Streaming telemetry pushes the subscribed data from the router to one or more collectors. The telemetry infrastructure retrieves the data from the system database when you send a subscription request. Based on the subscription request or the telemetry configuration the cached generic counters data can be retrieved periodically based on the sample-interval. Data, such as interface statistics, is cached and refreshed at certain intervals. The TARGET_DEFINED subscription mode can be used to retrieve data when the cache gets updated, and is not based on a timer.

The application can register as a data producer with the telemetry library and the SysdB paths it supports. One of the data producers, Statsd, uses the library with a TARGET_DEFINED subscription mode. As part of this mode, the producer registers the sensor paths. The statistics infrastructure streams the incremental updates for statsd cache sensor path Cisco-IOS-XR-infra-statsd-oper:infra-statistics/interfaces/interface/cache/generic-counters. With this path in the subscription, whenever cache is updated, the statsd application pushes the updates to the telemetry daemon. The daemon sends these incremental updates to the collector. The cache updates are pushed for physical interfaces, physical subinterfaces, bundle interfaces, and bundle subinterfaces. You can subscribe to the sensor path for the cached generic counters with TARGET_DEFINED mode instead of the sensor path for the latest generic counters (Cisco-IOS-XR-infra-statsd-oper:infra-statistics/interfaces/interface/latest/generic-counters) to reduce the system load.

Configure the router to stream telemetry data from cache for generic counters using the following instructions:

Create a TARGET_DEFINED subscription mode for cached generic counters using one of the two options:

• Option 1: gRPC Network Management Interface (gNMI) subscribe request

  
  {
      "name": "SubscribeRequest",
      "subscribe": {
          "prefix": {"origin":
                  "Cisco-IOS-XR-infra-statsd-oper"
                 
                },
           "mode": "STREAM", "encoding": "PROTO", "updates_only": "false",
          "subscription": [
           { "path": {"elem": [ {"name":"infra-statistics"},
                              {"name":"interfaces"},
                              {"name":"interface"},
                              {"name":"cache"},
                              {"name":"generic-counters"}
                           ]
                  },
             "mode":   "TARGET_DEFINED" 
           }
                       ]
      }
  }

• Option 2: Model-driven telemetry configuration for non-gNMI requests

  Router(config)#telemetry model-driven
  Router(config-model-driven)#subscription sub1
  Router(config-model-driven-subs)#sensor-group-id grp1 mode target-defined 
  Router(config-model-driven-subs)#source-interface Interface1
  Router(config-model-driven-subs)#commit

After the subscription is triggered, updates to the stats cache are monitored. The statsd application pushes the cached generic counters to the client (collector).

View the number of incremental updates for the sensor path.

Router#show telemetry model-driven subscription .*
Fri Nov 12 23:36:27.212 UTC
Subscription: GNMI__16489080148754121540
-------------
   Collection Groups:
    ------------------
      Id: 1
      Sample Interval:      0 ms   (Incremental Updates)
      Heartbeat Interval:   NA
      Heartbeat always:     False
      Encoding:             gnmi-proto
      Num of collection:    1
      Incremental updates:  12
      Collection time:      Min:     5 ms Max:     5 ms
      Total time:           Min:     6 ms Avg:     6 ms Max:     6 ms
      Total Deferred:       1
      Total Send Errors:    0
      Total Send Drops:     0
      Total Other Errors:   0
      No data Instances:    0
      Last Collection Start:2021-11-12
                23:34:27.1362538876 +0000
      Last Collection End:  2021-11-12   23:34:27.1362545589
              +0000
      Sensor Path:          Cisco-IOS-XR-infra-statsd-oper:infra-statistics/interfaces/
                            interface/cache/generic-counters

In this example, the incremental updates of 12 indicates that the cache is updated 12 times.

Router#show telemetry model-driven subscription statsd-target internal
Fri Nov 12 08:51:16.728 UTC
Subscription: statsd-target
-------------
State: ACTIVE
Sensor groups:
Id: statsd
Sample Interval: 0 ms (Incremental Updates)
Heartbeat Interval: NA
Sensor Path: Cisco-IOS-XR-infra-statsd-oper:infra-statistics/interfaces/interface/cache/
             generic-counters
Sensor Path State: Resolved

Destination Groups:
Group Id: statsd-target
Destination IP: 192.0.2.1
Destination Port: 56000
Encoding: json
Transport: grpc
State: Active
TLS : False
Total bytes sent: 623656
Total packets sent: 13
Last Sent time: 2021-08-16 08:51:15.1304821089 +0000

Collection Groups:
------------------
Id: 2
Sample Interval: 0 ms (Incremental Updates)
Heartbeat Interval: NA
Heartbeat always: False
Encoding: json
Num of collection: 1
Incremental updates: 3
Collection time: Min: 94 ms Max: 94 ms
Total time: Min: 100 ms Avg: 100 ms Max: 100 ms
Total Deferred: 0
Total Send Errors: 0
Total Send Drops: 0
Total Other Errors: 0
No data Instances: 0
Last Collection Start:2021-08-16 08:51:04.1293895665 +0000
Last Collection End: 2021-08-16 08:51:04.1293996284 +0000

The sample interval of 0 indicates that the data is streamed whenever an event occurs. Here, the event represents the updates to the cache state.

Related Commands:

• show tech telemetry model-driven

• show running-config telemetry model-driven

• show telemetry producers trace producer name info

• show telemetry producers trace producer name err

gNMI supports a dial-in session where a client connects to the router via gRPC server with the gNMI specification. This feature introduces support to use a tunnel service for gNMI dial-out connections based on the recommendation from OpenConfig forum.

With the gNMI dial-out through tunnel service, the router (tunnel client) dials out to a collector (tunnel server). Once the session is established, the tunnel server can act as a client and request gNMI services and gNMI Subscribe RPCs over the tunnel session. This feature allows a change in direction of session establishment and data collection without altering the gNMI semantics. Using gRPC tunnel dial-out session, the router initiates the connection to external collector so that the management software is automatically aware when a new device is introduced into the network.

For more information about gNMI dial-out via gRPC tunnel, see the Github repository.

Note	Only the gNMI Subscribe RPC over the tunnel is supported.

Note	The tunnel service supports only Transport Layer Security (TLS) session.

Perform the following steps to configure gNMI dial-out via tunnel service:

You can stream telemetry data about PBR decapsulation statistics for GRE and GUE encapsulation protocols that deliver packets using IPv4 or IPv6. The encapsulated data has source and destination address that must match with the source and destination address in the classmap. Both encapsulation and decapsulation interfaces collect statistics periodically. The statistics can be displayed on demand using show policy-map type pbr [vrf vrf-name] address-family ipv4/ipv6 statistics command. For more information on PBR-based decapsulation, see Interface and Hardware Component Configuration Guide for Cisco NCS 5500 Series Routers.

With this release, the decapsulation statistics can be displayed using Cisco-IOS-XR-infra-policymgr-oper.yang data model and telemetry data. You can stream telemetry data from the sensor path:

Cisco-IOS-XR-infra-policymgr-oper:policy-manager/global/policy-map/policy-map-types/policy-map-type/vrf-table/vrf/afi-table/afi/stats

The following steps show the PBR configuration and the decapsulation statistics that is streamed as telemetry data to the collector.