Split Tunneling Proxies
What is Split Tunneling
Split tunneling is a technology where a portion of network traffic is directed through a proxy (or VPN), while the rest goes directly through the primary internet connection.
Instead of routing all traffic through a proxy (full tunneling), split tunneling allows you to selectively direct only the necessary traffic. This saves proxy resources and increases speed for regular traffic.
Why Split Tunneling is Needed
Traffic Savings
When using residential proxies with per-GB billing, it is critically important not to route unnecessary traffic (OS updates, streaming, downloads) through them.
Speed Preservation
Regular browsing goes directly at maximum speed. Only target traffic (parsing, account management) goes through the proxy.
Local Service Access
Access to the local network, intranet resources, and printers is maintained when using a proxy for external traffic.
Compatibility
Some services (banking, government services) block traffic through proxies. Split tunneling allows you to direct them directly.
Types of Split Tunneling
By Domain (Domain-based)
Traffic to specific domains goes through the proxy; the rest goes directly.
Example: Only amazon.com, google.com go through the proxy. Everything else goes directly.
By IP Address (IP-based)
Traffic to specific IP ranges is routed through the proxy.
By Application (App-based)
Certain applications use the proxy; others do not.
Example: A browser for parsing goes through the proxy; other programs go directly.
By Port (Port-based)
Traffic on specific ports goes through the proxy.
Inverse Split Tunneling
All traffic goes through the proxy, except for specified exclusions. Useful when you only need to exclude specific services.
Implementing Split Tunneling
PAC File (Proxy Auto-Configuration)
A PAC file is a JavaScript script that determines which requests go through a proxy:
The FindProxyForURL function takes a URL and host, and returns an instruction – to use a proxy or a direct connection. Rules can be configured by domain, IP address, and any other logic.
PAC files are supported by all browsers and operating systems.
Browser Extensions
SwitchyOmega (Chrome) — rules by domain and URL patterns.
FoxyProxy (Firefox) — similar functionality for Firefox.
Extensions allow for quick switching of proxy profiles and rule configuration without manual PAC file editing.
Proxifier
A system-level application that allows you to configure split tunneling by:
- Applications
- Domains and IPs
- Ports
- Combinations of rules
System Settings
Linux (iptables/nftables) — routing traffic through a proxy at the kernel level using firewall rules.
Windows (route/netsh) — configuring routes via the command line.
macOS (route/pfctl) — similar tools for macOS.
Advantages of Split Tunneling
- Traffic Savings — up to 80-90% reduction in proxy traffic consumption
- High Speed — regular traffic is not slowed down by the proxy
- Flexibility — precise control over what goes through the proxy
- Compatibility — local services and banking work without issues
- Cost Reduction — less traffic = lower proxy costs
Disadvantages
- Configuration Complexity — rules need careful consideration
- Traffic Leaks — incorrect configuration can direct sensitive traffic directly
- DNS Leaks — DNS requests can go directly, revealing visited domains
- Maintenance — rules need to be updated when target site domains/IPs change
Best Practices
1. Start with inverse split tunneling
Direct all traffic through the proxy, then add exceptions for safe services. This is more reliable than selective proxying.
2. Handle DNS
Ensure that DNS requests for proxied domains also go through the proxy (use SOCKS5 with remote DNS or DNS-over-HTTPS through the proxy).
3. Test for Leaks
Regularly verify that sensitive traffic genuinely goes through the proxy and not directly.
4. Log Routing
Maintain a log of which traffic is routed where, for troubleshooting issues.
5. Automate Rule Updates
If target domains change, set up automatic updates for your PAC file or routing rules.
Conclusion
Split tunneling is an essential technique for effective proxy usage. It allows you to direct only the necessary traffic through a proxy, saving resources and preserving speed for other traffic. Proper split tunneling configuration can reduce proxy costs severalfold.