Dear webmaster, I need a suggestion from you all regarding rel="nofollow" or rel="external nofollow" html tag. I know that this tag doesn't allow to pass the link juice to the anchored link but i need to know that if this tag prevent search engine crawler to index the target link or not. Say if i have a link of xyz[.]com in any blog comment, then is it possible that during caching or indexing the blog the crawler can traverse to xyz[.]com through the blog without passing the link juice.
Google has hinted in Webmaster Central that it DOES consider external nofollow tags (probably for crawling), but it was not very explicit. I got the impression that if you use nofollow within your own site, Google will accept that directive and not follow the links for crawling, but that if you include a nofollow tag to an external site then it WILL crawl it but not pass link juice. In any case, I believe it is a BAD idea to mark all external links as nofollow - Google is not smart enough to detect "link juice hoarding", and after Panda is unlikely to consider it "bad quality" (not confirmed, mind you). The policy I follow for my own sites is the following: Internal links are FOLLOW, except if pointing to forms or internal pages that I do NOT want to be indexed, in which case I make the links NOFOLLOW, NOINDEX. External links to reputable places (usually with higher page rank than mine) are FOLLOW, but dubious links being NOFOLLOW. Comments to my blog are FOLLOW (but moderated, and I trash ruthlessly comment spam). I believe it incentivates good commenting and therefore additional content on my blog.