Description

Flow Logs is a feature that enables users to capture information about the IP traffic going to and from network interfaces in an organization’s VPC subnets. Once a flow log is created, the user can view and retrieve its data in Stackdriver Logging. It is recommended that Flow Logs is enabled for every business-critical VPC subnet.

Default value

By default Flow Logs is set to Off when a new VPC network subnet is created.

Rationale

VPC networks and subnetworks that are not reserved for internal HTTP(S) load balancing provide logically isolated and secure network partitions from which GCP resources can be launched. When Flow Logs are enabled for a subnet, VMs within that subnet start reporting on all Transmission Control Protocol (TCP) and User Datagram Protocol (UDP) flows. Each VM samples the TCP and UDP flows it sees, inbound and outbound, whether the flow is to or from another VM, a host in the on-premise datacenter, a Google service, or a host on the Internet. If two GCP VMs are communicating, and both are in subnets that have VPC Flow Logs enabled, both VMs report the flows.

Flow Logs supports the following use cases:

• Network monitoring
• Understanding network usage and optimizing network traffic expenses
• Network forensics
• Real-time security analysis

Flow Logs provides visibility into network traffic for each VM inside the subnet and can be used to detect anomalous traffic or provide insight on security workflows. The Flow Logs must be configured such that all network traffic is logged. The interval of logging is granular enough to provide detailed information on the connections, where no logs are filtered and metadata to facilitate investigations are included.

• Note: Subnets reserved for use by internal HTTP(S) load balancers do not support VPC Flow Logs.

Impact

Standard pricing for Stackdriver Logging, BigQuery, or Cloud Pub/Sub applies. VPC Flow Logs generation will be charged when it’s generally available, as described in this reference: https://cloud.google.com/vpc/

Remediation

From the console

1. Go to the VPC network GCP Console page by visiting: https://console.cloud.google.com/networking/networks/list
2. Click the name of a subnet to display the subnet details page.
3. Click EDIT .
4. Set Flow Logs to On.
5. Expand the Configure Logs section.
6. Set Aggregation Interval to 5 SEC.
7. Check the box for Include metadata.
8. Set Sample rate to 100.
9. Click Save.

• Note: You can only configure a log filter from the command line.

From the command line

To enable VPC Flow Logs for a network subnet, run the following command:

gcloud compute networks subnets update [SUBNET_NAME] --region [REGION] --
enable-flow-logs --logging-aggregation-interval=interval-5-sec --logging-
flow-sampling=1 --logging-metadata=include-all

References

1. https://cloud.google.com/vpc/docs/using-flow-logs#enabling_vpc_flow_logging
2. https://cloud.google.com/vpc/