Configuring OSPF and OSPFv3 1119
Flood blocking cannot be enabled on virtual interfaces. While the feature
could be allowed on virtual interfaces, it is less likely to be used on a virtual
interface, since virtual interfaces are created specifically to allow flooding
between two backbone routers. So the option of flood blocking on virtual
interfaces is not supported.
See "Configuring Flood Blocking" on page 1195 for a configuration example.