Skills
skills/mukul975/anthropic-cybersecurity-skills/implementing-zero-trust-dns-with-nextdns

implementing-zero-trust-dns-with-nextdns

SKILL.md

Implementing Zero Trust DNS with NextDNS

Overview

NextDNS is a cloud-based DNS resolver that provides encrypted DNS resolution (DNS-over-HTTPS and DNS-over-TLS), real-time threat intelligence blocking, ad and tracker filtering, and granular DNS policy enforcement. In a zero trust architecture, DNS is a critical control point -- every network connection begins with a DNS query, making DNS filtering an effective layer for blocking malicious domains, preventing data exfiltration via DNS tunneling, enforcing acceptable use policies, and gaining visibility into all network communications. NextDNS processes queries using threat intelligence feeds containing millions of malicious domains updated in real-time, blocks cryptojacking and phishing domains, detects DNS rebinding attacks, and supports CNAME cloaking protection. For enterprise environments, Microsoft's Zero Trust DNS (ZTDNS) feature on Windows 11 extends this concept by enforcing that endpoints can only resolve domains through approved protected DNS servers.

Prerequisites

  • NextDNS account (free tier: 300,000 queries/month; Pro: unlimited)
  • Network devices supporting DoH or DoT configuration
  • Administrative access to endpoint DNS settings
  • Understanding of DNS protocol and resolution chain
  • Familiarity with organizational acceptable use policies

Architecture

    Endpoint Device
         |
    DNS Query (Encrypted)
         |
    +----+----+
    |  DoH/DoT |  (DNS-over-HTTPS or DNS-over-TLS)
    |  Tunnel  |
    +----+----+
         |
    +----+----+
    | NextDNS  |
    | Resolver |
    +----+----+
         |
    +----+----+------+--------+
    |         |       |        |
  Threat   Ad/Tracker Privacy  Parental
  Intel    Blocklists Controls Controls
  Check    Check      Check    Check
    |         |       |        |
    +----+----+------+--------+
         |
    ALLOW or BLOCK
         |
    Response to Endpoint

Configuration Setup

NextDNS Profile Configuration

Dashboard: https://my.nextdns.io

Configuration ID: abc123 (unique per profile)

Endpoints:
  DNS-over-HTTPS: https://dns.nextdns.io/abc123
  DNS-over-TLS:   abc123.dns.nextdns.io
  DNS-over-QUIC:  quic://abc123.dns.nextdns.io
  IPv4:           45.90.28.x, 45.90.30.x (linked to config)
  IPv6:           2a07:a8c0::xx, 2a07:a8c1::xx

Security Settings

Security Tab Configuration:
  [x] Threat Intelligence Feeds - Block domains from curated threat feeds
  [x] AI-Driven Threat Detection - Machine learning-based detection
  [x] Google Safe Browsing - Cross-reference with Google's threat database
  [x] Cryptojacking Protection - Block crypto mining domains
  [x] DNS Rebinding Protection - Prevent DNS rebinding attacks
  [x] IDN Homograph Attacks - Block internationalized domain name attacks
  [x] Typosquatting Protection - Block common typosquatting domains
  [x] DGA Protection - Block domain generation algorithm domains
  [x] NRD (Newly Registered Domains) - Block domains < 30 days old
  [x] DDNS (Dynamic DNS) - Block dynamic DNS services
  [x] Parked Domains - Block parked/unused domains
  [x] CSAM - Block child sexual abuse material domains

Privacy Settings

Privacy Tab Configuration:
  Blocklists:
    [x] NextDNS Ads & Trackers Blocklist
    [x] OISD (Full)
    [x] EasyPrivacy
    [x] AdGuard DNS Filter

  Native Tracking Protection:
    [x] Block Windows telemetry
    [x] Block Apple telemetry
    [x] Block Samsung telemetry
    [x] Block Xiaomi telemetry
    [x] Block Huawei telemetry
    [x] Block Roku telemetry
    [x] Block Sonos telemetry

  [x] Block Disguised Third-Party Trackers (CNAME cloaking)
  [x] Allow Affiliate & Tracking Links (optional, for business)

Allowlist and Denylist

Allowlist (domains that bypass all blocking):
  - login.microsoftonline.com
  - graph.microsoft.com
  - *.company.com

Denylist (always blocked regardless of other settings):
  - known-malicious-domain.com
  - unauthorized-cloud-storage.com
  - personal-email-provider.com  (if policy requires)

Endpoint Deployment

Linux (systemd-resolved)

# Configure DNS-over-TLS with systemd-resolved
sudo tee /etc/systemd/resolved.conf << 'EOF'
[Resolve]
DNS=45.90.28.x#abc123.dns.nextdns.io
DNS=45.90.30.x#abc123.dns.nextdns.io
DNS=2a07:a8c0::xx#abc123.dns.nextdns.io
DNS=2a07:a8c1::xx#abc123.dns.nextdns.io
DNSOverTLS=yes
Domains=~.
EOF

sudo systemctl restart systemd-resolved

# Verify
resolvectl status
resolvectl query example.com

Linux (NextDNS CLI)

# Install NextDNS CLI
sh -c 'sh -e $(curl -sL https://nextdns.io/install)'

# Configure with your profile
sudo nextdns install \
  -config abc123 \
  -report-client-info \
  -auto-activate

# Verify
nextdns status
nextdns log

macOS

# Install via Homebrew
brew install nextdns/tap/nextdns

# Configure
sudo nextdns install \
  -config abc123 \
  -report-client-info

# Or configure via System Settings > Network > DNS
# Add DNS-over-HTTPS: https://dns.nextdns.io/abc123

Windows

# Install NextDNS CLI for Windows
# Download from: https://nextdns.io/download/windows

# Or configure DoH natively (Windows 11)
# Settings > Network & Internet > Ethernet/Wi-Fi > DNS
# Preferred DNS: 45.90.28.x
# DNS over HTTPS: On (Manual template)
# DoH Template: https://dns.nextdns.io/abc123

# PowerShell: Configure DoH
Set-DnsClientDohServerAddress -ServerAddress "45.90.28.x" `
  -DohTemplate "https://dns.nextdns.io/abc123" `
  -AllowFallbackToUdp $false `
  -AutoUpgrade $true

Router-Level Configuration

# Most routers support custom DNS servers
# For DoH/DoT-capable routers (pfSense, OPNsense, OpenWrt):

# pfSense DNS Resolver (Unbound):
# Services > DNS Resolver > Custom Options:
server:
  forward-zone:
    name: "."
    forward-tls-upstream: yes
    forward-addr: 45.90.28.x@853#abc123.dns.nextdns.io
    forward-addr: 45.90.30.x@853#abc123.dns.nextdns.io

# OpenWrt (using https-dns-proxy):
opkg update && opkg install https-dns-proxy
uci set https-dns-proxy.default.resolver_url='https://dns.nextdns.io/abc123'
uci commit https-dns-proxy
/etc/init.d/https-dns-proxy restart

Mobile Devices

iOS:
  Install NextDNS app from App Store
  Or: Settings > General > VPN & Device Management
  Install NextDNS configuration profile

Android:
  Settings > Network > Private DNS
  DNS Provider: abc123.dns.nextdns.io

  Or: Install NextDNS app from Play Store

Microsoft Zero Trust DNS (Windows 11)

For enterprise Windows environments, Microsoft's ZTDNS enforces that endpoints can only communicate with domains resolved through approved DNS servers.

# Enable ZTDNS (Windows 11 23H2+)
# Requires Windows Defender Firewall in enforcing mode

# Configure Protected DNS Servers via Group Policy:
# Computer Configuration > Administrative Templates > Network > DNS Client
# > Configure DNS over HTTPS (DoH) name resolution
# > Protected DNS servers: https://dns.nextdns.io/abc123

# Windows Firewall blocks all traffic to domains not resolved
# through the protected DNS server

Monitoring and Analytics

Log Analysis

NextDNS Analytics Dashboard provides:
  - Total queries over time
  - Blocked queries by category
  - Top domains (allowed and blocked)
  - Top blocked reasons (threat, ad, tracker)
  - Device-level breakdown
  - Geographic query distribution

Log Settings:
  Retention: 1 hour / 6 hours / 1 day / 1 week / 1 month / 3 months / 1 year / 2 years
  Storage Location: US / EU / UK / Switzerland
  Logging: [ ] Enable / [ ] Disable

API Integration

# NextDNS API for automated monitoring
# Get analytics data
curl -H "X-Api-Key: your-api-key" \
  "https://api.nextdns.io/profiles/abc123/analytics/domains?from=-24h"

# Get blocked domains
curl -H "X-Api-Key: your-api-key" \
  "https://api.nextdns.io/profiles/abc123/analytics/domains?from=-24h&status=blocked"

# Export logs for SIEM integration
curl -H "X-Api-Key: your-api-key" \
  "https://api.nextdns.io/profiles/abc123/logs?from=-1h" \
  | jq '.data[] | select(.status == "blocked")'

Zero Trust DNS Policy Framework

Policy Tiers

Tier 1 - Security (Mandatory for all):
  - Threat intelligence blocking
  - Cryptojacking protection
  - DNS rebinding protection
  - DGA detection
  - NRD blocking (< 30 days)

Tier 2 - Privacy (Recommended):
  - Tracker blocking
  - Native telemetry blocking
  - CNAME cloaking protection

Tier 3 - Compliance (Organization-specific):
  - Category-based blocking
  - Custom allowlists/denylists
  - Time-based access policies
  - Log retention per regulatory requirements

Security Best Practices

  1. Enforce encrypted DNS: Block plaintext DNS (port 53 UDP/TCP) at the firewall
  2. Use NextDNS CLI on endpoints: Ensures per-device identification and logging
  3. Enable NRD blocking: Newly registered domains are overwhelmingly malicious
  4. Block DNS-over-HTTPS bypass: Ensure browsers use system DNS, not built-in DoH
  5. Review blocklists quarterly: Remove false positives, add organizational blocks
  6. Enable CNAME cloaking protection: Prevents tracker evasion via CNAME records
  7. Set appropriate log retention: Balance privacy with forensic needs (90 days recommended)
  8. Monitor for DNS tunneling: Watch for unusual query patterns and high entropy domains
  9. Deploy at router level: Catches all devices including IoT and unmanaged endpoints
  10. Combine with endpoint DNS: Defense in depth with both router and per-device filtering

References

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