Monitoring BIND9 logs: Comparing syslog and dnstap for DNS visibility

As system and network administrators know, DNS logs are essential for understanding what’s happening across your infrastructure, whether you’re troubleshooting slow lookups, investigating odd traffic patterns, or monitoring your security posture.

We recently had the opportunity to help a customer set up monitoring for BIND9 logs and discovered that the two main options, syslog and dnstap, offer very different experiences in setup, performance, and the level of DNS visibility they provide.

After digging into the details and testing configurations, we found that there’s no one-size-fits-all solution. Syslog is familiar and integrates easily with existing pipelines, while dnstap requires more setup and configuration knowledge but delivers richer telemetry. In this blog post, we’ll share what we learned to help you understand the trade-offs and decide which approach best suits your environment.

BIND9 logging options

When it comes to monitoring BIND9 logs, you have two options: syslog and dnstap. Each method takes a different logging approach, and understanding these differences is key to choosing the right method for your environment.

syslog: Syslog is the classic BIND9 logging method. It’s easy to activate and integrate with existing telemetry data pipelines. Because syslog is a common logging format, you’re probably already familiar with setting it up.

The trade-off is that syslog messages are unstructured, meaning they require custom regex parsing to extract information and lack details like the transport type and incomplete responses. Heavy syslog logging can also increase CPU and disk usage, which is something to consider if you’re dealing with high-volume DNS logging.
dnstap: dnstap is a more recent alternative that provides structured DNS logging. This format produces a binary stream that includes detailed DNS query and response data, metadata, and fine-grained timestamps. You can convert the binary data to JSON using tools like dnstap-tools so that other systems in the pipeline, such as SIEMs and observability platforms, can ingest and process it.

Using the BIND9 dnstap format has clear benefits for getting full visibility into your DNS infrastructure. However, the downside is that it introduces dependencies on more tools, including fstream, protobuf, and dnstap-tools, and has a larger storage footprint. It also requires additional setup and familiarity with the toolchain.

Side-by-side comparison: syslog vs. dnstap

The following table compares the two BIND9 logging options to see how they stack up side by side. This comparison highlights the key differences in setup, performance, and data format, so you can make an informed decision between the two.

Table 1. BIND9 syslog vs. dnstap
Feature	syslog	dnstap
Setup complexity	Easy to activate and works out of the box with existing telemetry pipelines.	More complex to set up and requires `fstrm`, `protobuf`, and `dnstap-tools`.
Data structure	Unstructured text that typically requires regex parsing.	Structured binary that can be converted to JSON. It includes rich metadata.
Query/response details	Provides basic information and lacks transport details and the complete response.	Contains the full context, including query/response, transport details, and metadata.
Timestamps	Standard syslog timestamps.	Fine-grained timestamps for precise analysis.
Performance impact	Can add CPU and disk load when processing high volumes of DNS requests.	Lower processing overhead in high-volume setups but has a larger storage footprint.
Integration	Works seamlessly with existing telemetry pipelines.	Requires additional data conversion for other tools to ingest and process.
Best for	Small-to-medium environments that require quick setup and basic monitoring.	Security-focused, high-volume DNS environments that need detailed analytics for monitoring and forensic investigations.

Key takeaways:

syslog is familiar, quick to deploy, and works with standard logging infrastructure, but it provides limited, unstructured data.
dnstap provides detailed and structured telemetry, making it ideal for security monitoring and high-volume environments, but it requires additional setup and storage.

Choosing the right BIND9 logging approach

Once you understand how syslog and dnstap differ, the next step is deciding which option makes the most sense for your environment. The choice often comes down to how much detail you need from your DNS logs, how complex your setup can be, and what your existing telemetry pipeline supports.

When to choose BIND9 syslog

Activating logging in syslog format is easy, but the output is unstructured and can be cryptic. A typical BIND9 query event might look like the following:

<134>Nov 17 15:58:40 DNS-01 named[336426]: 2025-11-17T15:58:40.517 client @0x7f126927a000 192.168.1.10#34363 (google.com): query: google.com IN A +E(0)K

You will notice that:

The client IP, port, and queried domain are logged.
Flags like +E(0)K require additional interpretation.
It does not include response data and transport type.
You need to parse the event using regex to extract the fields.

Despite its limitations, syslog works well for quick operational monitoring or smaller infrastructures where you don’t need the full DNS context. Syslog will be enough if:

You want a fast deployment.
Your existing telemetry pipeline already handles syslog.
You only need basic operational visibility.
You need to keep the storage and CPU overhead low.

If you rely on a Unix or Linux syslog pipeline for BIND9, our comparison of rsyslog vs syslog-ng can help you evaluate which syslog daemon best fits your environment.

When BIND9 dnstap is a better fit

Once converted to JSON, dnstap logs provide much more context. For example, the following is an example of a query event:

{
  "type": "MESSAGE",
  "identity": "DNS-01",
  "version": "BIND 9.21.11-dev",
  "message": {
    "type": "RESOLVER_QUERY",
    "query_time": "2025-11-17T12:50:50.638731878Z",
    "socket_family": "INET",
    "socket_protocol": "UDP",
    "query_address": "0.0.0.0",
    "response_address": "192.54.112.30",
    "query_port": 43445,
    "response_port": 53,
    "query_zone": "com.",
    "query_message": ";; opcode: QUERY, status: NOERROR, id: 12202\n;; flags:; QUERY: 1, ANSWER: 0, AUTHORITY: 0, ADDITIONAL: 1\n\n;; QUESTION SECTION:\n;google.com.\tIN\t DS\n\n;; ADDITIONAL SECTION:\n\n;; OPT PSEUDOSECTION:\n; EDNS: version 0; flags: do; udp: 1232\n; COOKIE: 1fcfbf622c4b6de0\n"
  }
}

With dnstap events, you get:

Full query and response context.
Transport details.
Metadata and flags.
High-resolution timestamps.

This information makes dnstap events more suitable for security monitoring, forensic analysis, and environments that require granular DNS visibility. Dnstap is the stronger option when:

You need full DNS query and response telemetry.
You rely on SIEM, security analytics, or DNS forensics.
Your environment generates a high volume of DNS traffic.
You want precise timing, metadata, and structured logs.

Conclusion

Understanding the differences between BIND9 syslog and dnstap logging is key to choosing the right DNS logging strategy for your environment. Syslog offers simplicity and quick integration with existing pipelines, while dnstap delivers structured telemetry for deeper visibility and security analysis.

NXLog Platform’s agent supports both syslog-based BIND9 logs and dnstap collection, making it easy to integrate your chosen approach into a reliable and scalable telemetry pipeline. If you’re planning to refine your DNS monitoring strategy, our team can guide you through the setup. Reach out to us for more information.

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