You might have listened about a WordPress plugin called SEO Smart Links, it provides automatic SEO benefits for your WordPress blog in addition to custom keyword lists, nofollow and much more.
It auto interlinks certain keywords and phrases inside your posts and pages with other posts, tags, pages and categories. After installing and activating SEO Smart Links you can easily configure it by entering keywords relevant to older posts and pages. When keywords are found this plugin links them to their respective articles.