CIDR Subnet to Dot Notation

gistfile1.rb

class SubnetCalc

	def self.dot_notation_to_prefix(netmask)
		netmask = ipv4_to_binary(netmask).split(//)
		netmask.select{ |i| i == "1"}.length
	end

	def self.ipv4_to_binary(ipv4addr)
		ia = ipv4addr.to_s.split('.')
		if ia.size != 4
			raise "Invalid IP address"
		end
		output = ""
		i = 1
		for octett in ia
			output = output + "%08d" % octett.to_i.to_s(2)
			i += 1
		end
		return output
	end

	def self.cidr_to_binary(prefix)
		binary=""
		1.upto(prefix) { binary << "1" }
		(prefix + 1).upto(32) { binary << "0" }
		return binary
	end

	def self.cidr_to_dot_notation(prefix)
		bin = SubnetCalc.cidr_to_binary(prefix)

		a = bin[0,8].to_i(base=2).to_s
		b = bin[8,8].to_i(base=2).to_s
		c = bin[16,8].to_i(base=2).to_s
		d = bin[24,8].to_i(base=2).to_s
		return ("#{a}.#{b}.#{c}.#{d}")
	end

end

puts SubnetCalc.dot_notation_to_prefix("255.255.255.0")
puts SubnetCalc.cidr_to_dot_notation(12)