  We consider the problem of sending a message from a sender $s$ to a receiver
$r$ through an unreliable network by specifying in a protocol what each vertex
is supposed to do if it receives the message from one of its neighbors. A
protocol for routing a message in such a graph is finite if it never floods $r$
with an infinite number of copies of the message. The expected reliability of a
given protocol is the probability that a message sent from $s$ reaches $r$ when
the edges of the network fail independently with probability $1-p$.
  We discuss, for given networks, the properties of finite protocols with
maximum expected reliability in the case when $p$ is close to 0 or 1, and we
describe networks for which no one protocol is optimal for all values of $p$.
In general, finding an optimal protocol for a given network and fixed
probability is challenging and many open problems remain.
