[Under dog]

A situation came up where me and a friend disagreed on regarding the Under raise.

In this situation with blinds at 300/600 in a live MTT player A limps for 600, player B raises to 3000 and player C reraises all in for 4,200.

Now my friend states that player A can only call the extra 3,600 as player C's all in is an underraise of player B's raise. I agrued that once player A limped, the fact player B made a normal raise (more than the BB amount of 600) that now player A has the options Call Raise or Fold open to him again?

I thought this was pretty standard but he is isnt backing down on this one, just keeps saying "ya cant raise an underraise!"

So amirite?