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What is DNS resolver

The DNS resolver is a critical component of your SlipStream VPN setup. It determines which DNS server will be used to resolve domain names while the VPN is active.
The DNS resolver setting should point to a DNS server that can properly resolve your SlipStream server domain and route traffic through the VPN tunnel.

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Default setting

By default, SlipStream GUI uses: 
8.8.8.8:53
This points to Google’s public DNS server on the standard DNS port (53).

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Custom DNS resolver

You can specify any DNS server in the format: 
IP_ADDRESS:PORT
For example:
  • 1.1.1.1:53 (Cloudflare DNS)
  • YOUR_SERVER_IP:53 (Your SlipStream server’s DNS)
  • 9.9.9.9:53 (Quad9 DNS)

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DNS Checker feature

The DNS Checker is a powerful tool that tests multiple DNS servers concurrently to help you find the fastest and most reliable option.

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Key capabilities

Concurrent testing

Tests up to 100 DNS servers simultaneously for fast results

Real-time results

Shows response times and resolution status for each server

One-click apply

Apply any working DNS server with a single click

Status validation

Verifies that each DNS server can properly resolve your test domain

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How to use DNS Checker

1

Open DNS Checker

Click the “DNS Check” button in the header, or click the “DNS Checker” button in the settings panel.
2

Enter test domain

In the modal that appears, enter a domain to test (e.g., google.com).
Use a well-known domain that should always be resolvable for accurate testing.
3

Enter DNS servers

Paste your list of DNS server IPs in the text area. You can:
  • Enter one IP per line
  • Paste large lists (up to 100 servers)
  • Mix formats (the tool will extract valid IPs)
Example:
8.8.8.8
1.1.1.1
9.9.9.9
208.67.222.222
4

Click Check DNS

Click the “Check DNS” button to start testing all servers concurrently.
5

Review results

The results table will populate in real-time showing:
  • DNS Server: The IP address being tested
  • Status: OK (green), WARN (yellow), or BAD (red)
  • Response Time: How long the resolution took
  • Action: “Use” button for successful servers

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Understanding DNS Checker results

Status indicators:
The DNS server successfully resolved the test domain.
  • Response time is shown in milliseconds
  • Safe to use as your DNS resolver
  • Click “Use” to apply immediately

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Applying DNS results

When you find a DNS server that works:
1

Identify successful servers

Look for servers with OK status (green) in the results table.
2

Click Use button

Click the “Use” button next to your chosen DNS server.
3

Automatic configuration

The DNS Checker will:
  • Set the DNS Resolver field to IP_ADDRESS:53
  • Force port 53 (standard DNS port)
  • Save the setting automatically
  • Close the DNS Checker modal
4

Restart VPN if running

If the VPN is currently running, stop and restart it to apply the new DNS resolver.
The DNS Checker automatically appends port :53 to the selected IP address, as this is the standard DNS port.

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Troubleshooting DNS issues

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All DNS servers show BAD status

If all servers fail, check your internet connection first.
Possible causes:
  • No internet connection
  • Firewall blocking DNS queries (port 53)
  • Network restrictions on DNS
  • Test domain is invalid or blocked
Solutions:
  1. Try a different test domain (e.g., google.com, cloudflare.com)
  2. Check your firewall settings
  3. Ensure you’re not behind a restrictive corporate proxy

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DNS resolution works but VPN doesn’t connect

Possible causes:
  • DNS resolver can’t access your SlipStream server
  • Domain configuration is incorrect
  • Server is down or unreachable
Solutions:
  1. Use your SlipStream server’s IP as the DNS resolver (e.g., YOUR_SERVER_IP:53)
  2. Verify your Domain setting matches your server configuration
  3. Check your server deployment and DNS records

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Slow DNS resolution

Symptoms:
  • Websites load slowly
  • Initial connection takes a long time
  • High response times in DNS Checker
Solutions:
  1. Choose a DNS server with lower response time (< 50ms is ideal)
  2. Use a geographically closer DNS server
  3. Try public DNS services:
    • Cloudflare: 1.1.1.1:53
    • Google: 8.8.8.8:53
    • Quad9: 9.9.9.9:53

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DNS Checker timeout

The DNS Checker tests up to 100 servers concurrently, which may take 5-30 seconds depending on network conditions.
If the checker seems stuck:
  1. Wait up to 30 seconds for all tests to complete
  2. Close and reopen the DNS Checker modal
  3. Test fewer servers at once (10-20 at a time)

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Manual DNS configuration

If you prefer to manually configure DNS:
  1. Find a reliable DNS server IP
  2. Enter it in the DNS Resolver field in this format: IP:PORT
  3. Use port 53 for standard DNS
  4. Click outside the field or press Enter to save
  5. Restart the VPN to apply changes
The DNS resolver setting is stored in settings.json along with your other configuration. It persists between application restarts.

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Best practices

Test regularly

DNS server performance can change. Run the DNS Checker periodically to ensure optimal performance.

Use your server's DNS

For best results with SlipStream, use your own server’s DNS resolver if available.

Save working configs

Use workspace presets to save different DNS configurations for different networks.

Monitor logs

Enable verbose logging to see DNS resolution activity and diagnose issues.

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