Introducing DHCP
Subject:   Broadcast of ?
Date:   2003-05-23 03:56:07
From:   anonymous2
Response to: Broadcast of ?

This is the right way to specify it. If you mean by "all bits on" the binary representation, then you are right. 255 in Decimal can be interpreted 11111111 in binary representation. So if you take a closer look at the network address, we have 4 times 8 bit.
that is:
11111111 11111111 11111111 11111111
in binary or
FF FF FF FF in hex.