What is difference between no follow, dofollow and external nofollow

No Follow:This is an attribute and/or a meta tag that is used to instruct robots to not follow the link and/or view the page. The no follow meta tag is used for content that a webmaster does not want a user to view via a search engine. The no follow attribute on links is used to NOT give link backs

Do Follow: DoFollow is simply an internet slang term given to web pages or sites that are not utilizing "NoFollow." NoFollow is a hyperlink value that tells search engines not to pass on any credibility or influence to an outbound link. Originally created to help the blogging community reduce the number of inserted links into a "comment" area of a blog page, the attribute is typically standard in blog comments. It helps overwhelmed webmasters disallow spammers from gaining any kind of advantage by inserting an unwanted link on a popular page.

external nofollow Outbound links are a drain on a site's total PageRank. They leak PageRank. To counter the drain, try to ensure that the links are reciprocated. Because of the PageRank of the pages at each end of an external link, and the number of links out from those pages, reciprocal links can gain or lose PageRank. You need to take care when choosing where to exchange links.

 

Dofollow is considered by default and no need to add with code
ex- <a href="link">Text</a>
Nofollow is need to put using 'rel' or 'content' meta tag
ex- <a href="link" rel="nofollow">Text</a> For single link
<a href="link" content="nofollow">Text</a> For whole page links

 

NoFollow Links: Tells the Google Bot or any other Search Engine Bot, not to follow the link. Attribute rel=”nofollow” is mostly used when we add a link to any untrustable or bad websites in our blog post.
DoFollow Links: Every search engine Bot will follow these links and certain value will be given to them, based on the quality of your blog. Attribute rel=”dofollow” is used when we interlink the articles on the same blog.

 

This is good post to read about external nofollow. Till date I don't have idea that we can also use nofollow tag for content so we can block all page links using content="nofollow" tag.