These docs are for Cribl Stream 4.2 and are no longer actively maintained.

See the latest version (4.13).

Firewall Logs: VPC Flow Logs, Cisco ASA, Etc.

Recipe for Sampling Firewall Logs

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Firewall logs are another source of important operational (and security) data. Typical examples include Amazon VPC Flow Logs, Cisco ASA Logs, and other technologies such as Juniper, Checkpoint, pfSense, etc.

As with Access Logs, bringing in everything for operational analysis might be cost-prohibitive. But sampling with Cribl Stream can help you:

• Ingest enough sample events from the majority category that your aggregate analysis remains statistically significant. E.g., sample all ACCEPTs at 5:1.

• Ingest all events from the minority categories, and perform troubleshooting and introspection with full-fidelity data. E.g., bring in all REJECTs.

Sampling VPC Flow Logs

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AWS’ VPC Flow Logs feature enables you to capture information about the IP traffic going to and from network interfaces in your VPC. Flow Log data can be published to Amazon CloudWatch Logs and Amazon S3.

Typical VPC Flow Logs look like this:

2 123456789010 eni-abc123de 172.31.16.139 172.31.16.21 20641 22 6 20 4249 1418530010 1418530070 ACCEPT OK
2 123456789010 eni-abc123de 172.31.9.69 172.31.9.12 49761 3389 6 20 4249 1418530010 1418530070 REJECT OK

Let’s use a very simple Filter condition and only look for ACCEPT events:

1. Add a Regex Extract Function that looks at: sourcetype=='aws:cloudwatchlogs:vpcflow'

2. Configure that Function to extract a field called __action with this regex:/(?<__action>ACCEPT)/

3. Add a Sampling Function to sample 5:1 when __action=="ACCEPT".
4. Save.

Note About Sampling

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Each time an event goes through the Sampling Function, an index-time field is added to it: sampled: <rate>. It’s advisable that you use that in your statistical functions, as necessary.

Other Sourcetypes

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Other sourcetypes that will benefit from sampling, but might need a different __action extraction regex: