Confined to a domain or VLAN, multicast IEEE 802.1ag Ethernet Continuity Check (ETH-CC) heartbeat messages are exchanged periodically between endpoints, thereby allowing them to discover each other or any intermediary devices. These OAM messages can detect the loss of a link and incorrect network connections. When these connectivity failures occur within a specific maintenance association, ETH-CC and can be used to trigger protection switching within 3.33ms. Hardware and software faults can also be detected with continuity check messages.