404 in react-router 2.0.0?

Question

React

There was a problem while learning react-router. The course uses router 2.0.0-rc5 version.
If you write a route like this:

<Route path='/' component={App}>
    <IndexRoute component={PostsIndex} />
    <Route path="posts" component={PostsNew} /> 
  </Route>

Then following the link ..../posts produces the PostsNew component, as it should.
But if the route is written like this:

<Route path='/' component={App}>
    <IndexRoute component={PostsIndex} />
    <Route path="posts/new" component={PostsNew} /> 
  </Route>

Then the link .../posts/new issues 404. What could be the problem?