rules for interface naming for on-board cards

Hi,

I am trying to understand the way interface names are given.
So one way is hard coding in net_device->name.

If the name contains a %d format string, the first available device
name with the given base is used; assigned numbers start at zero.

On my base machine, I have 1 NIC card which is onboard, rest I can
remove and plug.
For the onboard card I get the interfaces as em1-4, while all the
other cards I get names as p1p2, p3p4 etc.

Does Udev know the difference.

How are these names given, definitely there must be some configuration
which is used to distinguish on-board card vs removable.

Thanks.