DNS Leak Prevention Architecture
Overview
DNS leaks happen when DNS queries, which are utilized to convert domain names into IP addresses, are transmitted outside the secure VPN tunnel. User activity may be inadvertently exposed to ISPs, DNS providers, or malicious observers, thereby compromising privacy despite the active VPN connection.
Anon VPN employs a comprehensive DNS leak prevention framework designed to guarantee that all DNS traffic is encrypted, tunneled, and anonymized, safeguarding against deliberate redirection, fallback behaviors, and operating system-level leaks.
1. Importance of DNS Leaks
Even with an active VPN tunnel, a misconfigured system may still exhibit the following issues:
Utilize system-resolved DNS configurations (e.g., through
/etc/resolv.confon Linux or the DNS settings in Windows).Depend on insecure fallback resolvers in the event of primary DNS failure.
Enable the passage of IPv6 DNS traffic through the default network interface.
Exposure to operating system or browser-level DNS prefetching and caching is recommended.
A DNS leak has the potential to disclose:
Websites accessed
User navigation behaviors
User's actual IP address (in cases where requests circumvent the VPN)
2. Anon VPN DNS Architecture
Anon VPN implements robust DNS leak prevention through the following architecture:
1. DNS-over-VPN Tunneling
All DNS queries are routed through the encrypted VPN tunnel to Anon VPN’s internal DNS resolvers. All DNS requests remain within the tunnel and do not exit.
Implementation:
The VPN client disables the system's DNS settings when a connection is established.
The client modifies resolver rules to route traffic to internal VPN DNS endpoints (e.g.,
10.8.0.1or resolvers based on WireGuard).
2. Custom Encrypted DNS Resolvers
Anon VPN employs DNSCrypt, DNS-over-HTTPS (DoH), and DNS-over-TLS (DoT) protocols to ensure the encryption of DNS traffic from source to destination.
DNSCrypt
Provides authentication and encryption for DNS traffic
UDP/443
DoH
Encapsulates DNS queries within HTTPS protocol
TCP/443
DoT
Secures DNS queries using TLS encryption
TCP/853
All protocols are fully supported across Anon’s private resolvers, guaranteeing forward secrecy and resistance to man-in-the-middle attacks.
3. Firewall-Based DNS Blocking (Integration of Kill-Switch)
Anon VPN utilizes DNS egress filtering through the implementation of platform-specific firewall rules.
Linux: Use
iptablesornftablesto block outbound UDP/TCP traffic on port 53 that is not routed through the VPN interface (tun0orwg0).Windows: Implements the Windows Filtering Platform (WFP) to restrict access to public DNS servers while the VPN is operational.
macOS: Adjusts
/etc/resolv.confand implements PF rules to restrict port 53 egress traffic unless originating from the VPN interface.
Outcome: In the event of a VPN disconnection, DNS queries are promptly restricted, preventing a fallback to the default system DNS.
4. DNS Leak Detection and Integrity Monitoring
Anon VPN executes internal DNS verification processes at the initiation of a session and at regular intervals throughout the session.
Mechanisms consist of the following components:
Query known public test domains (e.g.,
leaktest.anon/) and monitor route paths.Verify that DNS resolver IP addresses correspond with the DNS endpoints assigned by the VPN.
Client-side integrity verification of DNS configuration status (e.g.,
resolv.conf, Windows Registry).
Upon detection of a DNS route inconsistency, the kill switch is activated without delay, and audit logs are generated accordingly.
3. IPv6 DNS Management
Numerous DNS leaks arise from the escape of IPv6 traffic from the tunnel. Anon VPN manages this through:
Comprehensive IPv6 Tunnel Functionality: Anon VPN provides the capability to route IPv6 packets through the VPN tunnel for users who need IPv6 support.
Default IPv6 Suppression: In scenarios where IPv6 is unnecessary, Anon VPN deactivates IPv6 on client adapters to mitigate potential DNS leak vulnerabilities.
Custom AAAA Record Filtering: When enabled, Anon VPN has the capability to block or remove IPv6-related DNS queries unless they are specifically permitted.
4. Advanced Protections
DNS Caching Control
Local DNS caching services such as
systemd-resolved,dnsmasq, or browser caches are cleared when a connection is established and subsequently reestablished.The Anon VPN client actively purges the DNS cache during the VPN handshake process.
Application-Level DNS Hardening
For users needing comprehensive protection:
Anon VPN incorporates application whitelisting functionality, which restricts applications such as browsers or torrent clients from issuing DNS queries beyond the secure tunnel.
5. Example: Linux DNS Leak Prevention
DNS Routing on VPN Connection:
# Configure VPN DNS
echo "nameserver 10.8.0.1" > /etc/resolv.conf
# To block external DNS requests, utilize the iptables command
iptables -A OUTPUT -p udp --dport 53 ! -o tun0 -j DROP
iptables -A OUTPUT -p tcp --dport 53 ! -o tun0 -j DROPDNS Reversion Upon Disconnection:
# Restore system DNS configuration
mv /etc/resolv.conf.backup /etc/resolv.conf6. Comparison: Anon VPN versus Legacy DNS Handling
DNS encrypted via tunnel
Often optional
Enforced via DoH/DoT
Uses own DNS servers
Sometimes
Yes, private + encrypted
IPv6 DNS leak protection
Not guaranteed
Enforced or disabled entirely
Kill-switch DNS blocking
Rare
Integrated at firewall level
DNS prefetch/cache hardening
Manual setup
Handled at client level
Leak detection engine
Absent
Periodic validation + logging
Overview
Anon VPN employs a comprehensive, multi-tiered DNS leak prevention framework aimed at addressing all identified DNS vulnerability pathways. Anon VPN employs a combination of encrypted DNS protocols, tunnel-only resolvers, firewall-based blocking, real-time leak detection, and IPv6 management to guarantee that your DNS traffic is maintained with the same level of privacy as your VPN traffic.
This architecture complies with contemporary privacy standards, including GDPR and CCPA, while also surpassing the requirements of developers, researchers, and professionals who require stringent DNS hygiene.
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