# Multihop

## Overview

See [MultiHop](/paas/sdk/unified-vpn-sdk/features/multihop.md)

## Implementing MultiHop

To enable multihop routing, you need to pass an additional location to the `withLocation` method of the `SessionConfig.Builder` class. Both the main location and the proxy location can be fetched using the Backend API.

```kotlin
import unified.vpn.sdk.*

val sdk = UnifiedSdk.getInstance()

sdk.vpn.start(SessionConfig.Builder()
    // ...
    .withLocation("US", "YOUR_ACTUAL_PROXY_LOCATION")
    // ...
    .build(), object : CompletableCallback {
    override fun complete() {}
    override fun error(e: VpnException) {}
})
```

In this example, `"US"` is the main location, and `"YOUR_ACTUAL_PROXY_LOCATION"` is the proxy location.

## Fetching Available Virtual Locations

To fetch the available locations for multihop routing, you can use the `locations` method of the `Backend` class, specifying the `ConnectionType.HYDRA_TCP` parameter.

```kotlin
import unified.vpn.sdk.*

val sdk = UnifiedSdk.getInstance()

sdk.backend.locations(ConnectionType.HYDRA_TCP, object : Callback<AvailableLocations> {
    override fun success(availableLocations: AvailableLocations) {
        // Handle the available locations
    }

    override fun failure(e: VpnException) {
        // Handle any errors
    }
})
```

## Optimal Proxy

To automatically select the optimal proxy location based on network conditions and server load, you can pass an empty string (`""`) as the proxy parameter in the `withLocation` method. Passing `null` as the proxy parameter means that no proxy location is used.

```kotlin
import unified.vpn.sdk.*

val sdk = UnifiedSdk.getInstance()

val sessionConfig = SessionConfig.Builder()
    // ...
    .withLocation("US", "")  // Use optimal proxy
    // ...
    .build()

sdk.vpn.start(sessionConfig, object : CompletableCallback {
    override fun complete() {}
    override fun error(e: VpnException) {}
})
```


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