The Fundamentals of Clash DNS

Understanding Clash DNS is the first step toward a secure proxy environment. In most modern Clash cores (like Mihomo), the DNS module is not just a simple resolver; it is a sophisticated traffic router. When an application makes a request, Clash intercepts the DNS query and decides how to handle it based on your dns block settings. By default, many users rely on fake-ip, which returns a reserved IP address (e.g., 198.18.0.1) to the application immediately, delaying the actual DNS resolution until the traffic hits the Clash core.

However, this "lazy" resolution can lead to issues if not configured correctly. The nameserver and fallback pools play critical roles here. The nameserver list is used for domestic or unproxied domains, while the fallback list is reserved for domains that might be poisoned or require proxying. If your configuration lacks a proper fallback-filter, Clash might inadvertently use a poisoned result from a domestic DNS server, leading to connection failures or, worse, DNS leaks where your real ISP's DNS activity is visible to third parties.

ℹ Pro Tip: Always use https:// or tls:// (DoH/DoT) for your fallback servers to prevent MITM attacks and tampering.

Identifying and Fixing DNS Leaks

A DNS leak occurs when your browser or OS sends DNS queries to your ISP's servers instead of through the encrypted Clash tunnel. This happens most frequently when using Real-IP mode without a strict fallback-filter. To identify a leak, you should use tools like dnsleaktest.com. If you see your ISP's name or your actual country's flags in the results while your proxy is active, you have a leak.

To fix this, you must ensure that proxy-server-nameserver is configured. This allows Clash to resolve the IP of your proxy nodes using a secure, local DNS before the tunnel is even established. Furthermore, enabling system-stack: gvisor in TUN mode helps isolate the network stack, preventing the OS from "leaking" queries through parallel network interfaces.

Configuring the Fallback Filter

The fallback-filter is your shield against poisoning. It tells Clash which DNS results to trust. If a result from a nameserver matches a known poisoned IP range (like the GeoIP of your local country for a global site), Clash will wait for the fallback result.

Illustrative YAML fragment for DNS

dns:
  enable: true
  ipv6: false
  enhanced-mode: fake-ip
  nameserver:
    - https://dns.google/dns-query
    - 1.1.1.1
  fallback:
    - https://8.8.8.8/dns-query
    - tls://1.0.0.1:853
  fallback-filter:
    geoip: true
    geoip-code: US
    ipcidr:
      - 240.0.0.0/4

Fake-IP vs. Real-IP: When to Switch

The debate between fake-ip and redir-host (now mostly Real-IP) is ongoing. Fake-IP is generally faster because it eliminates the "DNS wait" time for the application. The application gets 198.18.x.x instantly and starts sending data. Clash then resolves the actual domain at the proxy level. This is excellent for most web browsing and streaming.

However, fake-ip can break certain applications that perform strict IP validation or peer-to-peer (P2P) connections, such as some VOIP software or legacy enterprise tools. In these cases, Real-IP is necessary. In Real-IP mode, Clash performs a real DNS lookup before responding to the app. While slightly slower, it ensures compatibility. If you are a gamer or use specialized software, Real-IP combined with a very fast DoH server is often the better choice.

"Fake-IP is a performance optimization, but Real-IP is a compatibility guarantee. Choose based on your specific application needs."

Resolving TUN Mode and Stack Conflicts

TUN Mode creates a virtual network interface, capturing all traffic from the OS. This is more powerful than a simple system proxy. However, conflicts often arise between the Clash TUN stack and other virtual adapters (like those from VMware, VirtualBox, or other VPNs).

To resolve these, you must manage the interface-name and auto-route settings. If auto-route is true, Clash attempts to become the default gateway. If another VPN is also trying this, your internet will drop. The solution is to use strict-route: true, which forces traffic through the TUN interface more aggressively by managing routing tables more strictly.

Sniffing and Rule-Provider Optimization

In fake-ip mode, Clash often doesn't know the domain of a connection—it only sees the fake IP. This makes domain-based rules useless unless Sniffing is enabled. Sniffing looks at the TLS SNI or HTTP Host header to "recover" the domain name.

By enabling sniffing: true and specifying sniff-name: [TLS, HTTP], you allow Clash to re-route traffic based on the actual destination domain even after the application has been given a fake IP. This is crucial for rule-providers. Rule providers allow you to pull massive lists of domains (like those for Netflix, Steam, or Telegram) from remote URLs, keeping your config file clean and always updated.

Rule Provider Example

rule-providers:
  netflix:
    type: http
    behavior: classical
    url: "https://example.com/netflix.yaml"
    path: ./rules/netflix.yaml
    interval: 86400

The 100% Leak-Proof Checklist

To ensure your setup is truly secure, follow this final checklist. First, ensure ipv6 is set to false unless your proxy provider fully supports it; IPv6 is a notorious source of DNS and IP leaks. Second, always use tls or https for your DNS servers. Third, verify that your fallback-filter includes the geoip: true flag.

Finally, test your setup. A successful configuration will show a Fake-IP range in your local logs but correctly resolved destinations in the Clash dashboard. If you see any requests going to your ISP's DNS IP (usually your router's IP), re-examine your nameserver list and consider moving those servers to fallback.

⚠ Compliance Reminder: Always comply with local laws and regulations. This guide is for technical educational purposes regarding Clash network routing and DNS optimization. Do not use these tools to bypass organizational security policies or for illegal activities.

Conclusion

Mastering Clash DNS and TUN modes takes time, but the rewards are a faster, more private, and more reliable internet experience. By understanding how Fake-IP interacts with the stack and ensuring your rules are backed by robust rule-providers, you can eliminate common pitfalls like DNS leaks and connection timeouts.

→ Download Clash V.CORE now to implement these advanced configurations and take full control of your network traffic.