DNS Security & Logging Best Practices with Securd's Greywall

DNS is the foundation of every internet connection. Before a browser loads a page, before malware phones home to its command server, before an employee accesses an unauthorized AI tool — a DNS query is sent. This makes DNS both the most critical infrastructure layer and the most valuable source of security telemetry. Organizations that invest in DNS logging and analysis gain visibility that no other single data source provides.

The first best practice is straightforward: log everything. Every DNS query from every endpoint should be logged with timestamp, source IP, queried domain, response code, and action taken (allow, block, greywall). This creates a complete record of every connection attempt on your network. When an incident occurs, DNS logs are often the fastest way to determine scope — which endpoints communicated with the malicious domain, when, and how frequently.

The second practice is more nuanced: don't trust by default. Traditional DNS security uses blocklists — known-bad domains are blocked, everything else resolves normally. This model assumes that any domain not on a blocklist is safe. That assumption is wrong. 300,000+ domains are registered every day. Blocklists can't keep pace. Securd's Greywall inverts this model: first-seen domains are held for review, not trusted automatically.

Deploy Greywall in learning mode for 7-14 days. During this period, it observes every domain your organization resolves — building a baseline of known, trusted traffic. After learning, switch to enforce mode. Now any domain outside your baseline is held for review. Users see a block page. Admins see a review queue. This catches zero-day phishing, DGA domains, and newly registered infrastructure that no blocklist has catalogued.

Compartmentalize your DNS. Create separate tenants for different security zones — corporate endpoints, guest WiFi, development environments, IoT devices. Each tenant gets its own Greywall baseline, its own policies, and its own analytics. A domain that's normal for developers (npm registries, GitHub APIs) might be suspicious for accounting endpoints. Per-tenant isolation prevents less-sensitive traffic from diluting your security posture.

Forward your DNS logs to your SIEM in real-time. Securd supports log forwarding in CEF format (for ArcSight, QRadar, Splunk) and JSON format (for Elasticsearch, Datadog, custom pipelines). Correlate DNS queries with endpoint telemetry, authentication logs, and network flow data. When your EDR detects suspicious behavior on an endpoint, DNS logs tell you exactly which domains that endpoint was resolving in the minutes and hours before the alert.

Review your Greywall regularly. Threat actors adapt. New phishing infrastructure appears daily. New AI services emerge weekly. Your Greywall should be a living system — review held domains, approve legitimate new services, permanently block confirmed threats. Over time, your Greywall becomes increasingly accurate, with the review queue shrinking as your trusted baseline grows.

Finally, educate users about block pages. When Securd blocks a domain, users see a customizable block page. Use this as a security awareness opportunity. Explain why the domain was blocked. Provide a path to request access if the domain is legitimate. Custom block pages in Securd support your logo, custom messaging, and redirect URLs — turning a blocking event into a teaching moment.