gnmi-telemetry

gnmi-telemetry

gNMI streaming telemetry operations for multi-vendor network devices. Query device state via structured YANG model paths, subscribe to real-time telemetry streams, apply ITSM-gated configuration changes, browse YANG capabilities, and compare gNMI data against CLI output.

MCP Server

gnmi-mcp — gNMI Streaming Telemetry MCP Server (stdio transport)

Tools Used

1. gnmi_get — Retrieve device state/config via gNMI Get with YANG paths
2. gnmi_set — Apply configuration via gNMI Set (requires ServiceNow CR)
3. gnmi_subscribe — Create SAMPLE or ON_CHANGE telemetry subscriptions
4. gnmi_unsubscribe — Cancel active subscriptions
5. gnmi_get_subscriptions — List all active telemetry subscriptions
6. gnmi_get_subscription_updates — Retrieve latest telemetry updates
7. gnmi_capabilities — Discover YANG models and encodings on a device
8. gnmi_browse_yang_paths — Explore YANG path tree under a module
9. gnmi_compare_with_cli — Compare gNMI vs CLI state for validation
10. gnmi_list_targets — List configured gNMI target devices

Workflows

Query Device State

1. gnmi_list_targets — identify available devices
2. gnmi_capabilities — discover supported YANG models
3. gnmi_browse_yang_paths — explore available paths
4. gnmi_get — retrieve structured state data

Monitor Real-Time Telemetry

1. gnmi_subscribe — create subscription (SAMPLE or ON_CHANGE)
2. gnmi_get_subscriptions — verify subscription is active
3. gnmi_get_subscription_updates — poll for latest updates
4. gnmi_unsubscribe — clean up when monitoring is complete

Apply Configuration Change

1. gnmi_get — capture current baseline state
2. gnmi_set — apply change with ServiceNow CR number
3. gnmi_get — verify change was applied correctly

Validate gNMI vs CLI

1. gnmi_compare_with_cli — side-by-side comparison with pyATS data

Supported Vendors

• Cisco IOS-XR (port 57400, JSON_IETF encoding)
• Juniper (port 32767, JSON_IETF encoding)
• Arista (port 6030, JSON encoding)
• Nokia SR OS (port 57400, JSON_IETF encoding)

Required Environment Variables

Variable	Description
GNMI_TARGETS	JSON array of target devices (name, host, port, credentials, vendor)
GNMI_TLS_CA_CERT	CA certificate for TLS server verification
GNMI_TLS_CLIENT_CERT	Client certificate for mTLS (optional)
GNMI_TLS_CLIENT_KEY	Client private key for mTLS (optional)

Example Usage

Query interface state:

"Show me the interface status on router1 using gNMI"

Subscribe to counters:

"Set up a SAMPLE telemetry subscription for interface counters on switch1 every 30 seconds"

Apply configuration:

"Change the description on GigabitEthernet0/0/0/1 on router1 to 'Uplink to spine' using CR CHG0012345"

Browse capabilities:

"What YANG models does router1 support?"

Safety

• gNMI Get, Subscribe, Capabilities, and Browse are read-only (safe)
• gNMI Set is ITSM-gated: requires a ServiceNow Change Request in "Implement" state
• TLS is mandatory for all connections; mTLS is supported
• All operations are logged to the GAIT audit trail
• Maximum 50 concurrent subscriptions (configurable via GNMI_MAX_SUBSCRIPTIONS)

Failure Behavior

• On a tool error (timeout, unreachable host, malformed response), report the failure and its error message directly to the user rather than fabricating or guessing at results.
• For a confirmed read-only call, check connectivity and retry once if appropriate. For any call that changes state or sends a message, a timeout does not prove the action failed: inspect current state or delivery status before retrying, preserve the required approval/change gates, and do not repeat an action whose outcome is unknown.