestamp,
Pop and Forward)
Figure 4: 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 endpoint node adds the receive timestamp (at the fixed location locally provisioned consistently in the network) in the payload of the received TWAMP Light or STAMP probe message without punting the probe message in control-plane. The reflector endpoint node only adds the receive timestamp if the source address in the probe message matches the local node address to ensure that the receive timestamp is returned by the intended endpoint node. In addition, the UDP port in the probe message must be locally programmed for adding the timestamp in the probe message. The end-to-end one-way delay is measured using the receive (t2) and transmit (t1) timestamps in the probe message.
Timestamp format recommended is 64-bit PTPv2 [IEEE1588] as specified in [RFC8186] implemented in hardware. Note that the timestamp format can be locally provisioned as part of enabling the network programming function. In addition to adding the timestamp in the message, the "Error Estimate" field in the payload of the message is updated using the procedure defined in [RFC4656].
The network programming function is enabled to add receive timestamp in the payload of the probe message at a specific location which is also locally provisioned. In TWAMP Light message defined in Section 4.2.1 of [RFC5357] or STAMP message defined in [I-D.ietf-ippm-stamp] for delay measurement, the 64-bit receive timestamp is added at byte-offset 16 which is from the start of the payload.
Liveness failure is notified when consecutive N number of probe messages are not received back at the sender, where N is locally provisioned value. Similarly, delay metrics are notified when consecutive M number of probe messages have measured delay values violate user-configured threshold, where M is also locally provisioned value.
In this document, new Timestamp Label (special purpose label with value TBD1) is defined for SR-MPLS to enable network programming function for timestamp, pop and forward the received packet.
In the loopback mode enabled with network programming for SR-MPLS, Timestamp Label is added in the MPLS header as shown in Figure 5, to collect "Receive Timestamp" field in the payload of the TWAMP Light [RFC5357] or STAMP probe message. When a node receives a message with Timestamp Label, other than timestamping the message at a fixed location, the node pops the Timestamp Label and forwards the packet using the next label or IP header in the packet (just like the 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 = Endpoint 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 STAMP | . . +---------------------------------------------------------------+
Figure 5: Probe Message Header for SR-MPLS with Timestamp Label
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.
In this document, new Endpoint function "Timestamp and Forward (TSF)" (value TBD2) is defined for Segment Routing Header (SRH) [I-D.ietf-6man-segment-routing-header] for SRv6 to enable network programming function for timestamp and forward the received message.
In the loopback mode enabled with network programming for SRv6, END.TSF function is added for the Endpoint SID in SRH [I-D.ietf-6man-segment-routing-header] as shown in Figure 6, 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, other than 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).
+---------------------------------------------------------------+ | SRH | . <Segment List> . +---------------------------------------------------------------+ | IP Header | . Source IP Address = Endpoint IPv6 Address . . Destination IP Address = Sender 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 STAMP | . . +---------------------------------------------------------------+
Figure 6: Probe Message Header for SRv6 with Endpoint Function
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 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 different ECMP paths in loopback mode as long as the reverse path is also an SR-MPLS or SRv6 path. The Flow Label field in the outer IPv6 header can also be used for sweeping ECMP paths.
The Performance 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 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 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. 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 allocations:
+-------------+---------------------------------+---------------+
| Value | Endpoint Behavior | Reference |
+-------------+---------------------------------+---------------+
| TBA2 | END.TSF (Timestamp and Forward) | This document |
+-------------+---------------------------------+---------------+
TBD