Understanding Network Extensions and VPN Configuration in iOS for Persistent Connections

Understanding Network Extensions and VPN Configuration in iOS

As a developer, configuring and connecting a Virtual Private Network (VPN) on an iOS device can be a complex task. In this article, we will delve into the world of Network Extensions and explore how to configure a VPN programmatically using the Network Extension framework.

Introduction to Network Extensions

Network Extensions allow developers to extend the network stack on an iOS device, enabling them to intercept and manipulate network traffic. The Network Extension framework provides a set of classes and protocols that enable developers to create custom network extensions, such as VPNs, routers, and proxies.

Configuring a VPN Programmatically in iOS

To configure a VPN programmatically in iOS, we use the NEVPNManager class, which provides a convenient interface for managing VPN connections. The NEVPNManager class is responsible for loading and saving VPN configurations from the keychain.

In our example code, we first load the VPN configuration from the keychain using the loadFromPreferencesWithCompletionHandler: method. We then create an instance of the NEVPNIKEAuthenticationMethodCertificate protocol and set its properties to match the desired VPN configuration.

Understanding On-Demand Rules

When a VPN is connected to an iOS device, the device automatically switches between Wi-Fi and mobile data networks when it detects an available network. However, this switching can cause issues with the VPN connection.

To solve this problem, we need to add rules to keep the connection persisted. Specifically, we need to enable on-demand mode for our VPN extension. We do this by setting the onDemandEnabled property of the NEVPNManager instance to YES.

In addition to enabling on-demand mode, we also need to configure a rule that ensures the VPN connection persists even when the device switches between Wi-Fi and mobile data networks.

Configuring On-Demand Rules

To configure an on-demand rule, we create an instance of the NEOnDemandRuleConnect class and set its properties to match the desired behavior. We set the interfaceTypeMatch property to .any, which means that the rule applies to all interfaces (Wi-Fi and mobile data).

We also need to configure a disconnect rule that ensures the VPN connection is terminated when the device switches to mobile data.

To do this, we create an instance of the NEOnDemandRuleDisconnect class and set its properties to match the desired behavior. We set the probeURL property to the URL of the VPN server, which tells iOS to probe for the presence of the VPN server on the mobile data network.

Example Code

Here is the updated code that includes on-demand rules:

let connectRule = NEOnDemandRuleConnect()
connectRule.interfaceTypeMatch = .any

let disconnectRule = NEOnDemandRuleDisconnect()
disconnectRule.probeURL = URL(string: VPNCredentialsModel.instance.vpnProbeURL()!)

Conclusion

Configuring a VPN programmatically in iOS can be a complex task, but with the right understanding of Network Extensions and on-demand rules, it is possible to create a persistent and reliable VPN connection.

By enabling on-demand mode and configuring appropriate on-demand rules, we can ensure that our VPN connection persists even when the device switches between Wi-Fi and mobile data networks. In this article, we have explored how to configure a VPN programmatically in iOS using the Network Extension framework and provided example code to illustrate the process.