pathauto works but Google indexes node/432423. how ?

Probably there's a direct link to the unaliased node path, either from an external site, or a badly written module, or manually entered in a node body, or...
You can prevent this by installing the global redirect module. This will automatically 301-redirect the internal node paths to their aliases, so that even if a stray link to the node path appears somewhere, search engines will see the redirect and index the correct alias.