How Split Tunneling Actually Routes Traffic

Split tunneling lets some network traffic pass through a VPN's encrypted tunnel while other traffic travels directly over the regular internet connection — a routing decision made at the device level, before any traffic actually leaves.

This piece explains how a device technically decides which traffic goes where, and what that decision changes about the overall system's behavior.

The mechanism is fundamentally about routing rules, not about encryption strength — traffic that goes through the tunnel is encrypted the same way regardless of split tunneling being enabled.

How Routing Rules Direct Traffic

A device maintains a routing table that determines which network interface a given piece of outgoing traffic should use. Without split tunneling, a VPN connection typically becomes the default route for all traffic, meaning everything is sent through the tunnel unless a specific exception exists.

Split tunneling modifies that routing table with additional rules — based on the destination address, the specific application generating the traffic, or a defined range of addresses — that direct matching traffic to bypass the VPN interface and use the regular network connection instead.

These routing decisions happen before encryption is applied at all; traffic destined for the regular connection never reaches the VPN's encryption process in the first place at all, rather than being encrypted first and then somehow later excluded from the tunnel afterward.

What Determines Which Traffic Splits

Application-based split tunneling identifies traffic by which program generated it — a specific application can be configured to always use the VPN tunnel or always bypass it, regardless of what specific destination that traffic is headed to.

Address-based split tunneling instead routes based on destination — traffic headed to a defined set of addresses uses one path, and everything else uses the other, independent of which application generated the request.

Some implementations combine both approaches, letting an administrator or user define rules by application, by destination, or by a combination of the two, which requires the routing table to evaluate multiple criteria rather than a single simple rule for every packet.

Where Split Tunneling Changes the System's Exposure

Traffic routed outside the tunnel travels with the same visibility to an observing network that it would have without a VPN at all — split tunneling does not partially encrypt that traffic; it simply does not encrypt it through the VPN's mechanism.

Misconfigured routing rules can direct traffic outside the tunnel unintentionally, particularly when an application's destination addresses change or when a new application is added without updating the routing rules to account for it.

Because DNS lookups — the process that translates a domain name into an address — can themselves be routed independently of the traffic that follows, a split-tunnel configuration that handles DNS incorrectly can reveal which destinations are being requested even when the resulting traffic itself is properly tunneled.

How Routing Configuration Is Actually Checked

Network diagnostic tools can trace which interface a given piece of traffic actually used, providing a direct technical verification of whether split-tunnel routing rules are being applied as configured rather than assuming the configuration is working correctly.

Because routing tables can be modified by multiple sources — the operating system, the VPN client software, and other network configuration changes — verifying actual behavior against the intended configuration is a distinct step from simply reviewing the configuration settings themselves.

This distinction between configured intent and actual routing behavior is why split-tunnel setups are generally tested with real traffic rather than assumed correct based on the settings alone.

A common verification method involves generating traffic to a known destination and confirming from the destination side which network address the request actually arrived from — a VPN address indicating tunneled traffic, or the device's regular address indicating the connection bypassed the tunnel as configured, giving a direct, observable result rather than an inference from settings alone.

Some VPN clients include a built-in routing-verification feature specifically for this purpose, displaying which interface a given application's traffic is currently using without requiring a separate external diagnostic tool, which is particularly useful for confirming complex, multi-rule split-tunnel configurations behave as intended across many different applications running at once on the same device.

Split tunneling is a routing decision made before encryption, directing some traffic through the VPN tunnel and some around it — a configuration of the network path, not a partial or reduced form of encryption itself.

Note: This explains how digital privacy and security tools work technically. It is not legal or cybersecurity advice, and it is not a substitute for a reader's own judgment about a real security concern. Check the cited sources for current guidance.