Honestly, I have no idea. However, Tibetan Mastiffs were used as guardians so it may be true. This is what Wikipedia says: "As a flock guardian dog in Tibet and in the West, it is tenacious in its ability to confront predators the size of wolves and leopards."
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That would never happen until the tiger is striving or dogs enter in it's territory, tiger would simply run away rather than risk an injury by confronting dogs. In all other scenarios any adult cat especially bengal/Siberian Tiger or African Lion will simply rip the dog apart in seconds no matter what breed and in a pack or alone.Cats are killing machine with one paw a lion takes the head of a spotted hyena when they were attacking a female lion to takeover the hunt. Only chance a dog(any breed/size/health) alone or in a pack has if the Lion or tiger is not in a mood to engage in a fight but if a big cat especially Male Lion and Bengal Tiger is in an angry attacking mode they will tear the pack into pieces. I have witnessed both Attacking Lion and Tiger it's just about what they are thinking fight play frighten or hunting. If it's fight then game is over before it actually it's begin