Broadcasting Internet datagrams in the presence of subnets

We do not assume, however, that broadcasts are reliably delivered. (One might consider providing a reliable datagram broadcast protocol as a layer above IP.) It is quite expensive to guarantee delivery of broadcasts; instead, what we assume is that a host will receive most of the broadcasts that are sent. This is important to avoid excessive use of broadcasts; since every host on the network devotes at least some effort to every broadcast, they are costly.