Well, that depends. There's two different definitions of what people call "tanking":
- Survivability (Which makes you get attacked less)
- Aggro (Which makes you get attacked more)
A Bear Totem Barbarian is a Survivability Tank, but it doesn't do anything to make enemies attack him. Enemies can ignore the Bear Barbarian, and they'll be all better for it, which is why Bear Totem Barbarians usually grab feats to provide more Aggro, either as a means of keeping enemies from ignoring them through force (Sentinel), or by just dealing more damage (Polearm master).
An Ancestral Guardian Barbarian is an Aggro tank, but it doesn't do anything to help itself survive. If enemies are already going to be attacking the Barbarian, the Ancestral Guardian Barbarian does
literally nothing. This is why Ancestral Guardian Barbarians focus on survivability, with feats like Tough.