it's normal?

[whitefemale]

go to gnomeregan and get hit by first mob 400 critical? I have shield too.

[Sorrowind]

Gnomer mobs are the first real step up in tanking difficulty for vanilla dungeons, I actually have seen the mechanical knights hit me harder as a tank than anything in scarlet monestary.

That said if you are being hit for that much it probably comes down to one of (or a combination) these things.

1. Crushing Blows

My guess this is likely what happened if you are a few levels lower than the mob and don't have any +def, or dodge through bear form, it's quite possible to take a crushing blow especially if they are slightly behind you when you get hit.

2. Not enough Damage Resist through armor

If you are below 30% dmg reduction stuff in gnomer is going to slap you around especially if you leave the beaten path to go take out Crowd Pummeller. It can be hard on a tank when X5 exp gets you to levels 26-30 but doesn't really give you gear to sustain it.

3. Too many attacks per frame.

I'm going to rule this one out since it's not really applicable to early gnomer and I don't recall having this issue until I got to cathedral. There seem to be some cap limits that move up with levels in terms of how many enemies you can get defensive rolls for if they are all attacking in the same 1 second frame. I find around 30 mobs hitting you all at once some of the attacks seem to go through without AC reduction when you are tanking at level (pal/war).

Best way to deal with the issue is gear (try to fill all slots with some green or blue mail/leather), use item enhancements to get your base DR up like leather armor patches, or potions and food to give you the edge you need.

Alternatively grind easier dungeons =/

[lulumahami]

Mechanical bird mob is bugged and ignores armor, it has nothing to do with being hard.
You can test it by equipping/unequpping shield and getting hit for same amount of dmg.