A computer network is said to provide hop integrity if, when any router, p, in the network receives a message, m, supposedly from an adjacent router, q, then p can check that m was indeed sent by q, was not modified after it was sent and was not a replay of an old message sent from q to p. We describe three protocols that can be added to the routers in a computer network so that the network can provide hop integrity, and thus overcome most denial-of-service attacks. These three protocols are a secret exchange protocol, a weak integrity protocol and a strong integrity protocol. All three protocols are stateless, require small overhead and do not constrain the network protocol in the routers in any way.

A computer network is said to provide hop integrity iff when any router p in the network receives a message m supposedly from an adjacent router q, then p can check that m was indeed sent by q, was not modified after it was sent, and was not a replay of an old message sent from q to p. We describe three protocols that can be added to the routers in a computer network so that the network can provide hop integrity. These three protocols are a secret exchange protocol, a weak integrity protocol, and a strong integrity protocol. All three protocols are stateless, require small overhead, and do not constrain the network protocol in the routers in any way.

Heartbeat protocols are used by distributed programs to ensure that if a process in a program terminates or fails, then the remaining processes in the program terminate. We present a class of heartbeat protocols that tolerate message loss. In these protocols, a root process periodically sends a beat message to every other process then waits to receive a reply beat message from every other process. If the root process does not receive a reply (possibly due to message loss), the root process reduces by half the period for sending beat messages. We show that in practical situations, the parameters of these protocols can be chosen to achieve a good compromise between three contradictory objectives: reduce the rate of sending beat messages, reduce the detection delay, and still keep the probability of premature termination small.