By being part of a larger, routable prefix. gnfargbl didn't say the _address_ was unroutable, but that effectively, routing policies mean that /48 is a common

By being part of a larger, routable prefix. gnfargbl didn't say the _address_ was unroutable, but that effectively, routing policies mean that /48 is a common minimum unit for administrative purposes (similar to how /24 has a special “minimum size” meaning for IPv4).