Implementing OCI Capture Filters for Network Traffic Monitoring

Introduction

When you work inside Oracle Cloud Infrastructure, network visibility is everything. But blindly logging all traffic creates noise — slow dashboards, bloated log storage, and harder troubleshooting.

The solution is OCI Capture Filters — a powerful feature that lets you define exactly which traffic gets logged inside your Virtual Cloud Network (VCN).

In this blog post, I’ll walk you through how I implemented Capture Filters and linked them to VCN Flow Logs for targeted, efficient network monitoring.

What is a Capture Filter?

A Capture Filter defines which network traffic should be logged or mirrored inside OCI. Instead of recording everything, you set rules that decide what’s included and what’s excluded.

Key characteristics:

• Rules are processed in sequence — the first match determines the action
• A single Capture Filter can be reused across multiple Flow Logs
• Filters are created per compartment and are fully reusable

Step 1 — Creating the Capture Filter

Navigate to your OCI Console → Networking → Virtual Cloud Networks → your VCN → Capture Filters.

Create a new Capture Filter in your required compartment. After creation, validate:

• Type: Flow Log
• Rule Count: At least one rule configured
• Lifecycle State: Available

Once the lifecycle state shows Available, the filter is ready to attach to a Flow Log.

Step 2 — Configuring Capture Filter Rules

Rules inside the capture filter define exactly which traffic gets selected. You can filter by:

• Ingress or Egress direction
• Source or Destination CIDR blocks
• Protocol and Port Numbers (TCP/UDP)
• ICMP / ICMPv6 traffic

This means you only log what matters — not everything passing through your VCN.

Step 3 — Enabling Flow Logs on Subnets

Navigate to your subnet under Networking → go to the Logs section → enable Flow Logs.

Select the Capture Filter you created in Step 1. This links your filter rules to the subnet’s traffic logging.

Step 4 — Setting Up Log Groups

Log Groups are logical containers that organize and manage your logs. They also provide fine-grained access control.

If a Log Group doesn’t exist yet, create one before enabling the Flow Log. Once created, your Flow Log will be stored inside it.

Step 5 — Validating the Flow Log

After setup, validate your Flow Log:

• A Flow Log entry appears under the Logging section
• The log is associated with the correct Log Group
• Lifecycle state transitions from Creating → Active

Note: Flow Logs only generate records when actual traffic flows through the monitored subnet. If traffic is low, graphs may take time to populate

Technical Outcome

By completing this setup:

• Network traffic visibility is enabled inside OCI
• Only relevant traffic is logged — reducing noise and storage costs
• The environment now supports security monitoring, network troubleshooting, and compliance auditing

Conclusion

OCI Capture Filters are a simple but powerful tool for taking control of your network logging. Instead of drowning in data, you define exactly what you need — and let OCI do the rest.

If you’re on OCI and haven’t set up Capture Filters yet, this is your sign to start. 🚀

Mohammed Abdul Omaise | Oracle ACE Apprentice | Netsoftmate