diff --git a/ostp-gui/src/index.html b/ostp-gui/src/index.html
index b3fb663..addc692 100644
--- a/ostp-gui/src/index.html
+++ b/ostp-gui/src/index.html
@@ -174,7 +174,10 @@
 
           <div class="field-group">
             <label class="field-label" for="in-dns" data-i18n="label_dns">DNS Server</label>
-            <input id="in-dns" class="field-input" type="text" placeholder="1.1.1.1" />
+            <div style="display: flex; gap: 8px;">
+              <input id="in-dns" class="field-input" type="text" placeholder="1.1.1.1" style="flex: 1;" />
+              <button id="btn-use-builtin-dns" class="btn" style="padding: 0 12px; white-space: nowrap; cursor: pointer;" data-i18n="btn_use_builtin_dns">Use Built-in</button>
+            </div>
           </div>
 
           <div class="field-group">
diff --git a/ostp-gui/src/main.js b/ostp-gui/src/main.js
index cd78cec..ea4f002 100644
--- a/ostp-gui/src/main.js
+++ b/ostp-gui/src/main.js
@@ -381,6 +381,14 @@ window.addEventListener('DOMContentLoaded', async () => {
   btnBack.addEventListener('click',          () => showScreen('home'));
   btnImport.addEventListener('click',        handleImport);
   btnPeekKey.addEventListener('click',       togglePeek);
+  const btnUseBuiltinDns = $('btn-use-builtin-dns');
+  if (btnUseBuiltinDns) {
+    btnUseBuiltinDns.addEventListener('click', () => {
+      inDns.value = '10.1.0.1';
+      saveConfig();
+      showToast('DNS set to built-in server (10.1.0.1)', 'success');
+    });
+  }
   inTun.addEventListener('change',           () => { groupTunStack.style.display = inTun.checked ? 'block' : 'none'; });
   importInput.addEventListener('keydown', e => { if (e.key === 'Enter') handleImport(); });