- Run several servers that all respond to the same multicast registration address ("warm standby"). As long as multicast requests are mostly reliable, this ensures a consistent registration picture.

- If a registration server is rebooted and does not have complete knowledge of the local UA population, it could multicast any incoming INVITE requests.

- Use some of the available hardware redundancy solutions.

For servers separated from their client by a wide-area network, use of multicast is not appropriate, so that these servers have to rely on traditional backup techniques to achieve reliability. For example, the designated registrar could multicast registration updates within its local network to keep standby servers synchronized.