The Site Multihoming by IPv6 Intermediation (SHIM6) protocol is an Internet Layer[1] defined in RFC 5533.
The SHIM6 architecture defines failure detection and locator pair exploration functions.
The first is used to detect outages through the path defined by the current locator pair for a communication.
The second function is used to determine valid locator pairs that could be used when an outage is detected.
These approaches are not needed for IPv4 because of the short address length (32 bits).