Netmask to CIDR in ruby

Question

I\'ve been using the ip-address gem and it doesn\'t seem to have the ability to convert from a netmask of the form

255.255.255.0 

into the

Answer 1

Just as a FYI, and to keep the info easily accessible for those who are searching...

Here's a simple way to convert from CIDR to netmask format:

def cidr_to_netmask(cidr)
  IPAddr.new('255.255.255.255').mask(cidr).to_s
end

For instance:

cidr_to_netmask(24) #=> "255.255.255.0"
cidr_to_netmask(32) #=> "255.255.255.255"
cidr_to_netmask(16) #=> "255.255.0.0"
cidr_to_netmask(22) #=> "255.255.252.0"