Why Split Tunneling Matters for Performance and Control

VPNs provide essential privacy, encryption, and location-flexibility for businesses and developers. However, routing all traffic through a VPN can create unnecessary latency, higher bandwidth usage, and additional load on central VPN gateways. Split tunneling solves this by selectively routing traffic: sensitive or corporate-bound traffic goes through the VPN, while non-sensitive or performance-sensitive traffic (e.g., video conferencing, SaaS, CDN content) uses the direct internet path. This yields better throughput, lower latency, and reduced gateway costs—without giving up security where it matters.

Split-Tunneling Approaches and Use Cases

There are two primary split-tunneling strategies, each with particular benefits and trade-offs:

  • Route-based (Network) Split Tunneling — configured at the network layer by manipulating routing tables. Ideal for site-to-site VPNs and per-host routing where destination subnets determine the path.
  • Application-based Split Tunneling — routes traffic from specific applications through or outside the VPN. Best for end-user workstations where you want to force enterprise apps through VPN but allow non-critical apps to go direct.

Common enterprise use cases include:

  • Protecting access to internal resources (databases, intranet) while allowing cloud application traffic to go direct.
  • Reducing bandwidth and latency for CDN downloads, VoIP, and video calls.
  • Complying with regional licensing or regulatory access while maintaining secure corporate connections.

Core Technical Components of a Secure Split-Tunnel Setup

To implement split tunneling effectively, you must control these technical elements:

  • Routing table rules — precise IP prefixes and metrics determine which traffic traverses the tunnel.
  • DNS handling — ensure internal name resolution goes to corporate DNS over the VPN while public DNS queries avoid leaks.
  • Firewall rules — block accidental direct access to protected services from non-VPN interfaces.
  • Traffic selectors / policies — for IPsec/modern VPNs, use traffic selectors or policy-based routing to bind flows to the tunnel.
  • Client enforcement — for app-based split tunneling, use endpoint agent controls to prevent bypasses and maintain policy compliance.

Design Principles

  • Prefer whitelisting (only route explicitly allowed subnets via VPN) over blacklisting to reduce accidental exposure.
  • Keep configuration deterministic—avoid overlapping routes and ambiguous metrics.
  • Document and centrally manage policies—use configuration management (Ansible, Puppet) or MDM for endpoints.

Implementing Route-Based Split Tunneling

Route-based split tunneling is common on servers and gateways. The principle: add routes for specific internal networks pointing at the VPN interface, and ensure the default route remains the system WAN when desired.

OpenVPN (TUN) Example: Push Specific Routes

On the server side, push network routes to clients so only those subnets go via the tunnel:

<code>server.conf (server-side)</code>

push “route 10.10.0.0 255.255.0.0”

push “route 10.20.0.0 255.255.255.0”

On the client, ensure you do not accept redirect-gateway (which forces all traffic through VPN). If using OpenVPN options, avoid redirect-gateway def1.

WireGuard Example: AllowedIPs for Precise Control

WireGuard uses the AllowedIPs directive to control routing. Example peer section to route only 10.0.0.0/8 through the tunnel:

<code>[Peer]<br>PublicKey = <server_pubkey><br>Endpoint = vpn.example.com:51820<br>AllowedIPs = 10.0.0.0/8</code>

Any traffic whose destination matches AllowedIPs is routed into the WireGuard interface; everything else follows the system’s default route.

Linux ip route / ip rule Approach

For advanced scenarios, use policy-based routing (multiple routing tables) to direct traffic from specific source addresses or marks through the VPN:

1) Create a table for VPN egress in /etc/iproute2/rt_tables (e.g., table 200).

2) Add route via VPN gateway on that table:

<code>ip route add default dev wg0 table 200</code>

3) Add policy rule for source IPs:

<code>ip rule add from 192.168.1.0/24 table 200</code>

This approach enables per-host or per-subnet split tunneling without changing the global default route.

Application-Based Split Tunneling

Application-based split tunneling is preferable where the decision is tied to a process or application identity. Approaches vary by OS and VPN client capability.

Windows

Commercial VPN clients often provide per-application rules. For more control on Windows, use Windows Filtering Platform (WFP) to mark flows and add routes, or leverage third-party agents that integrate with enterprise endpoint management. Group Policy Objects (GPO) and Intune can enforce VPN client configurations.

macOS

macOS supports per-app VPNs via Network Extension and per-app VPN profiles through MDM. This is effective for forcing corporate apps through the VPN while allowing personal apps to use Wi‑Fi/LTE directly.

Mobile (iOS/Android)

Both platforms support per-app VPN through their MDM frameworks (Apple MDM with Network Extensions, Android Enterprise with VPN lockdown policies). Use these for BYOD or managed device fleets to prevent app-level leakage.

DNS and Leak Prevention

DNS leak is a common vulnerability in split-tunnel setups. If internal resources are resolved via corporate DNS, but the client uses public DNS for other queries, you must ensure queries for internal zones go to corporate resolvers over the VPN. Techniques include:

  • Split-horizon DNS provisioning: Configure the client to use internal DNS servers for specific zones.
  • DNS proxying over the tunnel: Force DNS queries for internal domains to the VPN endpoint and resolve publicly only for other zones.
  • Using DNS over HTTPS/TLS selectively and ensuring it’s proxied into the VPN when internal names are involved.

Additionally, enforce DNS settings at the client level and audit with tools like dig or nslookup to validate resolution paths.

Security Considerations and Hardening

Split tunneling introduces potential attack paths—malicious or compromised endpoints could access internet resources and then pivot into VPN-accessible systems if policies are lax. Mitigate risks by implementing:

  • Least privilege network segmentation—design internal services to accept connections only from specific, authenticated hosts/networks.
  • Zero Trust—require per-request authentication and microsegmentation (service-level authentication rather than trusting network location).
  • Host posture checks—ensure endpoints meet baseline security (EDR, patch level, disk encryption) before granting access to sensitive resources.
  • Firewall and ACL enforcement on VPN concentrators and internal firewalls to restrict inbound traffic to only expected ports and IP ranges.
  • Logging and monitoring—collect VPN connection logs, DNS queries, and flow records to detect anomalies and lateral movement.

Authentication, Authorization, and Session Policies

Use strong mutual authentication (certificates + MFA) and apply session policies that limit what users or devices can access over the VPN. Implement granular RBAC and ephemeral credentials for critical services.

Testing and Validation

After deploying split tunneling, verify behavior across these dimensions:

  • Routing: use traceroute/tracert to validate path for internal vs external destinations.
  • DNS: confirm internal domains resolve only via VPN-resolvers and public names resolve via direct path when intended.
  • Leak tests: test for IP/DNS/WebRTC leaks with standard tools or custom scripts to ensure no unintended exposure.
  • Performance: measure latency and throughput for routed and direct paths; monitor gateway resource usage.

Automate periodic checks using CI/CD test runners or endpoint compliance scripts to catch drift early.

Operational Best Practices

  • Document tunnel policies and keep a change log for configuration updates.
  • Centralize policy management through MDM/endpoint management for consistency at scale.
  • Use telemetry: aggregate VPN, firewall, and DNS logs into a SIEM for correlation and alerting.
  • Plan for disaster recovery: ensure fallback routes or alternate gateways are available if split routes fail.
  • Train users and IT staff: explain why certain apps use direct paths and when to force traffic through the VPN for troubleshooting.

Conclusion: Balancing Performance and Security

Split tunneling, when implemented correctly, delivers significant performance and cost benefits by reducing unnecessary VPN traffic and improving end-user experience. The key is to pair selective routing with robust security controls—DNS safeguards, firewall rules, host posture validation, and continuous monitoring—so that you do not trade performance for a weakened security posture. Use route-based split tunneling for predictable network-level control, and application-based approaches when you need per-process granularity. Standardize configurations, centrally manage policies, and validate behavior regularly to maintain both performance and security over time.

For more detailed deployment guides, real-world configuration snippets, and enterprise-grade recommendations, visit Dedicated-IP-VPN at https://dedicated-ip-vpn.com/