Fabric Management#

gNMI#

Overview#

gRPC Network Management Interface (gNMI) is a gRPC-based protocol that defines a service or set of services (set of RPC methods) used to configure and retrieve data from network devices. The gNMI gRPC service is comprised of four RPCs: CAPABILITIES, GET, SET and SUBSCRIBE. The gNMI spec and associated protobuf defines the type of messages and the data structures used to get, set or stream information to and from network devices.

gNMI Subscription#

A gNMI Subscription to a server consists of the following key attributes:

• One or multiple paths to subscribe to (what data should be sent to client by server)
• A subscription mode

gNMI SUBSCRIBE RPC defines three subscription modes:

• ONCE: A subscription to a server is created and a single request is sent. The server creates an update message for the requested path and sends it to the client. The subscription is then terminated.
• POLL: A subscription to a server is created for a given path, the client will then send a specific message to the server on a timed interval, upon receipt of this message the server will send the data for the path on which the subscription is created.
• STREAM: A subscription to a server is created for a given path, the server is then expected to send data back to the client for that given path in one of three ways, on_change, on_sample or target_defined

gNMI Server Configuration#

--{ + running }--[ system gnmi-server ]--
A:srl2# info detail
    admin-state enable
    timeout 7200
    rate-limit 60
    session-limit 20
    commit-confirmed-timeout 0
    include-defaults-in-config-only-responses false
    network-instance mgmt {
        admin-state enable
        use-authentication true
        port 57400
        tls-profile tls-profile-1
    }
    unix-socket {
        admin-state disable
        use-authentication true
    }

Configuration explanation:

admin-state: enabled under the global gNMI context it will allow for gNMI to be enabled under network-instances or unix-socket. If disabled, all gNMI servers will be disabled.

timeout: specify the number of seconds the a gNMI connection will remain idle before closing the connection 

rate-limit: set the max number of connection attempts allowed per minute

session-limit: sets the limit on the number of simultaneous active gNMI sessions

network-instance: specify the network-instance under which a gNMI server should be reachable

admin-state: enabled under the network-instance or unix-socket in order to enable or disable an instance of the gNMI server under a given network-instance

use-authentication: specifies whether the RPC should be authenticated against a user using aaa_mgr

port: specifies the port on which the gNMI server should listen, by default it will listen on 57400

tls-profile: a TLS profile must be configured, see TLS workshop for details around configuring the profile itself.

source-address: specifies an IP address which the gNMI server will listen on, the IP address must be present in the given network-instance. The IP address can be either IPv4 or IPv6. If set to 0.0.0.0 it will listen on any address within the network-instance for IPv4. If set to :: then it will listen on all IPv4 and IPv6 addresses.

unix-socket: specifies whether the RPC should be authenticated against a user using aaa_mgr

gNMI Examples#

GET Example#

demo@demo-sf03:~$ gnmic -a 172.20.20.2:57400 -e json_ietf -u admin -p admin --skip-verify get --path "/system/name/host-name"

Get Response:
[
  {
    "timestamp": 1604412647649136431,
    "time": "2020-11-03T15:10:47.649136431+01:00",
    "updates": [
      {
        "Path": "srl_nokia-system:system/srl_nokia-system-name:name/host-name",
        "values": {
          "srl_nokia-system:system/srl_nokia-system-name:name/host-name": "srl1"
        }
      }
    ]
  }
]

SET Example#

demo@demo-sf03:~$ gnmic -a 172.20.20.2:57400 -e json_ietf -u admin -p admin --skip-verify set --replace /system/name/host-name:::string:::test1

Set Response:
{
  "timestamp": 1604412698946981257,
  "time": "2020-11-03T15:11:38.946981257+01:00",
  "results": [
    {
      "operation": "REPLACE",
      "path": "system/name/host-name"
    }
  ]
}

SUBSCRIBE once Example#

demo@demo-sf03:~$ gnmic -a 172.20.20.2:57400 -e json_ietf -u admin -p admin --skip-verify subscribe --mode once --path "/system/name/host-name"

{
  "source": "srl1:57400",
  "subscription-name": "default",
  "timestamp": 1604412764363675969,
  "time": "2020-11-03T15:12:44.363675969+01:00",
  "updates": [
    {
      "Path": "srl_nokia-system:system/srl_nokia-system-name:name/host-name",
      "values": {
        "srl_nokia-system:system/srl_nokia-system-name:name/host-name": "srl1"
      }
    }
  ]
}

SUBSCRIBE on_change Example#

demo@demo-sf03:~$ gnmic -a 172.20.20.2:57400 -e json_ietf -u admin -p admin --skip-verify subscribe --mode stream --stream-mode on_change --path "/interface[name=ethernet-1/1]/statistics/in-octets"

{
  "source": "srl1:57400",
  "subscription-name": "default",
  "timestamp": 1604412831614958694,
  "time": "2020-11-03T15:13:51.614958694+01:00",
  "updates": [
    {
      "Path": "srl_nokia-interfaces:interface[name=ethernet-1/1]/statistics/in-octets",
      "values": {
        "srl_nokia-interfaces:interface/statistics/in-octets": "16170673"
      }
    }
  ]
}
{
  "source": "srl1:57400",
  "subscription-name": "default",
  "timestamp": 1604412833881891643,
  "time": "2020-11-03T15:13:53.881891643+01:00",
  "updates": [
    {
      "Path": "srl_nokia-interfaces:interface[name=ethernet-1/1]/statistics/in-octets",
      "values": {
        "srl_nokia-interfaces:interface/statistics/in-octets": "16170778"
      }
    }
  ]
}