canonical URls

i have read about the canonical url, is it realy benificial touse Link tag??

can anybody show me live examplee..

 

It should be used every time you have duplicate content so that Google knows the major page...

 

Yes, you can either use the canonical attribute or simply choose a preferred version for your URLs (with or without the www prefix), then redirect the index.html or index.php to the preferred domain version, as well as the un-preferred domain URL to the one you chosen initially to use.
This will help not to loose ranking (separated on all 4 versions otherwise) as well as with the duplicate content issues...

 

here is the live example for canonical tags.. check the headers of these urls and see how canonical tag is hepling out with duplicate content http://starwars.wikia.com/wiki/Nelvana_Limited v/s http://starwars.wikia.com/wiki/Nelvana.