the IVs the egg inherits are an average between the IVs of the two parents, e.g. if one parent has 10 att and the other 20, the IVs will usually be 15, though there is a small chance for them to be 10 or 20.
This means that if the parent's IVs overlap they are guaranteed to inherit it. You can also equip braces on the pokemon to ensure a corresponding IV gets passed down.