Clash TUN Mode Deep Dive: Prevent DNS Leaks with Advanced Fake-IP Config

Why TUN Mode is the Gold Standard for Clash

Traditional "System Proxy" settings are often ignored by applications that use custom networking stacks, such as command-line tools (curl, git), game launchers, and even some browsers using DNS-over-HTTPS. This creates what we call "leak zones"—traffic that bypasses your proxy rules and reveals your true IP or destination to your ISP.

TUN mode solves this by creating a Virtual Network Adapter at the OS level. Instead of relying on apps to "respect" proxy settings, the OS routes all traffic through this virtual interface. Clash then intercepts every packet, inspects the destination, and applies your YAML rules. This is transparent proxying at its finest.

• Native Support: No need for third-party tools like Proxifier or Postman.
• Packet-Level Control: Supports UDP, ICMP (Ping), and TCP traffic universally.
• Bypass Incompatible Apps: Forces apps that normally ignore proxies to follow your routing logic.

The DNS Leak: Your Silent Privacy Killer

Even if your data traffic is proxied, your DNS queries might not be. When you type google.com, your OS might still ask your ISP's nameserver for the IP address. This reveals your browsing history to your ISP, even if the subsequent connection is encrypted.

In Clash, this is managed through the dns block. If misconfigured, Clash might resolve the IP locally before deciding whether to proxy the traffic. This "resolve-then-route" behavior is the primary cause of DNS leaks in standard configurations.

Deep Dive: How Fake-IP Eliminates Leaks

When enhanced-mode: fake-ip is enabled, Clash behaves differently. Instead of resolving a domain to its real IP, Clash immediately returns a "fake" IP address (usually from the 198.18.0.0/16 range) to the application.

The application then attempts to connect to this fake IP. Clash intercepts that connection, looks up the original domain associated with that fake IP, and then performs the resolution remotely through the proxy node. This ensures that no DNS query ever leaves your local network via your ISP.

Advanced TUN Configuration for 2026

To implement a leak-proof setup, your tun and dns blocks must work in perfect harmony. Below is a high-performance configuration optimized for Clash Verge Rev and Mihomo cores.

tun:
  enable: true
  stack: system # or gvisor for better performance on some systems
  auto-route: true
  auto-detect-interface: true
  dns-hijack:
    - "any:53"
    - "tcp://any:53"

dns:
  enable: true
  listen: 0.0.0.0:1053
  ipv6: false
  enhanced-mode: fake-ip
  fake-ip-range: 198.18.0.1/16
  fake-ip-filter:
    - '+.lan'
    - '+.local'
    - 'localhost.ptlogin2.qq.com'
  nameserver:
    - 223.5.5.5
    - 119.29.29.29
  fallback:
    - https://dns.cloudflare.com/dns-query
    - https://dns.google/dns-query
  fallback-filter:
    geoip: true
    geoip-code: CN
    ipcidr:
      - 240.0.0.0/4

System vs. gVisor vs. Mixed Stacks

Choosing the right stack is crucial for stability. The system stack uses the OS's native networking, which is generally reliable but can sometimes conflict with other VPNs. The gVisor stack implements a userspace network stack, offering better isolation and preventing certain types of packet leaks, though it may consume slightly more CPU.

Troubleshooting Common TUN Issues

Even with a perfect config, environment variables can cause issues. Here are the most common symptoms and their fixes:

Why can't I access local network devices (NAS/Printers)?

This happens when local domains are caught by the TUN interface. Use the fake-ip-filter or skip-proxy settings to ensure local CIDRs (like 192.168.1.0/24) are routed DIRECT and bypass the TUN processing.

Browsers show "DNS_PROBE_FINISHED_NXDOMAIN"

This usually indicates a conflict with "Secure DNS" (DoH) in your browser. Browsers like Chrome and Firefox often try to bypass the system resolver. Disable DoH in your browser settings to let Clash handle the resolution.

Optimizing for Gaming and Real-time Apps

TUN mode can introduce slight overhead. To minimize latency for gaming:

1. Use UDP-over-TCP: If your proxy server supports it, enable UDP nodes for better performance in competitive shooters.
2. Strict Rules: Place your gaming rules (e.g., Steam, Riot Games) at the very top of your rules list to reduce processing time.
3. Process-based Rules: On Windows, you can use PROCESS-NAME,valheim.exe,Proxy to ensure only the game traffic is touched.

Related Reading

If you found this deep dive useful, check out our other technical guides: «Fixing "Connected, No Internet" and DNS Issues», «Complete Clash for Windows Setup Guide», and «The Ultimate Clash Beginner Guide».

Summary

Manual configuration is powerful, but it can be daunting for users who just want a working setup. Many legacy VPN tools fail to address these low-level networking nuances, leaving you vulnerable to leaks despite the "Connected" status. Clash's open-source core provides the transparency and control needed for a truly secure 2026 internet experience.

Ready for a more secure connection? Download Clash for free and start your journey today.