diff --git a/BUILD.md b/BUILD.md
new file mode 100644
index 0000000..c865cfd
--- /dev/null
+++ b/BUILD.md
@@ -0,0 +1,396 @@
+# SoftEtherRust Build Guide
+
+> Complete build instructions for all platforms and architectures.
+
+---
+
+## Table of Contents
+
+- [Prerequisites](#prerequisites)
+- [Android Build](#android-build)
+- [iOS Build](#ios-build)
+- [Desktop Build](#desktop-build)
+- [Troubleshooting](#troubleshooting)
+
+---
+
+## Prerequisites
+
+### 1. Install Rust
+
+```bash
+curl --proto '=https' --tlsv1.2 -sSf https://sh.rustup.rs | sh
+source ~/.cargo/env
+```
+
+### 2. Verify Installation
+
+```bash
+rustc --version
+cargo --version
+rustup --version
+```
+
+---
+
+## Android Build
+
+### Step 1: Install Android NDK
+
+**Option A: Via Android Studio**
+1. Open Android Studio → Settings → SDK Manager
+2. SDK Tools tab → Check "NDK (Side by side)"
+3. Install NDK version 25.x or higher
+
+**Option B: Via Command Line**
+```bash
+# macOS
+sdkmanager "ndk;25.1.8937393"
+
+# Linux
+$ANDROID_HOME/cmdline-tools/latest/bin/sdkmanager "ndk;25.1.8937393"
+```
+
+### Step 2: Set Environment Variables
+
+Add to your `~/.zshrc` or `~/.bashrc`:
+
+```bash
+# Android SDK & NDK
+export ANDROID_HOME="$HOME/Library/Android/sdk"           # macOS
+# export ANDROID_HOME="$HOME/Android/Sdk"                 # Linux
+
+export ANDROID_NDK_HOME="$ANDROID_HOME/ndk/25.1.8937393"  # Adjust version as needed
+
+# Detect host OS
+case "$(uname -s)" in
+    Darwin) NDK_HOST="darwin-x86_64" ;;
+    Linux)  NDK_HOST="linux-x86_64" ;;
+    *)      NDK_HOST="windows-x86_64" ;;
+esac
+
+# Android toolchain paths
+export PATH="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin:$PATH"
+
+# Cargo linkers for each Android architecture
+export CARGO_TARGET_AARCH64_LINUX_ANDROID_LINKER="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin/aarch64-linux-android21-clang"
+export CARGO_TARGET_ARMV7_LINUX_ANDROIDEABI_LINKER="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin/armv7a-linux-androideabi21-clang"
+export CARGO_TARGET_X86_64_LINUX_ANDROID_LINKER="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin/x86_64-linux-android21-clang"
+export CARGO_TARGET_I686_LINUX_ANDROID_LINKER="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin/i686-linux-android21-clang"
+
+# CC compilers for ring crate (required for TLS)
+export CC_aarch64_linux_android="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin/aarch64-linux-android21-clang"
+export CC_armv7_linux_androideabi="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin/armv7a-linux-androideabi21-clang"
+export CC_x86_64_linux_android="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin/x86_64-linux-android21-clang"
+export CC_i686_linux_android="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin/i686-linux-android21-clang"
+
+# AR archivers
+export AR_aarch64_linux_android="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin/llvm-ar"
+export AR_armv7_linux_androideabi="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin/llvm-ar"
+export AR_x86_64_linux_android="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin/llvm-ar"
+export AR_i686_linux_android="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin/llvm-ar"
+```
+
+**Reload shell:**
+```bash
+source ~/.zshrc  # or ~/.bashrc
+```
+
+### Step 3: Install Rust Targets
+
+```bash
+# Install all Android targets
+rustup target add aarch64-linux-android      # arm64-v8a (64-bit ARM)
+rustup target add armv7-linux-androideabi    # armeabi-v7a (32-bit ARM)
+rustup target add x86_64-linux-android       # x86_64 (64-bit Intel)
+rustup target add i686-linux-android         # x86 (32-bit Intel)
+```
+
+### Step 4: Check Your Device Architecture
+
+```bash
+adb shell getprop ro.product.cpu.abi
+```
+
+| Output | Architecture | Rust Target |
+|--------|--------------|-------------|
+| `arm64-v8a` | 64-bit ARM | `aarch64-linux-android` |
+| `armeabi-v7a` | 32-bit ARM | `armv7-linux-androideabi` |
+| `x86_64` | 64-bit Intel | `x86_64-linux-android` |
+| `x86` | 32-bit Intel | `i686-linux-android` |
+
+### Step 5: Build for Your Architecture
+
+**For armeabi-v7a (32-bit ARM):**
+```bash
+cd SoftEtherRust
+cargo build --release --target armv7-linux-androideabi --features android
+```
+
+**For arm64-v8a (64-bit ARM):**
+```bash
+cd SoftEtherRust
+cargo build --release --target aarch64-linux-android --features android
+```
+
+**For x86_64:**
+```bash
+cd SoftEtherRust
+cargo build --release --target x86_64-linux-android --features android
+```
+
+**For x86:**
+```bash
+cd SoftEtherRust
+cargo build --release --target i686-linux-android --features android
+```
+
+**Build ALL architectures:**
+```bash
+cd SoftEtherRust
+cargo build --release --target aarch64-linux-android --features android
+cargo build --release --target armv7-linux-androideabi --features android
+cargo build --release --target x86_64-linux-android --features android
+cargo build --release --target i686-linux-android --features android
+```
+
+### Step 6: Copy Libraries to Android App
+
+```bash
+# Create jniLibs directories
+mkdir -p ../app/src/main/jniLibs/{arm64-v8a,armeabi-v7a,x86_64,x86}
+
+# Copy libraries (only copy the ones you built)
+cp target/aarch64-linux-android/release/libsoftether.so ../app/src/main/jniLibs/arm64-v8a/
+cp target/armv7-linux-androideabi/release/libsoftether.so ../app/src/main/jniLibs/armeabi-v7a/
+cp target/x86_64-linux-android/release/libsoftether.so ../app/src/main/jniLibs/x86_64/
+cp target/i686-linux-android/release/libsoftether.so ../app/src/main/jniLibs/x86/
+```
+
+### Step 7: Build and Install APK
+
+```bash
+cd ..  # Back to WorxVPN-Android root
+./gradlew installDebug
+```
+
+---
+
+## Quick Build Commands
+
+### Build for your device only (faster)
+
+```bash
+# Check device arch first
+ARCH=$(adb shell getprop ro.product.cpu.abi)
+echo "Device architecture: $ARCH"
+
+cd SoftEtherRust
+
+case "$ARCH" in
+    arm64-v8a)
+        TARGET="aarch64-linux-android"
+        JNI_DIR="arm64-v8a"
+        ;;
+    armeabi-v7a)
+        TARGET="armv7-linux-androideabi"
+        JNI_DIR="armeabi-v7a"
+        ;;
+    x86_64)
+        TARGET="x86_64-linux-android"
+        JNI_DIR="x86_64"
+        ;;
+    x86)
+        TARGET="i686-linux-android"
+        JNI_DIR="x86"
+        ;;
+esac
+
+echo "Building for $TARGET..."
+cargo build --release --target $TARGET --features android
+
+mkdir -p ../app/src/main/jniLibs/$JNI_DIR
+cp target/$TARGET/release/libsoftether.so ../app/src/main/jniLibs/$JNI_DIR/
+
+cd ..
+./gradlew installDebug
+```
+
+---
+
+## iOS Build
+
+### Step 1: Install Xcode
+
+Install Xcode from the Mac App Store.
+
+### Step 2: Install Rust Targets
+
+```bash
+rustup target add aarch64-apple-ios           # Device (arm64)
+rustup target add aarch64-apple-ios-sim       # Simulator (Apple Silicon)
+rustup target add x86_64-apple-ios            # Simulator (Intel)
+```
+
+### Step 3: Build
+
+```bash
+cd SoftEtherRust
+
+# For iOS Device (arm64)
+cargo build --release --target aarch64-apple-ios --features ios
+
+# For iOS Simulator (Apple Silicon Mac)
+cargo build --release --target aarch64-apple-ios-sim --features ios
+
+# For iOS Simulator (Intel Mac)
+cargo build --release --target x86_64-apple-ios --features ios
+```
+
+### Step 4: Create XCFramework
+
+```bash
+./scripts/build-ios.sh
+```
+
+---
+
+## Desktop Build
+
+### macOS
+
+```bash
+cargo build --release
+# Output: target/release/libsoftether.dylib
+```
+
+### Linux
+
+```bash
+cargo build --release
+# Output: target/release/libsoftether.so
+```
+
+### Windows
+
+```bash
+cargo build --release
+# Output: target/release/softether.dll
+```
+
+---
+
+## Troubleshooting
+
+### Error: "linker not found"
+
+**Problem:** `linker 'aarch64-linux-android21-clang' not found`
+
+**Solution:** Set the linker environment variable:
+```bash
+export CARGO_TARGET_AARCH64_LINUX_ANDROID_LINKER="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/darwin-x86_64/bin/aarch64-linux-android21-clang"
+```
+
+Or add all linkers to your shell profile (see Step 2 above).
+
+---
+
+### Error: "CC compiler not found" (ring crate)
+
+**Problem:** `failed to find tool "aarch64-linux-android-clang"`
+
+**Solution:** Set the CC environment variable:
+```bash
+export CC_aarch64_linux_android="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/darwin-x86_64/bin/aarch64-linux-android21-clang"
+```
+
+---
+
+### Error: "No space left on device"
+
+**Problem:** Build fails with temp directory errors.
+
+**Solution:** Use a different temp directory:
+```bash
+export TMPDIR=/path/to/external/drive/tmp
+mkdir -p $TMPDIR
+cargo build --release --target armv7-linux-androideabi --features android
+```
+
+---
+
+### Error: "ANDROID_NDK_HOME not set"
+
+**Solution:** Set the NDK path:
+```bash
+# Find your NDK version
+ls $ANDROID_HOME/ndk/
+
+# Set it (replace version number)
+export ANDROID_NDK_HOME="$ANDROID_HOME/ndk/25.1.8937393"
+```
+
+---
+
+### UnsatisfiedLinkError on Android
+
+**Problem:** App crashes with `java.lang.UnsatisfiedLinkError: dlopen failed: library "libsoftether.so" not found`
+
+**Solution:** 
+1. Check you built for the correct architecture:
+   ```bash
+   adb shell getprop ro.product.cpu.abi
+   ```
+2. Verify the .so file exists:
+   ```bash
+   ls -la app/src/main/jniLibs/*/libsoftether.so
+   ```
+3. Rebuild and reinstall:
+   ```bash
+   ./gradlew clean installDebug
+   ```
+
+---
+
+### Check NDK Toolchain
+
+Verify toolchain exists:
+```bash
+ls $ANDROID_NDK_HOME/toolchains/llvm/prebuilt/*/bin/*-clang
+```
+
+Expected output:
+```
+.../bin/aarch64-linux-android21-clang
+.../bin/armv7a-linux-androideabi21-clang
+.../bin/i686-linux-android21-clang
+.../bin/x86_64-linux-android21-clang
+```
+
+---
+
+## Architecture Reference
+
+| Device Type | ABI | Rust Target | JNI Folder |
+|-------------|-----|-------------|------------|
+| Modern Android phones | arm64-v8a | aarch64-linux-android | arm64-v8a |
+| Older Android phones | armeabi-v7a | armv7-linux-androideabi | armeabi-v7a |
+| Android Emulator (Intel) | x86_64 | x86_64-linux-android | x86_64 |
+| Old Android Emulator | x86 | i686-linux-android | x86 |
+| iOS Device | arm64 | aarch64-apple-ios | - |
+| iOS Simulator (M1/M2) | arm64-sim | aarch64-apple-ios-sim | - |
+| iOS Simulator (Intel) | x86_64 | x86_64-apple-ios | - |
+
+---
+
+## One-Liner Quick Build
+
+**For your connected device:**
+```bash
+ARCH=$(adb shell getprop ro.product.cpu.abi) && \
+case "$ARCH" in arm64-v8a) T=aarch64-linux-android;; armeabi-v7a) T=armv7-linux-androideabi;; x86_64) T=x86_64-linux-android;; x86) T=i686-linux-android;; esac && \
+cargo build --release --target $T --features android && \
+mkdir -p ../app/src/main/jniLibs/$ARCH && \
+cp target/$T/release/libsoftether.so ../app/src/main/jniLibs/$ARCH/ && \
+cd .. && ./gradlew installDebug
+```
diff --git a/scripts/build-android.sh b/scripts/build-android.sh
index b187a64..afcd521 100755
--- a/scripts/build-android.sh
+++ b/scripts/build-android.sh
@@ -98,12 +98,25 @@ build_android() {
     
     NDK_HOST=$(get_ndk_host)
     LINKER_EXT=$(get_linker_ext)
+    TOOLCHAIN="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin"
     
-    # Configure cargo for Android
-    export CARGO_TARGET_AARCH64_LINUX_ANDROID_LINKER="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin/aarch64-linux-android21-clang$LINKER_EXT"
-    export CARGO_TARGET_ARMV7_LINUX_ANDROIDEABI_LINKER="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin/armv7a-linux-androideabi21-clang$LINKER_EXT"
-    export CARGO_TARGET_X86_64_LINUX_ANDROID_LINKER="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin/x86_64-linux-android21-clang$LINKER_EXT"
-    export CARGO_TARGET_I686_LINUX_ANDROID_LINKER="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin/i686-linux-android21-clang$LINKER_EXT"
+    # Configure cargo LINKERS for Android
+    export CARGO_TARGET_AARCH64_LINUX_ANDROID_LINKER="$TOOLCHAIN/aarch64-linux-android21-clang$LINKER_EXT"
+    export CARGO_TARGET_ARMV7_LINUX_ANDROIDEABI_LINKER="$TOOLCHAIN/armv7a-linux-androideabi21-clang$LINKER_EXT"
+    export CARGO_TARGET_X86_64_LINUX_ANDROID_LINKER="$TOOLCHAIN/x86_64-linux-android21-clang$LINKER_EXT"
+    export CARGO_TARGET_I686_LINUX_ANDROID_LINKER="$TOOLCHAIN/i686-linux-android21-clang$LINKER_EXT"
+    
+    # Configure CC compilers for ring crate (TLS)
+    export CC_aarch64_linux_android="$TOOLCHAIN/aarch64-linux-android21-clang$LINKER_EXT"
+    export CC_armv7_linux_androideabi="$TOOLCHAIN/armv7a-linux-androideabi21-clang$LINKER_EXT"
+    export CC_x86_64_linux_android="$TOOLCHAIN/x86_64-linux-android21-clang$LINKER_EXT"
+    export CC_i686_linux_android="$TOOLCHAIN/i686-linux-android21-clang$LINKER_EXT"
+    
+    # Configure AR archivers
+    export AR_aarch64_linux_android="$TOOLCHAIN/llvm-ar"
+    export AR_armv7_linux_androideabi="$TOOLCHAIN/llvm-ar"
+    export AR_x86_64_linux_android="$TOOLCHAIN/llvm-ar"
+    export AR_i686_linux_android="$TOOLCHAIN/llvm-ar"
     
     # Build for each architecture
     log_info "  Building aarch64-linux-android (arm64-v8a)..."
@@ -157,7 +170,11 @@ build_android_arm64() {
     
     NDK_HOST=$(get_ndk_host)
     LINKER_EXT=$(get_linker_ext)
-    export CARGO_TARGET_AARCH64_LINUX_ANDROID_LINKER="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin/aarch64-linux-android21-clang$LINKER_EXT"
+    TOOLCHAIN="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin"
+    
+    export CARGO_TARGET_AARCH64_LINUX_ANDROID_LINKER="$TOOLCHAIN/aarch64-linux-android21-clang$LINKER_EXT"
+    export CC_aarch64_linux_android="$TOOLCHAIN/aarch64-linux-android21-clang$LINKER_EXT"
+    export AR_aarch64_linux_android="$TOOLCHAIN/llvm-ar"
     
     log_info "  Building aarch64-linux-android (arm64-v8a)..."
     cargo build --release --target aarch64-linux-android --features android
@@ -175,13 +192,112 @@ build_android_arm64() {
     fi
 }
 
+# Build only armv7 (32-bit ARM - older devices)
+build_android_armv7() {
+    log_info "Building for Android (armv7 only)..."
+    
+    if [ -z "$ANDROID_NDK_HOME" ]; then
+        log_error "ANDROID_NDK_HOME not set"
+        exit 1
+    fi
+    
+    NDK_HOST=$(get_ndk_host)
+    LINKER_EXT=$(get_linker_ext)
+    TOOLCHAIN="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin"
+    
+    export CARGO_TARGET_ARMV7_LINUX_ANDROIDEABI_LINKER="$TOOLCHAIN/armv7a-linux-androideabi21-clang$LINKER_EXT"
+    export CC_armv7_linux_androideabi="$TOOLCHAIN/armv7a-linux-androideabi21-clang$LINKER_EXT"
+    export AR_armv7_linux_androideabi="$TOOLCHAIN/llvm-ar"
+    
+    log_info "  Building armv7-linux-androideabi (armeabi-v7a)..."
+    cargo build --release --target armv7-linux-androideabi --features android
+    
+    mkdir -p target/android/jniLibs/armeabi-v7a
+    cp target/armv7-linux-androideabi/release/libsoftether.so target/android/jniLibs/armeabi-v7a/
+    
+    log_info "Android armv7 build complete: target/android/jniLibs/armeabi-v7a/"
+    
+    # Copy to Android app if it exists
+    if [ -d "../app/src/main" ]; then
+        mkdir -p ../app/src/main/jniLibs/armeabi-v7a
+        cp target/android/jniLibs/armeabi-v7a/libsoftether.so ../app/src/main/jniLibs/armeabi-v7a/
+        log_info "Copied to Android app: app/src/main/jniLibs/armeabi-v7a/"
+    fi
+}
+
+# Build for connected device automatically
+build_android_auto() {
+    log_info "Detecting connected device architecture..."
+    
+    if ! command -v adb &> /dev/null; then
+        log_error "adb not found. Install Android SDK platform-tools."
+        exit 1
+    fi
+    
+    ARCH=$(adb shell getprop ro.product.cpu.abi 2>/dev/null | tr -d '\r')
+    
+    if [ -z "$ARCH" ]; then
+        log_error "No device connected or adb not responding."
+        exit 1
+    fi
+    
+    log_info "Detected device architecture: $ARCH"
+    
+    case "$ARCH" in
+        arm64-v8a)
+            rustup target add aarch64-linux-android
+            build_android_arm64
+            ;;
+        armeabi-v7a)
+            rustup target add armv7-linux-androideabi
+            build_android_armv7
+            ;;
+        x86_64)
+            log_info "Building for x86_64..."
+            rustup target add x86_64-linux-android
+            NDK_HOST=$(get_ndk_host)
+            LINKER_EXT=$(get_linker_ext)
+            TOOLCHAIN="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin"
+            export CARGO_TARGET_X86_64_LINUX_ANDROID_LINKER="$TOOLCHAIN/x86_64-linux-android21-clang$LINKER_EXT"
+            export CC_x86_64_linux_android="$TOOLCHAIN/x86_64-linux-android21-clang$LINKER_EXT"
+            export AR_x86_64_linux_android="$TOOLCHAIN/llvm-ar"
+            cargo build --release --target x86_64-linux-android --features android
+            mkdir -p target/android/jniLibs/x86_64 ../app/src/main/jniLibs/x86_64
+            cp target/x86_64-linux-android/release/libsoftether.so target/android/jniLibs/x86_64/
+            cp target/android/jniLibs/x86_64/libsoftether.so ../app/src/main/jniLibs/x86_64/ 2>/dev/null || true
+            ;;
+        x86)
+            log_info "Building for x86..."
+            rustup target add i686-linux-android
+            NDK_HOST=$(get_ndk_host)
+            LINKER_EXT=$(get_linker_ext)
+            TOOLCHAIN="$ANDROID_NDK_HOME/toolchains/llvm/prebuilt/$NDK_HOST/bin"
+            export CARGO_TARGET_I686_LINUX_ANDROID_LINKER="$TOOLCHAIN/i686-linux-android21-clang$LINKER_EXT"
+            export CC_i686_linux_android="$TOOLCHAIN/i686-linux-android21-clang$LINKER_EXT"
+            export AR_i686_linux_android="$TOOLCHAIN/llvm-ar"
+            cargo build --release --target i686-linux-android --features android
+            mkdir -p target/android/jniLibs/x86 ../app/src/main/jniLibs/x86
+            cp target/i686-linux-android/release/libsoftether.so target/android/jniLibs/x86/
+            cp target/android/jniLibs/x86/libsoftether.so ../app/src/main/jniLibs/x86/ 2>/dev/null || true
+            ;;
+        *)
+            log_error "Unknown architecture: $ARCH"
+            exit 1
+            ;;
+    esac
+    
+    log_info "Build complete for $ARCH"
+}
+
 # Print usage
 usage() {
     echo "Usage: $0 [command]"
     echo ""
     echo "Commands:"
     echo "  build    Build for all Android architectures"
-    echo "  arm64    Build for arm64-v8a only (faster)"
+    echo "  auto     Build for connected device (auto-detect arch)"
+    echo "  arm64    Build for arm64-v8a only"
+    echo "  armv7    Build for armeabi-v7a only (32-bit ARM)"
     echo "  clean    Clean Android build artifacts"
     echo ""
     echo "With no command, builds for all Android architectures."
@@ -198,10 +314,17 @@ case "${1:-build}" in
         install_targets
         build_android
         ;;
+    auto)
+        build_android_auto
+        ;;
     arm64)
         rustup target add aarch64-linux-android
         build_android_arm64
         ;;
+    armv7)
+        rustup target add armv7-linux-androideabi
+        build_android_armv7
+        ;;
     clean)
         log_info "Cleaning Android build artifacts..."
         rm -rf target/aarch64-linux-android