def grow()
			addr = self.network.addr
			mask = self.netmask.mask
			prefix_len = self.netmask.prefix_len
			self.netmask.prefix_len.downto(0) do
				mask = (mask << 1) & NetAddr::F128
				if addr|mask != mask || prefix_len == 0 # // bit boundary crossed when there are '1' bits in the host portion
					break
				end
				prefix_len -= 1
			end
			
			return IPv6Net.new(IPv6.new(addr),Mask128.new(prefix_len))
		end
def grow()
			addr = self.network.addr
			mask = self.netmask.mask
			prefix_len = self.netmask.prefix_len
			self.netmask.prefix_len.downto(0) do
				mask = (mask << 1) & NetAddr::F128
				if addr|mask != mask || prefix_len == 0 # // bit boundary crossed when there are '1' bits in the host portion
					break
				end
				prefix_len -= 1
			end
			
			return IPv6Net.new(IPv6.new(addr),Mask128.new(prefix_len))
		end
grow decreases the prefix length as much as possible without crossing a bit boundary.