/google-cloud-networking-observability

Cloud NAT Analysis Reference

Use Cloud NAT logs (compute.googleapis.com/nat_flows) to audit traffic going through NAT gateways or troubleshoot port exhaustion.

🤖 Agent / Gemini CLI Instructions (MCP)

You should use Cloud Logging MCP for exploratory analysis or BigQuery MCP for high-volume trends. Fallback to the CLI if the MCP tools are not available.

1. View Logs (Cloud Logging MCP)

Tool: list_log_entries

Filter:

resource.type="nat_gateway"
logName="projects/{project_id}/logs/compute.googleapis.com%2Fnat_flows"

Filter for dropped packets (potential port exhaustion):

jsonPayload.allocation_status="DROPPED"

2. Aggregate Trends (BigQuery MCP)

Tool: execute_sql_readonly

SQL Pattern:

SELECT
JSON_VALUE(json_payload.gateway_details.internal_ip) AS internal_ip, COUNT(*) AS
drop_count FROM `{project_id}.{dataset_id}._AllLogs` WHERE log_name LIKE
'%nat_flows%' AND JSON_VALUE(json_payload.allocation_status) = 'DROPPED' GROUP BY
1 ORDER BY drop_count DESC LIMIT 10

3. CLI Fallback

If MCP tools are unavailable, use the following gcloud and bq commands:

View Logs (gcloud)

gcloud logging read 'resource.type="nat_gateway" AND logName="projects/{project_id}/logs/compute.googleapis.com%2Fnat_flows"' --project {project_id} --limit 10 --format json --quiet

To filter for dropped packets:

gcloud logging read 'resource.type="nat_gateway" AND logName="projects/{project_id}/logs/compute.googleapis.com%2Fnat_flows" AND jsonPayload.allocation_status="DROPPED"' --project {project_id} --limit 10 --format json --quiet

Aggregate Trends (bq)

bq query --use_legacy_sql=false --project_id {project_id} '
SELECT
  JSON_VALUE(json_payload.gateway_details.internal_ip) AS internal_ip,
  COUNT(*) AS drop_count
FROM `{project_id}.{dataset_id}._AllLogs`
WHERE
  log_name LIKE "%nat_flows%"
  AND JSON_VALUE(json_payload.allocation_status) = "DROPPED"
GROUP BY 1
ORDER BY drop_count DESC
LIMIT 10
'

gcloud

To get the status of the router used by the NAT gateway:

gcloud compute
routers get-status {router_name} --region {region} --quiet

Key Fields

• jsonPayload.gateway_details.external_ip / external_port: NAT exit point.
• jsonPayload.gateway_details.internal_ip / internal_port: Source VM.
• jsonPayload.allocation_status: DROPPED indicates failure to allocate a NAT port.

Scenarios

• Audit Traffic: Link internal sources to external destinations.
• Port Exhaustion: Use jsonPayload.allocation_status="DROPPED" to identify impacted VMs.